Abstract:
Disposable, pre-sterilized, and pre-calibrated, pre-validated conductivity sensors are provided. These sensors are designed to store sensor-specific information, such as calibration and production information, in a non-volatile memory chip on the sensor on in a barcode printed on the sensor. The sensors are calibrated using 0.100 molar potassium chloride (KCl) solutions at 25 degrees Celsius. These sensors may be utilize with in-line systems, closed fluid circuits, bioprocessing systems, or systems which require an aseptic environment while avoiding or reducing cleaning procedures and quality assurance variances.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a divisional of co-pending U.S. application Ser. No. 11/741,162, filed Apr. 27, 2007, which is a continuation-in-part of U.S. application Ser. No. 11/294,296, filed Dec. 5, 2005, both hereby incorporated by reference hereinto. 
    
    
     FIELD OF THE INVENTION 
     The invention generally relates to disposable, pre-sterilized, pre-calibrated, in-line sensors. More specifically, the invention relates to disposable, pre-calibrated, pre-validated probes or sensors that contain non-volatile memory capable of storing specific conductivity and preferably also information concerning the “out-of-box” performance of the probe or sensor. 
     BACKGROUND OF THE INVENTION 
     Pre-sterilized, single-use bag manifolds such as those used in bio-pharmaceutical production (see U.S. Pat. No. 6,712,963, incorporated here by reference) lack the ability to monitor and validate important, analytical solution parameters during the processing of biopharmaceutical solutions. The use of such bag manifolds, for example, in preparative chromatography or tangential flow filtration (TFF) or fluid transfer generally, is severely limited by the general lack of pre-sterilized, pre-calibrated, pre-validated in-line sensors and detectors 
     In-line, flow through-type sensors and detectors are well known in industry and are extensively used in analytical laboratories, pilot plants and production facilities. In-line conductivity detectors, in particular, are used in ion chromatography, preparative chromatography, flow injection analysis (FIA), tangential flow filtration (TFF), as well as water purity analysis. However, prior-art in-line flow through conductivity sensors and detectors are typically made out of machined, stainless steel or plastic materials. These sensors and detectors are intended for permanent installations and long-term use. Prior-art in-line sensors and detectors are difficult to sterilize, require in-field calibration and validation by an experienced operator before use, and are very expensive, often costing thousands of dollars. Consequently, prior art sensors and detectors are not suited for a single-use sensor application. 
     The use of a memory device imbedded in disposable clinical sensors has been reported. For example, U.S. Pat. No. 5,384,028 deals with the fabrication of an enzyme-based glucose biosensor that utilizes a sensor-imbedded data memory device. However, this patent utilizes barcodes and memory devices for purposes of sensor traceability and inventory control. Furthermore, this patent requires sensor calibration and/or validation by the clinician immediately prior to each use. 
     In line sensors for use in bioprocessing applications must be designed to meet government regulations regarding device traceability and validation. In addition, in-line sensors must meet the application requirements for accuracy and precision. These requirements present extra challenges and pose unique problems when the in-line sensor is to be disposable and suitable for single use as desired. Another problem is how to provide disposable in-line sensors that are pre-calibrated. Also for aseptic sensor applications, each single-use sensor, must meet sterilization requirements. Furthermore, single-use sensors must meet economic requirements, i.e. sensors must be low cost, easy to replace with negligible disposal expense. 
     Meeting sensor sterilization requirements represents another very significant sensor design challenge. This is especially the case, when the sensor is intended for single-use bag manifold applications such as those described in the U.S. Pat. No. 6,712,963 (which is incorporated herein by reference). The biotechnology and bio-pharmaceutical industries utilizes four different sterilization methods: (1) autoclaving (i.e. timed exposure to pressurized steam at approximately 125° Celsius); (2) time-limited exposure to an ethylene oxide gas; (3) gamma ray irradiation up to 50 kGy; and (4) electron-beam irradiation. 
