Patent Grant
RE49221
The invention generally relates to the aseptic transfer of solutions out of one or more biological fluid and/or process fluid storage or supply containers. Single-use manifold systems carry out transfers needed in bioprocessing applications. With the invention, automated dispensing is accomplished, preferably in association with one or more disposable conductivity sensors and often with one or more remotely controlled pinch valves.
Good manufacturing practices and governmental regulations are at the core of any pharmaceutical, biotechnology and bio-medical manufacturing process or procedure. Such manufacturing processes and procedures as well as associated equipment must undergo mandated, often lengthy and costly validation procedures. Similar issues exist for sensors when needed in such systems, such as conductivity sensors.
For example, the equipment used for the separation and purification of biomedical products must, for obvious reasons, meet stringent cleanliness requirements. The cleaning validation of new or re-commissioned purification equipment (including sensor equipment such as equipment for preparative chromatography or tangential flow filtration) may require as many as 50 test-swabs of exposed surfaces and subsequent biological assays of such test-swabs. For a single piece of purification equipment, the associated and reoccurring cost of a single cleaning validation may readily exceed multiple thousands of dollars.
To reduce such cleaning validation costs and expenses, and/or to reduce the occasions when cleaning is needed or required, the pharmaceutical and biotech industries are increasingly employing, pre-sterilized, single-use, plastic tubing and collapsible, plastic bags for solution transfer and storage. Sterilization is accomplished by exposing the complete tube/bag manifold to gamma irradiation, or to an ethylene oxide atmosphere. The pre-sterilized, aseptically packaged tube/bag manifolds are commercially available (currently from TC Tech; HyClone; St Gobain Performance Plastics, for example) and are used for the manual transfer of solutions. Typically, the solution transfer procedure requires a technician to operate a peristaltic pump and to manually open and close tube clamps for diverting the solution from the reservoir to the storage bags. Although this procedure reduces the cleaning efforts and cleaning validation expense, operator interaction and time still are required, and these approaches are dependent upon operator expertise for consistent accuracy and precision.
Dispensing approaches having automated features (which can include sensors, monitors and programmable controllers) are generally known. Keys et al. U.S. Pat. No. 5,480,063 and U.S. Pat. No. 5,680,960 describe fluid dispensing units which control fluid volumes in conjunction with a closed loop approach, which these patents suggest can avoid the need for venting. The fluid to be dispensed exits the closed loop apparatus through a fill tube, as directed by a controller. Such approaches do not address the cleaning needs and/or cleaning validation costs and expenses, were these types of systems to be used in pharmaceutical and biotech industries for dispensing, directing, combining or separating biological or chemical fluids.
Prior systems can incorporate diaphragm valves, which come into direct contact with the process solution, and these valves are a potential source of contamination. Thus diaphragm valves require costly cleaning validation procedures. In addition, such systems typically lack suitable sensors, especially conductivity sensors.
It has been found that, by proceeding in accordance with the present invention, significant cost savings and better performance can be realized in a system which incorporates automated, aseptic manifolds and sensors within the field of technology which embraces pre-sterilized, single-use plastic tubing and containers having at least one collapsible portion. The components and sensors which contact the biological or chemical fluid are each presterilized and disposable after use.
The present invention is directed to manifold units which include at least one sensor and which are presterilized and disposable, making them single-use units which are sterilized and packaged so as to be usable “off the shelf” and which thus directly address the problem of tedious and time consuming cleaning and testing at the use site. Multiple embodiments are disclosed. Each includes tubing lengths, at least one sensor and a plurality of single-use storage or collection bags, each having multiple inlet and/or outlet passages which are selectively openable and closeable. The tubing lengths can interact with one or more pinch valves which are operable remotely. Remote operation is automated by a controller programmed to carry out procedures according to a selected embodiment.
It is a general aspect or object of the present invention to provide improved single-use manifolds with at least one sensor for automated, aseptic transfer of solutions in bio-processing or chemical processing applications.
Another aspect or object of the present invention is to provide improved apparatus and method which combine pinch valve use with disposable, sterilized manifold dispenser units that incorporate at least one disposable sensor.
Another aspect or object of this invention is to provide improved apparatus and method which greatly reduce the expenditure of time and resources devoted to cleaning procedures for transfer equipment used in pharmaceutical and biological industries and laboratories where contamination of biological and/or chemical fluids cannot be tolerated.
