Abstract:
A self-calibrating pressure transducer is disclosed. The device uses an embedded zirconia membrane which pumps a determined quantity of oxygen into the device. The associated pressure can be determined, and thus, the transducer pressure readings can be calibrated. The zirconia membrane obtains oxygen from the surrounding environment when possible. Otherwise, an oxygen reservoir or other source is utilized. In another embodiment, a reversible fuel cell assembly is used to pump oxygen and hydrogen into the system. Since a known amount of gas is pumped across the cell, the pressure produced can be determined, and thus, the device can be calibrated. An isolation valve system is used to allow the device to be calibrated in situ. Calibration is optionally automated so that calibration can be continuously monitored. The device is preferably a fully integrated MEMS device. Since the device can be calibrated without removing it from the process, reductions in costs and down time are realized.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   ORIGIN OF INVENTION 
   The invention described herein was made by employees of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor. 

   FIELD OF THE INVENTION 
   The present invention relates to a self-calibrating pressure transducer, and more specifically, a pressure transducer having a membrane or fuel cell capable of pumping a known quantity of gas into a chamber to calibrate the transducer in situ. 
   BACKGROUND OF THE INVENTION 
   Pressure transducers are used in numerous industries, including refineries, other chemical industries, aircraft, automobiles, space travel, etc. A serious problem with pressure transducers is that they need to be calibrated at regular intervals to ensure accurate operation. This usually involves the removal of the transducer from the process being monitored, and taking the transducer to a calibration facility where a series of pressures is applied to the device and its response is compared to the nominal or previous calibration curve. This process will give a certain degree of confidence that the transducer was working during the period since the last calibration, but does not ensure that the transducer will work properly at any time in the future. The removal and calibration is expensive, and the process is either without a measurement during this time or a replacement transducer is installed. Either way, additional costs are incurred either as down time, or the cost of additional transducers. 
   Various technologies involving pressure transducers have been previously disclosed. For example, U.S. Pat. No. 6,298,731, issued to Wade et al., is directed toward a pressure sensor and regulator for direct injection engine fuel systems. The system combines a pressure transducer with a solenoid valve in order to allow direct control of the fuel line pressure. However, the issue of calibration of the transducer is not disclosed. 
   U.S. Pat. No. 6,029,524, issued to Klauder et al., discloses a pressure transducer having a redundant fluid pressure sensor which can be used to determine whether the transducer needs to be recalibrated. Similarly, U.S. Pat. No. 5,672,808, issued to Klauder et al., discloses a pressure transducer having a redundant fluid pressure sensor that can be used to determine if the pressure transducer needs to be recalibrated. Two readings from separate sensors are compared to indicate whether they may be an error in one, however, no embedded calibration system is suggested. 
   U.S. Pat. No. 6,012,336, issued to Eaton et al., discloses a micro electro-mechanical capacitance pressure sensor integrated with electronic circuitry on a common substrate. Again, no calibration system is suggested. 
   U.S. Pat. No. 5,377,524, issued to Wise et al., discloses a self-testing capacitive pressure transducer. However, this disclosure only pertains to low range capacitive pressure transducers, and does not teach or suggest a calibration system as described herein. 
   Thus, there is a need to develop a pressure transducer having a built in calibration device capable of generating a series of pressures to thoroughly calibrate the device without removing it from the process. Such a calibration system could also be activated whenever the operation of the transducer is in question, as well as for routine calibration. 
   SUMMARY OF THE INVENTION 
   In view of the insufficiencies discussed above, it is an object of the present invention to provide a self-calibrating pressure transducer having various features and advantages. 
   The present invention is an integrated pressure transducer and calibration mechanism, preferably in a silicon MEMS device that allows the self calibration of the pressure transducer on demand. Calibration can be achieved in as little as within a few seconds. It is adaptable to both low and high range pressures, and includes the ability to internally check the performance of the calibrating device with an accuracy compatible with the pressure transducer calibration requirements. 
   The device includes a pressure transducer membrane which measures the process pressure. Calibration can be implemented on either the working side of the pressure membrane, or on the reference side. In one embodiment, a zirconia membrane is used to pump a known amount of oxygen into communication with an interior chamber. Thus, a known pressure is created. The resulting effect on the pressure membrane can be measured, and repeated measurements can be taken to calibrate the transducer. 
   In various embodiments, oxygen can be supplied by the surrounding environment, by an oxygen reservoir, or by surrounding carbon dioxide or water via an electrolysis process. The system may be configured with valves to selectively isolate the calibration portion of the device or the process pressure, as desired. The system may also be automated to insure continuous calibration of the device. 
   In another aspect of the invention, a reversible fuel cell assembly is used to pump gas into a chamber to calibrate the device. A membrane-electrode assembly (“MEA”) is used to pump oxygen and hydrogen into the calibration chamber. The oxygen and hydrogen are pumped into separate sections of the chamber, and slack diaphragms communicate the pressure to an interior transducer chamber. Since the fuel cell assembly pumps a known amount of gas into the system, the pressure can be calculated and compared to the transducer pressure readings in order to calibrate the device. 