     For many single-use sensor application, e.g. for bag manifolds, the preferred sterilization method by the industry is by gamma or electron-beam irradiation. The main advantage of gamma and electron-beam irradiation lies is that the entire, pre-assembled manifold, including bags, tubing, connectors and sensors, can be first sealed in a shipping bag and then exposed to sterilizing radiation or electron-beam bombardment. The entire manifold assembly within the shipping bag remains sterile for a rated period, unless the shipping bag is comprised during shipment or storage. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the aforementioned shortcomings and problems faced by the industry by providing a low-cost, pre-sterilized, pre-calibrated, in-line sensor capable of being traced and validated. The invention further provides a barcode or other printed means, and/or a sensor-embedded, non-volatile memory chip for storing device-specific information for instant recall by the user. 
     The preferred embodiment is an in-line conductivity sensor system used to measure the conductivity of the process flow solution. The present embodiment has two main components: the user interface and the sensor assembly module. 
     The sensor assembly module contains a short tubular fluid conduit, one or more sensor or probe components, referred to herein at times as a sensor or a sensor component. The sensor assembly module further includes a printed circuit board (PCB) with a sensor-embedded non-volatile memory chip. Sensor components can include electrodes, toroidal sensors or other arrangements. All components are designed or selected for highly automated production methods such as those used in surface mounted electronic assemblies. The present disclosure focuses on multiple electrode arrangements as the preferred embodiment for carrying out the sensing function. 
     In the illustrated preferred embodiment, four electrodes are press-fitted into and through four, linearly arranged holes in the fluid conduit wall. The electrodes are epoxied, cemented or sealed into place to prevent leaks or contamination. The electrodes are connected to a PCB. The PCB contains a thermistor, in thermal contact with two of the conductivity electrode pins. The PCB also contains a non-volatile memory chip or EEPROM, which is used to store sensor-specific information, which typically includes the sensor&#39;s ID number, a Cell Constant, a Temperature Offset Value, and the calibration date. 
     Furthermore, each sensor has an “out-of-box” performance variance value which is also stored in the non-volatile memory chip. This “out-of-box” value is a statistically derived performance variance (measured for example in 0.100 molar KCl at 25.0° C.) that represents the maximum measurement error for that specific sensor within a 98% confidence limit. The statistically derived variance value is based on the performance analysis of all calibrated sensors within a production run, typically of between about 100 and about 500 sensors. The factory determined performance variance represents a predictive, “out-of-box” sensor performance level. 
     The user interface performs the conductivity measurement by monitoring the current across the two inner working electrodes. Prior to the conductivity measurement, the user interface retrieves the Cell Constant from its own memory (after it has decoded the barcode and retrieved that information) or from the sensor memory. The measured solution conductance is multiplied by the Cell Constant to arrive at the actual conductivity of the tested process solution. The sensor-specific Cell Constant is determined during factory calibration using a solution (for example 0.100 molar KCl at 25.0° C.) with a known conductivity. The Cell Constant is subsequently stored in the non-volatile memory of the sensor assembly module. 
     Typically, after the sensor module is prepared, it is placed in a shipping bag and then sterilized. The sensor may be sterilized by any of the different sterilization methods utilized in the biotechnology, bio-pharmaceutical or medical industries. However, it has been found that when the sensor assembly modules are exposed to gamma ray and electron-beam irradiation, the irradiation erases or destroys the non-volatile memory chip or EEPROM. Thus, the sensor assembly module of the present invention is equipped with means for storing sensor specific information that is unaffected by gamma ray and electron-beam irradiation. 
     It is a general aspect or object of the present invention to provide a disposable conductivity sensor. 
     Another aspect or object of the present invention is to provide a disposable sensor suitable for one-time use, which may be integrated with other disposable equipment, including bag manifolds, employed in the separation and purification of fluids that are suitable for single-use applications. 
     An aspect or object of the present invention is to reduce the cost associated with the construction of conductivity sensors. 
     Another aspect or object of the present invention is to provide a sensor having a stored “out-of-box” performance variance value. 
     Another aspect or object of the present invention is to provide a Sensor having a means to store sensor specific information, which is not affected by gamma ray or electron-beam irradiation techniques. 