An aspect or object of the present invention is to reduce the need for validation procedures for equipment used in separation and purification of fluids such as in conjunction with the preparation, separation, sensing and dispensing of bio-medical products.
Another aspect or object of this invention is that it handles cleanliness requirements for procedures including a sensing function, such as fluid dispensing, preparative chromatography and tangential flow filtration while automating operation thereof.
Another aspect or object is to integrate disposable conductivity sensors with the equipment used in the separation and purification of fluids.
Another aspect or object is to provide the ability to connect disposable conductivity sensors with either a system controller or a user interface.
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.
In the course of this description, reference will be made to the attached drawings, wherein:
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 particularly designed for use as an automated, aseptic solution transfer system is illustrated in
In the pharmaceutical and biotechnology industries, media preparation departments typically prepare the solutions used in a solution production protocol which follows good manufacturing practices. Media preparation departments are responsible for maintaining solution recipes, preparing and storing buffer solutions and other tasks demanding consistency and accuracy. For example buffer solutions are prepared in large vats, then pumped through a sterilizing filter, such as one having a porosity of 0.1μ. Typically such solutions need to be filled into presterilized, single use storage bags for later use. A media preparation department may also be responsible for providing inoculating solutions to the operators of a bioreactor. At the completion of a bioreactor batch, the reactor broth often is filled into sterile storage bags for later processing.
The second tube connection 26 consists of a short piece of tubing connected to the bag with a closed manual shut-off clamp. This tubing and clamp arrangement is used to relieve any gas and/or pressure build-up inside the bag during the filling operation. The third tube connection 27 is identical to the second connection and includes a short piece of tubing and a clamp. This can be used as an auxiliary inlet and/or outlet for recirculation of the bag contents.
During a typical bag-filling operation, the first and/or last collection bag can serve the purpose of quality control bags. Often these quality control bags will be smaller in volume, such as one liter. During the initial system priming cycle, the first such quality assurance (QA) bag is filled with process solution. At the end of the dispensing cycle when all of the bags containing the product of the operation, usually larger in volume that the QA bag(s), have been filled, the second QA bag is filled. The solutions contained in the QA bags are subsequently analyzed for contamination or for other quality assurance needs.
When the bag-filling process is completed, the manual shut-off clamps on each bag are closed and the aseptic tube connections are disconnected. During storage, the aseptic connector ends are protected with end caps (not shown).
Turning now to the single-use, sterilized manifold and transfer tubing assembly of
Access to the storage bags is provided via the pinch valves. The pinch valves are normally closed, and typical pneumatic pinch valves require pressurized air (for example 80-100 psi) to open. When such a pinch valve is pressurized, solution is allowed to enter the storage bag while the air in the bag escapes through an integral vent filter. The pinch valve(s) are pneumatic or electrically operated pinch valves (currently available from ACRO Associates, Inc). They are installed external to the tubing and are operated by a multi-valve controller (currently available from SciLog Inc.), or another computer-based process logic control (PLC) device. The external pinch valves divert the solution inside the manifold without compromising the sterile environment inside the tubing. Diaphragm valves used in other systems are in constant contact with the process solution, whereas pinch valves do not contact the process solution.
The optional, disposable pressure sensor 32 continuously monitors the filter back pressure. This sensor can provide information to a suitable controller to avoid undesired events. For example, a controller can issue an alarm when a safe, user-defined pressure limit has been exceeded, indicating that the capacity of the sterilizing filter has been exhausted. Details in this regard are found in U.S. Pat. Nos. 5,947,689, 6,350,382 and 6,607,669. These patents and all other references noted herein are incorporated by reference hereinto.
The controller can be a stand-alone unit or be associated with another device. In a preferred arrangement, the controller is associated with the pump unit 45. This is shown at 46 in
Typically, a user-determined program will be provided for the automated filling of storage bags according to
An exemplary solution transfer program for controlling the manifold is as follows. In a SciPro edit mode, the user enters and stores a multi-bag metering program. The following is an example of a simple program to fill three, 20-liter storage bags 21, 22, 23.