   The present invention allows the practical construction of a compact Micro Electro-Mechanical System (“MEMS”) device capable of developing a series of pressures to calibrate a pressure transducer incorporated into the same or attached substrate. The basic concept utilizes a Zirconia membrane which is used to pump known quantities of oxygen into a closed chamber attached to the pressure transducer, either a permanent or temporary connection, to allow calibration of the pressure transducer. The zirconia device can act as both an accurate coulometric oxygen pump, and as an oxygen concentration readout device. Thus, a controlled and known quantity of oxygen can be transported into the closed chamber in contact with the pressure transducer&#39;s active element to generate a known pressure through the known volume of the captive space, and then, using the potentiometric measurement capability of the same zirconia cell, measure the resulting oxygen concentration within the closed space, giving an independent check on the pressure created with the coulometric pumping. Preferably, an accurate temperature measurement can be incorporated into the gas chamber to correct for any change in the gas temperature. 
   The gas pressure can be applied to either the working side of the pressure transducer, through suitable isolation valves to remove the effect of the measured process pressure, or to the back side of the transducer to yield an offset to the process pressure. If the process pressure is stable for the duration of the calibration check, then no valving may be required for the latter mode of operation. 
   The two modes of operation are shown in  FIGS. 1 and 2 .  FIG. 1  shows a simplified schematic with a directly mounted zirconia cell. The oxygen from the surrounding air can be pumped by the zirconia cell into the cavity behind the pressure membrane to offset the working fluid pressure.  FIG. 2  shows a more complex system which applies calibration pressures to the working side of the pressure membrane. The oxygen pressure acts through an isolation membrane and valves to remove the influence of the process fluid during calibration.  FIG. 2  also incorporates an absolute pressure reference and an oxygen source chamber for use in atmospheres that do not contain oxygen or a gas which can be converted to oxygen by the zirconia cell. 
   The system can make use of a zirconia amperometric and potentiometric cell to generate and measure oxygen pressure for the purposes of calibrating an integrated or attached pressure transducer. The generation and transport of oxygen using zirconia is well known and is the basis of commercial oxygen sensors. It is likewise known that zirconia can be used in a potentiometric mode to measure the concentration of oxygen with an appropriate oxygen reference concentration present on one side of the cell. Using these properties to generate an oxygen pressure for the purpose of calibrating a pressure transducer has not been previously proposed. The coulometric transport of oxygen allows the exact amount of oxygen transported to be substantially exactly known from the current and time used to do the transport. Coupled with a calibration volume of known size, the resulting pressure can be calculated. The potentiometric measurement allows the direct measurement of the resulting oxygen pressure. 
   The only requirements are that the current and time of coulometric transport are measured accurately, and the volume and temperature of the enclosed gas are known and measured accurately. In one system it has been found that a resolution of 0.1 mV on the zirconia cell potentiometric readout can detect a pressure change of 0.05%. A zirconia cell of 0.01 square cm can pump enough oxygen to raise the pressure in a 100 micron deep chamber of the same area by 0.58 atmospheres per second. In 10 seconds, this oxygen pumping rate would achieve over 90 psi in the same chamber, and the potentiometric readout would measure that resulting concentration and pressure to 0.5% with a 0.1 mV resolution on the readout. 
   In another embodiment of the invention, the basic concept utilizes an electrochemical cell which is used to pump known quantities of an electroactive gas into a closed chamber attached to the pressure transducer, either a permanent or temporary connection, to allow calibration of the pressure transducer. The device can act as both an accurate coulometric pump, and as a concentration readout device in some cases. Thus, a controlled and known quantity of gas can be transported into the closed chamber in contact with the pressure transducer&#39;s active element to generate a known pressure through the known volume of the captive space. Then, using the potentiometric measurement capability of the same, or another, cell, measure the resulting gas concentration within the closed space, giving an independent check on the pressure created with the coulometric pumping. To increase accuracy, an accurate temperature measurement can be incorporated into the gas chamber to correct for any change in the gas temperature. 
   Again, the gas pressure can be applied to either the working side of the pressure transducer, through suitable isolation valves to remove the effect of the measured process pressure, or to the back side of the transducer to yield an offset to the process pressure. If the process pressure is stable for the duration of the calibration check, then no valving may be required for the latter mode of operation. 
   In one embodiment of the invention utilizing the zirconia cell, the zirconia cell is heated to an operational temperature by deposited heater attached to the membrane or its support in intimate contact with the membrane. This temperature would be above 600EC. Once the zirconia begins to conduct, the cell can be operated in one of two modes. In the potentiometric mode, the voltage generated by the cell is related to the ratio of oxygen concentrations across the membrane by the well known Nernst Equation:
 
