Patent Publication Number: US-11654219-B2

Title: Fluid management and measurement systems, devices, and methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. application Ser. No. 16/621,827 filed Dec. 12, 2019 which claims the benefit of priority to U.S. national stage filing under 35 U.S.C. § 371 of International Application No. PCT/US2018/039191, filed Jun. 24, 2018 which claims the benefit of priority to U.S. provisional application No. 62/524,498, filed Jun. 24, 2017; U.S. provisional application No. 62/524,490, filed Jun. 24, 2017; U.S. provisional application No. 62/524,495 filed Jun. 24, 2017; and U.S. provisional application No. 62/524,513 filed Jun. 24, 2017, all of which are hereby incorporated by reference in their entireties. 
    
    
     BACKGROUND 
     There are many types of blood processing and fluid exchange procedures, each providing different therapeutic effects and demanding different processing criteria. Some procedures entail the removal of blood or another fluid from an individual and the return of blood or another fluid to the individual in a controlled fashion. Other types use natural body tissues to exchange blood components with a medicament. Examples of such procedures include hemofiltration (HF), hemodialysis (HD), hemodiafiltration (HDF), and peritoneal dialysis (PD). A common requirement of such procedures is the provision of large quantities of medicament such as dialysate that has a precise mixture of solute components and is free of contaminants and pyrogenic materials. 
     Some known systems for preparing medicaments such as dialysate are continuous proportioning systems and batch mixing systems. Carrying out treatment procedures using medicaments may employ special-purpose machinery. In the dialysis treatments listed above, devices called cyclers are often used. These pump fluid and may also pump blood, depending on the treatment. In the process of pumping, they precisely proportion the net amounts of fluid supplied and discharged and ensure safety by various means including monitoring of pressure, temperature, leaks, and other treatment conditions. In principle, these treatments are relatively simple, but because of the need for patient safety and health outcomes, treatment procedures and treatment systems are complex. 
     Home delivery of these treatments raises concerns about safety and treatment efficacy. One of the drawbacks of home treatment is the need for a supply of purified water. In clinics, large reverse osmosis plants provide a continuous supply of purified water. In the home, such large systems may not be practical because they require high volume of water and drainage. Installing and using relevant components can be a difficult and expensive task and may require modifications to a patient&#39;s home. In addition, the systems for the production of properly mixed medicaments in pure form require a high level of precision and safeguards as well as training and maintenance. To provide effective and safe systems for home delivery of blood treatments, there is an on-going need for innovations in these areas and others. For example, PCT publication number WO2016049542, which is incorporated herein by reference in its entirety, discloses a medicament preparation system that includes a water purification module and a medicament proportioning module, where the system is configured to allow convenient and safe use in a home environment or a critical care environment as well as others affording safety, reliability, and a compact form factor. 
     Some medical devices combine two or more substances to produce a medicament. One example is the preparation of dialysate for dialysis, where different fluids are mixed, such as a concentrated dialysate and a diluent such as water. It is desirable to control precisely the amount of the dialysate concentrate, or other fluids, as they are combined with the diluent. In certain situations, uncontrolled or accidental mixing may take place due to gravimetric action or due to pressure or vacuum created downstream in the fluid channel. 
     Many medical devices have portions that are replaced regularly and other portions that replaced less frequently or are permanent. The latter may be used repeatedly, depending on the application, for preparation of treatment fluids or treatment with treatment fluids as well as other applications. 
     In some treatment systems or fluid preparation systems (generically identified herein as fluid management systems) a common component is a portion of the fluid circuit that directs waste fluid to a drain. Such components can become fouled due to the repeated use. Examples of such systems include treatment devices, fluid preparation such as admixing devices, and water purification systems. 
     A disposable medical device may benefit from the ability to accurately measure conductivity or resistivity of a liquid. To this end, a conductivity sensor can be formed from two electrodes positioned at two locations in a fluid chamber. A current is generated between the electrodes with a current source as the voltage between the electrodes is measured. With knowledge of the size and shape of the volume between the electrodes and the contact areas of the electrodes (sensor dimensions) a “cell constant” can be calculated and used to calculate the conductivity of the fluid. The cell constant can be measured for a representative sensor such that the sensor dimensions need not be known explicitly by calibrating using a fluid having known conductivity. The driving current and detected voltage are typically alternating to avoid signal drift due to various known chemical and physical drivers. 
     The accuracy of the conductivity sensor is influenced by assurance of consistent sensor dimensional parameters. The latter include the physical relationship between the two electrodes and their relationship to the fluid volume defining the conduction path. Therefore, it is advantageous to control the placement of the electrodes within the housing of the conductivity sensor during the manufacturing process. The conductivity sensor may be a part of a disposable medical component such as a portion of a fluid circuit, where the manufacturing process may constrain the achievable manufacturing tolerances. These issues, and others, are addressed by embodiments of the present disclosure. 
     SUMMARY 
     An elastomeric electrical contact is formed by a parallel array of wires supported on an elastomeric block. The wires may span a relief formed in a side surface of the block. The wires may wrap over three sides of the elastomeric block and make contact with contacts in a silicone housing. The contacts in the housing may be, for example, on the side or on the bottom side opposite the top surface of the elastomeric block. The elastomeric contact may be used in a replaceable component of a medicament preparation system to establish a reliable electrical connection with a sensor in a permanent component of the medicament preparation system. The medicament preparation system may include a water purification module and a medicament proportioning module, and may be configured to allow convenient and safe use in a home environment or a critical care environment as well as others, thus affording safety, reliability, and a compact form factor. The sensor may be a conductivity cell in which current and voltage measurement contacts are reliably connected, by way of the elastomeric contact disclosed herein, to wetted electrodes in a replaceable component, so that the conductivity of a fluid is measured accurately. 
     Generally, a compliant multiconductor element is positioned between multiple terminal contacts that, whose function requires these multiple terminal contacts to make electrical contact by being forced against a single electrode to contact it at different positions on the electrode surface. The electrode element may be positioned at variable distances from the multiple terminal contacts due to manufacturing variability or uncertain engagement by a user, creating a potential for a high resistance connection between the electrode and the multiple terminal contacts. This may arise, in part, where the multiple terminal contacts a minor fraction of the size of the electrode such that a member carrying both elements would have to be perfectly aligned with the surface of the electrode in order for all of the multiple terminal contacts to make sure electrical contact with the electrode. This is because one of the contacts may begin to resist the forcing against before another of the multiple terminal contacts makes full electrical contact with the electrode. That is, one of the multiple terminal contacts, or a substrate carrying them, may “block” the another of the multiple terminal contacts from making full electrical contact with the electrode. For example, but not limited to this example, one of the multiple terminal contacts is connected to a current source and the other one of the multiple terminal contacts is connected to a voltage measurement device. According to the disclosed subject matter, a resilient element with many flexible conductors running from one surface of the element to the opposite surface is positioned between the multiple terminal contacts forming a connection between each of the multiple terminal contacts and the single electrode. The number of the flexible conductors may be sufficient for there to be redundant connections between each of the multiple terminal contacts and the single electrode. In that case, the redundancy can help ensure that if some conductors make incomplete contact with the electrode and a respective one of the multiple terminal contacts, the other may still do so. In the above arrangement, an electrode that is tilted relative to the surface of the compliant multiconductor element or relative to the path of closure between the multiple terminal contacts and the electrode, the compliance of the compliant multiconductor element will prevent the blocking effect described above. 
     In the disclosed embodiments, the compliant multiconductor element is mated to a disposable device containing the electrode. A housing forms a sealed connector that holds the compliant multiconductor element in place adjacent the electrode. In embodiments, a conductivity cell with two electrodes are each provided with a housing and compliant multiconductor element. A permanent excitation component (a device with a current source and a voltage measurement device to which a disposable device carrying the electrodes is attached) with multiple terminal contacts to be electrically connected to each of the electrodes is engaged with the device carrying the electrodes by forcing them together. The housing holds the compliant multiconductor element on the electrode. The compliant multiconductor element is thus used only for duration of the use of the disposable device and is advantageously carried by it. In alternative embodiments, the compliant multiconductor element is attached to the permanent excitation component. 
     The general form of the compliant multiconductor element may be like that of so-called zebra connectors. The zebra connectors are used to connect a component with multiple contacts one-to-one to multiple contacts. They are in the general category of electronic interconnect devices. Designers employ them where a large number of very small contacts, for example a row of contact pads, each a fraction of a millimeter across, must be contacted with each other, the rows being parallel and facing each other. Then the zebra connector can be placed between them rows and pressed together to cause the contacts to make electrical contact through the zebra connector conductors. A common application example is connecting LCD panels. In the present embodiments, the same type of zebra connector may be used in a device having larger contacts, for example, ones that are more than a millimeter in size. The zebra connector may be used to connect a pair of contacts with a single electrode rather than corresponding contacts in one-to-one fashion. Also, the zebra connector is used in applications where the contact strips are thin and known to be flexible requiring a compliant mechanism to form a sandwich to make the electrical contacts. In the present application of a single electrode connecting to a small number of contacts, other solutions such as pogo pins or leaf spring contacts would generally be used. 
     Embodiments of the present disclosure provide conductivity sensor with a housing that can be manufactured by various processes such as injection molding, casting, or extrusion, optionally combined with thermal or mechanical machining. The disclosed embodiments provide resistance to variation in critical sensor dimensions due to manufacturing variability such as applied forces, quantities of cement, offsets in assembly of components, etc. In particular, the critical sensor dimension of the electrode fluid contact area, position, and shape are precisely controlled with effective and reliable sealing of the electrodes to a housing. It may be appreciated that while embodiments below are focused on a conductivity sensor that includes an insertable electrode in an opening of a housing, the disclosure is also applicable to a multitude of other applications where it is necessary to press, push, insert, or force an object into an opening and obtain a repeatable and predictable fit within that opening. 
     It is desirable to precisely and repeatedly position an electrode within openings of a housing according to embodiments of the disclosure. The housing may define a flow channel for continuous monitoring of conductivity of a flowing fluid. The housing may also be a vessel where fluid is stored. Each electrode is positioned in an opening whose axial profile (“axial” referring to a central axis of the opening connecting the interior of the housing with the exterior along the most direct line). The opening may have a stepped profile so that moving from outside to inside the housing, the area of the opening diminishes. That is, an outside portion of the opening has a larger diameter than an inside portion of the opening. The outside portion may include one or more spacers that project radially inward but which do not extend across the circumference of the opening inside portion. The inside portion may have a rim that extends axially toward the outside of the housing. The rim defines a trough. When an electrode is pressed into the outer portion it is over-constrained by the spacers which are the only parts in contact with the inserted electrode until the electrode lands against the rim to seal the opening fully. The placement of the spacers provides precise centering of the inserted electrode within the opening, and minimizes deformation of the inserted electrode and the housing. Further, the spacers may have a shape that allows the electrode to be pressed in with force that is low, consistent, and uniform along a length of the traversal while confining the position of the electrode as it is pressed home. When the electrode reaches home, the resistance force is no longer frictional (or due to scraping of the spacers) but rather generated by interference caused by seating on the rim. An assembly line robotic press can exploit the sudden rise in resistance force exerted to determine that the electrode has been fully inserted when the assembly line machine exerts a predetermined maximum force on the electrode. 
     As the electrode is pressed into the opening of the housing, the spacers are physically deformed since the space for the electrode may be made slightly smaller than the electrode. It is possible that a part or parts of the spacers may be scraped or shaved off to produce one or more shaving or burrs. These may remain attached or break off when each electrode is pressed into an opening of the housing. To prevent any shaving or burr from interfering with consistent placement of the electrode, such shavings or burrs are received in a trough so that they cannot become trapped between the electrode and a final seating surface defined by the rim. Thus, any burrs or shavings can bend away or fall away into the trough thereby leaving an arrest surface (e.g., the top of the rim) free of obstructions whereby the electrode is fully pressed into its intended position, providing for highly precise positioning of the electrode within the housing. 
     Various embodiments of the present disclosure provide a medicament preparation system that includes a fluid circuit having fluid channels with at least one junction, the junction joining a common flow channel that leads from a water inlet to a medicament outlet. The junction may be joined to a pumping tube segment connected to a source of medicament concentrate by a concentrate channel. The fluid circuit may be oriented in a predefined way relative to the force of gravity. The concentrate channel has a chicane that curves sharply up and sharply down before the concentrate channel meets the common flow channel. 
     In embodiments, the chicane&#39;s length may be no greater than ten internal diameters of the concentrate channel local to the chicane. 
     In embodiments, the chicane is immediately adjacent a point where the common flow channel and the concentrate channel meet. 
     In embodiments, the internal cross-sectional flow area of the chicane is smaller than that of the remainder of the concentrate channel. 
     In embodiments, the chicane is operable as a trap when fluid of a first density remains in the concentrate channel while fluid of a second density remains in the common flow channel at the junction, where the first density is higher than the second density, whereby gravity siphoning is prevented. 
     In embodiments, the fluid circuit may be formed in a rigid structure and/or in a rigid cartridge. 
     In embodiments, an overhang may be present to reduce or prevent the diluent from entering the concentrate channel. 
     In embodiment, a flap that is biased in the closed position may be present in addition to, or instead of, the chicane. The flap bias force is sufficient to prevent flow of the concentrate due to gravimetric action, but the bias force is overcome when the concentrate is pumped along the concentrate channel to allow mixing with the diluent. 
     In embodiments, a gravity trap in a fluid path or fluid circuit reduces the occurrence, or prevents, unintended mixing of fluids of different densities caused by gravimetric action. In an exemplary embodiment, the gravity trap can be included in an online dialysis proportioning system that prepares dialysate from a concentrate. In this example, the fluids that are admixed may be a dialysate concentrate and purified water, but other concentrates and diluents are envisioned. In an embodiment, one of the fluids is a mixture of purified water and bicarbonate, while the other fluid is an acid. 
     Objects and advantages of embodiments of the disclosed subject matter will become apparent from the following description when considered in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Embodiments will hereinafter be described in detail below with reference to the accompanying drawings, wherein like reference-numerals represent like elements. The accompanying drawings have not necessarily been drawn to scale. Where applicable, some features may not be illustrated to assist in the description of underlying features. 
         FIGS.  1 A and  1 B  show a contact issue that arises in connection with multiple point electrode contacts for an article of manufacture containing an electrode which interfaces with a permanent multi-point contact element. 
         FIGS.  1 C and  1 D  illustrate a mechanism for overcoming a contact issue that arises in connection with multiple point electrode contacts for an article of manufacture containing an electrode which interfaces with a permanent multi-point contact element according to embodiments of the disclosed subject matter. 
         FIG.  1 E  shows a compliant multiconductor element according to embodiments of the disclosed subject matter. 
         FIG.  2    shows an overview of an online system that includes a water purification module, proportioning medicament proportioning module, and a cycler forming an online treatment system, according to embodiments of the disclosed subject matter. 
         FIG.  3    shows details of the water purification module of the embodiment of  FIG.  1   , according to embodiments of the disclosure subject matter. 
         FIG.  4    shows an overview of an online water purification, proportioning medicament generation, and treatment system, according to embodiments of the disclosed subject matter. 
         FIG.  5    shows details of an embodiment of medicament proportioning module, according to embodiments of the disclosed subject matter. 
         FIG.  6    shows further details of a fluid circuit cartridge according to embodiments of the disclosed subject matter. 
         FIGS.  7 A through  7 E  show features of a conductivity and temperature measurement cell that, according to embodiments, can be integrated in the fluid circuit cartridge of  FIG.  6    and others disclosed herein, according to embodiments of the disclosed subject matter. 
         FIGS.  8 A through  8 C  show an arrangement of elements that show how electrical, thermal, and mechanical engagement (contact) with sensor instrumentation and actuated elements can be made according to embodiments of the disclosed subject matter. 
         FIGS.  9 A and  9 B  show embodiments of a conductivity measurement component that may be used with any cartridge embodiments, or substituted with equivalent conductivity measurement components thereof in any of the embodiments disclosed or claimed. 
         FIGS.  10 A and  10 B  show oblique views of embodiments of an elastomeric contact insert of an elastomeric contact that may be used with a conductivity measurement component in any of the embodiments disclosed or claimed. 
         FIGS.  11 A and  11 B  show oblique views of additional embodiments of an elastomeric contact insert of an elastomeric contact that may be used with a conductivity measurement component in any of the embodiments disclosed or claimed. 
         FIGS.  12 A- 12 C  show cross-sectional views of embodiments of an elastomeric contact insert of an elastomeric contact that may be used with a conductivity measurement component in any of the embodiments disclosed or claimed. 
         FIGS.  13 A- 13 D  show various views of embodiments of a housing that supports an elastomeric contact insert in an elastomeric contact that may be used with a conductivity measurement component in any of the embodiments disclosed or claimed. 
         FIG.  14    shows a schematic view of various components forming a 4-terminal sensing circuit in a fluid conductivity cell that may be used in any of the embodiments disclosed or claimed. 
         FIGS.  15 A and  15 B  show cross-sectional views of additional embodiments of a housing that supports an elastomeric contact insert in an elastomeric contact that may be used with a conductivity measurement component in any of the embodiments disclosed or claimed. 
         FIG.  16    illustrates a view of a fluid circuit according to embodiments of the disclosed subject matter. 
         FIG.  17    illustrates a closeup view of a portion of  FIG.  16   . 