Changes in the RATE and TIME program steps will accommodate any storage bag volume. Additional “RUN” program blocks can be inserted to increase the number of bags (up to 12 in the example) to be filled. However, an analogous software program can be generated in which storage bags are filled based upon either VOLUME or WEIGHT program commands. A scale with an appropriate capacity is required for bag filling by weight. An optional scale or load cell 47 can be provided to supply data to the controller in this regard. It will be appreciated that this embodiment meters user-defined volumes of fluid, then automatically switches to the next empty storage bag to be filled.
A second embodiment, which is generally illustrated in
The result is a concentration as well as a separation of the bio-molecule from the rest of the process solution matrix. The introduction of an elution buffer will change the local chemical environment of the stationary phase, thereby causing the bio-molecule to be released and thus able to be collected outside the column in a relatively small volume of elution buffer.
In automated preparative chromatography, the column containing the stationary phase first is washed and/or equilibrated with an appropriate buffer solution. This wash and/or equilibration cycle is followed by a loading cycle during which the process solution is pumped through the column. The bio-molecule of interest adheres to the stationary phase. The loading cycle can take many hours, depending on the process solution volume and pump rate with which the solution is pumped through the column. The loading cycle is followed by a second wash cycle to remove any un-adsorbed biomaterial off the column.
An elution buffer then is introduced to remove the bio-molecule from the column. This removal of the bio-molecule is accomplished either with a step gradient or a linear gradient. After peak collection has been completed, the chromatography column is regenerated and re-equilibrated using appropriate buffer solutions as generally known in the art.
Manifold and transfer tubing assembly 48 represents a generalized manifold for automating preparative chromatography procedures. In operation, and utilizing the controller system, the exemplary pneumatically controlled pinch valve 51 is pressurized and thus opened, thereby providing access to the wash and/or equilibration buffer bag 54. At a user-definable pump rate, the wash buffer is pumped through a disposable, in-line pressure sensor 55, through a bubble trap (not shown), through the chromatography column 56, and through a detector or UV flow cell 57. On exiting the flow cell, the wash/equilibration buffer is collected in a waste container or bag 58 while pinch valve 49 is pressurized and thus open.
During the loading cycle, pinch valves 51 and 49 are opened/pressurized, while the pinch valves 52, 53 and 59 remain closed. The pump unit 45 pumps the process solution through the manifold system 48, the column 56 and the flow cell 57 and is collected in the waste container or bag 58. In some chromatography applications, the process solution exiting the flow cell needs to be stored separately in a “process receiving bag” (not shown) for possible re-processing. Another pinch valve (not shown) would provide access to such a “process receiving bag”.
The loading cycle is followed by a wash cycle (valves 51 and 49 are open/pressurized, all other pinch valves are closed) which carries away any un-absorbed material from the column to waste. By opening pinch valves 53 and 49, elution buffer in bag 63 is introduced into the column and is initially pumped to waste. However, when the signal from the UV detector 57 exceeds a user-defined value, pinch valve 59 is opened thereby providing access to a peak collection bag 61 while valve 49 is closed. On the backside of the eluted peak, valve 59 is again closed, while at the same time, valve 49 is opened.
After the material of interest has been collected in bag 61, the chromatographic column 56 requires regeneration and re-equilibration. The column regeneration process is readily automated via access to appropriate buffer solutions (not shown), which are generally as known in the art. Depending on the underlying chromatographic complexity of the application, access to five or six buffer solutions may be required, and these can be provided in their own single-use bags as desired. Similarly, if multiple product peaks are to be collected, additional peak collection bag(s) as well as additional pinch valve(s) may have to be incorporated into manifold and transfer tubing assembly 48.
The single-use, presterilized components of the manifold and transfer tubing assembly 48, shown as a feed section, and of a second tube and bag assembly 64 for chromatographed fluid are shown in
The second tube and bag assembly 64 consists of a short piece of tubing 68 connected to the bag with a closed manual shut-off clamp 69. The second tubing/clamp arrangement 71 is used to relieve any gas and/or pressure build-up inside the bag during the filling operation. The third tube connection 72 is identical to the second tubing/clamp arrangement 71 and is used as an auxiliary inlet/outlet for recirculation of the bag contents.
