Patent Publication Number: US-2022218888-A1

Title: Systems and methods for measuring electrical characteristic of medical fluids

Description:
TECHNICAL FIELD 
     This invention relates to measuring conductivity of a medical fluid. 
     BACKGROUND 
     During hemodialysis, impurities and toxins are removed from the blood of a patient by drawing the blood out of the patient through a blood access site, typically via a catheter, and then passing the blood through an artificial kidney (often referred to as a “dialyzer”). The artificial kidney includes a semi-permeable membrane that separates a first conduit from a second conduit. Generally, a dialysis solution (often referred to as a “dialysate”) flows through the first conduit of the dialyzer while the patient&#39;s blood flows through the second conduit of the dialyzer, causing impurities and toxins to be transferred from the blood to the dialysate through the semi-permeable membrane. The impurities and toxins can, for example, be removed from the blood by a diffusion process. After passing through the dialyzer, the purified blood is then returned to the patient. 
     Maintaining a substantially constant concentration of sodium in the patient&#39;s blood throughout the hemodialysis treatment can help to reduce or prevent discomfort experienced by the patient. Therefore, sodium concentrations in the patient&#39;s blood can be modified through the level of sodium in the dialysate which requires this level to be monitored during hemodialysis treatment. 
     SUMMARY 
     Implementations of the present disclosure are directed to a device for measuring electrical characteristics of medical fluids, such as sodium in the dialysate solution. 
     In an aspect, a circuit for measuring the conductivity of a medical fluid includes a data collecting cell through which a medical fluid is configured to flow, an input voltage source that provides set input voltage to the data collecting cell, a voltage measurement unit configured to measure the input voltage and an output voltage of the data collecting cell, and a switch in communication with the voltage measurement unit. The switch is configured to switch the voltage measurement unit between a first state in which it is configured to measure the input voltage and a second state in which the voltage measurement unit is configured to measure the output voltage of the data collecting cell. 
     Implementations can include one or more of the following features. 
     In some implementation, a cell voltage is determined by taking a difference between the input voltage and the output voltage. 
     In some implementations, a cell current is determined by measuring a current through a resistor connected in series with the output of the data collecting cell. 
     In some implementations, a cell conductance is determined by dividing the cell current by the cell voltage. 
     In some implementations, the conductivity of the medical fluid flowing through the data collecting cell is determined by multiplying the cell conductance by a cell constant. 
     In some implementations, the cell constant is determined by measuring one or more conductivities of known solutions by the circuit. 
     In some implementations, the cell constant is pre-calibrated such that the cell constant is known before the conductivity of the medical fluid is measured. 
     In some implementations, a precise calibration of the voltage measurement unit is not required to provide an accurate measurement of the cell conductance. 
     In some implementations, the input voltage source operates at a frequency of about 100 kHz. 
     In some implementations, the input voltage source can operate at other frequencies based on the fluid to be measured and a specific parameter that may be the focus of detection. 
     The example implementation described takes advantage of a constant voltage source exciting the cell circuit. It is also possible to construct a complementary system where the cell is driven by a constant current source and measurements made with a current measurement device. 
     In some implementations, the data collecting cell is a conductivity cell. 
     In some implementations, the data collecting cell includes two electrodes. 
     In some implementations, the data collecting cell includes an inlet and an outlet, wherein the medical fluid enters the data collecting cell through the inlet and flows out of the data collecting cell through the outlet. 
     In some implementations, the data collecting cell is calibrated for a specific cell constant that is determined based at least in part on locations of two electrodes of the data collecting cell with respect to each other. 
     In some implementations, the data collecting cell is calibrated for a specific cell constant that is determined based on the dimensions of the two electrodes. 
     In some implementations, the data collecting cell is calibrated for a specific cell constant that is determined based on the conductive material make-up of the two electrodes. 
     In some implementations, the circuit is configured to be attached to a dialysis system. 
     In some implementations, the dialysis system includes a peritoneal dialysis machine. 
     In some implementations, the medical fluid includes dialysate or saline. 