         FIG.  18    illustrates a closeup view of another portion of  FIG.  16   . 
         FIG.  19    illustrates a junction of a common flow channel and a concentrate channel according to embodiments of the disclosed subject matter. 
         FIG.  20    illustrates a junction of a common flow channel and a concentrate channel according to embodiments of the disclosed subject matter. 
         FIG.  21    illustrates a junction of a common flow channel and a concentrate channel according to embodiments of the disclosed subject matter. 
         FIG.  22    illustrates a junction of a common flow channel and a concentrate channel according to embodiments of the disclosed subject matter. 
         FIG.  23    illustrates a water purification system according to embodiments of the disclosed subject matter. 
         FIG.  24    illustrates a medical treatment system according to embodiments of the disclosed subject matter. 
         FIG.  25    illustrates a waste water line according to embodiments of the disclosed subject matter. 
         FIG.  26    illustrates another waste water line according to embodiments of the disclosed subject matter. 
         FIG.  27    illustrates another waste water line according to embodiments of the disclosed subject matter. 
         FIG.  28    illustrates a medicament admixing system according to embodiments of the disclosed subject matter. 
         FIG.  29    illustrates another medicament admixing system according to embodiments of the disclosed subject matter. 
         FIG.  30    illustrates another waste water line according to embodiments of the disclosed subject matter. 
         FIG.  31    illustrates a view of an opening of a housing of a conductivity sensor according to embodiments of the disclosed subject matter. 
         FIG.  32    illustrates an axial section of the embodiment of  FIG.  31    taken along plane II-II. 
         FIG.  33    illustrates a view of an exemplary housing according to embodiments of the disclosed subject matter. 
         FIGS.  34  through  36    illustrate views of housings with rectangular, elliptical, and triangular openings according to embodiments of the disclosed subject matter. 
         FIGS.  37 A and  37 B  illustrate a portion of an axial section through the plane indicated by VII-VII of  FIG.  31   . 
         FIG.  38 A  illustrates a portion of a cross-section view of a spacer according to another embodiment of the disclosure. 
         FIG.  38 B  illustrates a portion of a cross-section view of a spacer according to another embodiment of the disclosure with an inserted electrode. 
         FIGS.  39 ,  40 A, and  40 B  show alternative embodiments in which, rather than using standoffs extending from the aperture to focus the forces for aligning and engaging the electrode, the electrode itself is shaped to provide a similar effect by forming a non-round electrode that engages the walls of the aperture at predefined points. 
         FIGS.  41 A and  41 B  show an electrode embodiment in which the entire circumference engages the outer aperture and is shaped as an annular barb and the electrode may have a recess with an inner aperture pressing against the base of the recess to form a seal while the electrode is pressed into engagement with the inner aperture wall. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1 A  shows an interface element  135  having contacts  137 A and  137 B which are positioned to engage an electrode  146 , or other conductive element, at two points thereon. The electrode  146  is supported by a member  136  which has an opening  143  covered and sealed by the electrode  146 . The member  136  may be a portion of a wall of a conductivity measurement device such as described with reference to  FIGS.  7 A- 7 E . The interface element  135  and member  136  are moved toward each other so that the contacts  137 A and  137 B are moved toward the electrode  146  as shown by the arrows.  FIG.  1 B  shows the interface element  135  and member  136  have stopped moving due to interference engagement with contact  137 A. This leaves contact  137 B spaced apart from the electrode  146 . This is due to the angles position of the electrode  146  relative to the contacts  137 A and  137 B. The angled position of the electrode  146  circumstance is exaggerated in the figures and the contact failure may not be as clear cut in a real-world circumstance due variability due to imperfect manufacturing of the member  136  and electrode  146 . 
       FIGS.  1 C and  1 D  show how the interposition of a compliant multiconductor element  140  may allow complete contact between the electrode and both of the contacts  137 A and  137 B. Referring briefly to  FIG.  1 E  the compliant multiconductor element  140  has an elastomeric block  142 , which may have additional features cut out of it to make it more compliant as discussed below. Flexible conductors  141  (only one of many parallel conductors is indicated by the reference numeral) are attached on opposite faces  145 A and  145 B of the elastomeric block  142  which, as illustrated, are perpendicular to the plane of the drawing page, of the elastomeric block  142 . The flexible conductors  141  may be thin wires or metallic tape or conductive traces deposited on the elastomeric block  142 . The flexible conductors  141  wrap around the opposing faces  145 A and  145 B and bridge across (in the direction parallel to the plane of the drawing page) so that when interposed between interface element  135  and the member  136 , this creates an electrical continuity between a region  138 A of the electrode  146  and contact  137 A and between region  138 B of the electrode  146  and contact  137 A. The electrical continuity contact may be formed by multiple conductors  141 . It can be observed that the compliant multiconductor element  140  deformation when the interface element  135  and the member  136  are forced together allows continuity to be made between the electrode  146  and the contacts  137 A and  137 B. The scales of the elements shown are not necessarily representative of a real-world embodiment and the sizes and numbers of elements are modified to for description purposes. 
     The compliant multiconductor element  140  may conform to the so-called Zebra elastomeric connector used commonly for making one-to-one electrical contact between a row of contacts of a liquid crystal display panel and corresponding contacts pads of a graphics processing unit. Note that instead of conductors  141 , the compliant multiconductor element  140  may be a many-layered sandwich of conductive and insulating materials. The conductive layers may be, for example, carbon-filled elastomeric material. In typical applications, known elastomeric connectors are used for extremely high pitch contact spacing applications in which the contact size and spacing is no more than a millimeter or two and commonly a minor fraction of a millimeter. The present system may employ contacts that are several millimeters wide. Another difference from conventional uses of Zebra connectors is the number of contacts. Zebra connectors are generally used to map many contact pads, in the tens, hundreds, or thousands rather than two as in the present embodiments. Yet another difference is that the multiple contacts, for example,  137 A and  137 B are electrically connected by the compliant multiconductor element  140  to a single electrode  146  at multiple positions, rather than respective contacts. Still another difference is that the disclosed compliant multiconductor element  140  has an aspect ratio of about unity so that it can maximally fill the area of a round electrode. As discussed below, the compliant multiconductor element  140  may be captured and held to the electrode by a housing to form a part of a consumable component of a medical treatment device. Other differences in the application will be revealed in the following embodiments. 
       FIG.  2    shows an overview of an online water purification, proportioning medicament generation, and treatment system  100 , according to embodiments of the disclosed subject matter. A water purification module  102  receives tap water  108  from a municipal water supply. The water purification module  102  purifies the water and checks its purity, under control of a controller  112  and using a water quality sensor ( 219  in  FIG.  2   ). The water quality sensor  219 , in embodiments, includes a conductivity sensor. The water purification module  102  utilizes one or more filter modules  130  which are replaced at intervals to help maintain the ability to generate product water that is sterile and ultra-pure. Product water  109  from the water purification module  102  is conveyed to a medicament proportioning module  104  which mixes one or more concentrates and the product water  109  in a replaceable fluid circuit  132  to generate a medicament  111 . The medicament concentrates are diluted in a predefined proportion to generate product medicament  111 . One or more concentrates may be utilized and combined in the product medicament  111 . The water purification and medicament generation are performed in in-line fashion and on-demand, which means water is purified and mixed with medicament concentrate as a continuous process, at a rate of consumption and as demanded by a final consumer, in this case, a cycler  106 . Waste produced by the medicament proportioning module  104  is conveyed as indicated at  115  to a drain  117 . Waste  110 , for example spent medicament, is conveyed to the same or other drain  117 . 
     Each of the water purification module  102 , the medicament proportioning module  104 , and the cycler  106  may include a respective controller  112 ,  114 , and  116 . All of the controllers  112 ,  114 , and  116  may be in communication as indicated by lines  122  and  124 . In alternative embodiments, a smaller or larger number of controllers may be used and they may be associated with each module  102 ,  104 , and cycler  106  or shared among the modules  102 ,  104 , and cycler  106 . One or more user interfaces, figuratively indicated at  101  and  103 , may be connected to one, two, or the entire water purification module  102 , medicament proportioning module  104 , and/or cycler  106 . Connections between the user interfaces  101 ,  103 , indicated at  123  and  125 , may be wired or wireless. In embodiments, control may be provided through a single user interface  103 , and each module may transmit commands responsive to commands from the user interface  103  to the respective controllers  112  and  114  of the water purification and medicament proportioning modules  102  and  104 , in parallel or serially. In embodiments, the cycler  106  receives and returns blood in arterial and venous lines  120 A and  120 B, respectively. In other embodiments, medicament is conveyed to and from a patient, for example in a peritoneal dialysis treatment. 
       FIG.  3    shows details of the water purification module  102  of the embodiment of  FIG.  2   . Referring now to  FIG.  3   , a water purification module  102  receives tap water from an inlet  214 , the tap water being pumped by a pump  212  and passed through a sediment filter  202 , a water quality sensor station  219 , and an activated carbon filter  204 . Water from the activated carbon filter  204  is received by a two-stage deionization filtration element  244  that includes a primary resin cation stage  205 , a primary resin anion stage  206 , and a secondary mixed resin bed  208 . The primary resin cation stage  205  and the primary resin anion stage  206  may be combined in a single replaceable unit  242  or may be separately replaceable. The primary resin cation stage  205 , the primary resin anion stage  206 , and the secondary mixed resin bed  208  may also be combined in a single replaceable unit in alternative embodiments. Deionized water from the two-stage deionization filtration element  244  passes through a diverter valve  230  which is controlled by a controller  240 . The diverter valve  230  may selectively direct a flow of deionized water to a drain outlet  232 . Deionized water passing through the diverter valve  230  for the generation of product water is directed to a heater  220 , a degassing filter  222 , and two or more sterile filters connected in series to form sterile filter stage  210  from which product water may be drawn through a product water outlet  216 . A vacuum pump (not shown) may be provided on an air side of the degassing filter  222 . The degassing filter  222  may have a hydrophobic membrane to allow gas to be removed from water flowing through it. The water purification module  102  may contain a replaceable unit  113  that includes a conductivity sensor according to any of the disclosed embodiments for detecting initial water quality. 
     The water quality sensor station  219  may output a signal indicating water quality, for example, a signal indicating conductivity of the water, which may be numerically cumulated by the controller  112  to generate, for any point in time, a remaining life of any of the filters provided herein. The water quality sensor station  219  may include a particle counter, a conductivity sensor, an optical opacity sensor, a pH sensor, a lab-on-a-chip chemical assay sensor, and/or another type of water quality sensor. The user interface  101  and/or  102  may allow the entry of other data regarding water quality. For example, a worst-case upper bound, or data related thereto, of raw water constituents may be provided. An algorithm that predicts the rate of the various components, based on a measured indicator, may then be used to predict the rate of all contaminant constituents. In an example embodiment, the algorithm may predict that all contaminants are in the same proportion as a predefined value such that an indication of conductivity by the water quality sensor station  219  may thereby indicate the concentrations of the various contaminants. In embodiments, the controller  112  may output an indication of the remaining life of the various components or an indication that a component is at or near expiration. In a particular embodiment, the useful life of the deionization resin beds may be estimated based on conductivity indicated by water quality sensor station  219 . The estimation of the remaining life may be based on the data carried by the data carrier of the replaceable tagged component indicating characteristics such as the capacity or type of decontaminating media employed thereby. The water quality sensor station  219  may be positioned at any suitable point downstream of the inlet  214 , even though shown downstream of the sediment filter  202 . 
     The pump  212  and sediment filter  202  may form permanent or infrequently-replaced components that are ordinarily not replaced by the user. The entire water purification module  102  is adapted for use by a home-bound patient and/or a helper although its features of compact size and low water volume requirement make it attractive for use in critical care environments. The tap water inlet  214  may be fitted with an adapter suitable for connection to an accessible permanent or temporary connection so that, for example in critical care environments, the water purification module  102  may be wheeled to a point of use and connected to a nearby water tap with such a connection fitting. In embodiments, the water purification module  102  is combined with the medicament proportioning module  104  in a single housing so that it can be wheeled to a point of use and/or compactly housed for use in a home. 
     Each of the replaceable components (activated carbon filter  204 , primary resin cation stage  205 , primary resin anion stage  206 , replaceable unit  242 , or sterile filter stage  210 ) may be fitted with a respective data carrier  201 ,  203 ,  209 ,  207 ,  211  such as a bar-code or radio-frequency identification (RFID) tag that carries a unique identifier respective to the attached component (again, attached component may be any of the activated carbon filter  204 , primary resin cation stage  205 , primary resin anion stage  206 , replaceable unit  242 , or sterile filter stage  210  and will generally be referred to as replaceable tagged component). Product water may be drawn through the product water outlet  216 . 
     A reader  245  may be attached to the purification module  102  and may be positioned so as to actively or passively read the data carrier  201 ,  203 ,  209 ,  207 ,  211  of the replaceable tagged component. Reader  245  may be a scanner for an RFID, a bar-code scanner, a smart-chip reader, or any other type of data carrier reader, and may connect optically, electromagnetically, electrically through conductive contacts, or by any other suitable means. The information stored on data carriers may allow the controller  240  to verify that the correct type of replaceable tagged component is installed. The controller  240  may detect the removal or disconnection of a replaceable tagged component as well. In an embodiment, the controller  240  may generate a refuse signal and take corrective action (such as preventing use of the water purification module  102  or blocking installation of the replaceable tagged component or some other action). 
       FIG.  4    shows an overview of an online water purification, proportioning medicament generation, and treatment system  351 . The water purification module  102  and medicament proportioning module  104  form a medicament generation system  355  and are commonly housed in a housing  350  with a user interface  101 . The cycler  356  (or generally, a medical treatment device that consumes medicament generated by the medicament generation system  355 ) may form a separately housed device that is signally and fluid connected to the medicament generation system  355 . Communications module  358  interconnects the controllers  304  and  116  of the medicament generation system  355  and cycler  356  respectively. 
     By combining the medicament generation system  355  with a cycler, a system suitable for use in a home, critical care, or clinic may be provided without a need for specialized services such as high capacity municipal water supply, power, or drainage. For example, high volume water supply is typically required in reverse osmosis-based water purification system. In the present embodiments, municipal water  360  is deionized using consumable deionization filter beds, allowing normal rates of water flow and drainage  317  in a services supply  362  that is typical of a home or the room services of a hospital. With power requirements at residential or typical hospital-room voltages and currents, available services allow the proportioning medicament generation, and treatment system  351  to be used for home and critical care, as well as in clinics. For clinics, the rapid set-up of a new installation can be facilitated as well because expensive capital infrastructure of an online medicament generation system can be avoided. 
     As in the embodiment of  FIG.  2   , the water purification module  102  receives tap water  108  from a municipal water supply. The water purification module  102  purifies the water and checks its purity under control of controller  304 . The water purification module  102  utilizes one or more filter modules  130  which are replaced to help maintain its ability to generate product water that is sterile and ultra-pure. Product water  109  from the water purification module  102  is conveyed to a medicament proportioning module  104  which mixes concentrates provided in a replaceable fluid circuit  132  in a predefined proportion to generate a medicament  311 . The water purification and medicament generation are performed in on-line fashion and on-demand, which means water is purified and mixed with medicament concentrate as a continuous process, at a rate of consumption and as demanded by a final consumer, in this case, a cycler  356 . Waste produced by the medicament proportioning module  104  is conveyed as indicated at  115  to a drain  317 . Waste  110 , for example spent medicament, is conveyed to the same drain or another drain  317 . The cycler  356  may be of any type including hemodialysis and peritoneal dialysis as well as other types of treatment systems. 
     The communication module may allow the controller  116  to send specific command signals to the medicament generation system  355 , for example, to start and stop medicament generation. In a system in which the cycler  356  is not adapted to send specific commands, a status vector can be translated by the communications module  358  to convert it to one or more suitable commands A status vector may include information such as whether a blood pump of the cycler  356  is running. 
     Controller  364  and  366  may communicate, respectively, with the medicament generation system  355  and cycler  356 . The controllers  304  and  116  may generate operation or treatment logs and/or maintenance information which they may send the controller  366  for further distillation, synthesis, storage, or communication to other facilities and/or remote professional care management or maintenance personnel. 
       FIG.  5    shows details of an embodiment of medicament proportioning module  104  shown in  FIG.  2   . A sealed fluid circuit  401  is partially supported by a cartridge support  406 . Flow lines supported by the cartridge support  406 , shown generally at  408  may be tubes attached to the cartridge support  406  or formed therein by molded and sealed channels or in attached seam-welded flexible panels or by other suitable means. The sealed fluid circuit  401  may also include all the other lines and fluid circuit elements illustrated including such as waste line  422 , inlet line  431 , medicament concentrate lines  433 , product medicament line  435 , control valve  420 , junction  437 , and inlet sterile filter  445  to form a single pre-connected sterile disposable unit along with the flow lines  408  (and other elements supported by the cartridge support  406  described below). As explained, the entire sealed fluid circuit  401  shown in  FIG.  5   , save for the inlet line  431  inlet and product medicament line  435  are pre-connected and sealed from the external environment. The sealed fluid circuit  401  may be sterilized as a unit, for example, gamma-sterilized or heat-sterilized. 
