Method and apparatus for pressure transducer calibration and simulation

What is claimed is:

1. In a pressure monitoring system having an on-line pressure transducer and a monitor for displaying an operator readable output electronically derived from said on-line pressure transducer, a device for selectively calibrating said on-line pressure transducer from known test pressures and for selectively bypassing said on-line pressure transducer to isolate defective electrical components of said pressure monitoring system, said device comprising:

(a) operator-variable means for generating a known test pressure;

(b) pressure calibration means coupled to said known test pressure for displaying on said device a calibrated output indicating the level of said known test pressure;

(c) bypass means for transforming said known test pressure into an electrical output signal of the type derived from said on-line pressure transducer in said monitoring system, said output signal corresponding to the level of said known test pressure;

(d) first output means selectively couplable to said monitoring system for applying said known test pressure to said on-line pressure transducer to produce on said monitor a first operator readable output so that said first operator readable output on said monitor can be checked against said calibrated output on said device when calibrating said monitoring system; and

(e) second output means selectively couplable to said monitoring system for electrically bypassing said on-line pressure transducer with said bypass means, said output signal of said bypass means producing on said monitor a second operator readable output so that said second operator readable output on said monitor can be checked against said calibrated output on said device to isolate defective electrical components of said pressure monitoring system.

2. A device as recited in claim 1, wherein said operator-variable means comprises a manually operable pressure cylinder.

3. A device as recited in claim 2, wherein said pressure cylinder comprises means for generating both positive and negative pressures.

4. A device as recited in claim 1 wherein said pressure calibration means comprises:

(a) a precision pressure transducer coupled to said known test pressure for producing said electrical output signal corresponding to the level of said known test pressure;

(b) a test pressure level display panel; and

(c) an electronic circuit for receiving said electrical output signal from said precision pressure transducer and driving said test pressure level display panel to display said calibrated output indicating the level of said known test pressure.

5. A device as recited in claim 1, wherein said pressure calibration means is battery operated.

6. A device as recited in claim 1 wherein said bypass means comprises:

(a) a dielectric substrate having first and second sides and an aperture therebetween, said first side being coupled at said aperture to said known test pressure;

(b) a substitute pressure transducer supported on said second side of said dielectric substrate referenced to atmospheric pressure; and

(c) electrical connections coupling said substitute pressure transducer to said second output means.

7. A device as recited in claim 6, wherein said substitute pressure transducer comprises:

(a) a semiconductor pressure diaphragm sealed at the periphery thereof on said second side of said dielectric substrate over said aperture therein;

(b) a piezoresistive strain gauge formed on said diaphragm on the side thereof opposite said aperture; and

(c) a temperature compensation circuit on said second side of said dielectric substrate electrically connected to said piezoresistive strain gauge.

8. A device as recited in claim 7, wherein said strain gauge and said temperature compensation circuit of said substitute pressure transducer are substantially identical to any strain gauge and temperature compensation circuit employed in said on-line pressure transducer in said pressure monitoring system.

9. A device as recited in claim 6, wherein said substitute pressure transducer is powered by said pressure monitoring system through said second output means when said second output means is electrically coupled to said pressure monitoring system.

10. A device as recited in claim 1, wherein said device is dimensioned so as to be held in the hand of an operator.

11. In a direct blood pressure monitoring system having an on-line pressure transducer referenced at a first side thereof to atmospheric pressure and coupled at a second side thereof through a fluid in a catheter adapted to be inserted into a circulatory vessel of a patient, and having a monitor for displaying an operator readable output electronically derived from said on-line pressure transducer, a device for selectively calibrating said on-line pressure transducer from known test pressures and for selectively bypassing said on-line pressure transducer to isolate defective electrical components of said pressure monitoring system, said device comprising:

(a) a manually operable pressure cylinder that generates a known test pressure;

(b) pressure calibration means coupled to said known test pressure for displaying on said device a calibrated output indicating the level of said known test pressure;

(c) a substitute pressure transducer coupled to said known test pressure and referenced to atmospheric pressure that transforms said known test pressure into an electrical output signal of the type derived from said on-line pressure transducer in said monitoring system, said output signal corresponding to the level of said known test pressure;

(d) a closeable output port connected to said pressure cylinder that selectively couples to said monitoring system to apply said known test pressure to said on-line pressure transducer in said monitoring system and to produce on said monitor thereof a first operator readable output, said first operator readable output reflective of the responsiveness of said monitoring system, inclusive of said on-line pressure transducer, to said known test pressure, so that said first operator readable output on said monitor can be checked against said calibrated output on said device in calibrating said monitoring system; and

(e) an electrical receptacle connected to said substitute pressure transducer, said electrical receptacle capable of receiving a cooperating electrical plug at one end of a connection cable, the other end of said connection cable couplable electrically to said monitoring system so as to bypass said on-line pressure transducer with said substitute pressure transducer, said output signal of said substitute transducer producing on said monitor a second operator readable output reflective of the electrical responsiveness of said pressure monitoring system with said on-line pressure transducer thereof removed, so that said second operator readable output on said monitor can be checked against said calibrated output on said device to isolate defective electrical components of said pressure monitoring system.