     Devices and methods in accordance with the present disclosure may include any combination of the aspects and features described herein. That is, devices in accordance with the present disclosure are not limited to the combinations of aspects and features specifically described herein, but also include any combination of the aspects and features provided. 
     Implementations of the present disclosure provide one or more of the following technical advantages and/or technical improvements over previously available solutions. The implementations allow monitoring fluid parameters (e.g., concentration, fluid elements, etc.) of a medical fluid by measuring electrical characteristics of the fluid. For example, a dialysate should have a conductivity that indicates that a certain amount and ratio of sodium bicarbonate is present, because an imbalance could impact the health of the patient and cause discomfort. The present implementations provide a sensor technique that can measure conductivity of the dialysate to determine patient treatment parameters without making direct contact (e.g., via electrodes) with the patient&#39;s body. 
     In some implementations, the devices, systems, methods, and techniques described herein can provide a number of additional advantages. For example, in some implementations, measuring conductivity using the techniques described herein allows for quick, accurate conductivity measurements without requiring calibration of the data collecting system. That is, the data collecting system which drives and interacts with the cell need not be calibrated ahead of time (e.g., prior to conductivity measurements being taken) because any errors included in the circuit are canceled out by common mode voltage measurement techniques described herein. In this way, the data collecting system may be said to be “self-calibrating.” Because calibration is not required, quicker measurements can be taken as compared to measurements taken by data collecting systems that require calibration ahead of time or in real time. 
     The cell constant is premeasured and known ahead of time which is set by the size, material of the electrodes and spacing of the electrodes. So long as these parameters do not change, the cell constant will remain constant. 
     Further, the data collecting system and the associated techniques described herein present no phase shift issues because the applied AC voltages and currents are essentially being rectified (e.g., such that they are converted to DC). In this way, the waveform is essentially integrated. In particular, any phase angle shift in the AC current from the AC voltage can be integrated out over time to steady state (e.g., DC) voltage and current values. Because patient parameters do not change instantaneously, instantaneous measurement of conductivity is not required thereby allowing the departure from conventional AC measurement techniques which required phase alignment and compensation in calculations. The details of one or more implementations of the present disclosure are set forth in the accompanying drawings and the description below. Other features and advantages of the present disclosure will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates an example of a peritoneal dialysis (PD) system with example placement of data collection cell positions. 
         FIG. 2  illustrates an example measurement circuit for connection to a data collection cell to determine the conductivity of fluid flowing through a data collecting cell. 
         FIG. 3  illustrates an example cross section of a data collecting cell. 
         FIG. 4  depicts an example process that can be executed in accordance with the implementations described herein. 
         FIG. 5  shows an example of a computer system and related components that can be used to automate the implementation of the techniques described herein. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     Implementations of the present disclosure provide a device that can be used to measure one or more electrical characteristics (e.g., electrical conductivity) of fluids in dialysis systems. The device has a data collecting cell that includes a chamber with an inlet and an outlet. Fluid enters the chamber through the inlet and flows out of the chamber through the outlet. Multiple electrodes (e.g., two electrodes) are located within the chamber to measure electrical characteristics of the fluid. 
     Implementations of the present disclosure also provide a circuit for measuring electrical characteristics (e.g., electrical conductivity) of fluid flowing through a data collecting cell (e.g., a conductivity cell). The circuit can accurately measure the conductivity of the fluid without requiring calibration, as described in more detail below. Thus, measurement systems can be easily employed without calibration and without sacrificing the accuracy of the measurements. 
     In general, the data collecting cell may be part of a medical system, such as a dialysis system (e.g., a peritoneal dialysis system, a hemodialysis system, etc.) or another type of medical systems such as a heart-lung system, a chemotherapy system, etc. Medical fluid flowing through the medical system and/or medical fluid flowing to and/or from the patient may flow through the data collection cell such that one or more properties of the medical fluid can be measured.  FIG. 1  shows an example of a medical system in which the data collecting cell may be implemented. In particular,  FIG. 1  shows an example peritoneal dialysis system  100 , although it should be understood that the data collecting cell may be implemented in other types of medical systems. In the illustrated example, the peritoneal dialysis system  100  includes a PD machine (also generally referred to as a PD cycler)  102  seated on a cart  104 . The PD machine  102  includes a housing  106 , a door  108 , and a cassette interface  110  that contacts a disposable PD cassette  112  when the cassette  112  is disposed within a cassette compartment  114  formed between the cassette interface  110  and the closed door  108 . A heater tray  116  is positioned on top of the housing  106 . The heater tray  116  is sized and shaped to accommodate a bag of PD solution such as dialysate (e.g., a 5 liter bag of dialysate). The PD machine  102  also includes a user interface such as a touch screen display  118  and additional control buttons  120  that can be operated by a user (e.g., a caregiver or a patient) to allow, for example, set up, initiation, and/or termination of a PD treatment. 