     A source of pure water can be connected by way of a connector  414  which is capped and sterile-sealed prior to connection. By sterile-sealed it is meant that a seal is formed sufficient to physically block any contaminants from entering. A resistivity sensor  107  of the form of any of the disclosed conductivity sensor embodiments may be provided in the water inlet line. A sterile filter  445  ensures that any contamination in the flow, for example, resulting from touch contamination or a contaminated connector on the pure water source, is trapped by the sterile filter  445 . Thus, sterile filter  445  forms part of the complete sterile barrier such that the entire sealed fluid circuit  401  has a continuous sterile barrier even after the connector  414  is unsealed, at least while the product medicament line  435  connector is capped with cap  421 . The sterile filter may be one with a 0.2 μm membrane to block bacterial contaminants. Note that by ensuring that completely sterile deionized water flows into inlet line  431  and because the entire sealed fluid circuit  401  is sealed and sterile, the unit once set up and ready for treatment can be filled and used over an extended treatment without the risk of proliferation of contaminants. For example, the sealed fluid circuit  401  can be prepared for use and primed and used, up to 24 hours later. Alternatively, it may be used for more than one treatment. 
     Pure water flows through the sterile filter  445  at a rate of pumping determined by the pump  442 . To match the rate of production of purified water with the rate of pumping by pump  442 , the source of purified water may generate a constant supply into an accumulator, it may pump continuously with overflow to a drain, or a pump of the water purification module  102  may be commanded in response to the controller  402  of the medicament proportioning module  104 . Reference numeral  432  indicates that a single concentrate, such as lactate buffered dialysate, can be substituted for the multiple-component concentrate. This is true of any of the embodiments. 
     The cartridge support  406  may be received in a medicament proportioning module  104  which may further be a stand-alone unit or combined with a water purification module  102 . As illustrated, the medicament proportioning module  104  is a stand-alone unit. Purified water is received at an inlet  431 , which forms a part of a disposable sterile fluid circuit that includes all the fluid lines and circuit components illustrated in the figure and/or discussed herein. Pump  442  pumps water that flows at a rate controlled by a controller  402 . Pumps  444  and  446  regulate flows of respective medicaments concentrates in medicament concentrate lines  433  so that they are diluted in a precisely controlled ratio by the flow of water pumped by the pump  442 . A first concentrate in container  428  pumped by pump  444  is combined in junction  437  with the flow of water pumped by pump  442 , thereafter flowing into a conductivity measurement module  415  which generates a signal indicative of the concentration of medicament concentrate in the mixture emerging from the junction  437 . A temperature signal indicating a temperature of the same flow is also generated by a temperature transducer  413 . The signals indicating conductivity and temperature are applied to the controller  402  which converts them to concentration responsively to stored (in a data store of the controller—not shown separately) conductivity-temperature curves for the solution of the diluted first concentrate stored in the container  428 . A secondary set of conductivity measurement modules  416 ,  417 ,  418  and temperature transducers  412 ,  411 ,  410  may be provided to provide signals indicating conductivity and temperature of the same flow as a confirmation. If the calculated concentrations differ, the controller  402  may generate a signal indicating a corresponding error condition. In response, the controller  402  may generate an error indication on a user interface  405  or halt the flow of medicament, or divert it through a diverting valve  420  to a waste line  422 , for example. 
     The conductivity measurement modules  415 ,  416 ,  417 , and  418  may each have a pair of electrodes sealed to a housing as described in more detail according to specific embodiments. Each electrode may be as described with reference to electrode  146  with a portion of a housing defining a fluid channel of each conductivity measurement module  415 ,  416 ,  417 , and  418  corresponding to member  136 . The interface element  135  corresponds to a permanent fixture, having the interface element and contacts  137 A, and further having excitation and voltage detection circuits connected to the contacts  137 A, the latter not being shown separately in the schematic of  FIG.  5   . 
     The second medicament concentrate is pumped by pump  446  from container  430  into a junction so that the second concentrate is mixed with the diluted first concentrate. The diluted and mixed first and second concentrates flow into a conductivity measurement module  417  which generates a signal indicative of the concentration of medicament concentrate in the mixture emerging from the junction. A temperature signal indicating a temperature of the same flow is also generated by a temperature transducer  411 . The signals indicating conductivity and temperature are applied to the controller  402  which may convert them to concentration or some other parameter or the values may be used directly for comparison to a reference value. The temperature may be used to compensate the conductivity by a scaling factor to adjust for a difference between reference conductivity value taken at one temperature and an actual temperature at which the fluid conductivity is measured. In the present disclosure, in embodiments where concentration is an identified output from conductivity measurement it should be understood that temperature compensated conductivity or a raw signal may be used as well in any embodiment. As indicated, the conductivity measurements are made by the conductivity measurement modules  415 ,  416 ,  417 , and  418 . Note that a conductivity module of the same description may also be used for water quality sensing as described with reference to reference numeral  219 . 
     A secondary (or redundant) set of conductivity measurement module and temperature transducers may be provided to provide signals indicating conductivity and temperature of the same flow as a confirmation. If the calculated concentrations differ, the controller  402  may generate a signal indicating a corresponding error condition. A final medicament product concentration flows through the line indicated at  408  into an accumulator  404  which has an expandable volume whose pressure may be substantially determined by a spring constant due to a spring-based restoring force. A pressure sensor  127  may measure the pressure in the accumulator  404 . A connected device, such as cycler  106  can draw medicament through line  435 . A cap  421  at the connector ensures a sterile output line and is removed before connection. 
     Referring now to  FIG.  6   , an embodiment of a fluid circuit cartridge  500  is illustrated such as the fluid circuits of the medicament proportioning module  104  of any of the foregoing embodiments. The cartridge has a generally planar support  529  for the various fluid circuit elements. In embodiments, a fluid circuit is embodied in by a fluid circuit pattern defined in the support  529 , for example by molded channels or seam welding or a combination thereof. Alternatively, the fluid circuit may be made up of discrete channel elements such as tubes, junctions, and valves. A fluid circuit  533  supported by the support  529  has channel elements  503  (indicated at  503  but also appearing at various locations as indicated), temperature measurement cells  504 ,  507 ,  508 ,  511 , concentration measurement modules  535 A,  535 B,  535 C, and  535 D, pumping tube segments  526 ,  527 ,  528 , an accumulator  502 , and pinch valve tube segments  522 ,  523 , junctions  501 ,  509 . Cutouts  513  in the support  529  allow pumping actuators  532 ,  531 ,  530 , to mechanically access pumping tube segments  526 ,  527 ,  528 , respectively, and valve actuators  536 ,  537 , to access pinch valve tube segments  522 ,  523 , in order to pump fluid or halt or allow the flow of fluid. 
     Pure water enters in line  541  from a water purification module  102  pumped by pumping actuator  532  through pumping tube segment  526 . An inline sterile filter  515  ensures that any touch contamination, or any contamination, does not enter the cartridge fluid circuit. Pumping tube segment  526  (as well as segments  527  and  528 ) may be made of a specialized construction and material that provide low material creep and precise size to allow consistent and predictable rates to be provided through the regulation of the pumping actuator  532 . The rate of rotation of the pumping actuator  532  is regulated by a controller (not shown) to provide a medicament product flow required by a downstream treatment such as a flow commanded by a cycler  106  and received thereby, or some other consuming device such as storage container. 
     A first concentrate is received through a first medicament concentrate line  542  and is pumped at a rate controlled by the controller to provide a predefined dilution rate of the combined flow emerging from the junction  501 . The mixed diluted first concentrate flows into a first concentration measurement module  535 A. Each concentration measurement module  535 A- 535 D is described in more detail with reference to  FIGS.  7 A through  7 E , infra. The mixed diluted first concentrate flows into the first concentration measurement module  535 A and contacts conductive electrodes, one of which is indicated at  512 . A current is driven through a column channel of the concentration measurement module  535   a  and a voltage drop is measured across the conductive electrodes  512  using the conventional four-point conductivity measurement scheme in order to reduce contact resistance error. The fluid emerging from the column channel is received in a temperature measurement cell  511  and then flows into a second concentration measurement module  535 B with temperature measurement cell  508  and conductive electrodes  510  (only one indicated, but the other is evident by inspection). The second concentration measurement module  535 B provides a redundant indication of conductivity and temperature to confirm accuracy by agreement between concentration measurement module  535 A and concentration measurement module  535 B. The controller or an independent module may output a signal or data indicative of concentration based on temperature and conductivity. The signals indicating conductivity and temperature may be converted to concentration responsively to stored (in a data store of the controller—not shown separately) conductivity-temperature curves for the solution received thereby. The same is done using temperature and conductivity signals from concentration measurement module  535 C and concentration measurement module  535 D as well. 
     The diluted first concentrate is received at a junction  509  where it combines with a flow of second concentrate pumped through the pumping tube segment  528  by pumping actuator  530 . The second concentrate is drawn through a second medicament concentrate line  543 . The flow rate of the diluted first medicament is determined by the combined flow rates of the flows in pumping tube segments  526  and  527  which are regulated by the controller (not shown) through control of the actuator ( 532 ,  531 ) speeds. In a similar manner, the flow through the pump segment  528  is regulated by the rate of the pumping actuator  530  such that the concentration of the mixture emerging from the junction  509 , which includes the first and second concentrates plus the dilution water, is regulated by the relative rotation rates of the three pumping actuators  532 ,  531 , and  530 . In this example, the concentration of the mixture emerging from the junction  509  represents a final concentration of product medicament and it is measured using the concentration measurement module  535 C and then redundantly measured using the concentration measurement module  535 D. As described above, the concentration measurement module  535 C and the concentration measurement module  535 D have conductive electrodes  506  and  505 , respectively and temperature measurement cells  507  and  504 . The conductive electrodes  512 ,  510 ,  506 ,  505  (each of the numerals identifying a pair of conductive electrodes) make contact with fluid in a respective one of the conductivity measurement columns  516 ,  517 ,  518 ,  520  (shown in broken lines indicating they are behind the fluid circuit  533  support  529 ). 
     The product medicament flows into a diaphragm chamber of an accumulator  502  which reduces flow fluctuations by expanding and contracting with the help of an urging element. Flow enters the accumulator  502  at a junction  525  and flows out through a pair of pinch valve tube segments  522  and  523 , each leading to a respective outlet line  544  and  545 . The outlet line  544  is connected to a drain and the outlet line  545  is provided with a connector for connection to a consuming device such as cycler  106 . The cartridge  500  may be pre-connected with concentrate containers  492  and  493 , capped with caps  495  so that the entire assembly is sealed from the environment, and sterilized before packaging for delivery and/or storage. The cartridge  500  may be attached to a container  494 , which can be rigid, such a box such that it can be removed from the container  494  and slid onto a shelf while positioning the cartridge  500  in the medicament proportioning module  104 , where the first medicament concentrate line  542  and second medicament concentrate line  543  are of sufficient length to allow them to extend between the positioned cartridge  500  and a storage for the container  494 . In embodiments, the container  494  can be a cardboard box or plastic box. 
     Referring to  FIGS.  7 A through  7 D , a concentration measurement module  535  as described above is now detailed according to an example embodiment. A section of a cartridge support  556  may correspond to a portion of cartridge  406 , or the support  529  of cartridge  500  described above. Thus, the edges of the cartridge support  556  may be considered to extend and not be limited to the particular shape or size illustrated, the portion shown being merely a portion of a larger support structure. An inlet flow of conductive fluid enters through an inlet channel  566  molded into the cartridge support  556 . A wall  567  rises from the plane of cartridge support  556  to define the channel  566 . The edge of the wall  567  may be sealed with a plastic film to make channel  566  pressure-tight. Flow, indicated by arrow  564 , entering the channel internal volume  557  from other parts of the cartridge support  556  leaves the channel  566  through an opening  568  where it flows into a flow column housing  575  as indicated by arrows  574 , and flows from an end opposite the entry to an opening  570  in cartridge support  556 , through a temperature sensing region  558 . From there, the flow traverses a temperature measurement chamber  563  toward an exit channel  572  which is on an opposite side from the opening  570  where the flow entered the temperature measurement chamber  563 . The flow leaves the concentration measurement module  535  as indicated by arrow  562 . The temperature measurement chamber  563  and the exit channel  572  may be sealed in the same fashion as channel  566  such that the temperature measurement chamber  563  forms a flat broad chamber. A temperature transducer may be placed against the face of the film that is used to close the temperature measurement chamber  563  providing a broad contact area for accurate temperature measurement that limits edge losses that can bias the temperature measurement. In addition, a zero-flux temperature sensor can be used which actively cancels heat flux due to conduction through the major face of the temperature measurement chamber  563 , providing an excellent application here because of the high sensitivity of concentration to temperature. Bosses  552  may be provided for support and additional structure and sealing competence in the cartridge support  556 . 
     Conductive electrodes  550  may be bonded, welded, press-fitted, molded or otherwise affixed to the cartridge support  556  (a portion being shown at  576 ). In one embodiment, in use, spring biased contacts  571  and  573  may be pressed into each conductive electrode  550  while at the same time, a temperature transducer  577  is held against the temperature measurement chamber  563  as a sensor backplane  587  portion is held against the concentration measurement module  535  as a result of the entire cartridge being positioned in place in medicament proportioning module  104  and engaged for use. That is, when a cartridge of any of the embodiments, carrying the concentration measurement module  535  is positioned in place in a medicament proportioning module  104  and registered, the spring biased contacts  571  and  573  and temperature transducer  577  are placed against the conductive electrodes  550  and temperature measurement chamber  563  so that measurements can be taken by the connected controller. Note that  FIGS.  7 B and  7 D  are exploded views. Alternatively, elastomeric contacts may be used in place of spring biased contacts  571  and  573  as will be described in detail below. 
     Referring to  FIG.  7 E , a concentration measurement module  535 ′ similar to concentration measurement module  535  in all respects except that a compliant multiconductor device  583  is used to connect contact pads  571 ′ and  573 ′ to the conductive electrodes  550  shown by hidden lines. The compliant multiconductor device  583  has an elastomeric contact insert  754  partially enclosed by a housing  752 . Further details are described infra. The elastomeric contact insert  754  connects contact pads  571 ′ and  573 ′ to respective points on the conductive electrodes  550 . This replaces the contacts the spring biased contacts  571  and performs the same function with greater reliability and tolerance of manufacturing variability. 
     Note in any of the embodiments described herein, other types of tubing closures may be used. For example, frangible-seal valve-type closures may be used. An example of a frangible-seal valve is described in U.S. Pat. No. 4,586,928. The medicament proportioning module  104  may be equipped with an actuator to open a frangible-seal valve automatically during a set-up procedure. In a method, after installing the fluid cartridge, a linear actuator aligned with a frangible-seal valve by the positioning of the cartridge, may be controlled to open the valve in response to a command from a controller. The command may follow the complete preparation for a treatment, for example and a user input to a user interface indicating that the system should begin priming in preparation for treatment. 
     Note in any of the embodiments, a single sterilizing filter may be used to fill the concentrate containers of multiple fluid circuits. This may be done by connecting multiple fluid circuits to a single filter with a manifold. The latter may be sterilized prior to use. The fluid circuits connected to the filter and manifold may be sterilized after connection to prevent touch contamination from making the connection or the connection may be done in a sterile environment. The circuits may be filled and then sealed. 
       FIG.  8 A  shows a portion of a fluid circuit cartridge  800  to illustrate how electrical, thermal, and mechanical engagement of actuators and sensors are provided using the fluid circuit cartridge device. A fluid circuit base planar element  812 , for example, injection molded plastic has molded walls that define channels  826  having a generally uniform cross section and may be covered by film by welding or adhesive. The wall extends from a base portion of the planar element forming a trough and the edges of the walls remote from the base element are then sealed with the film, fully closing the trough to form the channel. The film may be thin to minimize thermal resistance between a temperature sensor  815  (supported on a support  814 ) and the fluid carried by the channel  826 . A channel  826  portion for engagement with temperature sensor  815  may be flattened out to reduce edge flux effects on the temperature measurement. In general, the channels  826  may be straight or curved segments that convey fluid with minimal resistance. Openings such as indicated at  804  allow the flow in the channels  826  to flow (see arrows  813 ) into other features such as a column channel  802  for measuring conductivity using electrodes  808  and the accumulator (not shown). 
     In one embodiment, the electrodes make electrical contact with contact pins  806  (which may be four in number for measuring contact resistance and for four-point measurement to minimize the effect of contact resistance on the conductance signal) also supported on an opposing planar actuator support indicated by dot-dash line along support  814  but which may be any type of support or supports. The temperature sensor  815  and contact pins  806  may be backed by urging elements such as springs. 
     In an alternative embodiment, instead of contact pins  806 , the electrodes make electrical contact with elastomeric elements (which may also be four in number for measuring contact resistance and for four-point measurement to minimize the effect of contact resistance on the conductance signal) as will be described in detail below. 
     Pumping tube segments  820  can be clamped between a roller actuator  822  and a race  824 , respectively supported on support  814  and an opposing support  829 . A pinch clamp tube segment  832  of tubing can be positioned between clamping elements  830  supported on support  814  and clamped by a pinch clamp tubing segment. All of the engagements required are conveniently provided by moving the supports  814  and  829  in opposing directions as indicated by arrows  816  around the fluid circuit base planar element  812 . Further, some of the fluid carrying features are formed by the fluid circuit base planar element  812  including the channels. Connections to the tube segments can be formed in the channel by molding as well. A tubing segment with a valve  845  such as a frangible-seal valve may be positioned to be opened at a time of set up and priming by an actuator motor  843  and actuator  844 . Here the fluid circuit base planar element  812  may serve as a backstop to resist the force applied to the valve  845  or the actuator  844  may provide a clamping or scissor action that does not require an opposing support. 