 E=E   0 =( RT/nF )*(log( P 1 /P 2))  (1)
 
Where P 1  and P 2  are the partial pressures of oxygen on the two sides of the zirconia membrane. At a temperature of 900EC, the value of RT/nF is about 54 mV for a pressure ratio of 10 (IE per decade of concentration change). In this mode, the oxygen concentration in the calibration chamber can measured by the output of the zirconia cell.
 
   In the second mode of operation, the zirconia membrane can pump oxygen through the membrane via electrochemical reduction and oxidation of oxygen and oxide ions which are mobile in the heated zirconia. In this mode, the mass transport of oxygen is measured by the current and the time duration of that current. The governing equation in this case is the Faraday relationship:
 
Coulombs of electricity passed= n*F   (2)
 
Which translates to the following for oxygen transport:
 
Amps*seconds (coulombs)=4*96482.15 coul/mole of O2  (3)
 
   This relationship allows the precise metering of oxygen through the zirconia membrane. Any current in the milliamp to microamp range is easily applied to the zirconia cell using a constant current source and the time measured with a simple timer circuit. Such coulometric measurements can be done with great precision, with many examples of reproducibility in the 0.01% range or better in the chemical literature. 
   The initial measurement after conduction starts might be of the current oxygen concentration in the potentiometric mode. For this measurement, the temperature of the zirconia cell must be known to satisfy equation (1) above. The temperature of the gas in the closed cell is also necessary. A precision of 1EC is more than adequate for both temperatures. 
   Once the beginning oxygen concentration is measured, the coulometric pumping of oxygen can begin. The current level is selected, and the time of generation is precisely measured to achieve the calculated pressure desired. This concentration is then confirmed by another potentiometric measurement. If another pressure level is desired the process can be repeated for as many points as desired. When the calibration is completed, the polarity of the oxygen pump is reversed, and the excess oxygen is pumped out of the calibration chamber with the same precision, and the last potentiometric measurement is done to confirm that the sensor is in the same state as before calibration. 
   The heat transfer from the hot zirconia to the surrounding gas and transducer must be evaluated with respect to any given situation. Accurate temperature measurements and high temperature materials of construction should alleviate most problems. In one embodiment, the zirconia membrane is about 1 millimeter square. Suitable thermal isolation can be achieved by connecting the calibration gas chamber through a narrow channel. 
   In the fuel cell assembly embodiments, as shown in  FIG. 3 , a room temperature reversible fuel cell operates on the following reversible electrochemical reactions in acid media:
 