     These and other objects, aspects, features, improvements and advantages of the present invention will be clearly understood through a consideration of the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a preferred embodiment of the user interface and of the conductivity sensor assembly that is attached at both ends of a fluid conduit of a fluid transfer system; 
         FIG. 2  is a cut-away perspective view of the illustrated conductivity sensor assembly; 
         FIG. 3  is an exploded perspective view illustration of the illustrated conductivity sensor and the fluid conduit; 
         FIG. 4   a  is a perspective view of the component side of the illustrated conductivity sensor; 
         FIG. 4   b  is a perspective view of the underside of the illustrated conductivity sensor; 
         FIG. 5   a  is a plan view of the underside of another embodiment of a conductivity sensor; 
         FIG. 5   b  is an elevation view of the conductivity sensor of  FIG. 5   a ;  FIG. 5   c  is a plan view of the component side of the conductivity sensor of  FIG. 5   a;    
         FIG. 6  is a schematic circuit diagram of the illustrated conductivity sensor; 
         FIG. 7  is an illustration of a sensor with barcodes for storing sensor specific information; 
         FIG. 8  is an illustration of a user interface connected to a barcode reader for reading the sensor specific information from the barcodes located on the sensor assembly; and 
         FIG. 9  is a flowchart illustrating the lifecycle of a sensor. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriate manner. 
     A system designed to measure the conductivity of fluids in a closed fluid system by using a pre-calibrated disposable in-line electrical conductivity sensor is shown in  FIG. 1 . The electrical conductivity sensor assembly is generally designated as  100 . The assembly  100  is designed to be integrable with a fluid circuit and to be disposable. Contained with the conductive sensor assembly  100  is a short tubular fluid conduit  102 , designed for a particular manifold flow rate range of the fluid circuit. Typically, the fluid conduit  102  is tubular and has a diameter between about 3 mm and about 25 mm (about ⅛ inch and about 1 inch). The flow conduit  102  is made of a polymer such as a polyolefin, for example polypropylene, but any other appropriate plastic tubing or material may be substituted. The tubing material should be suitable for engaging and containing the fluid being handled, such as valuable proteins, biotechnical compositions or pharmaceutical solutions. The flow conduit  102  has molded-in fluid-tight connections  103  and  104 , which may consist of Luer, Barb, Triclover, or any connection method suitable to connect the flow conduit  102  in a processing system or fluid circuit, such as the illustrated polymeric tubing  106 . A sensing portion or conductivity sensor  108  protrudes through the wall of the conduit in a manner that will be more evident in the subsequent discussion and from the drawings. 
     Leads such as the illustrated electrical connecting wires  110  connect the conductivity sensor  108  to a conductivity readout device or user interface  112 . The user interface, generally designated as  112 , is any computer like device that communicates with the sensor  108  and measures conductivity by sending and receiving both digital and analog electrical signals along the leads  110 . The user interface  112  has a display  114  to display information, for example, the conductivity reading, the temperature reading, and information stored on the conductivity sensor  108  relating to the calibration, validation and tracking of the sensor. 
       FIG. 2  is a more detailed view of the conductivity sensor assembly  100 . The housing  200  of the assembly  100  preferably is over-molded with a durable material such as a hard polyurethane polymer such as TPE. The durable housing material seals and protects the interior components from moisture and outside contaminants. The sensor  108  can be further protected by a sheath  202  as illustrated. 
     The fluid conduit  102  traverses the assembly  100  such as along its width as illustrated. Electrodes  204  are in electrical communication with the interior of the fluid conduit  102 . In the illustrated embodiment, the fluid conduit is intersected by four electrodes of the conductivity sensor  108 . These electrodes  204  can be positioned along the interior of the conduit  102 , such as at the middle portion of the conduit. Gold-plated electrodes can be used such as ones that are about 1 mm to about 2 mm in diameter or between about 0.025 inches to 0.05 inches in diameter. Such electrodes preferably are arranged in-line approximately 2 to 2.5 mm (about 0.08 inch to 0.10 inch) apart. 
     In the illustrated embodiment, the electrode pins  204  are press-fitted into and through four linearly arranged holes in the wall of the fluid conduit  102  and extend into the hollow interior of the fluid conduit  102 . Typical protrusion into the conduit is on the order of about 3 mm to about 13 mm (about ⅛ inch to about 0.5 inch). The electrodes  204  are epoxied, cemented or otherwise sealed to the wall of the fluid conduit  102  to prevent leaks or contamination. Additionally, the electrodes  204  are in electrical communication with their respective traces on the sensor  108 . 