     Another fluid circuit feature that can be formed in the fluid circuit base planar element  812  is a pressure sensor region  847 , which may be formed similarly to the temperature channels  826 . The overlying film provides a compliant surface that can apply force to a strain gauge  848  pressed into engagement with the overlying film of the pressure sensor region  847  when the  816  are positioned to engage the fluid circuit cartridge  800  elements. Openings  804  and elbows  849  may also be made in the fluid circuit base planar element  812  with to flow fluid from channels  826  to tubular portions such as a pinch clamp tubing segment  832 , a valve  845 , or pumping tube segment  820  attached at the opposite side of the fluid circuit base planar element  812 . 
     As discussed above, the fluid circuit base planar element  812  may also support a data carrier  833  that is positioned when the cartridge is installed, to be read by a reader  831 . 
     In embodiments, the fluid circuit base planar element  812  may be molded such that all the side action mold parts can be drawn in the same direction. In embodiments, the fluid circuit cartridge  800  may position all the sensor and actuator surfaces on one side of the fluid circuit base planar element  812 . This allows all the actuators and sensors and their associated wiring and circuitry to be positioned on a first side and supported by only the support  814 . The opposing support  829  can be passive. In the example shown, the opposing support  829  supports only the race  824  (a member often called a “shoe”). To facilitate tight packing of the elements, some of the larger elements such as column channel  802 , pinch clamp tubing segment  832 , a valve  845 , and pumping tube segment  820  can be attached on the opposite side. This allows the sensors and actuators to be larger than they would be able to be if these elements were on the other side. Rather, most of the first side is flat or open. This can allow the cartridge to be much smaller than otherwise possible. 
       FIG.  8 B  shows a portion of a fluid circuit cartridge  801  similar to that of  FIG.  8 A  except that instead of contact pins  806 , the electrodes make contact with current source and voltage measurement contacts using the elements shown in  FIG.  8 C .  FIG.  8 C  shows a contact device  854  according to embodiments of the disclosed subject matter. A portion of the fluid circuit base planar element  812  defines a wall of the column channel  802 . The electrode  808  seals the flow space enclosing the fluid whose conductivity is to be measured. A housing  752  holds an elastomeric contact insert  754  against the electrode  808 . Elastomeric contact insert  754  is shown by hidden lines at  863 . The housing is attached to the fluid circuit base planar element  812  or the electrode itself by any suitable means including an interference fit, adhesive attachment, fasteners, or other means. A contact element  851  has a substrate  853  with current source  860  and voltage measurement  861  contacts. When a cartridge of which fluid circuit base planar element  812  is a part is moved relative to the other means the contact element  851 , the elastomeric contact insert  754  is squeezed between the electrode  808  and the current source  860  and voltage measurement  861  contacts. See  FIGS.  13 A through  13 D  for more. The configuration avoids the need for contact pins  806 . Other benefits of the elastomeric contact insert  754  and equivalents apply. Thus, the electrode  808  and other means the contact element  851  can 
     Referring now to  FIG.  9 A , as in the fluid circuit  533 , conductivity may be measured using series concentration measurement modules that are connected in series or series/parallel as described with reference to  FIG.  5   . In the present embodiment, which may be substituted into any of the foregoing or following embodiments, conductivity is measured based on multiple paths as well as the fluid column in a respective measurement column, such as columns  702 . A fluid flows through columns  702  which are joined by channel elements  703 . Additional channel elements may be included such as to inject concentrates or diluents as described with reference to  FIG.  6   . In the latter embodiment, the resistance of fluid to the flow of current was obtained between conductive electrodes at either end of a respective measurement column. In embodiments, additional measurements using the same conductive electrodes may be made. In  FIG.  9 A , conductive electrodes  701  are labeled A through H. Contact resistance on the dry side of each electrode may be made between current contacts and voltage sense contacts which are provided and used according to the well-known four-point resistance measurement technique. In the present embodiment, resistance is measured between multiple pairs that share a given conductive electrode  701 . Not all the conductive electrodes are indicated by a reference numeral to avoid clutter, but each is labeled with a respective letter. Here, conductive electrode pair A-B is used for a resistance measurement through a respective fluid column  702 . Further, conductive electrode pairs A-D and A-C are also used for a resistance measurement through a respective fluid column  702  plus channel element  703  and a respective fluid column  702  plus channel element  703  plus fluid column  702 , which form respective longer fluid paths. The same may be done with conductive electrode pairs B-C, B-D, and C-D. Given known properties of the respective channels, which may be stored explicitly or tacitly (e.g., by way of a formula or look up table), the fluid conductivity can be derived from these resistance measurements. Further measurement columns  702 , receiving the same fluid, may be added to provide additional fluid paths between additional conductive electrode pairs, such as A-E, A-F, E-F, E-H and so on. Additional conductive electrodes may also be added to each measurement column such as the conductive electrodes labeled J through M in  FIG.  9 B . In the latter example, additional conductive electrodes  708  forming pairs can be used for additional measurements of fluid conductivity, for example, A-J and A-K. Not all combinations of conductive electrodes are enumerated herein as it is straightforward to make a comprehensive list of conductive electrode pairs that can be formed with any such a conductivity measurement system based on a desired number and allocation of conductive electrodes. As in the embodiment of  FIG.  9 A , branch lines that admit diluent or concentrate may be included at any point, of course with diminution of the number of combinations of conducting electrodes that may be available for conductivity measurement. 
     In the foregoing embodiments, by forming multiple electrical conduction paths through interconnected conductivity cells, using additional conductive electrodes for each measurement column, and/or by measuring across fluid paths between measurement columns, additional measurements of the same fluid conductivity or measurements that include additional variables such as the electrode “wet-side resistance,” i.e., the resistance between an electrode and the fluid can be better gauged, at least for purposes of determining the reliability of a conductivity measurement. Where a resistance measurement appears faulty due to an unexpected resistance associated with an electrode, the multiple paths provide multiple equations to solve for the unknown additional resistance correction term that is used to compensate the resistance. The controller may perform these calculations automatically. 
     In any embodiments, an accumulator, such as accumulator  502 , can be omitted and an inline pressure sensor alone may be employed thereby relying on the compliance of tubing for providing smooth pressure signals for control. The elimination or reduction in size of the accumulator may be an optimization variable. Reducing this volume may speed the synchronization process. 
     In any of the embodiments, including the claims, two medicament concentrates may be diluted by a medicament proportioning system or module. In these arrangements where there is concentration detection, the buffer may be diluted first and then the acid may be diluted to form a dialysate or replacement fluid product. This has benefits in that the concentration signal of the acid is stronger than that of the dilute buffer thereby causing more sensitive concentration detection. 
     In any of the embodiments including cycler  106 , the latter may be replaced by any medicament consuming device or article such as a storage container for product medicament or a peritoneal dialysis cycler. In any of the foregoing embodiments, a pressure sensor may be positioned within an inlet or outlet of the accumulator to allow the controller to control flow through the accumulator. This may in effect be a mechanical pressure control signal from the device that demands fluid from any of the disclosed medicament proportioning system, medicament proportioning module, or other device. 
     In any of the foregoing embodiments, the flow channels and pumping mechanisms may be replaced with any equivalent elements adapted for fluid conveyance. They may be selected to handle flow rates in the range, in respective systems or in a single system to provide medicament to a consuming device at a rate of 25 through 400 ml/min. Any of the embodiments may be modified to provide an intermediate storage of medicament if the instantaneous demand of a consuming device exceeds the selected maximum generation rate of medicament. The medicament formed by the foregoing embodiments may be dialysate or replacement fluid for use any type of renal replacement therapy system, for example, peritoneal dialysis, hemodialysis, liver dialysis, and hemofiltration. The consuming appliance for any of the above systems may be a storage container to generate medicament to support a vacationing patient. It will be observed that in the embodiments disclosed, spent fluid (e.g., spent dialysate) from an attached cycler can be disposed of such that it never enters the medicament proportioning module  104  or any element upstream of the cycler. In embodiments, the cycler  106  is configured to prevent a backflow of fluid into the medicament proportioning module  104 . For example, a check valve may be provided in-line between the medicament proportioning module  104  and cycler  106  for such a purpose. 
     By providing ultrapure water that has been reliably sterilized and guarded against touch contamination, it is possible to ensure against risk for a primed medicament proportioning module  104  to treat multiple patients within a long time period, in an exemplary embodiment, up to 24 hours apart. Also, the medicament proportioning module  104  may be primed and readied for a treatment to occur many hours, for example up to 24 hours, from the time of set-up. 
     In any of the foregoing cartridge embodiments, the cartridge may include a data carrier (e.g.,  519 ) which may be or incorporate devices such as a bar code, RFID, smart chip, memory chip, or other device that includes data related to the concentrate or dry compound attached thereto for generation of medicament. Thus, by installing the cartridge, details related to the attached medicament concentrate can be communicated to the controller of the medicament proportioning module  104  or medicament preparation system (e.g.,  600 ). For example, the data carrier may include data responsive to an expiration date, whether the fluid circuit attached to the cartridge has been used prior to the most recent installation, how much fluid has been generated from it, how long since it was first primed with fluid, the makeup of the concentrates attached to the fluid circuit. The pre-attachment of the concentrates to the circuit cartridge (e.g.,  500 , cartridge  406  and others), when the cartridge includes a data carrier that refers to information about the concentrates and other components of the fluid circuit, provides the two benefits (1) of allowing the cartridge, which may be of a types that is registered in a specific position and therefore convenient to allow for reading of data on the data carrier by means of a reader and (2) preventing contamination of fluid circuit by avoiding the need to make a new connection to combine the concentrate containers with the other elements of the fluid circuit. The precise positioning of the cartridge, for engagement of actuators and sensors therewith, can ensure predictable and reliable interaction between the data carrier and a reader co-located with the sensors and actuators. Also, the cartridge may be of a type that is convenient and relatively small, making handling easier for less able-bodied users, since the cartridge may be tethered to the heavier concentrate containers which may be placed in separate positions and, in embodiments, with less accuracy. In embodiments, a receiving support for the concentrate containers may be low down next to the floor while the cartridge receiving position may be located above that receiving support for the concentrate containers. For example the medicament concentrate disposable package, which may contain the medicament concentrates as discussed with reference to the various embodiments, is positioned on a low shelf. A slide out tray (on roller rails for example) may be provided (not shown) to allow the medicament concentrate disposable package to rested thereon so that the medicament concentrate disposable package can be pushed into position without sliding. Similarly, for the ultrafilter module and any other similar components. 
     The controller of the medicament proportioning module  104  or medicament preparation system  700 A,  700 B, or any other of the modules or systems herein described may have an identifier of one or more patients correlated with the medicament that is prescribed for that patient. The data included in the data carrier may be used by the controller to confirm that the correct fluid circuit is loaded by verifying the circuit cartridge data carrier. The control of the proportioning by pumps may be regulated to conform to the required medicament product. When the cycler is attached to the medicament preparation system (e.g.,  600 ) or module  104 , a signal communication between the controller of the medicament proportioning module  104  or medicament preparation system  700 A,  700 B and the attached consuming device, such as cycler  106  (e.g., see lines  124 ) may contain data indicating the type of medicament required, an identification of the patient, a prescription, or other information that may be correlated by any of the controller with the parameters of the connected fluid circuit as indicated on the data carrier of the cartridge and a signal indicating permitted or non-permitted component installation generated by any of the controllers. Such a signal may cause the generation of an output indication or prevent further operation of the equipment, if a non-permitted component installation is performed. 
     The data carrier may also establish expected reading ranges for measured concentration of medicament concentrate indicated by concentration measurement module  535 A- 535 D. These data may be used to control the dilution rate of the respective medicament concentrates using feedback control from the concentration measurement modules or conductivity/temperature sensors in accord with the respective embodiments. Note that as used herein, a combination of a conductivity sensor and a temperature sensor may also be referred to as a concentration measurement module. The data carrier may include calibration data or data used for ensuring the accuracy of measurement using the cartridge or other parts of the fluid circuit. For example, in embodiments, the data carrier may communicate to the controller the cell constants or dimensions of the conductivity sensors of the cartridge for use in computing conductivity and thereby concentration. The data relating to disposables attached to and used with the system (e.g., water purification module  102  and medicament proportioning module  104 ) may be logged in a maintenance and/or procedure log for troubleshooting and service. The latter may be output by the user interface by maintenance, treatment, or service personnel. Solute concentration is used to set target conductivity values. Reading-in solute concentration allows addition of new catalogue numbers without requiring a software update. 
     The replaceable components used for water purification may include replaceable tagged components with data carriers permitting various similar functions as the data carriers described herein and other relevant to the cartridge. Generally, the function of the water purification module  102  (or the water purifying function of an integrated medicament preparation system), is to purify water to a same standard. However, the performance characteristics of the replaceable tagged components may vary. The control of the water purification module  102  may include determining whether the replaceable tagged component is correct for the particular water purification module  102 . In embodiments, the controller may predict a total amount of fluid that may be processed before replacement of certain replaceable tagged components is appropriate. 
     Referring now to  FIG.  9 A , a conductivity measurement portion  700 A of a fluid circuit includes multiple measurement columns  702  connected in series by channel elements  703 ,  705 ,  707 . Additional junctions may be provided as described with reference to  FIG.  10   . Four pairs of conductive electrodes A-B, C-D, E-F, G-H, are shown but the number of columns and number of electrodes can vary. As described with reference to  FIG.  10   , each conductive electrode pair can be used for an independent measurement of a conductivity of fluid (or fluids) flowing therethrough. In the present embodiments, resistance is measured across other pairs of conductive electrodes than the pairs, A-B, for example, at opposite ends of each measurement column  702 . For example, the resistance between conductive electrodes A-C and A-D as well as B-C and B-D may also be measured. With predefined channel properties between these pairs of conductive electrodes stored in a controller (or effectively stored in a lookup table or formula for computing fluid conductivity, multiple equations with multiple unknowns that include the contact resistances of the electrical contacts used to measure conductivity can be obtained. 
     In any of the foregoing embodiments, fluid circuits may include inline chambers (accumulators) to reduce water hammer due to interaction between interconnected peristaltic pumps. Additional lengths of tubing may also be included for the same purpose. Also, tubing diameters of pump tubing segments may be selected to minimize interaction issues which may reduce accuracy or cause breakage of circuit elements. 
     In any of the disclosed embodiments that measure the conductivity of a fluid by using conductivity cells, conductivity sensors, or conductivity measurement modules (e.g.,  415 ,  416 ,  417 ,  418  in  FIG.  8 A,  535 A -D in  FIG.  6   , or  535  in  FIGS.  7 A- 7 D ), electrical contact with wetted electrodes (e.g.,  505 ,  506 ,  510 ,  512  in  FIG.  8 A,  550 ,  577    in  FIGS.  7 A- 7 D , or  808  in  FIGS.  8 A,  8 B ) may be made through elastomeric contacts instead of spring-biased contacts. An embodiment of an elastomeric contact insert is shown in two oblique views  710   a  and  710   b  in  FIGS.  10 A and  10 B , respectively. The contact insert is configured to be inserted into a housing that exposes the top side and the bottom side of the contact insert such that the top side of the elastomeric contact can make electrical contact with appropriate electrical point/points in an electrical circuit of a conductivity measurement module, while the bottom side of the elastomeric contact can make electrical contact with a wetted electrode (further details of embodiments of the housing are described below with reference to  FIGS.  13 A and  13 B ). As compared to spring-biased contacts, using the disclosed elastomeric contacts allows for positional tolerance, for example, at least along the Z axis  718 . Further, the disclosed elastomeric contacts are less susceptible to fluid leaks as compared to spring-biased contacts such as pogo pens. This is due to the fact that pogo pens have sliding surfaces (to slide the pen to make contact with wetted electrodes) while the disclosed elastomeric contacts include no sliding surfaces. 
     Still referring to  FIGS.  10 A and  10 B , in one embodiment, the contact insert is formed by wrapping (along the Y axis  720  and the Z axis  718 ) at least a portion of an elastomeric block  714  with a parallel array of electrically conductive wires  712 , where each two adjacent wires are separated by an electrically insulating material. Alternatively, the contact insert may be formed by attaching/gluing/molding a ZEBRA® connector strip (i.e., an elastomeric connector strip with alternating electrically conductive and electrically insulating regions in an elastomeric matrix) around at least a portion of the elastomeric block  714 . The ends of the wires  712  may be protected by an adhesive protector  716 , for example, an adhesive film. The elastomeric block  714  may be of any suitable elastomeric material such as silicon, rubber, synthetic rubber, or other material. The elastomeric block  714  is preferably of an electrically insulating material. The wires  712  may be bonded to the elastomeric block  714 . The wires  712  may be of any electrically conductive material. In embodiments, the wires  712  are 0.002″ in diameter and made of gold over nickel-plated copper. 