2 H 2 O&lt;-&gt; O 2 +4 H + +4 e   −   (4)
 
4 H + +4 e   − &lt;-&gt; 2 H 2   (5)
 
The combined reactions yield the reversible electrolysis and fuel cell reactions of water:
 
2 H 2 O&lt;-&gt;O 2 +2 H 2   (6)
 
   In common practice, these reactions are typically accomplished at room temperature using a PEM (Proton Exchange Membrane) in a Membrane-Electrode Assembly (MEA) using a Nafion membrane for the PEM with electrodes deposited on each side of the Nafion to construct the MEA. By utilizing these room temperature reactions, we can effectively produce a known pressure of oxygen or hydrogen to achieve the same result as the previous example, without the difficulties of the large temperature gradients that are experienced with a zirconia design. As long as the products and reactants are kept in intimate contact with the MEA, the cell can continue to operate in a reversible fashion for an indefinite period of time. 
   One problem that can arise is that the generation of hydrogen and oxygen (Equations 4 &amp; 5 above) do not produce equal volumes of gas. In a situation where these two gases are evolved into separate chamber (as is desirable from a safety standpoint), the unequal volumes result in unequal or unbalanced pressures across the MEA. Since the MEA is typically quite thin (0.007″ or less), this unequal pressure will cause a distortion of the MEA, and an uncontrolled change in the volume and hence the pressures sought for the calibration process. This problem would limit the accurate pressure generation of such a reversible fuel cell to a few tens of psi before substantial errors would arise. By connecting the anode and cathodes chambers of the fuel/electrolysis cell through a flexible (“slack”) membrane, it is possible to keep the two reactive gases separated while allowing the two pressures to exactly equilibrate. While this design innovation is not necessary at lower pressures (approximately &lt;30 psia), many pressure transducers operate at much higher pressures where this concept would be necessary for even minimal accuracy. In such circumstances, it is possible to design suitable slack membranes with a low enough spring force as to not significantly impact the calibration process. Such designs for the reversible fuel cell are shown in  FIGS. 4 and 5 .  FIG. 4  incorporates a slack diaphragm which directly separates the two gases, while the design in  FIG. 5  utilizes two diaphragms and a fluid filled cavity or capillary between them. This latter feature gives a greater physical separation of the two reactive gases and minimizes the volume each gas must fill. This makes it easier to evolve the amount of gas needed to achieve higher pressures, and improves the safety of the device in circumstances where high pressures of oxygen and hydrogen would otherwise be deemed unsafe. 
   Calculations of the calibration pressures and times to achieve them with a nominal design of 300 mA current and 0.5 mL are shown in Table 1 below: 
   
     
       
             
             
             
             
           
             
             
             
             
           
             
             
             
             
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               Initial Volumes, Anode &amp; Cathode 
               0.5 
               mL 
             
             
                 
               Gas generation Rates 
             
           
        
         
             
                 
               Oxygen 
               1 
               mL/min 
             
             
                 
               Hydrogen 
               2 
               mL/min 
             
             
                 
                 
             
           
        
         
             
                 
               Total 
               Total 
                 
                 
                 
                 
             
             
               Time of 
               Vol of 
               Vol of 
               Total 
               Vol 
               Vol 
                 