     Dialysate bags  122  are suspended from fingers on the sides of the cart  104 , and a heater bag  124  is positioned in the heater tray  116 . The dialysate bags  122  and the heater bag  124  are connected to the cassette  112  via dialysate bag lines  126  and a heater bag line  128 , respectively. The dialysate bag lines  126  can be used to pass dialysate from dialysate bags  122  to the cassette  112  during use, and the heater bag line  128  can be used to pass dialysate back and forth between the cassette  112  and the heater bag  124  during use. In addition, a patient line  130  and a drain line  132  are connected to the cassette  112 . The patient line  130  can be connected to a patient&#39;s abdomen via a catheter and can be used to pass dialysate back and forth between the cassette and the patient&#39;s peritoneal cavity during use. This location is one position where a data collecting cell  190  can be located to evaluate the difference in the conductivity of fluid entering the patient to the fluid exiting the patient. The catheter may be connected to the patient line  130  via a port such as a fitting. The drain line  132  can be connected to a drain or drain receptacle and can be used to pass dialysate from the cassette  112  to the drain or drain receptacle during use. Line  132  in another location for a data collecting cell  190  to measure conductivity in the fluid being drained from the system. It should be understood that the two example positions for the data collecting cell listed in this paragraph are not exclusive. Such cells could be located in any of the lines. 
     The PD machine  102  also includes a control unit  139  (e.g., a processor). The control unit  139  can receive signals from and transmit signals to the touch screen display  118 , the control panel  120 , and the various other components of the PD system  100 . The control unit  139  can control the operating parameters of the PD machine  102 . In some implementations, the control unit  139  is an MPC823 PowerPC device manufactured by Motorola, Inc. 
     A data collecting cell with measurement system can be implemented in the medical system. With the presented implementations, the data collecting cell may be implemented in a way such that calibration of the data collecting cell measurement system is not required to yield accurate measurements. An example data collecting cell measurement system is shown in  FIG. 2 . In particular,  FIG. 2  shows an example circuit  200  that can be used to measure the conductivity of the fluid flowing through the data collecting cell. Measurements can be obtained using a “common mode” technique, as described in detail below. By utilizing common mode DC measurement techniques, phase angle shifts in AC current from AC voltage can be integrated out over time (e.g., over a few milliseconds) to steady state voltage and current values. In turn, various factors (e.g., that would otherwise need to be considered and accounted for using other measurement techniques) can be ignored because they essentially divide out from the calculation. For example, characteristics of the electrode posts (e.g., the material they are made of) need not be considered because any effects are equally present across the measurements. 
     In general, an excitation voltage (e.g., a fixed excitation voltage) or an excitation current (e.g. a fixed excitation current) is applied to the data collecting cell. For a fixed voltage excitation, current through the data collecting cell is measured. For a fixed current excitation, voltage across the data collecting cell is measured. In some implementations, two electrodes may provide the excitation, and the same two electrodes may be used to measure the resultant parameter. Circuit  200  in  FIG. 2  provides an illustrated example implementation of a measurement circuit which uses voltage excitation. 
     It should be understood that the circuit  200  includes various components that are used to tune the excitation voltage and such components are described with respect to  FIG. 2  for illustrative purposes only. Other components having various values and/or placements may be added to, removed from, or swapped from the circuit  200  without departing from the spirit and scope of the inventive concepts described herein. 