       FIGS.  11 A and  11 B  respectively show two oblique views  730   a  and  730   b  of an embodiment in which the elastomeric block  714  has a relief recess  732  that allows for improved positional tolerance along the Z axis  718 . That is, the relief recess  732  permits the elastomeric block to better flex. The wires  712  span the relief recess  732  at the corresponding side of the elastomeric block  714 . The shape, size, and location of the relief recess  732  in  FIGS.  11 A and  11 B  represent only one possible embodiment for improving flexibility of the elastomeric contact, and alternative shapes, sizes, locations, and numbers of relief recesses will be apparent to a skilled person in the relevant arts. 
       FIGS.  12 A,  12 B, and  12 C  respectively show cross-sectional views  734   a ,  734   b , and  734   c  (orthogonal to the X axis  709 ) of example embodiments of variations of the disclosed elastomeric contact. The elastomeric block  714  of the elastomeric contact insert illustrated in  FIG.  12 A  is solid, while the elastomeric block  714  of the elastomeric contact insert illustrated in  FIG.  12 B  has cutouts  736  to provide springiness, and the elastomeric block  714  of the elastomeric contact insert illustrated in  FIG.  12 C  has both the relief recess  732  and the cutouts  736  to provide better flexibility and springiness. 
       FIGS.  13 A- 13 D  show various views  750   a ,  750   b ,  750   c , and  750   d  of embodiments of a housing  752  that supports an elastomeric contact insert  754  for use. More specifically,  FIGS.  13 A and  13 B  show oblique views  750   a  and  750   b  of the housing  752  with the elastomeric contact insert  754  inserted,  FIG.  13 C  shows a cross-sectional view  750   c  of the housing  752  without the elastomeric contact insert  754  being inserted, and  FIG.  13 D  shows a cross-sectional view  750   d  of the housing  752  with the elastomeric contact insert  754  being inserted. The housing  752  may be a block of rigid plastic or other electrically insulating material. In embodiments, the housing is of silicone. The elastomeric contact insert  754  is configured to be inserted in a receiving well  756  of the housing  752 . The resilience of the elastomeric contact insert  754  allows for variations in the smoothness of the receiving well  756  to be accommodated. Adhesive may be inserted in the receiving well  756  prior to the insertion of the elastomeric contact insert  754 . 
     In one embodiment, the elastomeric contact insert  754  and the receiving well  756  of the housing  752  are configured such that when the elastomeric contact insert  754  is inserted in the receiving well  756 , the top portion of the housing  752  snugly fits the top portion of the elastomeric contact insert  754  while the bottom portion of the housing  752  is wide enough to allow for a void space being created between the inner surface of the bottom portion of the housing  752  and the outer surface of the bottom portion of the elastomeric contact insert  754 . 
     In one embodiment, the elastomeric contact insert  754  is inserted such that a top surface  758  of the elastomeric contact insert  754  slightly protrudes from the top portion of the housing  752 , while a bottom surface  760  of the elastomeric contact insert  754  slightly protrudes from the bottom portion of the housing  752 . 
     In one embodiment, once the elastomeric contact insert  754  is inserted, an array of wires at the top surface  758  of the elastomeric contact insert  754  are configured to make electrical contact with a wetted electrode in a conductivity measurement module when the housing  752  is forced against the wetted electrode. Further, an array of wires at the bottom surface  760  of the elastomeric contact insert  754  are configured to make electrical contact with wires or printed circuit board (PCB) traces that are forced against the bottom surface  760  of the elastomeric contact insert  754 , where the PCB traces may in turn be soldered or otherwise electrically connected to a sensor. As described herein with reference to various embodiments, for example, in  FIGS.  13 A,  13 B,  13 C, and  13 D , each wire in the array of wires at the top surface  758  of the elastomeric contact insert  754  is electrically connected to a corresponding wire in the array of wires at the bottom surface  760  of the elastomeric contact insert  754 . By pressing the top surface  758  of the elastomeric contact insert  754  against a flat wetted electrode and at the same time pressing the bottom surface  760  of the elastomeric contact insert  754  against the PCB traces, the array of wires provides redundant points of electrical contact between the wetted electrode and the sensor. Accordingly, the housing  752  and the elastomeric contact insert  754  form a contact device that is part of a fluid management system with associated electronics for completing the sensor as well as other elements. 
     In embodiments, the sensor may be a fluid conductivity cell of a disposable fluid circuit having wetted electrodes that are pressed against the elastomeric contact insert  754  when installed. In embodiments, the sensor may include driving and detection circuitry of a conductivity measurement electrical circuit such as a 4-terminal sensing circuit as described below with reference to  FIG.  5   . 
       FIG.  14    shows a schematic view  770  of various components forming a 4-terminal sensing circuit in a fluid conductivity cell of a disposable fluid circuit in order to measure the conductivity of a fluid that is in contact with a first wetted electrode  773  and a second wetted electrode  771 , according to an embodiment. 4-terminal sensing, also known as Kelvin sensing, refers to a method of measuring the electrical impedance between two points by driving current between the two points via a circuit formed between the first PCB current contact  778  and the second PCB current contact  782  while measuring the voltage between the first PCB voltage contact  780  and the second PCB voltage contact  784 . Accordingly, since the induced current does not go through the contacts that are used for measuring voltage, the impedance of the voltage measurement contacts cannot induce errors in the impedance measurement, and the impedance measurement is insensitive to contact resistance in the current portion of the circuit. 
     As shown in the embodiment of  FIG.  14   , 4-terminal sensing is implemented by a current source  772  and a voltmeter  774  that are both electrically connected to respective electrodes in a PCB  776 , where the PCB  776  is in electrical contact with the first wetted electrode  773  and the second wetted electrode  771  via a first elastomeric contact insert  786  and a second elastomeric contact insert  788 , respectively. The current source  772  drives an electrical current between a first PCB current contact  778  and a second PCB current contact  782  on the PCB  776 , while the voltmeter  774  measures the voltage difference between a first PCB voltage contact  780  and a second PCB voltage contact  784 . 
     The PCB  776  is pressed or held against a first side  796  of the first elastomeric contact insert  786  and a first side  798  of the second elastomeric contact insert  788  such that:
         a first group of parallel wires  790  on the first elastomeric contact insert  786  make electrical connection with the first PCB current contact  778  on the PCB  776 ,   a second group of parallel wires  792  on the first side  796  the first elastomeric contact insert  786  make electrical connection with the first PCB voltage contact  780  on the PCB  776 ,   a first group of parallel wires  794  on the second elastomeric contact insert  788  make electrical connection with the second PCB voltage contact  784  on the PCB  776 , and   a second group of parallel wires  795  on the second elastomeric contact insert  788  make electrical connection with the second PCB current contact  782  on the PCB  776 .       

     In one embodiment, the first PCB current contact  778  and the first PCB voltage contact  780  may be printed on the PCB  776  as a pair of adjacent parallel rectangular contact pads, collectively covering an area smaller in area than, or approaching the area of the first elastomeric contact insert  786  that in contact with the PCB  776 . Similarly, the second PCB current contact  782  and the second PCB voltage contact  784  may be printed on the PCB  776  as another pair of adjacent parallel rectangular contact pads, collectively covering an area smaller in area than, or approaching the area of the second elastomeric contact insert  788  in contact with the PCB  776 . 
     In the embodiment of  FIG.  14   , all PCB electrodes are printed on the same PCB  776 . However, in alternative embodiments, the PCB electrodes may be printed on more than one PCB. For example, in an alternative embodiment, the first PCB current contact  778  and the first PCB voltage contact  780  may be printed on a first PCB, while the second PCB voltage contact  784  and the second PCB current contact  782  may be printed on a second PCB different than the first PCB. In this alternative embodiment, the first PCB is forced against the first elastomeric contact insert  786 , while the second PCB is forced against the second elastomeric contact insert  788 . 
     A second side  797  of the first elastomeric contact insert  786  is forced against the first wetted electrode  773 , so that both the first group of parallel wires  790  and the second group of parallel wires  792  make electrical connection with the first wetted electrode  773 . Similarly, a second side  799  of the second elastomeric contact insert  788  is forced against the second wetted electrode  771 , so that both the first group of parallel wires  794  and the second group of parallel wires  795  make electrical connection with the second wetted electrode  771 . As a result, the current source  772  is in effect driving a current across the fluid in between the first wetted electrode  773  and the second wetted electrode  771 , and the voltmeter is in effect measuring the voltage drop across the fluid in between the first wetted electrode  773  and the second wetted electrode  771 . Accordingly, fluid conductivity may be determined as a linear function of the driven current value divided by the measured voltage value. 
     In any of the embodiments, the PCB  776  may provide test points for measuring the integrity of the electrical connections made between the PCB electrodes, the elastomeric contact inserts, and the wetted electrodes, as will be apparent to a skilled person in the relevant arts. Also, the resistance of the connection between the contacts and a respective electrode can be confirmed by a controller by applying a current between the first or second PCB current contact and its adjacent voltage contact and measuring a voltage drop. If a resistance above a threshold level is detected, the controller may generate an error output. 
       FIGS.  15 A and  15 B  show cross-sectional views  600   a  and  600   b  of an alternative housing  602  that can support the elastomeric contact insert  754  in embodiments. The elastomeric contact insert  754  may be inserted along the direction indicated as  604  into a receiving well  606  of the housing  602 . The insertion places the parallel wires  608  of the elastomeric contact insert  754  in electrical contact with a first electrical housing contact  610  and a second electrical housing contact  612  provisioned on the surface of an internal wall of the receiving well  606 . A first electrical housing contact  614  and a second electrical housing contact  616  may be electrically connected to a respective one of the first electrical housing contact  610  and the second electrical housing contact  612  to provide electrical connection access to respective ones of the first electrical housing contact  610  and the second electrical housing contact  612  from outside the housing  602 . The first electrical housing contact  610  and the second electrical housing contact  612  may be made of machined bores in the internal wall of the receiving well  606  of the housing  602  and may be round or have any other shape rather than being rectangular as illustrated. 
     Once inserted, each wire in an array of wires on a top surface  618  of the elastomeric contact insert  754  is electrically connected to a respective one of the first electrical housing contact  610  and the second electrical housing contact  612 , and thus is also connected to a respective one of the first electrical housing contact  614  and the second electrical housing contact  616 . The first electrical housing contact  614  and the second electrical housing contact  616  may in turn have wires or PCB traces connected to them which may then be soldered to a device such as driving and detection circuitry of a sensor as described herein with reference to various embodiment. A wetted electrode may then be forced against the top surface  618  of the elastomeric contact insert  754 , thereby allowing for electrical connections to be made between the wetted electrode and both of the first electrical housing contact  614  and the second electrical housing contact  616 . Accordingly, the housing configuration shown in the embodiment of  FIGS.  15 A and  15 B  may be used to implement 4-terminal sensing for fluid conductivity measurement as described herein with reference to  FIG.  14   . 
     Referring to  FIG.  16   , a medicament preparation system  1600  includes a fluid circuit  1601 . In the example of  FIG.  16   , the medicament preparation system  1600  is formed on a cartridge of a dialysis system, but system  1600  is not limited to this exemplary embodiment. In an embodiment, the cartridge may be the same as cartridge  500  in embodiments above. Embodiments disclosed below are also applicable in non-cartridge based fluid circuits, where two flow paths come together and where it is desirable to control the quantity of fluid in each flow path. 
     In the example of a cartridge, the cartridge may be rigid, thus forming a rigid fluid path on or within the cartridge. Thus, the fluid circuit  1601  may be formed in a rigid structure. The cartridge may be a disposable component of a dialysis system, or may be a part of a disposable component. 
     It will be understood that the present disclosure is not limited to a fluid circuit on cartridge, and other types of fluid circuits  1601  are contemplated by this disclosure. The cartridge  1607  may be a disposable component of a fluid machine, such as a dialysis machine, or may be a part of such a disposable component that includes tubes and other parts. In some embodiments the cartridge may be pre-connected to container of concentrated substance such that the cartridge, the connection to the concentrate container, and the concentrate container are all sterilized together. 
     The fluid circuit  1601  shown in  FIG.  16    may take various shapes and forms, and the particular arrangement is only exemplary. The fluid circuit  1601  includes one or more junctions  1602  and  1603 , as shown in  FIG.  16   . The junctions are oriented in a particular position relative to the force of gravity, and the entire fluid circuit may be oriented in a predefined way relative to the force of gravity when installed in a receiving portion of a fixed machine such as a fluid preparation system (not shown). In an embodiment, when the fluid circuit  1601  is in use, such as when mixing fluids, the junctions  1602  and  1603  are positioned such that a trough or valley  1704  is formed at the lowest position of the junction. An enlarged view of an example of junction  1602  is shown in  FIG.  17   , and an enlarged view of an example of junction  1603  is shown in  FIG.  18   . 
     Referring to  FIG.  17   , the junction  1602  may be generally “Y” shaped, where the left upper branch of the Y and the lower channel  1707  branch form common channel  1707 . It is contemplated that the channel  1707  carries a fluid with a particular density. In an exemplary embodiment, the fluid is purified water mixed with some medicament. In another embodiment, the fluid is a mixture of purified water and bicarbonate. In another embodiment, the fluid is a diluted dialysate. 
     The upper right branch of the junction  1602  is formed by concentrate channel  1706 , which carries a fluid with a density that is greater than the density of the fluid in the common channel. The relative difference in the density, together with a chicane formed in the concentrate channel  1706  and described below will be appreciated when considering the operation of the medicament preparation device. In embodiments, the fluid flowing through channel  1707  has different viscosity than the fluid flowing through channel  1706 , such that the fluid in channel  1706  has a greater viscosity. 
     As noted above, the medicament preparation system  1600  is used to create a medicament by admixing two fluids. In an exemplary embodiment, dialysate is produced by admixing purified water with a dialysate concentrate. To mix the two fluids, a mechanism, such as a pump, moves each of the fluids through the two upper branches of the junction. In some embodiments, the pump may be a peristaltic pump (not illustrated) that exerts force on a pumping segment to move the fluid(s) through the fluid circuit  1601 .  FIG.  19    illustrates flow  1901  of a diluent, or other fluid, in channel  1706  and concentrate flow  1902  in channel  1707 . 
     Staying with the example of producing dialysate, channel  1707  will be filled with purified water (or water with other chemicals mixed in, such as bicarbonate). The concentrate channel  1706  will be filled with a fluid that has a higher density that the fluid in the channel  1707  (for example concentrated dialysate or acid). 
     As shown in  FIG.  17   , the concentrate channel  1706  has a chicane  1701  that curves sharply upward and then sharply downward before the concentrate channel  1706  meets the common flow channel  1707 . The chicane  1701  can be created by a lower protrusion  1703  extending upward from the floor  1710  of the concentrate channel  1706  and an upper protrusion  1702  extending from the roof of concentrate channel  1706 . The chicane also includes a valley  1704  as shown in  FIG.  17   . By providing that the higher density fluid must flow upward in order to passively flow into the common channel, the chicane acts as a fluid gravity trap. 
     When the common flow channel  1707  is filled with a first fluid and the concentrate channel  1706  is filled with a second fluid, and the junction  1602  is oriented as shown in  FIG.  17    (relative to the force of gravity), it can be appreciated that the first fluid and the second fluid meet at the junction  1602 . Because the second fluid has a higher density that the first fluid, the second fluid fills the valley  1704 , but without a pumping force, will not flow over the upper edge of lower protrusion  1703  due to its higher density compared to the first fluid. In other words, the chicane  1701  prevents gravity siphoning or mixing of the second fluid into the common flow channel  1707  and concomitant mixing with the first fluid. When mixing is desired, pumping force is applied to convey the second fluid through the concentrate channel  1706  into the common flow channel  1707 . Likewise, pumping force may be applied to the first fluid to accurately meter an appropriate amount of each fluid into the mixture. As shown in  FIG.  16   , the first fluid can come from diluent supply  1605 , while the second fluid may come from concentrate supply  1606 . A feature that aids in the prevention of mixing is also the diameter of the channels relative to the viscosity of the fluids. Smaller diameter tubing helps to prevent mixing when the pump is stopped. 
     Referring to  FIG.  18   , another embodiment of junction  1603  is shown. The junction  1603  is different in the shape of the upper protrusion  1802  and the shape of the concentrate channel  1806 . The upper protrusion  1802  lies substantially parallel to the lower protrusion  1803 , but may be oriented at other angles as well. The upper protrusion  1802  extends away from the roof of the concentrate channel  1806  at an angle, which is imposed by the shape of the roof. The height of the concentrate channel  1806  is not constant, in contrast to the concentrate channel  1706 . The concentrate channel  1806  widens as it approaches the upper protrusion  1802 , creating a larger cross sectional area than farther upstream. In  FIG.  18   , diluent is provided from diluent supply  1605  and flows left (in  FIG.  18   ) and up. Concentrated fluid flows through concentrate channel  1806  and is admixed with the diluent when the concentrated fluid is pumped through the concentrate channel  1806 . 
       FIGS.  19 - 22    illustrate schematic examples of the junctions  1602  and  1603 . These figures can be thought of as cross-sectional views of the flow paths. While no particular shape of the flow channel is shown, it is contemplated that the concentrate channel  1706  and  1707  may be circular, oval, rectangular, or rounded rectangular in cross sectional shape. 