             
             
               Generation 
               Oxygen 
               Hydrogen 
               Pressure 
               Anode 
               Cathode 
               Pressure 
             
             
               (min) 
               mL 
               mL 
               Atm 
               mL 
               mL 
               PSI 
             
             
                 
             
             
               0 
               0.5 
               0.5 
               1 
               0.500 
               0.500 
               14.70 
             
             
               1 
               1.5 
               2.5 
               4 
               0.375 
               0.625 
               58.80 
             
             
               2 
               2.5 
               4.5 
               7 
               0.357 
               0.643 
               102.90 
             
             
               3 
               3.5 
               6.5 
               10 
               0.350 
               0.650 
               147.00 
             
             
               4 
               4.5 
               8.5 
               13 
               0.346 
               0.654 
               191.10 
             
             
               5 
               5.5 
               10.5 
               16 
               0.344 
               0.656 
               235.20 
             
             
               10 
               10.5 
               20.5 
               31 
               0.339 
               0.661 
               455.70 
             
             
               15 
               15.5 
               30.5 
               46 
               0.337 
               0.663 
               676.20 
             
             
               25 
               25.5 
               50.5 
               76 
               0.336 
               0.664 
               1117.20 
             
             
                 
             
             
               This spreadsheet calculates the pressure generated in a sealed Echem cell with pressure equalization 
             
           
        
       
     