The single-use storage/collection bags 58 and 61 are connected to the remaining tube manifold 72 as shown in
In a typical chromatography application, the single-use storage bags 54 (for wash buffer), 62 (for process solution) and 63 (for elution buffer) have been previously filled, for example by using the embodiment of
Referring further to the SciPro controller programmed for controlling the manifold arrangement for chromatography, a mode thereof allows entry and storage of a sequence of simple commands, i.e. RUN, RATE, TIME, VOLUME, P LIMIT 1 and Valve States such as V=000000 (all pinch valves are closed) or V=123456 (all pinch valves are open).
This controller mode is organized in subprogram blocks. The terminating statement of a program block can be a “VOLUME”, “TIME”, “P LIMIT D1 (or D2)” or “N LIMIT D1 (or D2)” statement. The statement “P LIMIT D1=5%” reads: “Positive Slope Signal of Detector D1 with a Threshold Value of 5% Full Scale (FS)”. See the Chromatography Program Example.
For example, in line 014, the SciPro switches from “Waste” to “Collect” when the D1 signal has a positive slope and a value greater than 5% FS (line 013). The statement “N LIMIT D1=10%” reads: “Negative Slope Signal of Detector D1 with a Threshold Value of 10% FS”. In line 016, the controller switches from “Collect” to “Waste” when the D1 signal has a negative slope (back side of peak) and a value of 10% FS (line 15).
The user can edit and/or modify the values of: RUN, RATE, TIME, VOLUME, P LIMIT 1, N LIMIT D1 and Valve States at any time during a chromatography run. User-designed application programs can be uploaded or downloaded from an external computer at any time by utilizing the computer's hyper terminal.
It will be appreciated that, with this embodiment, sequential scheduling of events are achieved. These include sequential scheduling of wash, load and elution cycles. The controller can initiate buffer selection, loading and peak volume collection. Typical in-line concentration detectors can be Wedgewood UV and/or pH detectors, which have outputs of 4-20 MA outputs which can be monitored simultaneously. A typical pump is a Watson Marlow 620 R peristaltic pump head capable of generating 60 psi at a pump rate of 15 liters per minute.
User-defined detection threshold levels are used for valve switching and peak volume collection. All solution-handling parameters, such as pump rates, column pressure, and valve positions can be monitored and documented in real time and can be printed out or electronically archived.
In a third embodiment, automated tangential flow filtration is carried out using a modified system designed for this use. Previously referenced U.S. Pat. No. 5,947,689, No. 6,350,382 and No. 6,607,669 disclose the automation of tangential flow filtration (TFF) procedures. These are combined with the use of disposable, single-use manifolds, which also include disposable pressure sensors and single-use, collapsible storage bags and the use of remotely operated pinch valve(s).
A typical TFF application that utilizes a single-use, pre-sterilized manifold is shown in
The pre-sterilized components of this embodiment are shown in
The second tube connection consists of a short piece of tubing 87 connected to the bag with a closed manual shut-off clamp 88. The second tubing and clamp arrangement is used to relieve any gas and/or pressure build-up inside the bag during the filling operation. The third tube connection 89 can be identical to the second tubing and clamp arrangement and is used as an auxiliary inlet and outlet for recirculation of bag contents.
Similarly, the process solution bag 82 has three inlet and/or outlet tube connections. The first tube connection 91 is used as an outlet to pump solution out of the bag. The second tube connection 92 serves as a return inlet to accommodate the re-circulated retentate. The third tube connection 93 again serves to relieve any excessive gas and/or pressure build-up inside the bag.
The permeate collection bag and the process solution bag are connected to the filtration tube manifold, generally designated at 94 in
Prior to starting the pump unit 45, all of the manual shut-off clamps are opened except those clamps that relieve any gas and/or pressure build-up inside the bags. Initially the valve 95 is closed and the valve 96 is open, while the pump unit 45 starts to recirculate the solution contained in the process solution bag 82 through a tangential flow filter system 101. The air volume contained in the tubing and tangential flow filter system 101 ends up in the process solution bag 82 where it is vented to the outside through a sterilizing air filter (not shown). Once the optimal pump recirculation rate has stabilized, pinch valve 95 is opened and permeate is collected.
The micro filtration or ultra filtration can be carried out either by constant rate or by constant pressure. Software programs which are suitable to automate the filtration process through the use of the controller 46 are described in U.S. Pat. No. 5,947,689, No. 6,350,382 and No. 6,607,669.