     In other embodiments, the electrodes  204  may only have two electrodes or pins rather than four of the preferred embodiment. In addition, the electrodes may be constructed from other materials, such as stainless steel wire, titanium wire, or any other non-corrosive material. Disposability is a criteria to be considered in selecting these or any other materials of the device. 
       FIG. 3  shows a component view of the fluid conduit  102 , sensor  108 , and sheath  202 . The illustrated sheath  202  has a top portion  302  and a bottom portion  304 . The illustrated electrodes  204  are press-fitted into and through the wall of the fluid conduit  102  and are connected to the printed circuit board (PCB)  306  of the conductivity sensor  108 . The preferred PCB  306  is a double sided PCB with conductive solder traces. Each pin of the electrodes  204  is in direct contact with its respective trace, and each is shown soldered onto the printed circuit board (PCB)  306 . 
     Opposite the electrodes  204 , the PCB  306  is wedged between two rows of five pins of a miniature, 8-pin DIN connector  308 . These five pins of the DIN connector  308  are in direct contact with the PCB  306  and are soldered to the PCB  306 . The three remaining pins of the DIN connector  308  are wired and soldered to the PCB  306 . The end of the sensor  1081   s  capped and sealed by the cap-ring  310 . The DIN connector  308  is detachably connected to the user interface  112  by the connecting wires  110 . Each pin of the DIN connector  308  is associated with an individual wire of the connecting wires  110 . 
       FIG. 4   a  shows the top view or the component view of the sensor  108 . The electrodes  204  are connected to the underside of the PCB  306 . A surface-mounted thermistor  402  is in thermal contact with two of the conductivity electrode pins when four are provided. A second, important function of the thermistor is to act as a pull-up resistor for the non-volatile memory chip, thereby assuring proper functioning of the memory device. The thermistor  402  is used to monitor the temperature of the solution in the fluid conduit  102 , via thermal conductance, such being transmitted to the user interface  112 . The user interface  112  reports the solution temperature data and utilizes the temperature data to correct or normalize the solution conductivity reading. 
     A sensor-embedded non-volatile memory chip or an EEPROM  404  is mounted on the surface of the PCB  304 . The non-volatile memory chip or EEPROM  404  is used to store sensor-specific information. This information can be called up, displayed and printed out, on demand, by the user interface  112 . 
     The PCB  306  also contains a surface-mounted capacitor  406  that is visible in  FIG. 4   a .  FIG. 4   b  is an illustration of the underside of the PCB  306  in the four electrode embodiment. The electrodes  204  are soldered to their respective traces  410 ,  411 ,  412 , and  413 .  FIG. 4   b  also further demonstrates the wedging of the PCB  306  between the pins of the DIN connector  308 . 
       FIG. 5   a  is a plan view of the underside of a PCB  306   a  of the conductivity sensor  108   a . Hand soldered connections  501  and  502  to the PCB connect two pins  503 ,  504  of the 8-pin DIN connector  308   a  that are not in direct contact. 
       FIG. 5   b  is an elevation view of the conductivity sensor  108   a .  FIG. 5   b  also shows how the PCB is sandwiched between the pins of the DIN connector. The low profiles of the capacitor  406   a , non-volatile memory chip  404   a  and the thermistor  402   a  are also evident in  FIG. 5   b.    
       FIG. 5   c  is a plan view of the conductivity sensor  108   a  that is shown in  FIG. 5   a  and  FIG. 5   b.    
       FIG. 6  is an electric circuit diagram illustrating the various connections of the sensor  108  in the preferred embodiment that is illustrated. Four connections from the 8-Pin DIN connector  308  are connected to the four pins of the electrode  204 . One pin of the DIN connector  308  provides a 5.0 Volt power supply to the capacitor  406 , the non-volatile memory chip (or EEPROM)  404 , and a bi-directional serial data line  602 . One pin of the DIN connector  308  provides the ground for the capacitor  406  and the non-volatile memory chip (or EEPROM)  404 . 