12. A device as recited in claim 11, wherein said pressure cylinder comprises means for generating both positive and negative pressures, such that by selecting an appropriate test pressure within said range, said output port on said pressure cylinder can be coupled to either said first or said second side of said on-line pressure transducer for calibrating said monitoring system.

13. A device as recited in claim 11, wherein said pressure calibration means comprises:

(a) a precision pressure transducer coupled to said known test pressure that produces said electrical output signal corresponding to the level of said known test pressure;

(b) a test pressure level display panel; and

(c) an electronic circuit for receiving said electrical output signal from said precision transducer and driving said test pressure level display panel to display said calibrated output indicating the level of said known test pressure in operator-readable form.

14. A device as recited in claim 11, wherein said pressure calibration means is battery operated.

15. A device as recited in claim 11, wherein said substitute pressure transducer is powered by said pressure monitoring system through said electrical receptacle when said electrical receptacle is coupled through said connector cable to said monitoring system.

16. A device as recited in claim 11, wherein said substitute pressure transducer comprises:

(a) a semiconductor pressure diaphragm having a first side thereof coupled to said known test pressure and having a second side thereof referenced to atmospheric pressure;

(b) a piezoresistive strain gauge formed on said diaphragm on the side thereof referenced to atmospheric pressure; and

(c) a temperature-compensation circuit connected to said piezoresistive strain gauge.

17. A device as recited in claim 16, wherein said strain gauge and said temperature compensation circuit of said substitute transducer are substantially similar to any strain gauge and temperature compensation circuit employed in said on-line pressure transducer in said pressure monitoring system.

18. A device as recited in claim 17, wherein said device is dimensioned so as to be held in the hand of an operator.

19. In a pressure monitoring system having an on-line pressure transducer and a monitor for displaying an operator readable output electronically derived from said on-line pressure transducer, a device for selectively bypassing said on-line pressure transducer to isolate defective electrical components of said pressure monitoring system, said device comprising:

(a) operator variable means for generating a known test pressure;

(b) pressure calibration means coupled to said known test pressure for displaying on said device a calibrated output indicative of said known test pressure;

(c) bypass means for transforming said known test pressure into an electrical output signal of the type derived from said on-line pressure transducer in said monitoring system, said bypass means being capable of producing electrical output signals within a continuous range of values and said output signal corresponding to the level of said known test pressure; and

(d) an electrical receptacle connected to said bypass means for receiving therein a cooperating electrical plug at one end of a connection cable, the other end of said connection cable couplable electrically to said monitoring system to replace with said output signal from said bypass means, said on-line pressure transducer as the source of operator readable output to said monitoring system, said output signal of said bypass means producing on said monitor an operator readable output reflective of the electrical responsiveness of said pressure monitoring system with said on-line pressure transducer thereof removed, so that said operator readable output on said monitor can be checked against said calibrated output on said device to isolate defective electrical components of said pressure monitoring system.

20. A device as recited in claim 19, wherein said means for generating said known test pressure comprises a manually operable pressure cylinder.

21. A device as recited in claim 19, wherein said pressure cylinder comprises means for generating both positive and negative pressures.

22. A device as recited in claim 19, wherein said bypass means comprises a substitute pressure transducer substantially identical to said on-line pressure transducer in said pressure monitoring system.