   
   Other features and advantages of the invention will be apparent from the following detailed description take in conjunction with the following drawings, wherein like reference numerals represent like features. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagrammatic view of one embodiment of the self-calibrating pressure transducer of the present invention showing the calibration on the reference side of the transducer. 
       FIG. 2  is a diagrammatic view of another embodiment of the self-calibrating pressure transducer of the present invention, showing an oxygen reservoir and valved system for fluid isolation and calibration on the working side of the transducer. 
       FIG. 3  is a diagrammatic view of another embodiment of the self-calibrating pressure transducer of the present invention, showing a reversible fuel cell assembly having a membrane-electrode assembly. 
       FIG. 4  is a diagrammatic view of another embodiment of the self-calibrating pressure transducer of the present invention, showing a reversible fuel cell assembly having a membrane-electrode assembly and valved system in a gas pressure equalization configuration. 
       FIG. 5  is a diagrammatic view of another embodiment of the self-calibrating pressure transducer of the present invention, showing a reversible fuel cell assembly having a membrane-electrode assembly and valved system in a fill fluid pressure equalization configuration. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   While this invention is susceptible of embodiments in many different forms, there are shown in the drawings, and will herein be described in detail, preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments illustrated. 
   The present invention relates to a self-calibrating pressure transducer  10 . The pressure transducer  10  includes a pressure transducer membrane  20 . The transducer membrane  20  is affected by a process pressure to be measured in some suitable property, such as a deformation. The resulting change can be measured by transducer measuring means to determine the process pressure from the associated state of the pressure transducer membrane  20 . Measurement can be made by a strain gauge, resistance change, piezo-electric measurement, or any suitable manner of determining the process pressure. 
   An interior transducer chamber  30  is in operable communication with the pressure transducer membrane  20 . Operable communication means that the pressure in the chamber  30  would be communicated to the membrane  20 , whether by direct contact with the chamber  30 , or through other media. 
   A calibration membrane  40  is provided. The calibration membrane  40  is in operable communication at its interior side with the interior transducer chamber  30 , at least when the system is in a calibration mode, either directly or through another one or more chambers. The calibration membrane  40  is capable of enabling a determinable quantity of a calibration substance to pass to the interior side of the calibration membrane  40  to cause a determinable change in a pressure in the interior transducer chamber  30 . Determinable quantity means that the quantity can be selected or determined by measurement and calculation. The transducer measuring means can be calibrated using a plurality of transducer measurements associated with a respective plurality of states resulting from a respective plurality of determinable quantities of calibration substance being caused to pass to the interior side of the calibration membrane  40 . 
   In various preferred embodiments, the calibration membrane  40  enables the calibration substance to pass to the interior side of the calibration membrane via a coulometric process. Potentiometric measurement can be utilized to determine the quantity of the calibration substance passed to the interior side of the calibration membrane  40 . In various preferred embodiments, the calibration substance is oxygen, hydrogen, or both oxygen and hydrogen. 
   The calibration membrane  40  of the present invention is preferably a mobile oxide ceramic cell. One particularly suitable membrane  40  is a zirconia membrane  40 . Zirconia membranes are well suited to be embedded on silicon substrates. 
   When oxygen is used as the calibration substance, the oxygen can be supplied by the ambient environment, if available. If oxygen is not available, such as in a vacuum, in space, or in other environments, oxygen can be supplied by an integrated oxygen reservoir  50 . Alternatively, oxygen can be supplied by surrounding carbon dioxide or water via electrolysis. 
   The calibration of the transducer  10  can be implemented on the reference side of the membrane  20 , as illustrated in  FIG. 1 , via a subtraction calculation, or on the working side, as illustrated in  FIG. 2 . In various embodiments, as illustrated in  FIG. 2 , the interior transducer chamber  30  includes a first section  60  adjacent the pressure transducer membrane  20  and is separated from a second section  70  by a first two-way valve  80 . The second section  70  is in operable communication with the first section  60  under the condition that the first two-way valve  80  is open. The second section  70  is operably isolated from the first section  60  under the condition that the first two-way valve  80  is closed. The second section  70  is adjacent a calibration isolation membrane  90 . The calibration isolation membrane  90  transfers the pressure in the calibration chamber  100  to second section  70 . Calibration chamber  100  is between the isolation membrane  90  and the calibration membrane  40 . 
   In a preferred embodiment, the first section  60  and the second section  70  of the interior transducer chamber  30  are substantially filled with a fill fluid. The fill fluid may be any suitable fluid, however, it is preferably a fluid with a low thermal expansion coefficient which is inert and compatible with the process fluids. Fluids such as silicon oils or mineral oils might be used. 
   The first section  60  of the interior transducer chamber  30  is further separated from a process isolation chamber  110  via a second two-way valve  120 . The process isolation chamber  110  is preferably separated from a process having a pressure to be measured via a process isolation membrane or process slack diaphragm  130 . The process isolation chamber  110  is also preferably substantially filled with the fill fluid. 