     In the illustrated example implementation, the circuit  200  includes an input frequency source  202  with an alternating current (AC) output. In some implementations, the input frequency source  202  is configured to provide a wave having sinusoidal properties (e.g., a sine wave). In some implementations, additional components may be connected to the input frequency source  202  to cause the voltage waveform to have sinusoidal properties. For example, in some implementations, a frequency source  202  producing a square wave output can be filtered with an additional series resistor between frequency source  202  and resistor R 4   208  and an additional capacitor to ground from the junction of the added resistor and resistor R 4   208 . The values of the added resistor and capacitor are adjusted to create a triangle waveform from the square wave output of frequency source  202  with near sinusoidal properties. In some implementations, the input frequency source  202  operates at a frequency of about 100 kHz. 
     The input voltage source  202  is provided to an op-amp  204 . In the illustrated example, the op-amp  204  provides a fixed voltage excitation source to the data collecting cell connected at  214 . In the illustrated example, the gain of the op-amp  204  is established by the ratio of R 3   206  divided by R 4   208 . In the illustrated example, values for R 3   206  relative to R 4   208  are chosen such that an output voltage of the op-amp  204  (e.g., Voltage A  210 ) is a constant voltage such as +/−2 Vp-p. In some implementations (e.g., depending on one or more characteristics of the op-amp  204  and the value of R 3   206 ), the op-amp  204  is compensated with a particular capacitor value of Cl  215  such that the frequency response is sufficient for passing 100 kHz. In some implementations, capacitor value Cl  215  may be adjusted to make the waveform more sinusoidal. To optimize phase margin to ensure stability (i.e., non-oscillation of the op-amp  204 ) in the circuit  200 , the ratio of R 3   206  divided by R 4   208  may be maintained close to unity (e.g.  1 ). In an op-amp circuit, this ratio of the feedback resistor R 3   206  divided by the input resistor R 4   208  is the pass-band gain of the op-amp. In some implementations, the input AC voltage source  202  is provided by a microcontroller that may have a 5V supply (resulting in an AC voltage swing of +/−2.5V when capacitively coupled to circuit  200 ) or a 3V supply (resulting in an AC voltage swing of +/−1.5V when capacitively coupled to circuit  200 ). Because the output impedance of the op-amp  204  is very low (e.g., on the order of 20 Ohms or less), the output voltage of op-amp  204  emulates a constant voltage source. In some implementations, R 1   212  provides a reference output load for op-amp  204  to maintain op-amp output characteristics of Voltage A  210  and minimize load transients during measurements. Though not critical in value, the illustrated example R 1   212  has a value of 4.7 k Ohms, sinking a minimal current of approximately 0.4 mA. 
     For the illustrated example, a two-post data collecting cell  230  of  FIG. 3  (or another similar data collecting cell) is connected at  214  of the measurement circuit  200  in  FIG. 2 . One post  232   a  of the data collecting cell  230  in  FIG. 3  is connected to Voltage A  210  through a first connection at  214  of  FIG. 2 . The other post  232   b  of the data collecting cell  230  in  FIG. 3  is connected to a fixed precision resistor R 2   216  through a second connection at  214  of  FIG. 2 . 
     The current path Icell for measurement of conductivity by circuit  200  in  FIG. 2  of the fluid in the data collecting cell  230  in  FIG. 3  is from the fixed excitation Voltage A  210  through a first connection at  214  in  FIG. 2 ; to a pin such as  232   a  in conductivity cell  230  in  FIG. 3 ; through the fluid in the data collecting cell  230  flowing between posts  232   a  and  232   b  in  FIG. 3 ; from post  232   b  of  230  in  FIG. 3  to a second connection of  214  in  FIG. 2 ; through a precision resistor R 2   216  in  FIG. 2  to ground potential. It is noted that the post connections  232   a ,  232   b  of the data collection cell  230  in  FIG. 3  are interchangeable. It is also noted that connector  214  in  FIG. 2  is for convenience in connecting the data collection cell  230  in  FIG. 3 . It is not required if the data collection cell  232  posts  232   a ,  232   b  in  FIG. 3  are directly connected to Voltage A  210  and R 2   216  in  FIG. 2 . For brevity, the data collection cell will hereafter be referred to as  214  even though these are convenient connection points for the conductivity cell. The value for R 2   216  may be chosen based on the conductivity values expected to be measured by the circuit  200  for improved resolution of a measurement device. In the illustrated example, R 2   216  has a value of 270 Ohms to optimize resolution of expected measured conductivity values in the 13.5 mS/cm to 14 mS/cm range. Different values for R 2  may be used to provide the best resolution at a different conductivity range of interest. 