     The non-volatile memory chip (or EEPROM)  404  uses the bi-direction serial data line  602  and a serial clock line  604  to communicate with the user interface. Different non-volatile memory chips or EEPROMS have different protocols, which are known in the art. In this embodiment, the serial data and serial clock lines allow a user interface  112  or a calibration device to read, erase, and write data to the non-volatile memory chip  404 . The serial data line  602  is an open drain terminal. Therefore, the serial data line requires a pull-up resistor  606  connected to the voltage source coming from the DIN connector  308 . In this embodiment, the thermistor  402  also serves as the pull-up resistor  606 . 
     The sensor-specific information is electronically entered into the non-volatile memory chip  404  during factory calibration of the conductivity sensor  108 . The sensor-specific information may include the following: Cell Constant (K), Temperature Offset, the unique Device ID, and the Calibration Date, the production lot number of the sensor, the production date of the sensor, the type of fluid used for calibration, the actual temperature of the fluid used, and “out-of-box” sensor performance value. 
     During production, small differentiations in the electrodes  104 , the respective angles of the electrodes, and the gaps between the individual electrodes will result in different conductivity readings for each sensor produced. These differences can significantly affect accuracy. In keeping with the invention, these differences are successfully addressed by having each sensor normalized or calibrated as a part of its manufacturing procedure. 
     In the illustrated example, each conductivity sensor  108  is calibrated using certified 0.100 molar KCl (potassium chloride) solution maintained at 25.0° C. The conductance, which is dependent on the cell geometry and the solution resistivity, is determined by measuring the voltage drop across the electrodes. The measured conductance together with known solution conductivity allows the calculation of the sensor-specific Cell Constant (K). The Cell Constant (K) is determined by the following equation:
 
[Solution Conductivity,( S /cm)]/[Conductance( S )]=[Cell Constant, K ,(cm −1 )]
 
The sensor-specific Cell Constant (K) is then stored in the non-volatile memory  404  of the conductivity sensor  108 .
 
     For example, the solution conductivity for a 0.100 molar KCl solution is known to be 12,850 μS (or 0.01285 S) at 25.0° C. The typical measured conductance for a 0.100 molar KCl solution using a sensor with a ⅛ inch Luer conductivity cell with a 0.10 inch electrode separation is 0.0379 Siemens. Using the equation above, the corresponding Cell Constant (K) for the particular disposable sensor of this illustration is calculated to be 0.339 cm −1 . 
     Once the Cell Constant (K) is calculated it is stored on the sensor. The user interface will recall the Cell Constant (K) from the sensor. When undergoing normal operations, the user interface  112  measures the conductance in Siemens of the solution flowing through the fluid conduit  102  by passing a current through the electrodes  204  and measuring the current across the two inner electrodes  204 . The user interface  112  will then use the Cell Constant (K) for this particular disposable sensor to determine the conductivity of the solution flowing through the fluid conduit. The user interface calculates the solution&#39;s conductivity by multiplying the measured conductance by the Cell Constant (K), as demonstrated in the following equation:
 
[Cell Constant, K ,(cm −1 )]×[Conductance( S )][Solution Conductivity,( S /cm)]
 
The sensor, once calibrated, provides a linear response for NIST traceable standard solutions ranging from 1 to 200,000 μS.
 
     The temperature of a solution will also affect its conductivity. As a result, the sensor must also measure and account for the temperature of the solution to achieve an accurate conductivity measurement. Ordinarily, un-calibrated thermistors will have a variance of ±5% between their measured reading and the actual temperature. A calibrated thermistor may achieve a variance of ±1% or less. 
     In this regard, a sensor-specific Temperature Offset is calibrated at the factory. To determine the Temperature Offset, temperature readings are made while a 25.0° C. KCl solution is pumped through the fluid conduit and over the electrodes. A comparison is then made between the temperature reading of the un-calibrated thermistor on the sensor (Tsen) with that of a NIST-traceable thermometer or thermistor (Tref). The difference between the two readings is the Temperature Offset (Tref−Tsen=TempOffset). The Temperature Offset may have either a positive or a negative value. The sensor-specific Temperature Offset is then stored in the non-volatile memory on the sensor. 