23. In a pressure monitoring system having an on-line pressure transducer and a monitor for displaying an operator readable output electronically derived from said on-line pressure transducer, a method for selectively calibrating said on-line pressure transducer from known test pressures and for selectively bypassing said on-line pressure transducer to isolate defective electrical components of said pressure monitoring system, said method comprising the steps of:

(a) generating a known test pressure;

(b) applying said known test pressure simultaneously to a pressure calibration means for displaying a calibrated output indicating the level of said known test pressure and to a substitute pressure transducer referenced to atmospheric pressure for transforming said known test pressure into an electrical output signal of the type derived from said on-line pressure transducer and said monitoring system, said output signal corresponding to the level of said known test pressure;

(c) selectively coupling said known test pressure to said on-line pressure transducer in said monitoring system to produce on said monitor thereof a first operator readable output, said first operator readable output reflective of the responsiveness of said monitoring system, inclusive of said on-line pressure transducer, to said known test pressure;

(d) checking said first operator readable output on said monitor against said calibrated output on said device to calibrate said monitoring system;

(e) selectively connecting said output signal of said substitute transducer to said monitoring system to replace said on-line pressure transducer with said substitute transducer as the source of said operator readable output to said monitoring system, said output signal of said substitute transducer producing on said monitor a second operator readable output reflective of the electrical responsiveness of said pressure monitoring system with said on-line pressure transducer thereof removed; and

(f) checking said second operator readable output on said monitor against said calibrated output to isolate defective electrical components of said pressure monitoring system.

24. A method as recited in claim 23, wherein said step of connecting said output signal of said substitute transducer to said monitoring system comprises the steps of disconnecting said on-line transducer from said pressure monitoring system, and precluding said known test pressure from being vented to atmosphere.

25. A method a recited in claim 23, wherein said step of generating a known test pressure comprises the step of generating said known test pressure with a manually operable pressure cylinder.

26. A method as recited in claim 25, wherein said pressure monitoring system comprises a direct blood pressure monitoring system, wherein said on-line pressure transducer is referenced at a first side thereof to atmospheric pressure and is coupled at a second side thereof through a fluid in a catheter inserted into a circulatory vessel of a patient, and wherein said method further comprises the step of selectively coupling said known test pressure to said first or said second said on-line pressure transducer depending upon whether a positive or negative known test pressure is generated by said pressure cylinder.

27. A method as recited in claim 23, wherein said step of generating a known test pressure comprises the step of generating said known test pressure with a manually operable pressure cylinder capable of generating test pressures within a range of test pressures that includes both positive and negative pressures.

28. A method as recited in claim 23, wherein said step of applying said known test pressure simultaneously to a pressure calibration means and to a substitute pressure transducer comprises the step of applying said known test pressure to a substitute transducer substantially identical to said on-line transducer in said monitoring system.

29. A method as recited in claim 23, wherein an additional known test pressure is generated before said step of checking said second operator readable output against said calibrated output.

30. In a pressure monitoring system having an on-line pressure transducer and a monitor for displaying an operator readable output electronically derived from said on-line pressure transducer, a device for selectively bypassing said on-line pressure transducer to isolate defective electrical components of said pressure monitoring system, said device comprising:

(a) a manually operable pressure cylinder that generates a known test pressure;

(b) pressure calibration means coupled to said known test pressure for displaying on said device a calibrated output indicating the level of said known test pressure;

(c) a substitute pressure transducer coupled to said known test pressure and referenced to atmospheric pressure that transforms said known test pressure into an electrical output signal of the type derived from said on-line pressure transducer in said monitoring system, said substitute pressure transducer being capable of producing electrical output signals within a continuous range of values and said output signal corresponding to the level of said known test pressure; and

(d) an electrical receptacle connected to said substitute pressure transducer, said electrical receptacle capable of receiving a cooperating electrical plug at one end of a connection cable, the other end of said connection cable couplable electrically to said monitoring system so as to bypass said on-line pressure transducer with said substitute pressure transducer, said output signal of said substitute transducer producing on said monitor an operator readable output reflective of the electrical responsiveness of said pressure monitoring system with said on-line pressure transducer thereof removed, so that said operator readable output on said monitor can be checked against said calibrated output on said device to isolate defective electrical components of said pressure monitoring system.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to pressure monitoring systems having an on-line transducer and a monitor for displaying operator readable output electronically derived from the on-line transducer, and more particularly to a method and apparatus for calibration verification of the on-line transducer with a known test pressure, and for selectively bypassing the on-line transducer in order to isolate defective electrical components of the pressure monitoring system.

The method and apparatus of the present invention has particular application to a system for direct monitoring of patient blood pressure and relates in part to subject matter disclosed in my copending U.S. patent application Ser. No. 654,373 for a PRESSURE TRANSDUCER filed on Sept. 25, 1984, and in copending U.S. patent application Ser. No. 608,761 for a DISPOSABLE PRESSURE TRANSDUCER APPARATUS FOR MEDICAL USE filed May 9, 1984, which are both incorporated herein by reference.

