Solid state current-to-pressure and current-to-motion transducer

• US 4,492,246 A
• Filed: 03/28/1983
• Issued: 01/08/1985
• Est. Priority Date: 03/28/1983
• Status: Expired due to Term

• Current Assignee: Dresser Incorporated (Nagano Keiki Company Limited)
• Original Assignee: Mcgraw-Edison Company (Eaton Corporation PLC.)
• Inventors: Gold, Calman, Prescott, Robert C., Anderson, Eric V.
• Primary Examiner(s): Cohan, Alan
• Application Number:
  US06/479,460
• Time in Patent Office: 652 Days
• Field of Search: 137/85, 137/86, 137/84, 137/82, 251/131
• US Class Current: 137/85
• CPC Class Codes: G05D 16/2013 using throttling means as controlling means
• CPC Class Codes: Y10T 137/2409 With counter-balancing pressure feedback to the modulating device

Abstract

A transducer for converting an electrical current signal to a pneumatic pressure. A solid state element such as piezo-electric flapper element 48 is used to vary the pressure drop through a nozzle 46 to provide a controlled pressure supply 28. A micro-power electronic circuit 59 controls the flapper. A solid state pressure sensor 24 detects the output pressure and provides a feedback signal for use in a negative feedback loop to control the flapper element. The flapper element may be triangularly shaped to reduce its responsiveness to relatively low frequency mechanical vibrations. In a exemplary embodiment, where intrinsic safety requirements limit terminal voltages, the flapper element is driven by a transconductance amplifier 94 which is powered through a shunt regulator 82 and a voltage tripler 92. The shunt regulator provides operating potentials which are derived from the signal current.

Claims

1. Control apparatus, comprising:

a. current sensing means for sensing a current signal and producing a first output signal and for producing a plurality of constant voltages generally independent of the magnitude of said current signal;

b. pressure source means for providing a controlled pneumatic pressure whose magnitude varies in response to a control signal, said pressure source means including;

(1) a supply of gas at a substantially constant pressure,

(2) a conduit having one end in flow communication with said supply and an outlet port at an opposite end,

(3) an exhaust valve in flow communication with said conduit, said valve including a fixed nozzle and an electrically movable flapper element which is adapted to cooperate with said nozzle to throttle the flow of gas through said nozzle in response to said control signal;

c. solid-state pressure sensing means, powered by said current sensing means, for sensing said controlled pneumatic pressure at said outlet port and for providing a second output signal proportional to the magnitude thereof; and

d. amplifier means, responsive to said current sensing means and to said pressure sensing means, for providing a control signal which varies in magnitude with the difference between said first output signal and said second output signal and which is adapted to drive said flapper element to reduce the magnitude of said difference,

whereby a pneumatic pressure is produced at said outlet port which is characteristic of said current signal.

2. The apparatus of claim 1, whereby said current sensing means includes:

a. non-resistive means for converting said current signal into at least two voltages of generally constant amplitude for powering said amplifier means; and

b. resistive means, operatively in series with said non-resistive means, for producing said first output signal.

3. The apparatus of claim 1, wherein said electrically movable flapper element is a piezo-electric device and wherein said amplifier means includes a current source adapted to drive said piezo-electric flapper element.

4. The apparatus of claim 3, wherein said current source is a transconductance amplifier powered by a voltage derived from said signal current.

5. The apparatus of claim 4, wherein said current sensing means includes a voltage multiplier for converting said at least two voltages of generally constant amplitude to at least one higher level voltage for powering said transconductance amplifier.

6. Apparatus for converting a first electrical current control signal into a pressure control signal, comprising:

a. means for converting said first electrical current signal to a voltage of generally constant amplitude;

b. voltage reference setting means for converting said generally constant amplitude voltage to a first reference voltage and a second reference voltage;

c. voltage multiplying means for converting said second reference voltages to higher level voltage;

d. temperature compensated solid-state pressure sensor means, powered by said voltage reference setting means, for producting a second electrical current signal characteristic of the pressure of a supply of gas under pressure;

e. difference means, powered by said first and second reference voltages, for providing an output current signal characteristic of the difference between said first current signal and said second current signal;