     Each sensor has an “out-of-box” performance variance value which is also stored on the sensor, typically in the non-volatile memory chip. This “out-of-box” value is a statistically derived performance variance (measured in 0.100 molar KCl at 25.0° C.) that represents the maximum measurement error for that specific sensor within a 98% confidence limit. The statistically derived variance value is based on the performance analysis of all calibrated sensors within a production run, typically of between about 100 and about 500 sensor assemblies. The factory determined performance variance represents a predictive, “out-of-box” sensor performance level. This statistical treatment is analogous to and representative of a sensor validation procedure. Factory pre-validated conductivity sensors are thereby provided. The meaning of “pre-validated” is further illustrated herein, including as follows. 
     In the illustrated embodiment, each conductivity sensor undergoes two factory measurements. The first measurement involves sensor calibration and determination of the specific Cell Constant (i.e. response factor) using a 0.100 molar KCl solution at 25.0° C. as described herein. In another separate and distinct measurement with 0.100 molar KCl solution at 25.0° C., the solution conductivity is experimentally determined using the pre-calibrated sensor. When taking into account the experimentally derived solution conductivities for all pre-calibrated sensors, the mean conductivity value closely centers around the theoretical value of 12,850 μS with a 3-sigma standard deviation of +/−190 μS or +/−1.5% An operator may access this information via the user interface  112  or Conductivity Monitor. 
     In addition to the calibration information, such as the Cell Constant (K) and the Temperature Offset, the sensor-specific Device ID, Calibration Date, and statistical information are store in the non-volatile memory. The Device ID is stored as a string of numbers, for example: nn-ss-xxxx-mmyy. In this example, the variables represent the sensor lot number (nn), fluid conduit size (ss), the device serial number (xxxx) and the manufacturing date by month and year (mmyy). For example, sensor containing the Device ID of 02-02-0122-1105 means that this sensor was the 122 nd  sensor made in lot  02  of conduit size 02 (a fluid conduit with a diameter of ⅜″ or 9.5 mm having a barb connector), manufactured in November of 2005. In this illustration, the sensor-specific Calibration Date or the date on which the sensor was calibrated using 0.100 molar KCl solution at 25.0° C. is also stored in the sensor&#39;s non-volatile memory as a separate data entry. 
     Additionally, statistical information or statistical data about the entire lot may also be stored in the non-volatile memory. For example, the average cell constant for lot  122  may be stored in the non-volatile memory of each sensor in lot  122 . The standard deviation for cell constants for each lot may also be stored (i.e. “out-of-box” variance value) in the non-volatile memory of each sensor produced in that lot. This allows the user to determine whether a particular sensor is within the statistical range to achieve the proper margin of error for a specific experiment or bio-processing operation. As those skilled in the art will appreciate, other known statistical methods may be utilized, the results of which may be stored in the non-volatile memory on the sensing device. 
     In addition to storing the Cell Constant (K), Temperature Offset, Device ID, the Calibration Date, and other information in the non-volatile memory on the sensor, a summary of this information may be printed on the outside of the sensor. This information may be consulted by the user, used to later re-calibrate the sensor, and allows the user to input the printed information directly into the user interface. Some or all the information which is stored in non-volatile memory may also be printed or etched on to the sensor in the form of a barcode or label containing a barcode. 
     As shown in  FIG. 7 , an etched or printed label  702  containing one or more barcodes  702   a  and  702   b  is affixed to the exterior housing  701  of the sensor assembly  700 . The sensor assembly has an 8-Pin DIN connector  704  which operates as described above. The sensor assembly also has a fluid conduit  706 , designed for receiving fluids at particular manifold flow rate range of the fluid circuit. The barcodes encode some or all of the sensor-specific information contained in the sensor memory device, EEPROM or memory chip. The barcodes are not affected by gamma or electron-beam irradiation. Thus, if the sensor memory is erased, becomes non-function, or is destroyed, the sensor-specific information is recoverable from the barcodes affixed to the sensor housing  701  by using a barcode reader or scanner. 
     As shown in  FIG. 8 , a handheld optical barcode scanner  300  is hooked up to a digital I/O port of the user interface device or monitor  112 . Additionally, the sensor  700  is also connected to the user interface  112  via the 8-pin DIN serial port  704  as described above. 