     In order to measure the conductance of the fluid in the data collection cell connected at  214 , Voltage A  210  and the voltage across R 2   216  (e.g., Voltage B  220 ) are required. Such voltage measurements are made by a voltage measurement unit such as an alternating current (AC) voltmeter  222  that is connected to a switch  218 . The switch  218  provides for easy switching of the AC voltmeter  222  between measurements of Voltage A  210  and Voltage B  220 . The AC voltmeter  222  must have a high enough input impedance such that the conductivity of the data collection cell in series with resistor R 2   216  are not loaded. The AC voltmeter  222  does not result in loading of the measurement circuit such as to modify the measurements being made. 
     The switch  218  is configured to switch between a first state in which the AC voltmeter  222  is configured to measure Voltage A  210  (e.g., the input voltage to the data collection cell  214 ) and a second state in which the AC voltmeter  222  is configured to measure Voltage B  220  (e.g., the output voltage of the data collection cell  214 ). The voltage across the data collection cell  214  is found by measuring Voltage A  210  at the top of the conductivity cell  214  (e.g., the input voltage) and Voltage B  220  at the bottom of the conductivity cell  214  (e.g., the output voltage) and subtracting: 
       Data Collection Cell Voltage=Voltage  A −Voltage  B   Equation (1)
 
     By using the same AC voltmeter  222  to measure both Voltage A  210  and Voltage B  220 , the measurements are made in “common mode.” As such, any calibration error in the AC voltmeter  222  will appear in both Voltage A  210  and Voltage B  220 , and will subsequently divide out as will be illustrated in the below equations. 
     The current through the data collection cell  214  is the same as the current through the series resistor R 2   216 . Thus, the current is: 
       Data Collection Cell Current=Voltage  B/ 270 Ohms  Equation (2)
 
     The conductance of the fluid in the data collection cell  214  is then found by dividing the cell current by the cell voltage: 
       Data Collection Cell Fluid Conductance=Cell Current/Cell Voltage  Equation (3)
 
     Conductivity is then determined by multiplying the data collection cell fluid conductance by the data collection cell constant, which is determined by measuring known solutions in the conductivity circuit  200 . In some implementations, the conductivity cell  214  “cell constant,” which relates the sensor posts  232   a  and  232   b  in the fluid, is pre-calibrated. That is, the cell constant for the data collection cell  214  with sensor posts connected to the terminals (e.g., sometimes collectively referred to herein as the electrodes) may be determined ahead of time such that the conductivity can be determined without further calibration being required. The data collection cell constant is a function of the data collection cell  230  geometry, placement of the sensor posts  232   a  and  232   b  within the data collection cell  230  and properties of the sensor posts  232   a  and  232   b . If manufactured through molding and/or other tight tolerance methods, the data collection cell constant should be as its name indicates—a constant. Therefore: 
       Conductivity=Data Collection Cell conductance×Data Collection Cell constant  Equation (4)
 
     The circuit  200  can be used to measure the conductivity without calibrating the system (e.g., the circuit  200 ). For example, so long as the AC voltmeter  222  is stable over the time of the Voltage A  210  and Voltage B  220  measurements, then specific calibration of the circuit  200  is not required. To illustrate this aspect, consider Condition 1 in which all components and calibrations are perfect. The resulting measurements are: 
         V  Data Collection Cell Perfect=Voltage  A  Perfect−Voltage  B  Perfect  Equation (5)
 
         I  Data Collection Cell Perfect=Voltage  B  Perfect/270 Ohms  Equation (6)
 
       Data Collection Cell Conductance Perfect= I cell Perfect/ V cell Perfect  Equation (7)
 
     Now consider a Condition 2 example in which the AC voltmeter  222  is out of calibration by a gain error of 20% to the positive (e.g., Vac=Vperfect*1.2) during the time period of the measurements. Then the following analysis applies: 
         V  Data Collection Cell=1.2*Voltage  A  Perfect−1.2*Voltage  B  Perfect  Equation (8)
 
         I  Data Collection Cell=1.2*Voltage  B  Perfect/270 Ohms=1.2*(Icell Perfect)  Equation (9)
 
       Data Collection Cell Conductance= I cell/ V cell=(1.2 *I cell Perfect/[1.2*(Voltage  A  Perfect−Voltage  B  Perfect)]= I cell Perfect/ V cell Perfect  Equation (10)
 
     Under Condition 2, the 1.2 factor divides out due to using the common mode of measurement with the same AC voltmeter  222 . Therefore, no calibration of the AC voltmeter  222 , the conductivity cell  230  or the other components of the circuit  200  is required. 