     Referring still to  FIG.  19   , the interaction between water (possibly with bicarbonate added) and an acid at a junction  1602  is shown. The water flow  1901  flows through channel  1707 , while the concentrate flow  1902  flows through channel  1706 . In this example, the concentrate is an acid, illustrated as a slanted line pattern. The water and acid is mixed to produce dialysate. The acid has a higher density than water, and thus remains in the valley  1704  unless sufficient pumping force is applied to the acid to raise it over the lower protrusion  1703  of junction  1602 . The flow in  FIG.  19    is the same as in  FIG.  17   , downward as indicated by arrows  1901  and  1902 . 
     Referring to  FIG.  20   , the junctions  1602  and  1603  may include all features of  FIG.  19   , and also an overhang  2001 . The overhang  2001  can be provided to reduce or avoid turbulence in flow  1901  through channel  1707 . As would be understood, the overhang  2001  has a sufficient length to shunt fluid in channel away from channel  1706 . The length of overhang  2001  can be set based on expected flow rate of flow  1901  and the expected back pressure in channel  1706 , which naturally opposes the ingress of fluid from channel  1707  into channel  1706 . 
     Referring to  FIG.  21   , a flap  2101  may be added in addition or instead of overhang  2001 . The flap  2101  can be biased such that biasing force keeps the flap  2101  closed until sufficient pressure builds up in channel  1706 , at which point the flap permits fluid from channel  1706  to flow and mix with fluid in channel  1707 . The flap  2101  is illustrated as a separate element with a hinge pin, but the flap  2101  can be molded at the same time as the flow channel, and can be made of a material that provides the necessary biasing force to keep the flap  2101  normally closed. The flap  2101  can be made of the same material as the rest of the flow channel, and the biasing force is controlled by selecting a particular thickness for the flap  2101 . In embodiments, the flap  2101  can be made of a different material than the rest of the flow channel, and it is molded in a two-step molding process so that the flap  2101  can move and flex relative to the rest of the flow channel structure. In embodiments the flap is coated with a hydrophobic coating that reduces the likelihood of the concentrate from sticking to the flap  2101 . 
       FIG.  22    illustrates an embodiment where the flap  2201  may be larger than the flap  2101 , and the lower protrusion  1703  is not present. The upper protrusion  1702  may also be absent in this embodiment. The flap  2201  is biased to keep the concentrate channel  1706  closed, but the biasing force is overcome when fluid in the concentrate channel  1706  is pumped toward the channel  1707 . 
     Build-up of chemical and biological material in waste lines and drains used in medical application can require premature replacement or extensive cleaning using aggressive chemical. This is often expensive, burdensome, and can result in exposure of the user to harmful chemicals. The disclosed embodiments include devices and methods for preventing or at least delaying waste build-up that would negatively affect system operation. This is particularly important in applications where the waste fluid has high hardness that can result in calcium carbonate deposit. Examples are reverse osmosis, electro-deionization, and capacitive deionization reject water. 
       FIG.  23    shows a water purification system  2300  which may be based on reverse osmosis (RO) electro-deionization (EDI), or capacitive deionization (CDI) all of which are examples of purification processes that generate a waste water product that is highly concentrated in solutes and therefore subject to precipitation of solids on the internal wetted walls of the drain lines. In  FIG.  1   , raw input water enters the system through inlet  2301 , the raw input water is purified, producing purified product water and waste water. The purified product water exits through product water outlet  2303  while the waste water exits through waste water outlet  2305 . It should be understood that this discussion also applies to other drain lines, such as drain line  545  described above. 
     In embodiments of the disclosed subject matter, the pipe, tube, conduit, channel that conveys waste water from waste water outlet  2305  is treated to make its normally-wetted surface hydrophobic. In embodiments, a coating is a fluoropolymer of tetrafluoroethylene. In embodiments, the coating is Polytetrafluoroethylene (PTFE). In embodiments the coating may be hydrophobic and also oleophobic. This may reduce or delay scaling. 
     In embodiments, the drain is made to be replaced on a longer-term schedule than other fluid handling elements such as filters and fluid circuit connections. The RO (or EDI or) CDI device may have a controller that generates a reminder on a user interface to notify personnel to replace the drain line on a different (longer-term) schedule than for replacing the raw and product water handling circuit. 
     According to embodiments, the drain line may be treated with chemicals that prevent attachment of material to the wall of a permanent or durable (i.e., long-term-use) waste line such as tube formed with a hydrophobic material. An example is known commercially as UltraEverDry. 
       FIG.  24    shows a cycler  2400  receiving medicament through inlet  2401 . This inlet is expected to be less susceptible to fouling and buildup of solutes due to the purified nature of the medicament. The cycler  2400  outputs waste fluid, which may be a mixture of the medicament and solutes that were extracted from patient  2420  during treatment, through drain line  2405 . The drain line  2405 , similarly to waste water outlet  2305  above, is at an increased risk of fouling and material buildup. As shown in  FIG.  24   , treatment device  2410  receives medicament from cycler  2400  through inlet port  2411 , conveys the medicament to a consumer process (that may be connected to patient  2420 ) through patient access  2421  and receives waste fluid through drain line  2425 . The waste fluid is returned to the cycler through drain line  2415 . In many treatments, such as peritoneal dialysis or hemodialysis, the waste fluid may contain organic material from the patient such as shed cells and proteins in spent dialysate. The organic material is susceptible to fouling and sticking to the drain lines that convey it. To mitigate such effects, one or more of the drain lines  2425 ,  2415 , and  2405  can be coated with a hydrophobic and/or oleophobic coating as discussed above. In an embodiment, only drain line  2405  is coated with the hydrophobic and/or oleophobic coating, as it may be reused multiple times, while the drain lines  2425  and/or  2415  may be replaced at a greater frequency when those lines are a part of a disposable fluid circuit used in medical treatments. In an embodiment, the drain lines  2425  and  2415  are connected to the cartridge  1607 , such that those drain lines are only used for the same number of treatments as the cartridge  1607 . It is envisioned that the cartridge  1607  can be used a single time for a treatment, such as hemodialysis of peritoneal dialysis, and then can be disposed, along with the drain lines  2425  and  2415 . 
     In other embodiments, the drain line&#39;s wetted surface may be provided with texturing (not illustrated) that prevents adhesion such as nano or micro textures known to have such effect. The texturing can be applied instead of, or in addition to, the hydrophobic and/or oleophobic coating. Biomimetic surfaces that mimic the surfaces of butterfly wings and shark skin have demonstrated such properties. 
     Referring now to  FIG.  25   , in further embodiments, the waste water outlet  2305  and drain line  2405  can be made of elastic tubing  2503  that contracts and expands with pressure. The contracted state  2505  is shown with a solid line, while the expanded state  2507  is shown with a broken line in  FIG.  25   . 
     The contraction and expansion of the elastic tubing changes the shape of interior of the tubing and hence breaks deposits off the inner wall of the tubing. A pump  2501  having a characteristic that generates pressure pulses may be provided and connected to such a tube to cause the expansion and contraction and thereby prevent scale buildup. The drawing is not to scale, and the effect of the contraction does not necessarily occur in the center of the tubing  2503 , but can be spread along the entirety of the tubing. For example, the pump  2501  can generate pulses at a specific frequency that may generate a standing wave in a particular length of tubing  2503 , such that expanded and contracted regions alternate along the length of the tubing  2503 . 
     Referring to  FIG.  26   , the flexible tubing  2503  can be supported in a rigid support  2601 . The support  2601  may not be completely rigid, but it is less elastic than the tubing  2503 . As shown in  FIG.  26   , the support  2601  may include a body  2603  with cut-outs  2605 , which provide visibility into the support  2601  and may also reduce the weight of the support  2601  and reduce manufacturing costs by reducing the amount of material needed. 
       FIG.  26    shows pump  2501  as in other embodiments, but the pump may be omitted and instead a different mechanism or force generator can apply force to the tubing  2503  to cause its movement and change of shape within the support  2601 . In an embodiment, the mechanism may apply a twisting force to the tubing  2503 , which will cause the tubing to collapse onto itself, but then return to the original shape when the twisting force is reversed. This can be thought of as wringing the tubing  2503 , and can be applied periodically or whenever the flow rate through the tubing  2503  is reduced. To this end, a flow rate monitor (not shown) may be provided to measure and report the flow rate to a controller, which determines when to take steps such as wringing the tubing or operating the pump  2501 . 
     Referring to  FIG.  27   , in an alternative embodiment, an active device such as a vibrator or an actuator bends or vibrates a flexible drain tube periodically to prevent or remove scaling. Tubing  2503  passes through holster  2701 . While only a single holster  2701  is illustrated, multiple such holsters  3001  can be provided, as shown in  FIG.  30   . 
     A motor  2703  can be a linear motor that moves the holster  2701  fore and aft to cause bending of the tubing  2503 . If multiple holsters  3001  are provided, they can move in opposite directions and be driven by motor  3003  through multiple drive shafts  3004  and  3006 . The drive shafts  3004  and  3006  may move in opposite directions to cause the tubing  2503  to flex in opposite directions to dislodge any accumulated or adhered on fouling matter. Alternative, a single motor  2703  can be linked to the multiple holsters  3001  by a cam-shaft system (not shown) to cause the alternating fore-aft movement. 
     In further embodiments, the drain channel  2815  is selectively flushed with deionized water to reduce scaling and minimize the possibility of bacterial or fungal growth. The drain channel  2815  may be permanently connected to the proportioning or treatment system  2800 , as opposed to being a component of a disposable unit. This embodiment may be implemented for example in a system that consumes deionized water such as a medicament admixing system shown in  FIG.  28   . Here concentrates C 1  and C 2  are admixed to form a product fluid. Ultrapure water is pumped through a common line, and may be provided from product water outlet  2303  of the water purification system  2300 . Concentrate, or partially or incompletely mixed, medicament may be selectively directed along channel  1707  to the drain for testing by a sensor  2810  under control of a switch valve  2805  controlled by a controller. At intervals, the control valve may divert pure water from the ultrapure source to the drain to flush it. 
     Referring to  FIG.  29   , flushing deionized water may be done in a system  2900  that does not ordinarily consume ultrapure water for other purposes by providing a source of deionized water (DI) connected to a control valve  2901  and used to flush a drain in the same way, as shown in  FIG.  28   . 
     Referring to  FIG.  31   , a view of housing  3100  opening  3112  is shown. This type of a housing could be a part of the cartridge  500  and used to securely position a conductivity sensor. The housing may be a portion of a flow through channel, a chamber, or any element that confines a determined volume of a fluid whose conductivity is to be measured. The housing  3100  may be a part of a fluid circuit, for example one taking the form of a disposable cartridge for a medical treatment device. For purposes of this disclosure, the specifics of the housing as a fluid containment device are not essential to understanding the structures related to the assembly of an electrode  3200  to it including a stepped opening  3103  that secures and seals an insertable electrode  3200 . 
     Referring now also to  FIG.  32   , which illustrates a cross-section view of the housing viewed along plane II-II in  FIG.  31   , opening  3103  is defined by riser  3108  extending axially from the housing  3107 . In some embodiments the riser  3108  may be omitted or reduced in size, such that the opening  3103  is defined in the housing  3107  outer surface. In other embodiments, a riser may extend into an interior of the housing  3107 . The rise has a top surface  3101  that surrounds the opening  3103 . In the illustrated embodiment the overall shape of the stepped opening  3103  is circular, but the opening may have other shapes as well, as illustrated in the embodiments in  FIGS.  34 - 36   , infra. 
     Referring again to  FIG.  32   , the top surface  3101  defines the opening  3103  which may be seen from  FIGS.  31  and  32    to be stepped defining an outer opening portion  3111  an inner opening portion  3112 . The outer opening portion  3111  is larger than the inner opening portion  3112 . The outer opening portion  3111  may have a rounded lip  3133  that forms a progressively narrowing entry to the outer opening portion  3111  from the riser top surface  3101  to a sidewall  3131  of the outer opening portion  3111 . In embodiments, the axial section profile of sidewall  3131  may be perpendicular the cross-section profile of the riser top surface  3101 , as shown in  FIG.  32   . However, in other embodiments, the axial section profile of the sidewall  3131  may be sloped. In addition instead of the rounded lip  3133 , the entry to the outer opening portion  3111  may be beveled or simply step-shaped. 
     The inner opening portion  3112  is defined by a sidewall  3132  which has a landing  3123  extending axially toward the outside of the housing thereby defining a trough  3120  between the end of the sidewall  3131  and a landing  3123  at the outside extend of the rim, as shown in  FIG.  32   . The trough  3120  may have a flat bottom as shown in  FIG.  32   , or a curved bottom (not shown). The depth and width of the trough  3120  permit shavings or burrs to be received therein when the electrode  3200  is inserted. The dimensions are discussed with reference to  FIGS.  37 A and  37 B . The electrode  3200  may be of a material that is harder or more rigid than the housing  3100 , so that pressing the electrode  3200  into the outer opening portion  3111  may produce burrs or shavings  3901  debris as an edge of the electrode  3200  scrapes against sidewall  3131 . The burrs or shavings  3901  occupy the trough  3120  such that they are retained in a position that cannot block the electrode  3200  from being seated on the landing  3122 , as shown in  FIGS.  37 B and  38 B . The electrode  3200  may have barbs as illustrated in  FIGS.  38 A and  38 B , but in various embodiments, the electrode  3200  can have smooth sides as shown in  FIGS.  37 A and  37 B . 
     Referring again to  FIGS.  31  and  32   , the landing  3123  forms a rim  3122  of the inner opening portion  3112 . The landing  3123  may provide a support against which a bottom surface  3220  of the electrode  3200  comes to rest. The landing  3123  ensures the electrode  3200  is consistently oriented at a precisely-defined axial position after insertion by providing an interfering engagement with the electrode  3200  which seats against it. The landing  3123  has a finite radial width that may be selected to ensure that it provides a positive stop and resists variable forces to prevent variation in the axial position of the electrode  3200 . A fluid-tight seal may be provided but is not essential. An additional function of the radial width of the landing  3123  is to define an elongate narrow fluid path  3710  (See  FIG.  37 B ) between the housing  3107  interior and the portion of the electrode overlying the landing  3123 . 
     After the electrode  3200  is positioned with the bottom surface  3220  resting against the overlying the landing  3123 , an open space remains between the radial edge of the  200  and the sidewall  3131  at locations around the sidewall  3131  that do not have a spacer  3140 . This open space may be filled with an adhesive substance. The adhesive substance may be a glue or a sealant that cures into a solid or semi-solid form, or may remain pliable even after curing. The adhesive may expand in volume as a part of the curing process, thereby filling any gaps between the bottom surface  3220  and the landing  3123 . The viscosity of the uncured adhesive is selected to enable the adhesive to flow into the gap between the sidewall  3131  and the electrode. The adhesive may fill the trough  3120 , and may seep onto the top surface of the electrode  3200 . It may be desirable to select the volume of the adhesive such that it does not seep onto the top surface, or at least not onto the entirety of the top surface. 
     Although  FIGS.  31  and  32    illustrate a circular embodiment, the housing is not limited to this shape.  FIGS.  34 - 36    illustrate rectangular, oval, and triangular shapes. 
     Three spacers  3140  function to constrain the lateral (relative to the opening axis) position of the electrode  3200 . The spacers  3140  may be evenly spaced around the perimeter of the opening  3103 . A greater number of spacers may be used in alternative embodiment. A smaller number of spacers may cooperate with the walls of the opening to constrain the electrode in further embodiments. 
       FIGS.  32  and  37 A,  37 B  illustrate details of an embodiment showing spacers  3140 . As seen in  FIG.  32   , spacer  3140  protrudes partially out of the sidewall  3131  of the outer opening portion  3111  and has a semi-circular profile. The general shape of each spacer  3140  may be a hemi-cylinder with an elongate portion  3142  and a rounded end  3141 . The spacer  3140  can have other shapes consistent with the function described herein, such as a flat bevel, conical shape, etc. The radial span of the spacer  3140  can be selected to constrain or over-constrain the electrode such that it is deformation or cut when the electrode  3200  slides along the space until it is seated on the overlying the landing  3123 . 
     Advantageously, the provision of the spacers  3140  reduces the contact area of the force of the sidewall against the electrode  3200  making it easier to deform the spacers  3140 . By permitting the spacers  3140  to deform or be cut with relatively low force, it possible to provide a relatively gentle over-constraint to the electrode  3200  to keep it centered as it is advanced. The deformation engagement also helps to secure the electrode  3200  axially after it seats against the landing  3123 . 
     Referring to  FIG.  33   , an embodiment of the housing  3100  includes a modified trough  3320  that does not extend around the entire perimeter of the opening  3103 . Instead, the modified trough  3320  is formed only in the vicinity of the spacers  3140  to accommodate burrs or shavings  3901 . No burrs or debris  3901  are scraped off from the sidewall  3131 . 
     The modified trough  3320  has a bottom  3327  and sidewall  3325  which terminates at the sidewall  3131  of the outer opening portion  3111 .  FIG.  33    illustrates the sidewall  3325  as sloping from the bottom  3327  up to a modified landing  3323 . This embodiment provides maximum rigidity of the landing  3323  due to the extra material present, and at the same time still provides the advantages of the trough that accommodates burrs from spacers  3340 . 
