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 conductivity sensor is shown in fig1 . the 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 . fig2 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 m ( 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 . fig3 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 pc 3 306 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 108 is 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 . fig4 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 fig4 a . fig4 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 . fig4 b also further demonstrates the wedging of the pce 306 between the pins of the din connector 308 . fig5 a is a plan view of the underside of a pcb 306 a of the conductivity sensor 10 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 . fig5 b is an elevation view of the conductivity sensor 108 a . fig5 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 fig5 b . fig5 c is a plan view of the conductivity sensor 108 a that is shown in fig5 a and fig5 b fig6 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 bidirectional 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 ( tref ) with that of a nist - traceable thermometer or thermistor ( tsen ). 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 kc 1 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 kc 1 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 fig7 , 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 fig8 , a handheld optical barcode scanner 800 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 fig7 the calibration factor is printed on the label as “ cf 0 . 182 ” and the temperature offset is printed as “ to − 06 .” other types barcodes or marking conventions may be used other than the linear barcodes as shown in fig7 . 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 fig2 - 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 fig8 , 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 fig9 , 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 .
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 0100 molar potassium chloride 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 .