Dynamic polymer pressure transducer with temperature compensation

• US 4,577,510 A
• Filed: 09/06/1984
• Issued: 03/25/1986
• Est. Priority Date: 09/06/1984
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Original Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Inventors: Bur, Anthony J., Roth, Steven C.
• Primary Examiner(s): WOODIEL, DONALD
• Application Number:
  US06/647,782
• Time in Patent Office: 565 Days
• Field of Search: 73/708, 73/714, 73/754, 73/766, 73/DIG. 4, 374/143, 374/179
• US Class Current: 73/708
• CPC Class Codes: G01L 9/0001 Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means G01L9/0026, G01L9/0033, G01L9/0082, G01L9/0089, G01L9/0091 take precedence
• CPC Class Codes: G01L 9/085 with temperature compensating means non electric temperature compensating means G01L19/04
• CPC Class Codes: Y10S 73/04 Piezoelectric

Abstract

Accurate dynamic pressure data in a changing thermal environment is obtained through the use of a pressure gage formed from polyvinylidene fluoride (PVDF) polymer material. The temperature compensation pressure gage has three major elements: an active PVDF transducer which obtains remote pressure readings which are uncorrected for thermal effects; a thermocouple having a short rise time allowing an output thermal signal which dynamically responds to changing thermal conditions; and a compensation amplifier circuit receiving the uncorrected pressure readings and the dynamic thermal signal and producing an output signal representing accurate pressure data which is corrected for changing thermal conditions. Also disclosed are the details of making an active PVDF transducer.

Claims

1. A pressure gage used to obtain accurate dynamic pressure data in a changing thermal environment, comprising:

an active transducer producing a transducer output signal which is uncorrected for thermal effects, said active transducer being composed of polyvinylidene fluoride;

a thermocouple having a short rise time and producing an output thermal signal which dynamically responds to changing thermal conditions, said thermocouple being a copper-constant thermocouple made with wire, said thermocouple residing within said transducer; and

a compensation means receiving said transducer output signal from said transducer and said output thermal signal from said thermocouple, said compensaton means producing a corrected pressure signal, said corrected pressure signal representing accurate pressure data which is corrected for changing thermal conditions.

2. A pressure gage as defined in claim 1, wherein said compensation means comprises:

first, second, third, fourth and fifth amplifier circuits, said first amplifier circuit receiving said transducer output signal from said transducer, and producing an uncorrected output signal, said uncorrected output signal being pressure data uncorrected for thermal changes in the environment of said transducer;

said second amplifier circuit receiving said uncorrected output signal from said first amplifier circuit, said second amplifier having a gain of unity producing a buffered uncorrected output signal;

said third and fourth amplifier circuits receiving said output thermal signal produced by said thermocouple; and

producing an amplified output thermal signal; and

said fifth amplifier circuit receiving and adding said buffered uncorrected output signal from said second amplifier circuit and said amplifier output thermal signal from said fourth amplifier circuit, said fifth amplifier circuit producing said corrected pressure signal.

3. A pressure gage as defined in claim 2, wherein said first amplifier circuit comprises:

an input resistor conducting transducer output signal from said transducer into said first amplifier circuit;

a first amplifier receiving said transducer output signal from said input resistor on its inverting input terminal and producing said uncorrected output signal on its output terminal, said first amplifier having its noninverting input terminal connected with a common electrical ground;

a first capacitor connecting said first amplifier output terminal with its inverting input terminal; and

a first resistor being in a parallel circuit with said first capacitor, said first resistor connecting said first amplifier'"'"'s output terminal with its inverting input terminal

4. A pressure gage as defined in claim 3, wherein said second amplifier circuit comprises:

a second resistor connecting the output terminal of said first amplifier with said second amplifier circuit;

a second amplifier having a gain of unity and receiving said uncorrected output signal on its noninverting input terminal, said second amplifier having its output terminal connected with its inverting input terminal, said second amplifier producing said buffered uncorrected output signal on its output terminal; and

a second capacitor connecting said second amplifier'"'"'s noninverting input terminal with a common electrical ground

5. A pressure gage as defined in claim 4, wherein said third amplifier circuit comprises:

a third amplifier receiving said output thermal signal from said thermocouple on its noninverting input terminal and producing a third amplifier circuit output signal in its output terminal;

a third resistor connecting said third amplifier'"'"'s inverting input terminal with a common electrical ground;

a fourth resistor connecting said third amplifier output terminal with it inverting input terminal; and

a third capacitor connecting said third amplifier output terminal with its inverting input terminal, said third capacitor being in a parallel circuit with said fourth resistor.

6. A pressure gage as defined in claim 5, wherein said fourth amplifier circuit comprises:

a fourth capacitor receiving said third amplifier circuit output signal from said third amplifier'"'"'s output terminal;

a fifth resistor receiving said third amplifier circuit output signal from said fourth capacitor;

a fourth amplifier receiving said third amplifier circuit output signal from said fifth resistor on its inverting input terminal, said fourth amplifier having its noninverting input terminal connected with a common electrical ground, said fourth amplifier producing said amplified output thermal signal on its output terminal; and

a sixth resistor having variable impedance, said sixth resistor connecting the output terminal of said fourth amplifier with its inverting input terminal.

7. A pressure gage as defined in claim 6, wherein said fifth amplifier circuit comprises:

a seventh and eighth resistors, said seventh resistor conducting said buffered uncorrected output signal from said second amplifier circuit into said fifth amplifier circuit;

said eighth resistor conducting said amplified output thermal signal from said fourth amplifier circuit into said fifth amplifier circuit;

a fifth amplifier receiving said buffered uncorrected output signal from said seventh resistor and said amplified output thermal signal from said eighth resistor on its inverting input terminal, said fifth amplifier having its non-inverting input terminal connected with a common electrical ground, said fifth amplifier adding said amplified output thermal signal with said buffered uncorrected output signal and producing said corrected pressure signal on its output terminal; and

a ninth resistor having variable impedance and connecting said fifth amplifier'"'"'s output terminal with its inverting input terminal.

8. A pressure gage as defined in claim 7, wherein said active transducer comprises:

first, second, third and fourth sheets, each being composed of polyvinylidene fluoride, said second and third sheets each having piezoelectrically active areas, said first, second, third and fourth sheets being laminated together with said first and fourth sheets on the outside and said second and third sheets laminated with their respective piezoelectrically active areas facing each other in the middle with their respective active areas having polarization vectors in opposite directions, said second and third sheets enclosing said thermocouple in their inactive areas, said thermocouple residing within said second and third sheets within two millimeters of said piezoelectrically active areas of said second and third sheets.

9. A process of making a polyvinylidene flouride transducer comprising the steps of:

(a) depositing aluminum electrodes on a portion of the surface areas of a first and second strips, said first and second strips being composed of polyvinylidene fluoride;

(b) activating said first and second strips after said depositing step, said activating step being conducted by exposing said first and second strips to an electric field of approximately two megavolts/centimeter;

(c) laminating said first and second strips together with their surface areas containing said aluminum electrodes facing each other such that all polarization vectors are pointed in opposite directions, said first and second strips containing a copper-constant thermocouple wire placed between said first and said second strip within approximately two millimeters of said surface areas containing said aluminum electrode;

said laminating step occuring after said activating step;

(d) surrounding said first and second strips by laminating a third and fourth strip of polyvinylidene flouride as outside layers to said first and second strips, said surrounding step occuring simultaneously or after said laminating step.