     In an embodiment, the modified trough  3320  extends 5 degrees (measured radially from the center of the outer opening portion  3111 ) on both sides of each of spacers  3140 . In another embodiment, the modified trough  3320  extends 10 degrees, 15 degrees, 20 degrees, 25 degrees, or 30 degrees on both sides of each of spacers  3140 . The angular extension of the modified trough  3320  can be selected based on the expected amount of burrs  3901  and debris from the spacers  3140  so that the modified trough  3320  can accommodate all of the burrs  3901  and debris. 
     Turning to  FIGS.  34 - 36   , alternate embodiments of the opening may have a rectangular, elliptical, or triangular shape. These shapes may encounter different challenges than those of the round disc embodiment, but nevertheless benefit from spacers  3140 .  FIG.  34    illustrates an embodiment with a rectangular trough  3420 , much like trough  3120  above.  FIG.  34    also shows a rectangular landing surface  3423 . It is noted that a sidewall  3425  is analogous to the sidewall  3125 . However, the slope of the sidewall  3425  (and of the sidewall  3125 ) may be varied with other aspects of the disclosed embodiments. To illustrate this point further,  FIG.  35    shows an embodiment with an elliptical outer opening portion  3511  and elliptical inner opening portion  3512 . While this embodiment also includes an elliptical or oval trough  3520  and a landing surface  3523 , the slope of the sidewall of the trough  3520  connecting to the surface  3523  is perpendicular to the page, hence not visible in this top view. Such a steeply sloped wall may be desirable space is at a premium, as the resulting stepped opening can be made smaller than other designs. 
     Referring to  FIG.  36   , a triangular stepped opening includes a triangular outer opening portion  3611  and a triangular inner opening portion  3612 . A triangular trough  3620  is similar to the other embodiments described above in terms of cross section, and can have varying slope of the sidewall (not visible in  FIG.  36   , as it portrays an embodiment with a side wall of the trough rising out of the page). 
       FIG.  37    illustrates dimensions of the cross-section of the spacer  3140  as well as the overall stepped opening  3103 . The distance from the lower surface  3102  to top surface  3101  is represented at H 1 . The distance from the lower surface  3102  to the top of the spacer  3104  is represented as H 2 . The distance from the lower surface  3102  to the landing surface  3123  is represented as H 3 . The distance from the surface of the bottom  3127  of the trough  3120  is represented as H 4 . Thus, the height of the spacer  3140  from the bottom  3127  is H 2 -H 4 , and must be less than H 1 . 
     Still referring to  FIG.  37 A , the distance from outer wall  3108  to inner wall  3131  of the outer opening portion is represented as d 1 . The distance from wall  3108  to the farthest point of the closes spacer  3140  is represented as d 2 . Therefore, the thickness of the spacer  3140  is d 2 -d 1 , and is less than the width of the bottom  3127  of the trough  3120 , as illustrated in  FIG.  37   . The distance from the wall  3108  to the farthest end of the bottom  3127  is represented as d 3 . Therefore, the thickness of the bottom surface  3127  of the trough  3120  is given by d 3 -d 1  in places without a spacer  3140 , and by d 3 -d 2  when radially adjacent to a spacer. Distance d 4  represents the distance from the wall  3108  to the boundary of the second sidewall  3125  of the trough and the top surface  3123  of the landing  3122 . It can be appreciated that varying the slope of the sidewall  3125  affects the thickness of the bottom  3127 . If the sidewall  3125  is perpendicular to the lower surface  3102 , d 3  becomes the same length as d 4 . The distance from the wall  3108  to the sidewall  3132  is represented as d 5 . 
     It has been found that certain ratios of the above-noted dimensions produce particularly desirable results. 
     Referring to  FIG.  39   , an alternative embodiment of the electrode  3300  has a shape that, rather than using standoffs extending from the aperture to focus the forces for aligning and engaging the electrode, provides a similar effect by forming a non-round electrode that engages the walls of the aperture at predefined points. In an exemplary embodiment, electrode  3300  has a substantially square profile with rounded corners, as shown in the dashed line in  FIG.  39   . The rounded corners are the outer-most contact points of the electrode  3300  when it is inserted into an opening  3103 , such that the rounded corners come into contact with sidewall  3131 , as is shown in  FIG.  32   . While  FIG.  32    illustrates standoff  3140  along sidewall  3131 , it is understood that the standoffs  3140  may be omitted. 
     Referring to  FIG.  40 A , another embodiment of electrode  3400  has a circular profile, like electrode  3200 , but may include spacers  3401 . The spacers  3401  may be an integral part of the electrode  3400 , manufactured as a part of the electrode  3400  during a casting and/or machining process. However, the spacers  3401  may also be added, attached, or machined into electrode  3400  at a later time, before the electrode  3400  is inserted into the opening  3103 . The spacers  3401  may be sized to extend radially outward from the electrode  3400  farther than the diameter of the sidewall  3131 , such that the sidewall  3131  may be at least partially deformed when the electrode  3400  is inserted. 
     The particular shape of the spacer  3401  may differ from that shown in  FIG.  40 A . For example,  FIG.  40 B  illustrates an embodiment of electrode  3402  that has spacers  3403  that have a more flat profile as compared to spacers  3401 . Thus, spacers  3403  may have a larger contact area that presses against sidewall  3131 , and may also be able to exert more force onto that larger area without deforming. 
       FIGS.  40 A and  40 B  show views that do not illustrate the extension of the spacers  3401  and  403  into the page. It would be understood that the spacers  3401  and  403  need not have the same height as the electrode. In other words, the spacers  3401  and  403  may be formed on only a portion of the electrode  3400 ,  402  sidewall. 
     It may be advantageous for electrode  3400  to have three spacers  3401 , but it is understood that a different number may be provided. In some embodiments, the electrode may have no spacers and spacers may be omitted from the opening  3103 . 
     Referring to  FIGS.  41 A-B , the electrode  3305  includes no spacers, but may include an annular barb  3308  and a recess  3312  at one end. The recess  3312  is bound but upper surface  3318  of the electrode  3305 . As shown in  FIG.  41 A , the annular barb  3308  may have an outer diameter that varies along the height (vertical in  FIG.  41 A ) of the barb. The upper surface  3318  engages with a rim surface  3314  forming a seal when the electrode  3305  is inserted into the opening  3306 . 
       FIGS.  41 A-B  illustrate the electrode  3305  prior to insertion into or coupling with a housing without any standoffs or spacers. The housing is as shown in  FIG.  32   , but includes no standoffs.  FIGS.  41 A and  41 B  can be thought of as  FIG.  32    flipped upside down, with the electrode  3305  being inserted from the bottom rather than from the top. 
     The housing in  FIGS.  41 A and  41 B  includes may include a riser  3301  with a bottom surface  3302 . The height of the riser  3301  may vary to accommodate the size of the electrode  3305 . The bottom surface  3302  defines the opening  3304  which may be seen from  FIG.  41 B  to be stepped defining an outer opening portion and an inner opening portion. The outer opening portion is larger than the inner opening portion. The outer opening portion may have a rounded lip or have a sharp edge. In embodiments, the axial section profile of sidewall  3331  may be perpendicular the cross-section profile of the bottom surface  3302 . However, in other embodiments, the axial section profile of the sidewall  3331  may be sloped. 
     As would be understood from  FIGS.  41 A and  41 B , when the electrode  3305  is pressed into the housing, outermost edge of the annular barb  3308  engages with the sidewall  3331  and the upper surface  3318  of the electrode  3305  comes to rest against the surface  3314 . This engagement may form an air tight or fluid tight seal between the electrode  3305  and the housing. Optionally, an adhesive or sealant may be added into the gap remaining between electrode  3305  and riser  3301  after the electrode is inserted to create an airtight or fluid tight seal. 
     According to first embodiments, the disclosed subject matter includes a method for measuring a conductivity in a fluid flowing in a fluid channel. The method includes contacting a flowing fluid with two electrodes spaced apart across a portion of the fluid channel. The method includes contacting each of the two electrodes to a current source contact and a voltage measuring contact by creating a continuity between each of two respective portions of the each of the two electrodes and a respective one of the current source and voltage measuring contacts with multiple conductors. 
     In variations thereof the first embodiments include ones in which the multiple conductors are located on a surface of a resilient insulating member. In variations thereof the first embodiments include ones in which the creating a continuity includes squeezing the resilient member for each of the two electrodes between the each of the two electrodes and a respective combination of the current source and voltage measuring contacts. In variations thereof the first embodiments include ones in which the insulating member and the multiple conductors form a Zebra connector. In variations thereof the first embodiments include ones in which the contacting includes attaching the resilient member to the fluid channel. In variations thereof the first embodiments include ones in which the contacting includes attaching the resilient member to the fluid channel loosely such that it can move in a limited range along an axis perpendicular to a surface of the each of the two electrodes. In variations thereof the first embodiments include ones in which the contacting includes attaching the resilient member to the fluid channel loosely by a housing such that it can move in a limited range along an axis perpendicular to a surface of the each of the two electrodes. In variations thereof the first embodiments include ones in which the contacting includes attaching the resilient member to the fluid channel loosely by a housing partially surrounding the resilient member such that it can move in a limited range along an axis perpendicular to a surface of the each of the two electrodes. In variations thereof the first embodiments include ones that include measuring a resistance of electrical continuity between a voltage measuring contact and a current source contact to detect contact resistance. In variations thereof the first embodiments include ones that include performing Kelvin sensing by electrical impedance between the two electrodes by driving current between the them and measuring a voltage between them. In variations thereof the first embodiments include ones in which the resilient member and all multiple conductors constitutes an elastomeric contact insert or a compliant multiconductor element as described in the embodiments. 
     According to second embodiments, the disclosed subject matter includes a conductivity measurement system. A single-use fluid circuit has at least two planar electrodes forming a part of a wall of a fluid channel such that the electrode has a wetted side facing an interior of the fluid channel and a contact side opposite the wetted side. Flexible electrically-conducting elements are attached to the fluid channel each with at least one conductor thereof facing a respective one of the electrode contact sides. A multi-use driver has a pair of electrical contacts connected to a current source and a voltage sensor for each of the electrodes. The multi-use driver has a receiving member shaped to receive the single-use fluid circuit fluid channel planar electrodes. The multi-use driving has a forcing member that opens to receive the single-use fluid circuit and closes to force each flexible electrically-conducting element between the each of the electrodes and a respective pair of the electrical contacts. 
     According to third embodiments, the disclosed subject matter includes a conductivity measurement system. A fluid channel has a first wetted electrode and a second wetted electrode configured to directly contact a fluid flowing in the fluid channel A first contact device includes a first electrically insulating block wrapped by a first array of parallel electrically conductive wires that span at least a first side of the first contact device and a second side of the first contact device. Conductors on the first side of the first contact device are in electrical contact with the first wetted electrode. A second contact device includes a second electrically insulating block wrapped by a second array of parallel electrically conductive wires that span at least a first side of the second contact device and a second side of the second contact device, wherein wires on the first side of the second contact device are in electrical contact with the second wetted electrode. A conductivity measurement circuit is in electrical contact with the first wetted electrode via wires on the second side of the first contact device and in electrical contact with the second wetted electrode via wires on the second side of the second contact device. A controller is programmed to control the conductivity measurement circuit to pass a current through the fluid between the first wetted electrode and the second wetted electrode and measure a voltage difference between the first wetted electrode and the second wetted electrode as the current is passed, the controller is further programmed to determine a conductivity of the fluid based on the passed current and the measured voltage difference. In variations thereof the third embodiments include ones in which each wire in the first array of parallel electrically conductive wires and in the second array of parallel electrically conductive wires is coated with gold. 
     In variations thereof the third embodiments include ones in which each adjacent pair of wires in the first array of parallel electrically conductive wires and in the second array of parallel electrically conductive wires are electrically isolated from each other by an electrically insulating material. In variations thereof the third embodiments include ones in which the first electrically insulating block is made of an elastomeric material. In variations thereof the third embodiments include ones in which the first electrically insulating block is made of silicon, rubber, or synthetic rubber. In variations thereof the third embodiments include ones in which the first electrically insulating bock has a recess on a third side of the first contact device, wherein wires spanning the recess are not in contact, over the recess, with the first electrically insulating block. In variations thereof the third embodiments include ones in which the first electrically insulating bock has at least one recess on a fourth side of the first contact device, wherein no wires span the fourth side of the first contact device over the at least one recess. In variations thereof the third embodiments include ones in which the conductivity measurement circuit is in electrical contact with the wires on the second side of the first contact device and in electrical contact with the wires on the second side of the second contact device via a printed circuit board (PCB). 
     In variations thereof the third embodiments include ones in which a first current contact, a second current contact, a first voltage contact, and a second voltage contact are printed on the PCB, wherein the first current contact is in electrical contact with a first group of wires on the second side of the first contact device, wherein the first voltage contact is in electrical contact with a second group of wires on the second side of the first contact device, wherein the second current contact is in electrical contact with a first group of wires on the second side of the second contact device, wherein the second voltage contact is in electrical contact with a second group of wires on the second side of the second contact device. In variations thereof the third embodiments include ones in which the first current contact and the second current contact are electrically connected to two sides of a current source in the conductivity measurement circuit, wherein the first voltage contact and the second voltage contact are electrically connected to two sides of a voltmeter in the conductivity measurement circuit, wherein the current passed through the fluid between the first wetted electrode and the second wetted electrode is sourced by the current source, wherein the voltage difference between the first wetted electrode and the second wetted electrode is measured by the voltmeter. In variations thereof the third embodiments include ones in which the first contact device includes a housing that supports the first electrically insulating block, wherein the housing is made of an electrically insulating material. In variations thereof the third embodiments include ones in which the first electrically insulating block is inserted into a receiving well of the housing. In variations thereof the third embodiments include ones in which the first side of the first contact device and the second side of the first contact device at least partially protrude from a first end of the receiving well and second end of the receiving well, respectively. 
     In variations thereof the third embodiments include ones in which the conductivity measurement circuit comprises a permanent electrical device of a treatment system, wherein the fluid channel comprises a replaceable component of the treatment system. In variations thereof the third embodiments include ones in which the treatment system comprises a fluid circuit for preparation of a medicament for renal replacement therapy. In variations thereof the third embodiments include ones in which the treatment system further comprises a water filtration module with a fluid circuit and a pump positioned in the fluid circuit to pump water therethrough, the water filtration module further comprising an inlet, an outlet, and at least one filtration stage has a replaceable filter component, the controller controlling the conductivity measurement circuit to detect the quality of water upstream of the at least one filtration stage and output a water quality signal and control the pump accordingly. In variations thereof the third embodiments include ones in which, when the water quality signal is below a threshold, the controller prevents operation of the pump until the replaceable filter component is changed. In variations thereof the third embodiments include ones in which the replaceable filter component includes a deionization filter or an activated carbon filter. In variations thereof the third embodiments include ones in which the treatment system further comprises a medicament preparation device comprising a medicament supply line that includes at least one concentration sensor station, the concentration sensor station includes the conductivity measurement system and a temperature sensor portion. 
     In variations thereof the third embodiments include ones in which the conductivity of the fluid is determined based on based on the current passed through the fluid, the voltage difference across the first wetted electrode and the second wetted electrode, and a temperature of the fluid as measured by the temperature sensor portion. In variations thereof the third embodiments include ones in which a supply of a medicament by at least one pump in the medicament preparation device is controlled based on the determined conductivity of the fluid. In variations thereof the third embodiments include ones in which the temperature sensor portion includes a flow chamber with a flat surface to permit a temperature sensor to be placed against the flat surface of a predefined sensor of the medicament preparation device. 
     According to fourth embodiments, the disclosed subject matter includes a medicament preparation system. A fluid circuit has fluid channels with at least one junction, the junction joining a common flow channel that leads from a water inlet to a medicament outlet. The junction is joined to a pumping tube segment connected to a source of medicament concentrate by a concentrate channel. the at least one junction is oriented in a predefined way relative to the force of gravity. The concentrate channel has a chicane that curves sharply up and sharply down before the concentrate channel meets the common flow channel. 
     In variations thereof the fourth embodiments include ones in which the chicane&#39;s length is no greater than ten internal diameters of the concentrate channel local to the chicane. In variations thereof the fourth embodiments include ones in which the chicane is immediately adjacent a point where the common flow channel and the concentrate channel meet. In variations thereof the fourth embodiments include ones in which the internal cross-sectional flow area of the chicane is smaller than that of the remainder of the concentrate channel. In variations thereof the fourth embodiments include ones in which the chicane is operable as a trap when fluid of a first density remains in the concentrate channel while fluid of a second density remains in the common flow channel at the junction, where the first density is higher than the second density, whereby gravity siphoning is prevented. In variations thereof the fourth embodiments include ones in which the fluid circuit is formed in a rigid structure. In variations thereof the fourth embodiments include ones in which the fluid circuit is formed in a rigid cartridge. 
     According to fifth embodiments, the disclosed subject matter includes a medical device with a fluid plant that includes a purification element, a patient treatment element, or an admixing element that generates a waste fluid. A drain channel includes means for avoiding fouling including one of, an elastic channel and a pump programmed to expand the elastic channel responsively to a pulsation generated by starting and stopping or reversing the pump. 
     According to sixth embodiments, the disclosed subject matter includes a medical device with a fluid plant that includes a purification element, a patient treatment element, or an admixing element that generates a waste fluid. A drain channel has a biomimetic surface on an interior surface thereof, the biomimetic surface is selected to prevent attachment or growth of non-flowing material thereon originating from a predefined waste material generated by the purification element, patient treatment element, or admixing element. 