     A similar analysis can be performed for the condition if Voltage A  210  changes slightly. So long as the change is constant during the time window when the measurements of Voltage A  210  and Voltage B  220  are made, then this change also divides out of the conductance calculations and no calibration of the circuit  200  is required. 
     The circuit  200  described with respect to  FIG. 2  can provide a number of advantages. In some implementations, measuring conductivity using the techniques described herein allows for quick, accurate conductivity measurements without requiring calibration of the data collecting cell  230 . That is, the data collecting cell  230  need only be calibrated once ahead of time to establish the conductance to conductivity cell constant. Once known, so long as the data collection cell  230  is manufactured the same way with the same dimensions and materials, all that is required is an accurate conductance measurement by the measurement circuit  200 . Because any errors included in the conductance measurement circuit  200  are canceled out by the common mode voltage measurement techniques described in this example embodiment and the data collection cell can be uniformly manufactured to produce a fixed, repeatable conductance to conductivity conversion factor, this composite conductivity measurement system may be said to be “self-calibrating”. Because calibration is not required, quicker measurements can be taken as compared to measurements taken by data collecting cells that require calibration ahead of time or in real time. 
     Further, the data collecting cell  230  and the associated techniques described herein present no phase shift issues because the applied AC voltage and current are being rectified (e.g., such that they are converted to DC). In this way, the AC waveform is largely integrated. Further, any phase angle shift in the AC current from the AC voltage can be integrated out over time to steady state (e.g., DC) voltage and current values. In other words, since instantaneous measurement of conductivity rarely (if ever) required, through facilitating a short integration time for the voltage and current measurements and DC analysis, the complexity and inaccuracies of making phase-corrected AC measurements are overcome. The result is a measurement circuit that can obtain measurements quicker (e.g., because calibration is not required), which is simpler, and which is lower cost. 
     The procedure disclosed for making measurements can be manually made or automated.  FIG. 4  depicts an example process  300  that can be executed in accordance with the implementations of the present disclosure. The process  300  can be implemented by a medical system, such as a dialysis system (e.g., the PD system  100 ), or another type of medical system that includes the data collecting cells described herein. 
     In this process, fluid is received through an inlet of a chamber of the data collecting cell, and flows about two electrodes located within the chamber ( 302 ). For example, fluid can be received at a chamber of the data collecting cell through an inlet. 
     An input voltage is applied to the data collecting cell ( 304 ). For example, an input voltage source can provide an input voltage to the electrodes of the data collecting cell. 
     A voltage measurement unit is configured to measure the input voltage and the output voltage at the electrodes. The voltage measurement unit may be an AC voltage measurement unit with a high impedance input (so as not to load the measurement) which rectifies and integrates the voltage to DC. A switch is in communication with the voltage measurement unit. When the switch switches states  308 , the voltage measurement unit switches from measuring the input voltage of the data collecting cell  306  and an output voltage of the data collecting cell  310 . The input voltage is measured at one of the electrodes of the data collecting cell  306 , and the output voltage is measured at the other electrode of the data collecting cell  310 , as described in detail above. First, the input voltage is measured ( 306 ). The switch then switches states ( 308 ), and the output voltage is measured ( 310 ). 