2. Background Art

The continuous monitoring of the pressure in a given environment is of importance in many aspects of manufacturing, transportation, health care, and energy production. Increasingly, pressure monitoring systems in these areas are of an electronic nature, utilizing a pressure transducer to convert the pressure in the environment monitored into an electrical signal reflective of the level thereof for display on a monitor.

For example, in medical science when monitoring direct patient blood pressure, it is known to couple a pressure transducer to a sterile fluid contained in a catheter inserted into a circulatory vessel of a patient. As the heart beats, the blood pressure waves are transmitted through the fluid in the catheter to the transducer, which produces an electrical output readable in digital or analog fashion on an electronic monitor. Advances in this area have produced miniature, yet sturdy, pressure transducers which are economical enough so as to be disposable after use with only a single individual patient.

With respect to pressure monitoring systems for use in this and other fields in which electronic pressure monitoring systems are significant, there is an important need to verify the accuracy of the monitoring system, both upon initial implacement and on a continuous basis during operation. The function of verifying an electronic pressure monitoring system involves two aspects.

First, the on-line pressure transducer of such a system must be tested through application thereto of a known test pressure to determine whether the transducer and its cooperating electronic equipment are functioning correctly together to read pressures monitored by the system. Calibration verification of the system against the known test pressure is thus one objective.

If, however, testing of the transducer and its cooperating electronic equipment reveals a malfunction in the monitoring system, a second aspect of verification requires that the source of the malfunction be isolated and then corrected. Typically, in order to accomplish this, electronic equipment has been required in addition to that used to check calibration of the on-line transducer. This additional electronic equipment simulates the electrical output behavior of the on-line transducer of the system and is connected to the system in place thereof, replacing it as the source of electrical signals to the monitoring system.

If this additional electronic equipment and procedure continues to reveal malfunctioning, then it can be assumed that the source of the malfunction resides, not in the on-line transducer, but in the electronic monitor or connecting cable of the monitoring system, although it is possible that both components and even the on-line transducer are each malfunctioning independently of the others. This knowledge then permits isolation of the defective electrical component, usually through interchanging one or the other of the monitor or cable used in the electronic system. On the other hand, if no malfunctioning of the electronic equipment of the system is manifested by this procedure, then the source of malfunction can be concluded to reside with the on-line transducer of the system. Understanding the location of any malfunction then permits its correction, usually by replacement of an appropriate component of the system.

Transducer simulators have in the past been devices which use complex resistive network circuitry to produce discrete levels of electronic signals imitating a transducer output through switching among an array of electronic components. These devices do not produce output signals within a continuous range of values, and in fact do not always reliably replicate the response of a transducer to a source of pressure within the range expected to be monitored.

Further, such transducer simulators, by not including transducers like those in place of which they are used, do not include the precise capacitive and inductive impedances thereof. They cannot, therefore, be expected to effectively simulate the interreaction of the transducer they replace with the monitor of the system being tested. This problem is only further compounded by the wide variety of monitors in use.

SUMMARY OF THE INVENTION

It is desirable that equipment for performing the two aspects of verification be inexpensive, simple in operation, and highly portable. Additionally, as the tasks of testing a transducer within its monitoring system and isolating any malfunction are so closely related, it is desirable to have the equipment for performing both functions available in a single unit. It is further desirable that the transducer simulator portion of such equipment be of an analog nature, including a transducer which, in the optimal situation would be similar in character to the transducer of the system being tested.

Consistent with the foregoing, one object of the present invention is to produce a method and apparatus for use therein which is at once capable of both verifying the calibration of an on-line transducer within a pressure monitoring system using a known test pressure and, by using a second transducer having electrical characteristics which very closely replicate those of the on-line transducer, selectively replacing the on-line transducer in the system when there is a need to locate defective electrical components therein.

Another object is to provide an apparatus for use in such a method which is sufficiently compact as to be held in the hand of an operator of the monitoring system.

Still another object of the present invention is to provide a device capable of bypassing the on-line transducer in a pressure monitoring system by using a bypass transducer that is capable of producing a continuous range of output virtually identical to that of the bypassed on-line transducer, the bypass transducer deriving its own output signal responsive to the application of a known test pressure.

Yet another object is to provide a method and apparatus which is readily connectable to the monitoring system being tested, which results in minimal difficulty to use even by unsophisticated personnel, and which is inexpensive to manufacture.

