Method and apparatus for pressure and level transmission and sensing

• US 5,406,828 A
• Filed: 11/16/1993
• Issued: 04/18/1995
• Est. Priority Date: 11/16/1993
• Status: Expired due to Fees

• Current Assignee: Yellowstone Environmental Science Incorporated
• Original Assignee: Yellowstone Environmental Science Incorporated
• Inventors: Stewart, Frank M., Hunter, Robert M.
• Primary Examiner(s): Chilcot, Jr., Richard E.
• Assistant Examiner(s): PATEL, HARSHAD R
• Application Number:
  US08/153,178
• Time in Patent Office: 518 Days
• Field of Search: 73/4 R, 73/747, 73/749, 73/750, 73/861.52, 73/861.63, 73/861.64, 73/215
• US Class Current: 73/1.62
• CPC Class Codes: G01F 1/363 with electrical or electro-mechanical indication G01F1/37 and G01F1/38 take precedence
• CPC Class Codes: G01F 1/44 Venturi tubes
• CPC Class Codes: G01F 23/168 with electric indicating or recording
• CPC Class Codes: G01N 1/10 in the liquid or fluent state burettes, pipettes B01L3/02; sampling of ground water E02D1/06; metering by volume of fluids or fluent solid material G01F11/00, G01F13/00
• CPC Class Codes: G01N 2001/1043 from sewers
• CPC Class Codes: G01N 2035/00782 reprogrammmable code
• CPC Class Codes: G01N 2035/00881 network configurations
• CPC Class Codes: G01N 35/00732 Identification of carriers, materials or components in automatic analysers
• CPC Class Codes: G01N 35/00871 Communications between instruments or with remote terminals
• CPC Class Codes: G01N 9/28 by measuring the blowing pressure of gas bubbles escaping from nozzles at different depths in a liquid

Abstract

This invention provides a method and apparatus for transmitting and sensing liquid pressure (head) and liquid level (depth) in flow metering, tide gauge and liquid salinity or slurry density measurement applications. The invention essentially eliminates the effect of pressure sensor temperature variations and the effect of long-term pressure sensor signal drift on pressure sensing accuracy by resetting the zero and gain of the pressure sensor prior to pressure measurement. A variety of sources of a known differential pressure may be used to reset the gain of the differential pressure sensor by simultaneously exposing both sides of the differential pressure sensor to the known differential pressure. In one embodiment of the invention, the head loss through exhaust port of a spring-biased comparitor is the known pressure differential used to reset the pressure sensor gain. In another embodiment, a U-tube manometer is used to set a known differential pressure across an adjustable differential pressure regulator or an adjustable spring-biased comparitor and that pressure differential is used. The invention provides accurate bubbler pressure measurement under conditions of rapidly varying liquid head by means of a single calibration of a differential pressure sensor instead of sequential calibrations of a gauge pressure sensor. The present invention provides a compact and lightweight manifold-mounted pneumatic integrated circuit and a method for in situ recalibration of relatively inexpensive pressure sensors.

Claims

1. An integrated pneumatic circuit comprising a plurality of components comprising:

a source of compressed gas,

a plurality of bubbler circuits connected to said source of compressed gas,

at least one means for controlling bubble release rate, one said means for controlling being associated with each said bubbler circuit,

at least one means for sensing differential pressure connected to said plurality of bubbler circuits, said means for sensing having a pressure side and a reference side, and said means for sensing producing a plurality of signals when excited,

means for simultaneously applying equal pressures to the pressure side and the reference side of each said means for sensing differential pressure to produce a zero pressure signal,

means for generating a known pressure differential,

wherein said means for generating a known pressure differential is selected from the group consisting of

means for generating a known head and a known head loss,

means for sensing pressures at a plurality of known elevations or depths in a liquid,

means for sensing pressures at known elevations or depths in liquids of known density,

means for generating a known gauge pressure that is referenced to atmospheric pressure, and

means for generation a gas pressure that is regulated above atmospheric pressure, and

means for simultaneously imposing said known pressure differential across each said means for sensing differential pressure to produce a known pressure signal,

wherein the plurality of components are mounted on and within a single manifold.

2. The apparatus of claim 1 wherein said means for sensing differential pressure comprises a temperature-compensated pressure transducer.

3. An apparatus for transmission and sensing of pressures comprising:

a source of compressed gas,

a plurality of bubbler circuits connected to said source of compressed gas,

means for releasing a plurality of bubbles of said gas, said means for releasing connected to each bubbler circuit, said plurality of bubbles being exposed to said pressures,

means for controlling bubble release rate,

at least one means for sensing differential pressure connected to said plurality of bubbler circuits, said means for sensing having a pressure side and a reference side, and said means for sensing producing a plurality of signals when excited, said plurality of signals being characterized by an offset or zero and a gain,

means for simultaneously applying a single pressure to the pressure side and the reference side of each said means for sensing differential pressure to produce a zero pressure signal,

means for resetting the zero of said means for sensing differential pressure by reference to at least said zero pressure signal,

means for generating a known pressure differential,

wherein said means for generating a known pressure differential is selected from the group consisting of

means for generating a known head and a known head loss,

means for sensing pressures at a plurality of known elevations or depths in a liquid,

means for sensing pressures at known elevations or depths in liquids of known density,

means for generating a known gauge pressure that is referenced to atmospheric pressure, and

means for generating a gas pressure that is regulated above atmospheric pressure, and

means for simultaneously imposing said known pressure differential across each said means for sensing differential pressure to produce a known pressure signal, and

means for resetting the gain of said means for sensing differential pressure by reference to at least said known pressure signal.