     Using at least the measured input voltage and output voltage, various calculations are performed to determine the conductance and conductivity of the medical fluid ( 312 ), as described in detail above. For example, a cell voltage is determined by taking a difference between the input voltage and the output voltage, and a cell current is determined by measuring a current through a resistor connected to the data collecting cell output. A cell conductance is determined by dividing the cell current by the cell voltage, and the conductivity is determined by multiplying the cell conductance by a cell constant (e.g., a previously-determined cell constant). Measuring the conductivity using this technique requires no calibration of the data collecting cell or the voltage measurement unit. 
       FIG. 5  is a block diagram of an example computer system  400  that can be used as part of a medical systems described herein, for example, to perform measurements and/or analyses related to the data collecting cell. A control unit, such as a computing device and/or a microcontroller, could be examples of the system processor  410  described here. The measurement unit and/or the data collecting unit described herein can be part of any medical system, such as dialysis systems (e.g., a hemodialysis system), a heart lung machine, a chemotherapy system, or any other system that introduces fluid into body. 
     The system  400  includes a processor  410 , a memory  420 , a storage device  430 , and an input/output device  440 . Each of the components  410 ,  420 ,  430 , and  440  can be interconnected, for example, using a system bus  450 . The processor  410  is capable of processing instructions for execution within the system  400 . The processor  410  can be a single-threaded processor, a multi-threaded processor, or a quantum computer. The processor  410  is capable of processing instructions stored in the memory  420  or on the storage device  430 . The processor  410  may a shared processor with a host system (such as a dialysis or PD system) which may also execute conductivity measurements. 
     The memory  420  stores information within the system  400 . In some implementations, the memory  420  is a computer-readable medium. The memory  420  can, for example, be a volatile memory unit or a non-volatile memory unit. In some implementations, the memory  420  stores information for causing the pumps of the dialysis system to operate as described herein. 
     The storage device  430  is capable of providing mass storage for the system  400 . In some implementations, the storage device  430  is a non-transitory computer-readable medium. The storage device  430  can include, for example, a hard disk device, an optical disk device, a solid-date drive, a flash drive, magnetic tape, or some other large capacity storage device. The storage device  430  may alternatively be a cloud storage device, e.g., a logical storage device including multiple physical storage devices distributed on a network and accessed using a network. 
     In an alternate example of implementation, the processing system  400  can be stand-alone to perform the conductivity measurements and interface via the input/output sub-system  440  with a similar input/output system of a host medical device to pass resulting conductivity data. In this example of implementation, the processing system  400  can be a stand-alone system which includes controls and a display interfaced to the input/output sub-system  440 . In some implementations, the system  400  is a microcontroller. A microcontroller is a device that contains multiple elements of a computer system in a single electronics package. For example, the single electronics package could contain the processor  410 , the memory  420 , the storage device  430 , and input/output devices  440 . 
     The input/output device  440  provides input/output operations for the system  400 . In some implementations, the input/output device  440  includes one or more of network interface devices (e.g., an Ethernet card), a serial communication device (e.g., an RS-232 10 port), and/or a wireless interface device (e.g., an 802.11 card, a 3G wireless modem, or a 4G wireless modem). In some implementations, the input/output device  440  may include short-range wireless transmission and receiving components, such as Wi-Fi, Bluetooth, and/or near field communication (NFC) components, among others. In some implementations, the input/output device includes driver devices configured to receive input data and send output data to other input/output devices, e.g., keyboard, printer and display devices (such as a touch screen display). In some implementations, mobile computing devices, mobile communication devices, and other devices are used. In some implementations, the input/output devices can be configured with drivers to complete the measurement steps and configurations of the conductivity circuit shown in  FIG. 4 . 
     While dialysate was used herein as an example fluid for describing the functionality of the embodiments, the data collecting unit, in general, and the data collecting cell, in particular, can be used for determining electrical characteristics of any other type of fluid, for example, fluids in which conductivity changes with a biological parameter. Examples of medical fluids include blood, effluent PD drainage, plasma, saline, and urine, to name a few. 
     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.