The foregoing and other objects and advantages of the invention are realized and obtained by means of the method and apparatus of the present invention. In one presently preferred embodiment of the invention, a small, hand-held device includes a manually operable pressure cylinder for generating a known test pressure. The known test pressure is applied to a pressure calibration circuit which derives and displays in operator readable form a calibrated output indicating the level of the known test pressure. The known test pressure is also applied to the on-line transducer of a pressure monitoring system so that the on-line transducer also derives an operator readable output that is displayed on the monitor of the pressure monitoring system. The output of the monitor can then be compared to the calibrated output indicated on the device. If the output on the monitor and the calibrated output are different, the on-line pressure transducer can then be unplugged from the monitor and connecting cable of the pressure monitoring circuit, which are then connected into a substitute pressure transducer provided in the device. The known test pressure is also applied to the substitute pressure transducer, which is powered from the monitor to which it is connected for testing, and the substitute pressure transducer then derives an operator readable output which is displayed on the monitor. If the output on the monitor and the calibrated output on the device are the same, the user then knows that the on-line transducer is defective and can replace it. If the output on the monitor and the calibrated output on the device continue to be different, the user then knows that either the connecting cable or the monitor is defective, and therefore can further isolate and then replace the defective component of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from a detailed description of the drawings, in which like parts are designated with like numerals throughout, and in which:

FIG. 1 is a schematic diagram illustrative of the method and apparatus of the present invention;

FIG. 2 is a plan view of the exterior of a device embodying the present invention;

FIG. 3 is an exploded perspective view of the device of FIG. 2;

FIG. 4 is a perspective view of the bottom and two sides of a connector and substitute pressure transducer mount for the device of FIG. 2;

FIG. 5 is an exploded perspective view of the connector of FIG. 4 shown in relation to other elements of the device in FIG. 2 to which it is assembled;

FIG. 6 is a cross-sectional view of the device shown in FIG. 5 taken along section lines 6--6;

FIG. 7 is an enlarged cross-sectional detail of one aspect of the device shown in FIG. 6;

FIG. 8 is a functional schematic diagram of the pressure calibration circuit and substitute transducer employed in the device shown in FIG. 2;

FIG. 9 is a detailed electrical schematic diagram of a preferred embodiment capable of implementing the functions illustrated in FIG. 8;

FIG. 10 is a diagram illustrating the use of the device of FIG. 2 to verify the calibration of an on-line transducer in a direct blood pressure monitoring system to a known test pressure;

FIG. 11 is a diagram illustrating the use of the device shown in FIG. 2 to bypass the on-line transducer of the system when isolating a defective component.

FIG. 12 is a diagram illustrating the use of the device shown in FIG. 2 to verify the calibration of a conventional pressure transducer in a direct blood pressure monitoring system; and

FIG. 13 is a diagram illustrating the use of the device shown in FIG. 2 to bypass the transducer of the system shown in FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A helpful overview of the method and apparatus of the present invention, which are for use with a pressure monitoring system having an on-line pressure transducer and a monitor for displaying operator readable output electronically derived from the on-line pressure transducer, can be obtained by reference first to FIG. 1. Therein it is shown that a device according to the present invention includes a display panel meter 10 and two outputs, namely an electrical output signal appearing at an electrical receptacle 12 and pressure or vacuum output produced at an output port 14. Output port 14 is selectively closeable according to the needs of is operator, as is suggested by a cap 16 therefor. Nevertheless, any means for selectively opening and closing output port 14, such as a valve integral therewith or a hose connected thereto incorporating a stopcock, is entirely appropriate in this regard.

In accordance with the present invention operator variable means is provided for generating a known test pressure at output port 14. Shown in FIG. 1, by way of illustration and not limitation, a manually operable pressure cylinder 18, including rotatable adjustment knob 20, is connected to output port 14. Depending on the direction of rotation of adjustment knob 20, a pressure or a vacuum can be made to appear at output port 14. Accordingly, it should be understood that the term "known test pressure" as used hereafter refers to a range of values including either or both positive and negative pressures.

The known test pressure generated by pressure cylinder 18 is applied simultaneously through pneumatic lines 21 to a pressure calibration circuit 22 and to a substitute pressure transducer 24. Pressure calibration circuit 22 and display panel meter 10 to which it is electrically connected together typify a pressure calibration means provided for displaying on a device of the present invention a calibrated output indicating the level of the known test pressure generated in pressure cylinder 18, as indicated by the number 100 appearing on the display panel meter 10. Substitute pressure transducer 24 transforms the known test pressure generated in pressure cylinder 18 to an electrical output signal at electrical receptacle 12 corresponding to the level of the known test pressure generated in cylinder 18 and being of the same type as the electrical signal derived from the on-line pressure transducer in the monitoring system with which the device of the present invention is utilized, as hereinafter more fully explained.