The forth, fifth, and sixth embodiments, which are generally illustrated in
The conductivity sensor monitors the conductivity levels of the solution. The levels are reported back either to a user interface, which displays the information, or to the manifold controller 46. Based on the information provided by the conductivity sensor or sensors, the manifold controller 46 (or the user interface in some embodiments) may then modify the operation of a flow imparting unit such as the pump unit 45, open and close the various pinch valves, start user-determined programs, or stop user-determined programs.
The fifth embodiment is generally illustrated in
The conductivity sensors monitor the conductivity levels of the solution entering the chromatography column 56 and the conductivity levels as the solution leaves the column. The levels are reported back either to a user interface, which displays the information, or to the manifold controller 46. Based on the information provided by the conductivity sensors, the manifold controller 46 (or the user interface in some embodiments) may then modify the operation of the pump unit 45, open and close the various pinch valves, start user-determined programs, or stop user-determined programs.
The sixth embodiment, shown in
The conductivity sensors monitor the conductivity levels of the fluid passing to the process solution bag 82. The conductivity levels are reported back either to a user interface, which displays the information, or to the manifold controller 46. Based on the information provided by the conductivity sensors, the manifold controller 46 (or the user interface in some embodiments) may then modify the operation of a flow imparting unit such as the pump unit 45, open and close the various pinch valves, start user-determined programs, or stop user-determined programs. The conductivity sensor 158 is useful in TFF as it monitors the concentration or absence of molecules passing through the tubing to the process solution bag 82. For example, if, the conductivity sensor measures abnormally high conductivity levels during the cleaning or operation of the tangential flow filter, it may signal to the controller or user that the filter is defective. On the other hand, if the conductivity sensor measures abnormally low conductivity levels during the cleaning or operation of the tangential flow filter, it may signal that the filter or tubing is clogged.
The preferred embodiment of an in-line conductivity sensor has two components: the user interface or the controller 46 and the disposable sensor assembly module. Further description of the in-line, single-use or disposable conductivity sensor is found in U.S. Pat. Nos. 7,788,047, 7,857,506 and 7,927,010 and in U.S. Patent Application Publication No. 2009/0180513, entitled “Disposable, Pre-Calibrated, Pre-Validated Sensors for use in Bio-processing Applications,” incorporated hereinto by reference. However, in other embodiments, the functionality of each component may be combined with or moved to the other component.
The disposable sensor assembly module, generally designated as 200 in
Toroidal electrical conductivity sensors may be used in place of the electrodes in the electrical conductivity sensor assembly 202module 200. The toroids of the toroidal sensors may be arranged in a non-obtrusive manner around the fluid circuit. Typically, two toroids are used. One toroid is used to “drive” or induce a current through the fluid, while the other “senses” or measures the induced current through the fluid.
The electrodes or toroids are connected to the PCB 204. The PCB may contain various components, such as a thermistor to measure the temperature of the fluid in the fluid circuit 202 or a non-volatile memory chip or EEPROM. The PCB is connected to a user interface, control unit, or controller 46. The controller 46 or user interface connects to and accesses the PCB 204, its components, and the electrodes 203 by a plug-in wires or leads (not shown).
The controller 46 or the user interface produces the current that drives the electrodes or toroids and measures the conductivity by measuring the current on the “sensing” electrodes or toroids. The conductivity of the fluid passing through the fluid conduit is measured by driving a current through one or more electrodes, and then using the remaining electrodes to measure the current that passes through the fluid. The current or the voltage drop measured is proportional to the conductivity of the fluid passing through the fluid conduit.
The user interface or controller 46 may access calibration information stored in the non-volatile memory of the sensor. During production of the disposable sensors 200, small variations in the design and placement of the electrodes 203 as well as variations in the accuracy of the thermistors may lead to inaccurate conductivity measurements. However, each sensor is individually calibrated to account for the adverse effects due to these small variations. The sensor specific calibration information is stored in the non-volatile memory of the sensor.
This calibration information may include a temperature offset and a conductivity constant. The temperature offset represents the linear difference between the known temperature of the fluid and the temperature measure by the sensor at the time of calibration. The conductivity constant represents the difference between the known conductivity of the fluid and the conductivity measure by the sensor at the time of calibration. When measuring the conductivity of the fluid in the fluid conduit, the user interface or controller 46 will retrieve the calibration information to use in the calculations for conductivity. The temperature offset and conductivity constant are later utilized by the user interface or controller 46 to calculate the actual conductivity of the biotechnology fluid passing through the fluid conduit 202.