4. The apparatus of claim 3 wherein said means for generating a known pressure comprises a pressurized manometer.

5. The apparatus of claims 3 wherein said means for releasing bubbles is a tide gauge.

6. The apparatus of claims 3 wherein said means for releasing bubbles is density gauge.

7. A method for transmission and sensing of pressures comprising:

compressing a gas,

connecting a plurality of bubbler circuits to a means for releasing bubbles,

releasing bubbles of said gas, said bubbles being exposed to said pressures,

controlling bubble release rate,

sensing at least one differential pressure by means of a means for sensing differential pressure connected to said plurality of bubbler circuits, said means for sensing having a pressure side and reference side, and said means for sensing producing signals when excited, said plurality of signals being characterized by an offset or zero and a gain,

simultaneously applying a single pressure to the pressure side and the reference side of each said means for sensing differential pressure to produce a zero pressure signal,

resetting the zero of said means for sensing differential pressure by reference to at least said zero pressure signal,

generating a known differential pressure,

wherein said means for generating a known pressure differential is selected from the group consisting of

means for generating a known head and a known head loss,

means for sensing pressures at a plurality of known elevations or depths in a liquid,

means for sensing pressures at known elevations or depths in liquids of known density,

means for generating a known gauge pressure that is referenced to atmospheric pressure, and

means for generating a gas pressure that is regulated above atmospheric pressure, and

simultaneously imposing said known pressure differential across each said means for sensing differential pressure to produce a known pressure signal, and

resetting the gain of said means for sensing differential pressure by reference to at least said known pressure signal.

8. The method of claim 7 wherein generating a known pressure is accomplished by means of a differential pressure regulator.

9. The method of claim 7 wherein generating a known pressure is accomplished by means of a pressurized manometer.

10. The method of claim 7 wherein said bubbles are exposed to pressures produced by a bubbler-type tide gauge.

11. The method of claim 7 wherein said bubbles are exposed to pressures produced by a bubbler-type density sensor.

12. The method of claim 7 further comprising purging each of the plurality of bubbler circuits in accordance with a mode operation selected from the group consisting of

simultaneously purging all bubbler circuits, and

sequentially purging each bubbler circuit.

13. An apparatus for transmitting and sensing the pressure head at a point in a liquid comprising

a bubbler system comprising a source of compressed gas and at least a first means for discharging bubbles,

at least one differential pressure sensor, said at least one differential pressure sensor having a pressure port and a reference port,

means for generating a pressure difference across said at least one differential pressure sensor, said pressure difference being fixed and known, the pressure on one side of said means for generating a pressure difference being relatively higher than the pressure on the other side of said means for generating a pressured

wherein said means for generating skid pressure difference is selected from the group consisting of

means for generating a known head and a known head loss, and

means for sensing pressures at a plurality of known elevations or depths in a liquid, and

wherein at least said reference port is adapted to be exposed to atmospheric pressure, and said pressure port and said reference port are adapted to be exposed to equal pressures to produce a zero pressure signal, and

wherein said reference port is adapted to be exposed to the pressure of the lower pressure side of said means for generating a pressure difference and said pressure port is adapted to be simultaneously exposed to the pressure on the one higher pressure side of said means for generating pressure to produce a signal that is characteristic of said pressure difference, and

wherein said pressure port is adapted to be exposed to said first means for discharging bubbles.

14. The apparatus of claim 13 wherein said means for generating a pressure difference comprises a needle valve and a differential pressure regulator.

15. A method for transmission and sensing of pressures comprising:

transmitting a pressure to a pressure sensor by means of a bubbler circuit,

measuring said pressure with said pressure sensor, said sensor having a pressure side, and a reference side, said pressure sensor producing a plurality of signals when excited, said plurality of signals being characterized by an offset or zero and a gain,

resetting said offset or zero by simultaneously exposing said pressure side and said reference side to equal pressures,

resetting said gain by simultaneously exposing said pressure side to a known pressure and said reference side to a different known pressure, and

wherein said known pressures are generated by a means selected from the group consisting of

means for generating a known head and a known head loss,

means for sensing pressures at a plurality of known elevations or depths in a liquid,

means for sensing pressures at known elevations or depths in liquids of known density,

means for generating a known gauge pressure that is referenced to atmospheric pressure, and

means for generating a gas pressure that is regulated above atmospheric pressure.