To calibrate the pressure monitoring system, the known test pressure generated in pressure cylinder 18 is coupled to the on-line pressure transducer in that system in order to produce on the monitor thereof a first operator readable output which reflects the direct responsiveness to the known test pressure of the monitoring system, including the on-line pressure transducer. Thereafter, by checking the first operator readable output on the monitor against the calibrated output on display panel meter 10 of the device, the monitoring system may be accurately calibrated. If calibration cannot be achieved, then it may be concluded that some component of the monitoring system is malfunctioning.

In such case, it will be further necessary to locate and eliminate the malfunction, an objective in which a device according to the present invention also has utility. The output signal of substitute pressure transducer 24 is used to replace the on-line pressure transducer of the pressure monitoring system as a source of operator readable output to that system. This is accomplished by connecting the electrical output signal appearing at electrical receptacle 12 to selected locations in the monitoring system. At each location, the electrical output signal from electrical receptacle 12 produces on the monitor of the pressure monitoring system a second operator readable output which can be checked against the output on display panel meter 10 of the device in order to isolate defective electrical components in the pressure monitoring system. In this light, substitute pressure transducer 24, shown in FIG. 1, is illustrative of a bypass means for transforming the known test pressure generated in pressure cylinder 18 into an electrical output signal of the type derived from the on-line pressure transducer in the monitoring system, and electrical receptacle 12 connected thereto functions as a second output means couplable by the operator to selected locations in the monitoring system to electrically bypass the on-line pressure transducer thereof.

In the process of bypassing the on-line transducer to isolate defective electrical components, the coupling of output port 14 to the pressure monitoring system can be maintained if permitted by the physical dimensions of the pressure monitoring system and the connectors being utilized to couple the device of the present invention. If it is necessary to uncouple output port 14, however, or if the process of connecting electrical receptacle 12 to the pressure monitoring system results in venting the known test pressure at output port 14 through components of the pressure monitoring system, then output port 14 should be closed, by a cap, such as cap 16, or any equivalent thereof. In this manner output port 14 functions as a closeable first output means selectively couplable by the operator to the pressure monitoring system for applying the known test pressure generated by pressure cylinder 18 to the on-line pressure transducer of the pressure monitoring system.

The method and apparatus of the present invention will now be described in detail and with specific reference to its use in connection with a direct patient blood pressure monitoring system having an on-line pressure transducer coupled through a fluid in a catheter inserted into a circulatory vessel of a patient, the system also having a monitor for displaying an operator readable output electronically derived from the on-line pressure transducer.

An example of such a device, and one further dimensioned so as to be held in the hand of an operator, is shown in its external aspects of FIG. 2 as device 26. In the upper surface of device 26 is formed a window opening 28 through which may be viewed display panel meter 10. A pressure cylinder adjustment knob, such as adjustment knob 20, projects from a side of device 26 opposite from a pressure/vacuum output port, such as output port 14. Device 26 is further equipped with an electrical switch 30 and an electrical connector 32.

Referring to FIG. 3, device 26 can be seen to include a number of components housed within a case consisting of an upper housing 34 and a lower housing 36. As illustrated, these components include a suitable pressure cylinder 18 operator variable through use of adjustment knob 20 and having an output port 14 formed as a conventional luer fitting. Pressure cylinder 18 is coupled pneumatically through tubing 38 to a cap 40 covering a precision pressure transducer mounted on a printed circuit board 42. Cap 40 functions in addition as an uninterrupted pneumatic coupling between tubing 38 and additional tubing 44 which communicates through an electrical connector 32 to a substitute pressure transducer mounted on the underside thereof in a manner to be explained in detail hereafter. Display panel meter 10 is supported on posts 46, 48, 50 above printed circuit board 42 and connected electrically to the circuitry thereon through the cooperating action of receptacle 52 mounted on printed circuit board 42 and pins 54 of display panel 10. All circuitry in the device with the exception of that included within the substitute pressure transducer on the underside of electrical connector 32 is powered through an electrical lead 56 from a battery 58 contained within device 26.

Referring to FIGS. 4 and 5 together, electrical connector 32 can be seen to include an electrical receptacle 12 which includes a number of electrical contact receiving bores 60. On the underside of electrical connector 32, facing printed circuit board 42 to which it is secured by screws 62, 64 a