     According to seventh embodiments, the disclosed subject matter includes a medical device with a fluid plant that includes a purification element, a patient treatment element, or an admixing element that generates a waste fluid. A drain channel is of flexible material, waste is pumped by a pulsatile pump, the flexible material is selected to expand and contract sufficiently to prevent the formation of scaling on the drain channel. 
     According to eighth embodiments, the disclosed subject matter includes a medical device with a fluid plant that includes a purification element, a patient treatment element, or an admixing element that generates a waste fluid. A drain channel is of expandable material and is connected to receive the waste fluid. An actuator is in engagement with the drain channel and adapted to shake or vibrate the drain channel to prevent fouling thereof by a predefined material generated by the purification element, patient treatment element, or admixing element. 
     According to ninth embodiments, the disclosed subject matter includes a conductivity sensor with a housing defining an internal fluid compartment. The housing has openings for receiving electrodes. The openings are round. Each of the openings has an inside, closer to the internal fluid compartment, and an outside portion further from the interior. The each of the openings has an axial section with a stepped profile such that the outside portion has a larger diameter than the inside portion. The inside portion has a rim extending axially at least partly into the outside portion. The outside portion has at least three spacers extending radially inward toward an axis of a respective one of the openings. 
     In variations thereof the ninth embodiments include ones in which the rim is shaped to define an annular trough surrounding a respective one of the openings. In variations thereof the ninth embodiments include ones in which the annular trough is interrupted by the at least three spacers. In variations thereof the ninth embodiments include ones in which the at least three spacers have an axial dimension that is greater than a radial dimension thereof. In variations thereof the ninth embodiments include ones in which the at least three spacers each has a rounded axial end facing away from the interior. In variations thereof the ninth embodiments include ones that include an electrode seated in each of the openings and forming a seal with the rim. In variations thereof the ninth embodiments include ones in which the annular trough is filled with a cement. In variations thereof the ninth embodiments include ones in which the electrode directly abuts the rim. In variations thereof the ninth embodiments include ones in which the trough contains burrs. In variations thereof the ninth embodiments include ones in which the trough contains burrs resulting from over-confinement of the electrode by the spacers and resulting from a press-fitting operation. In variations thereof the ninth embodiments include ones in which the spacers are sized to over-confine the electrode such that burrs are produced by press-fitting of the electrode, the burrs are received by and present in the trough. In variations thereof the ninth embodiments include ones in which the trough is continuous such that it encircles each opening. In variations thereof the ninth embodiments include ones in which the trough is shallower between the spacers than proximate the spacers. In variations thereof the ninth embodiments include ones in which the trough exists only proximate the spacers. In variations thereof the ninth embodiments include ones in which the rim has a base and a tip that is narrower than the base in axial section, the tip and base is spaced apart along the axis of the opening. In variations thereof the ninth embodiments include ones in which the cement partly covers the electrode. 
     According to tenth embodiments, the disclosed subject matter includes a medical treatment system with a fluid circuit that includes at least one junction where a first fluid line meets a second fluid line. The second fluid line includes a ceiling protrusion extending out of a ceiling of the second fluid line and at least partially blocking the second fluid line. The second fluid line further includes a floor protrusion extending out of a floor of the second fluid line and at least partially blocking the second fluid line. The ceiling protrusion is located farther away from the junction than the floor protrusion. 
     In variations thereof the tenth embodiments include ones that include a rigid cartridge that contains the fluid circuit. In variations thereof the tenth embodiments include ones in which the ceiling protrusion and the floor protrusion overlap and completely obstruct a central axis of the second fluid line, but leave open a tortuous path through the second fluid line. In variations thereof the tenth embodiments include ones in which the second fluid line has a circular cross sectional profile. In variations thereof the tenth embodiments include ones in which the ceiling protrusion and the floor protrusion cooperate to prevent or reduce flow of fluid through the second fluid line into the junction in the absence of pumping of the fluid when the junction is oriented in a predetermined orientation relative to force of gravity. In variations thereof the tenth embodiments include ones in which a valley is formed immediately adjacent to the floor protrusion and below the ceiling protrusion, and the predetermined orientation is with a center of the valley is vertically aligned with a center of a lowest portion of the ceiling protrusion. In variations thereof the tenth embodiments include ones in which a valley is formed immediately adjacent to the floor protrusion and below the ceiling protrusion when the fluid junction is oriented in a predefined orientation relative to force of gravity and a fluid in the second fluid line is prevented from flowing past the valley due to gravimetric action. In variations thereof the tenth embodiments include ones that include a first pump that selectively applies pumping force to the fluid in the second fluid line and the pumping force causes the fluid in the second fluid line to flow past the valley into the junction. In variations thereof the tenth embodiments include ones that include a second pump that selectively applies pumping force to a fluid flowing in the first fluid line. In variations thereof the tenth embodiments include ones in which the fluid flowing in the first fluid line has a lower density than the fluid flowing in the second fluid line. In variations thereof the tenth embodiments include ones in which the fluid from the second fluid line is mixed with the fluid from the first fluid line when the first and second pumps operate. In variations thereof the tenth embodiments include ones that include an upper protrusion at an intersection of a ceiling of the first fluid line and the ceiling of the second fluid line, the upper protrusion has a tapered cross-sectional shape that extends into a flow channel of the second fluid line. In variations thereof the tenth embodiments include ones in which the upper protrusion reduces turbulence in flow of the fluid in the first fluid line at the junction. In variations thereof the tenth embodiments include ones in which the upper protrusion is rigid. In variations thereof the tenth embodiments include ones that include a flap at an intersection of a ceiling of the first fluid line and the ceiling of the second fluid line, the flap extending from the intersection of the ceilings toward a side wall of the floor protrusion. In variations thereof the tenth embodiments include ones in which the flap is moveable about a pivot and is biased to be touching the side wall of the floor protrusion in the absence of external force applied to the flap. In variations thereof the tenth embodiments include ones in which the flap is a live hinge molded at the intersection of the ceilings. In variations thereof the tenth embodiments include ones in which the flap is movably attached to the pivot with a hinge pin. 
     According to eleventh embodiments, the disclosed subject matter includes a medical treatment system. A fluid circuit includes a first fluid line and a second fluid line meeting the first fluid line at an intersection. The first fluid line ceiling intersects the second fluid line ceiling at a first location. A fluid flows along the first fluid line in single direction. A flap extends from the first location and rests against a rim of the second fluid line at the intersection. The flap is biased in a closed position that reduces fluid leakage from the second fluid line into the first fluid line in the absence of force that overcomes the bias of the flap. 
     In variations thereof the eleventh embodiments include ones in which the flap is a living hinge made of a flexible material extending from the first location and substantially parallel to a flow direction of fluid flowing in the first fluid line. In variations thereof the eleventh embodiments include ones in which the flap is a rigid piece of material attached at a pivot location with a hinge pin. In variations thereof the eleventh embodiments include ones that include a fluid pump that pumps the fluid in the second fluid line with a pumping force sufficient to overcome the bias of the flap such that the fluid from the second fluid line flows into the intersection when the fluid pump operates. 
     According to twelfth embodiments, the disclosed subject matter includes a medical device cartridge insertable into a medical treatment device. The cartridge has a rigid frame that provides structure for the cartridge and a fluid circuit supported within the rigid frame. The fluid circuit includes fluid channels with at least one junction, the junction joining a common flow channel that leads from a water inlet to a medicament outlet. The junction is joined to a pumping tube segment connected to a source of medicament concentrate by a concentrate channel. The at least one junction is oriented in a predefined way relative to the force of gravity. The concentrate channel has a chicane that curves sharply up and sharply down before the concentrate channel meets the common flow channel. At least one conductivity sensor that measures conductivity of fluid in the fluid circuit, the conductivity sensor includes a housing defining an internal fluid compartment, the housing has openings for receiving electrodes, the openings being round. Each of the openings has inside portions closer to the internal fluid compartment and outside portions further from the interior of the internal fluid compartment, the each of the openings having an axial section with a stepped profile such that the outside portion has a larger diameter than the inside portion. The inside portion has a rim extending axially at least partly into the outside portion. The outside portion has at least three spacers extending radially inward toward an axis of a respective one of the openings. 
     In variations thereof the twelfth embodiments include ones that include a drain line fluidly attached to a drain channel of the fluid circuit, wherein the drain line conveys waste fluid. 
     In variations thereof the twelfth embodiments include ones in which the drain line includes means for reducing fouling in the drain line. In variations thereof the twelfth embodiments include ones in which the drain line is made of an elastic material that allows the drain line to expand and contract and the waste fluid is pumped by a pump with fluctuating pumping pressure that causes the drain line to expand and contract and thereby reduce attachment of fouling on an interior of the drain line. In variations thereof the twelfth embodiments include ones that include a support structure surrounding at least a portion of the drain line. In variations thereof the twelfth embodiments include ones in which the support structure is more rigid than the drain line. In variations thereof the twelfth embodiments include ones in which the support structure includes a plurality of cut-outs in a body of the support structure. In variations thereof the twelfth embodiments include ones that include a holster holding at least a portion of the drain line, the holster mechanically coupled to motor. In variations thereof the twelfth embodiments include ones in which the motor applies force to the holster and causes the holster to flex the drain line held by the holster to thereby remove fouling built up inside the drain line. In variations thereof the twelfth embodiments include ones that include multiple holsters arranged along at least a portion of the drain line, wherein the motor causes adjacent holsters to move in opposed directions to flex the drain line held by the holsters. 
     In variations thereof the twelfth embodiments include ones in which at least one of the drain line and the drain channel has a biomimetic surface on an interior surface thereof, the biomimetic surface is selected to prevent attachment or growth of non-flowing material thereon originating from a predefined waste material generated by a purification element, a patient treatment element, or an admixing element. 
     According to thirteenth embodiments, the disclosed subject matter includes a medical device cartridge insertable that is into a medical treatment device. The cartridge has a fluid circuit that includes fluid channels with at least one junction, the junction joining a common flow channel that leads from a water inlet to a medicament outlet. the junction is joined to a pumping tube segment connected to a source of medicament concentrate by a concentrate channel. The at least one junction is oriented in a predefined way relative to the force of gravity. The concentrate channel has a chicane that curves sharply up and sharply down before the concentrate channel meets the common flow channel. At least one conductivity sensor measures conductivity of fluid in the fluid circuit. The conductivity sensor includes a housing defining an internal fluid compartment. The housing has openings for receiving electrodes. The openings are round. Each of the openings has inside portions closer to the internal fluid compartment and outside portions further from the interior of the internal fluid compartment. The each of the openings has an axial section with a stepped profile such that the outside portion has a larger diameter than the inside portion. the inside portion has a rim extending axially at least partly into the outside portion. The outside portion has at least three spacers extending radially inward toward an axis of a respective one of the openings. A fluid channel has a first wetted electrode and a second wetted electrode configured to directly contact a fluid flowing in the fluid channel A first contact device includes a first electrically insulating block wrapped by a first array of parallel electrically conductive wires that span at least a first side of the first contact device and a second side of the first contact device, wherein conductors on the first side of the first contact device are in electrical contact with the first wetted electrode. A second contact device includes a second electrically insulating block wrapped by a second array of parallel electrically conductive wires that span at least a first side of the second contact device and a second side of the second contact device, wherein wires on the first side of the second contact device are in electrical contact with the second wetted electrode. a conductivity measurement circuit in electrical contact with the first wetted electrode via wires on the second side of the first contact device and in electrical contact with the second wetted electrode via wires on the second side of the second contact device. A controller is programmed to control the conductivity measurement circuit to pass a current through the fluid between the first wetted electrode and the second wetted electrode and measure a voltage difference between the first wetted electrode and the second wetted electrode as the current is passed, the controller is further programmed to determine a conductivity of the fluid based on the passed current and the measured voltage difference. 
     Features of the disclosed embodiments may be combined, rearranged, omitted, etc., within the scope of the disclosed subject matter to produce additional embodiments. Furthermore, certain features may sometimes be used to advantage without a corresponding use of other features. It is, thus, apparent that there is provided, in accordance with the present disclosure, a needle guard and associated manufactures, components, systems, and methods of use. Many alternatives, modifications, and variations are enabled by the present disclosure. While specific embodiments have been shown and described in detail to illustrate the application of the principles of the disclosure, it will be understood that the disclosed subject matter may be embodied otherwise without departing from such principles. Accordingly, Applicants intend to embrace all such alternatives, modifications, equivalents, and variations that are within the spirit and scope of the present disclosure. 
     In any of the embodiments described herein, including the claims, the terms compliant multiconductor element elastomeric contact element, elastomeric contact, and elastomeric contact insert may be interchanged to form alternative embodiments. In any of the embodiments, the terms compliant multiconductor element, elastomeric contact insert, or elastomeric contact may be loosely held to an electrode by a housing such as housing  752 . In embodiments, the housing may be a flexible material such as soft plastic, rubber, silicone, elastomer, or other compliant material. The housing (e.g.,  752 ) may be attached to the cartridge support  556  or equivalent conductivity measurement channel portion but not directly affixed to the compliant multiconductor element and elastomeric contact insert. That is, the housing may hold the element/insert in place over the electrode but permit it to move relative to the electrode so that it can be firmly pressed against it. 
     It will be appreciated that the modules, processes, systems, and sections described above can be implemented in hardware, hardware programmed by software, software instruction stored on a non-transitory computer readable medium or a combination of the above. For example, a method for controlling the generating of a medicament or treatment fluid (or methods therewithin such as for the generating of purified water) can be implemented, for example, using a processor configured to execute a sequence of programmed instructions stored on a non-transitory computer readable medium. For example, the processor can include, but not be limited to, a personal computer or workstation or other such computing system that includes a processor, microprocessor, microcontroller device, or is comprised of control logic including integrated circuits such as, for example, an Application Specific Integrated Circuit (ASIC). The instructions can be compiled from source code instructions provided in accordance with a programming language such as Java, C++, C#.net or the like. The instructions can also comprise code and data objects provided in accordance with, for example, the Visual Basic™ language, LabVIEW, or another structured or object-oriented programming language. The sequence of programmed instructions and data associated therewith can be stored in a non-transitory computer-readable medium such as a computer memory or storage device which may be any suitable memory apparatus, such as, but not limited to read-only memory (ROM), programmable read-only memory (PROM), electrically erasable programmable read-only memory (EEPROM), random-access memory (RAM), flash memory, disk drive and the like. 
     Furthermore, the modules, processes, systems, and sections can be implemented as a single processor or as a distributed processor. Further, it should be appreciated that the steps mentioned above may be performed on a single or distributed processor (single and/or multi-core). Also, the processes, modules, and sub-modules described in the various figures of and for embodiments above may be distributed across multiple computers or systems or may be co-located in a single processor or system. Exemplary structural embodiment alternatives suitable for implementing the modules, sections, systems, means, or processes described herein are provided below. 
     The modules, processors or systems described above can be implemented as a programmed general purpose computer, an electronic device programmed with microcode, a hard-wired analog logic circuit, software stored on a computer-readable medium or signal, an optical computing device, a networked system of electronic and/or optical devices, a special purpose computing device, an integrated circuit device, a semiconductor chip, and a software module or object stored on a computer-readable medium or signal, for example. 
     Embodiments of the method and system (or their sub-components or modules), may be implemented on a general-purpose computer, a special-purpose computer, a programmed microprocessor or microcontroller and peripheral integrated circuit element, an ASIC or other integrated circuit, a digital signal processor, a hardwired electronic or logic circuit such as a discrete element circuit, a programmed logic circuit such as a programmable logic device (PLD), programmable logic array (PLA), field-programmable gate array (FPGA), programmable array logic (PAL) device, or the like. In general, any process capable of implementing the functions or steps described herein can be used to implement embodiments of the method, system, or a computer program product (software program stored on a non-transitory computer readable medium). 
     Furthermore, embodiments of the disclosed method, system, and computer program product may be readily implemented, fully or partially, in software using, for example, object or object-oriented software development environments that provide portable source code that can be used on a variety of computer platforms. Alternatively, embodiments of the disclosed method, system, and computer program product can be implemented partially or fully in hardware using, for example, standard logic circuits or a very-large-scale integration (VLSI) design. Other hardware or software can be used to implement embodiments depending on the speed and/or efficiency requirements of the systems, the particular function, and/or particular software or hardware system, microprocessor, or microcomputer being utilized. Embodiments of the method, system, and computer program product can be implemented in hardware and/or software using any known or later developed systems or structures, devices and/or software by those of ordinary skill in the applicable art from the function description provided herein and with a general basic knowledge of control systems, sensors, electromechanical effecters and/or computer programming arts. 
     Moreover, embodiments of the disclosed method, system, and computer program product can be implemented in software executed on a programmed general-purpose computer, a special purpose computer, a microprocessor, or the like. 
     It is, thus, apparent that there is provided, in accordance with the present disclosure, medicament preparation and treatment devices, methods, and systems. Many alternatives, modifications, and variations are enabled by the present disclosure. Features of the disclosed embodiments can be combined, rearranged, omitted, etc., within the scope of the disclosed subject matter to produce additional embodiments. Furthermore, certain features may sometimes be used to advantage without a corresponding use of other features. Accordingly, Applicant intends to embrace all such alternatives, modifications, equivalents, and variations that are within the spirit and scope of the present disclosed subject matter.