     The user interface  112  has software for connecting with a barcode scanner  112  and decoding the barcode label  702  on the sensor  700  and memory for storing the information read from the barcode. By scanning the barcode with the barcode reader  800 , the sensor specific information is read and stored by the user interface  112 . The sensor specific information is then accessible to the user interface  112  such that the user interface  112  may use that information to calculate the sensor-specific response. When fluid or solution is passed through the fluid conduit  706 , the user interface  112  collects analog measurements from the sensor. The user interface  112  then uses this raw analog data along with the sensor-specific calibration factor (i.e. the Cell Constant) and the temperature offset factor (TempOffset) obtained from the barcodes to calculate the sensor-specific response (i.e. the actual conductivity of the fluid). As shown in  FIG. 7  the calibration factor is printed on the label as “CF 0.182” and the temperature offset is printed as “TO−0.6.” 
     Other types barcodes or marking conventions may be used other than the linear barcodes as shown in  FIG. 7 . For example multidimensional barcodes, 2D barcodes or matrix codes may be used in place of the linear barcodes. The barcodes may also be affixed or etched on portions other than the sensor housing, such as on the fluid conduit  706  or the shipping bag or container. 
     An important sensor design consideration is accessibility of the sensor analog circuitry (for example, the circuit connected to the thermistor and electrodes) by the user interface  112 , even when the sensor memory device is non-functional or destroyed. Experimentation by the applicant suggests that the analog circuitry of the sensor as depicted in  FIGS. 2-6  is unaffected by gamma or electron-beam irradiation. Thus, separation of analog circuits and digital circuits (i.e. circuits to the memory device) of the sensor is desirable. By separating the analog and digital circuits, the analog circuits maintain functionality and can provide the user-interface  112  with raw data. 
     As gamma or electron-beam irradiation renders the memory chip or EEPROM non-functional, it is contemplated that sensor units may be manufactured without memory chip. In these embodiments, the analog components are manufactured and assembled into sensors. The sensors are validated and the sensor specific information is then printed on the sensors or shipping bags in print or barcode form. The sensors are then placed in shipping bags or other suitable containers, irradiated via gamma rays or electron-beam, and then delivered to the user. The sensor specific information is entered into the user-interface  112  either by a barcode scanner  800  as shown in  FIG. 8 , or manually by the user. This embodiment saves the costs associated with the including the memory chip with the sensor. 
     The present invention also incorporates the method of preparing a sensor for use in bio-pharmaceutical industry. As shown in  FIG. 9 , the sensors are first manufactured. The sensors may be manufactured to include analog and/or digital circuits. The analog circuits may be used for data collection purposes, while the digital circuits may be used to store sensor specific information. The sensors are then calibrated and validated using the techniques mentioned above and/or those known in the art. The sensor specific information obtained during the calibration and validation steps is then stamped or printed on the sensor in the form of a barcode or other readable form. If the sensor includes a memory chip, the sensor specific information is also stored on the memory chip. The sensor is then placed in a shipping bag or other container  908 . The container and/or the sensor are then sterilized by autoclaving, time-limited exposure to an ethylene oxide gas, gamma ray irradiation, electron-beam irradiation, or by any other method known in the art  910 . The sensor and container are then stored until they are deliver to the user  912 . The user then removes the sensor from the shipping bag or other container  914 . The user then connects the sensor to the user interface  916 . If the sensor includes a memory chip containing sensor specific information, the user interface downloads that information  918 . Otherwise, the user uses a barcode scanner connected to the user interface to read and enter the information into the user interface  920  or enters the sensor specific information found on the label  922 . Either before or after entering the sensor specific information, the sensor is connected to the in-line system, closed-circuit or fluid transfer system  924 . The user interface and the sensor are then used to collect data  926 , such as conductivity, from the fluid passing through the system. Because the sensors are designed to be disposable, at the end of its life cycles the sensors may be destroyed, thrown out, or recycled. 
     The aforementioned embodiments include a selection of novel sensor materials, innovative circuit designs which separate the analog and digital circuits, labeling to preserve sensor-specific information, and a user interface that includes supporting software and procedures to accommodate, retrieve, interpret and calculate sensor-specific information. These materials, circuits, and labeling, are designed to withstand the conditions of the sterilization methods used by the bio-pharmaceutical industry. 
     It will be understood that the embodiments of the present invention which have been described are illustrative of some of the applications of the principles of the present invention. Numerous modifications may be made by those skilled in the art without departing from the true spirit and scope of the invention.