   Thus, in the calibration mode in which the first two-way valve  80  is open and the second two-way valve  120  is closed, the transducer  10  can be calibrated, and in the operation mode in which the first two-way valve  80  is closed and the second two-way valve  120  is open, the transducer  10  measures the process pressure. The valves  80  and  120  may be replaced with any suitable valve means  140 , which can accomplish the same modes of operation, such as a three-way valve  140 . 
   As the temperature of the calibration substances or gases can affect the parameters of the pressure calculations, particularly in higher temperature situations, a temperature sensor is preferably disposed within the calibration chamber  100 , or in the internal transducer chamber  30  if fill fluid is not used. Thus, the output from the temperature sensor can be incorporated into calibration of the transducer  10 . 
   In various other embodiments, the valve system described above can be utilized without the need for a separate calibration chamber  100  and second section  70 , and without the need for a fill fluid. 
   The calibration process is ideally automated via a computing device, and is preferably implemented in situ such that the device  10  need not be removed from the system. The device  10  can be calibrated at predetermined intervals, as frequently as desired. If a reading is obtained which does not meet certain expected parameters, the computing device can be triggered to provide an indication of such to an operator so that the situation can be further assessed. 
   In various other embodiments of the present invention, the calibration gas is provided via reversible fuel cell assembly  150  comprising an electrochemical cell which, at least in a calibration mode, is capable of pumping a determinable quantity of a calibration gas to directly affect the pressure in the interior transducer chamber  30 . The transducer measuring means can be calibrated using a plurality of transducer measurements associated with a respective plurality of states resulting from a respective plurality of determinable quantities of calibration gas being pumped by the electrochemical cell. Preferably, the electrochemical pump comprises a membrane-electrode assembly (“MEA”)  160 . The MEA  160  preferably operates to pump oxygen and hydrogen into the calibration chamber  100  affecting pressure in the interior transducer chamber  30 . The oxygen and the hydrogen are preferably respectively pumped into separate sections of the calibration chamber  100 . The oxygen and hydrogen are produced by the MEA  160  from a water source, such as water trapped in the chambers adjacent the MEA  160 . Alternatively, a water reservoir or environmental source of water can be used, however, in such a configuration, the water source pressures would need to be isolated from the internal pressures of the system such as by allowing the water to feed to the MEA  160  at a water contact side, and using only the opposite side of the MEA  160  as a pressure source for the system. 
   In certain configurations, an oxygen chamber  170  is adjacent a first side of the MEA  160  and bounded by a first slack diaphragm  180 , and a hydrogen chamber  190  is adjacent an opposite side of the MEA  160  and is bounded by a second slack diaphragm  200 . In one embodiment, as illustrated in  FIG. 4 , the oxygen chamber  170  is in fluid communication with an equilibrating section  210  which is adjacent a side of the second slack diaphragm  200  opposite the hydrogen chamber  190 , the first slack diaphragm  180  being in operable communication with the interior transducer chamber  30 . In an alternate embodiment, in which the oxygen and hydrogen are better separated, as illustrated in  FIG. 5 , the first and second slack diaphragms  180  and  200  are each in operable communication with the interior transducer chamber  30 . In either configuration, the interior transducer chamber  30  preferably comprises a first section  60  adjacent the pressure transducer membrane  20 , and a second section  70  in operable communication with the calibration chamber  100  via at least one slack diaphragm  180  or  200 . A process isolation chamber  110  is adjacent a process slack diaphragm  130  in operable communication with a process pressure to be measured. The first section  60 , the second section  70 , and the process isolation chamber  110  are substantially filled with a fill fluid and are interfaced via valve means  140  such as a three-way valve  140 , or other system of valves, wherein the first and second sections  60  and  70  are in operable communication and isolated from the process isolation chamber  110  in a calibration mode of the valve means  140 , and wherein the first section  60  and the process isolation chamber  110  are in operable communication and isolated from the second section  70  in an operation mode of the valve means  140 . 
   As above, the reversible fuel cell assembly  150  preferably enables the calibration gas to pass to the interior side of the calibration chamber  100  via a coulometric process. Potentiometric measurement can be utilized to determine the quantity of the calibration gas passed to the calibration chamber  100 . One or more temperature sensors can be used in the calibration chamber  100  to enable an output from the temperature sensors to be incorporated into calibration of the transducer  10 . Again, oxygen can be supplied by the ambient surroundings, by an integrated oxygen reservoir, or by surrounding carbon dioxide or water via electrolysis. Also, as above, the interior transducer chamber  30  can be on a side of the transducer membrane  20  opposite the process pressure to be measured, where calibration is achieved via a subtraction process, or it can be on the working side of membrane  20 . 
   As in the embodiments above, the embodiments incorporating the reversible fuel cell assembly  150  can be automated via a computing device and implemented in situ. The calibration can be repeated at predetermined intervals, as desired, and calibration measurements of a selected type can trigger the computing device to provide an indication to an operator. 
   The device  10  is preferably embedded on a silicon substrate, and may be a micro electromechanical system (“MEMS”) device. 
   While the specific embodiments have been illustrated and described, numerous modifications are possible without significantly departing from the spirit of the invention, and the scope of protection is only limited by the scope of the accompanying claims.