The calibration information may also include information about the method of calibration, the statistical variance among different sensors in the same lot, and the date when the sensor was last calibrated.
In addition to the calibration information, production information may be stored in the non-volatile memory on the sensor. Production information may include items such as the date, time, or lot number for when the sensor was manufactured.
The user interface 210 has a display 211 and several input keys on its face. These keys include the Menu key 222, the Up key 223, the Down key 224, the Re-Cal key 225, the Enter key 226, the Exit key 227 and the Sensor On/Sensor Standby key 228. To turn the user interface on, the user must press the Sensor On key 228. During normal operation, the display 211 typically reports the conductivity of the fluid being measured by the system in Siemens, the temperature of the fluid in degrees Centigrade, the percent of total conductivity, and a graphical representation of the percent of total conductivity.
The Menu key 222 allows users to progress through different menus as shown in
The user interface does not necessarily have to use the calibration information stored on the sensor. In the illustrated embodiment, the user may modify the calibration information utilized by the user interface 220 without permanently modifying the information stored in the non-volatile memory on the sensor. The user may manually change the calibration information utilized by the user interface 220 by selecting the Up or Down arrow keys 223, 224 when presented with the corresponding screen.
The modifiable calibration information may include the Reference Temperature 233, the Temperature Coefficient 234, and the Temperature Offset 235. By pressing the Menu Key 222, the user may modify by using the Up or Down arrow keys 223, 224 the units in which conductivity is displayed 236, the setting for the serial port 237, the different print times for the print option 238, the maximum conductivity measurement at which point the user interface 220 produces a high audible alarm 239 or low audible alarm 240. The user may also select to restore or re-install the factory calibration values 241, or change the date 242 and time 243. When presented with any of the above mentioned options, the user may return the user interface to normal operations without changing the option by pressing the Exit Key 227.
The user may also re-calibrate the sensor or overwrite the calibration information stored in the non-volatile memory chip by selecting the Re-cal key 225, which runs the recalibration program. As shown in
After the information is modified, the new value overwrites the stored information in the non-volatile memory of the sensor when the user presses the Enter Key 225. The display 211 will then report the current readings 250 as computed using the new calibration information. In the future, when the user selects “Factory Reset” 241, the current settings of the user interface are replaced with those values entered by the user during the last recalibration program. However, if the user wants to end the recalibration program without changing the options, he or she need only press the Exit key 227.
The user interface 220 may also include a sensor key (not shown). As shown in
A sensor-embedded non-volatile memory chip or an EEPROM is mounted on the surface of the PCB 204. The non-volatile memory chip or EEPROM is used to store sensor-specific information. This information can be called up, displayed and printed out, on demand, by the user interface 210.
The sensor-specific information is electronically entered into the non-volatile memory chip during factory calibration of the conductivity sensor 200. 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 203, 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 electrical conductivity sensor 108assembly module 200 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 electrical 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 of the conductivity sensor 200.
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 210 measures the conductance in Siemens of the solution flowing through the fluid conduit 202 by passing a current through the electrodes 203 and measuring the current across the two inner electrodes 203. The user interface 210 will then use the Cell Constant (K) for this particular disposable sensor to determine the electrical conductivity of the solution flowing through the fluid conduit. The user interface calculates the solution's electrical 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 electrical conductivity. As a result, the sensor must also measure and account for the temperature of the solution to achieve an accurate electrical 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 preferred 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 210 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 stored 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 122nd 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'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.
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.
This is a Reissue Application of U.S. Pat. No. 9,700,844, filed as application Ser. No. 13/769,971 on Feb. 19, 2013, which is a continuation of application Ser. No. 11/294,297, filed Dec. 5, 2005, now U.S. Pat. No. 9,283,521, which is a continuation-in-part of application Ser. No. 10/764,624, filed Jan. 26, 2004, now U.S. Pat. No. 7,052,603, which is a divisional of application Ser. No. 10/172,082 filed Jun. 14, 2002, now U.S. Pat. No. 6,712,963, each incorporated hereinto by reference.
| Number | Name | Date | Kind |
|---|---|---|---|
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