f. amplifier means, powered by said higher level voltage, for converting said output current signal into an output voltage signal;

g. a supply of gas, at a substantially constant pressure, defining a first outlet port operatively connected to said pressure sensor means and a second outlet port; and

h. piezo-electric means, cooperating with said second outlet port, for producing a pneumatic pressure signal whose magnitude varies in response to said output voltage signal, said piezo-electric means including a conductive strip which is sandwiched between two layers of piezoelectric ceramic material, each of said layers defining a fixed end and a free end, said output voltage signal being developed between said strip and each of said two layers such that said free ends bend towards and away from said second outlet port in response to the output of said amplifier means,

whereby the pressure of the gas supplied to said first outlet port varies in response to the magnitude of said first current signal relative to said second current signal.

7. The apparatus of claim 6, wherein said piezoelectric layers are trapezoidal in shape with the base of each of said layers being fixed and with the opposite disposed generally parallel end being free to move relative to said second outlet port.

8. The apparatus of claim 6, wherein said voltage multiplying means is a voltage tripler.

9. The apparatus of claim 6, wherein said temperature compensated solid-state pressure sensor means defines a four-armed resistive bridge in series with two diodes.

10. Apparatus for converting a first electrical current control signal into a pressure control signal, said pressure control signal being adapted to drive a pneumatic positioner having an output shaft whose relative position is responsive to said pressure control signal, comprising:

a. means for converting said electrical current signal to a plurality of voltages of generally constant amplitude;

b. sensor means, powered by at least one of said voltages of generally constant amplitude, for producing an electrical current signal characteristic of the position of said output shaft;

c. difference means for providing an output current signal characteristic of the difference between said first current signal and said second current signal;

d. amplifier means, for converting said output current signal into an output voltage signal;

e. a supply of gas at substantially constant pressure defining a first outlet port operatively connected to drive said positioner and a second outlet port having a nozzled end; and

f. piezo-electric means, cooperating with said nozzled end of said second outlet port, for producing a pneumatic pressure signal whose magnitude varies in response to said output voltage signal, said piezo-electric means including a conductive strip which is sandwiched between two layers of piezo-electrical ceramic material, each of said layers defining a fixed end and a free end, said output voltage signal being developed between said strip and each of said two layers such that said free ends bend towards and away from said nozzled end in response to the output of said amplifier means,

whereby the position of said output shaft varies in response to the magnitude of said first current signal relative to said second current signal.

11. Apparatus for converting a first electrical current control signal to a pressure control signal, comprising:

a. means for converting said first electrical current signal into a voltage of generally constant amplitude;

b. voltage reference setting means for converting said generally constant amplitude voltage into at least two reference voltages of generally constant amplitude;

c. solid-state pressure sensor means, powered by said voltage reference setting means, for producing a first digital control signal characteristic of the pressure of a supply of gas under pressure;

d. temperature sensing means for producing a second digital control signal characteristic of the temperature of said supply of gas under pressure as applied to said solid-state pressure sensor means;

e. linearization means, defining a plurality of pre-set digital values corresponding to the output of said solid-state pressure sensor means for a set of temperatures and pressures, for converting said first digital control signal and said second digital control signal into a second electrical current signal characteristic of the pressure of said supply of gas as applied to said pressure sensor means for the temperature of the gas;

f. difference means, powered by said voltage reference setting means, for providing an amplified output voltage signal characteristic of the difference between said second current signal and said third current signal;

g. a supply of gas at a substantially constant pressure, defining a first outlet port in flow communication with said pressure sensor means and a second outlet port;

h. piezo-electric means cooperating with said second outlet port, for producing a pneumatic pressure signal whose magnitude varies in response to said output voltage signal, said piezo-electric means having a conductive strip which is sandwiched between two layers of a piezo-electric ceramic material, each of said layers defining a fixed end and a free end, with said output voltage signal being developed between said strip and each of said two layers such that said free ends bend towards and away from said second outlet port in response to the output of said difference means,

whereby the pressure of the gas supplied to said first outlet port varies in response to the magnitude of said first current signal relative to said second current signal and to the temperature of the gas supplied at said pressure sensor means.