WO2000017618A1

WO2000017618A1 - Pressure-measuring device and method using flexible, light-reflective foil

Info

Publication number: WO2000017618A1
Application number: PCT/US1999/021839
Authority: WO
Inventors: Peter B. Hutton
Original assignee: Hutton Peter B
Priority date: 1998-09-22
Filing date: 1999-09-21
Publication date: 2000-03-30
Also published as: AU6054499A

Abstract

In a pressure sensing device (1), a flexible, light-reflective foil (7) bows in response to pressure. A light source (11) provides light incident on the foil (7). The light is reflected by the foil (7) onto a light detector (13). The bowing of the foil (7) changes the position of incidence of the reflected light on the detector (13), the intensity of the reflected light, or both. This change allows for a calculation, by a computing device (15), of the pressure on the foil (7).

Description

PRESSURE-MEASURING DEVICE

Field of the Invention

The invention is directed to a device and method for measuring pressure, particulary pressure in a gas or oil pipeline, by measuring a deflection of a light source impinging on a flexible, light-reflective foil. Description of Related Art

It is often desired to measure the pressure of a fluid (liquid or gas), particularly when the fluid is being contained in a closed vessel or transported in a pipeline. A common way to

measure pressure is by diverting part of the fluid into a chamber of which one wall is formed by

a plunger. The pressure of the fluid on the plunger is counteracted, e.g., by a spring. A

measurement of the displacement of the plunger allows calculation of the pressure.

However, in practice, it may be difficult to make such a pressure-measuring device both

durable and reliable, particularly when high sensitivity is also required.

Companies such as Barton, Honeywell and Rosemount have developed pressure sensors

based on other technologies. One such technology involves variable capacitance. A flexible diaphragm is exposed to the fluid which bows under the pressure. Fixed capacitive plates near

the diaphragm form a capacitor whose capacitance varies in accordance with the bowing. A measurement of the capacitance allows a calculation of the pressure. The fixed capacitive plates

can be disposed on both sides of the diaphragm to form two capacitors, in which case the

difference in the capacitances can be used to calculate the pressure. Another such technology

uses a piezoresistive element. A measurement of the resistance of such an element allows a

calculation of the pressure.

U.S. Patents 4,428,239 and 4,499,373 to Rosemont Engineering Company, Limited; U.S. Patents 4,242,826 and 5,262,641 to Honeywell, Inc. and U.S. Patent 5,319,978 to Dynisco, Inc.,

1

SUBSTITUTE SHEET (RULE 261 all teach optical-reflective sensors to determine pressure, and in some cases, a differential

pressure.

However, each of these prior art devices utilize complex mechanical/optical linkages to

determine the sensed pressure, leading to a multiplicity of components, the failure of any one of

which will increase the risk of failure of the system to properly perform its intended function.

Thus, it is still desirable to have a highly sensitive pressure-measuring device which is

both durable and reliable. Summary of the Invention

An object of the invention is to provide a device and method for measuring pressure

(either absolute or relative) while providing durability, reliability and sensitivity.

To achieve this and other objects, the invention is directed to a device for measuring a

pressure of a fluid, the device comprising: a flexible, light-reflective foil, which on the one hand

is designed to be exposed to a fluid so as to deform under an influence of the pressure of the

fluid; a light source for emitting light and causing the light to be incident on the side of the foil

opposite to the side which is exposed to the fluid and thus to be reflected by the foil; a detector

for receiving and detecting the light reflected by the foil and for outputting a signal representing a condition of the light reflected by the foil and received by the detector; and computing means

for receiving the signal and determining the pressure in accordance with the signal.

The invention is further directed to a method for measuring a pressure of a fluid, the

method comprising: (a) exposing one side of a flexible, light-reflective foil to the fluid so as to

deform the foil under an influence of the pressure of the fluid; (b) emitting light and causing the light to be incident on the side of the foil opposite to the side which is exposed to the fluid,

whereby the light is reflected by the foil; (c) receiving and detecting the light reflected by the foil

and outputting a signal representing a condition of the light reflected by the foil and received; and

(d) receiving the signal and determining the pressure in accordance with the signal. Brief Description of the Drawings

A preferred embodiment of the invention will now be set forth in detail with reference to the drawings, in which:

Fig. 1 shows a device according to the invention in the absence of pressure; and

Fig. 2 shows the same device under pressure. Detailed Description of the Preferred Embodiment

Fig. 1 shows a pressure-measuring device according to the invention in the absence of pressure. Device 1 includes base 3 defining inlet 5 for receiving the fluid whose pressure is to

be measured. Inlet 5 can be in communication with a pipeline or the like, normally though a

valved manifold (not shown), such as known in the art. Inlet 5 is closed by flexible, light-

reflective foil 1, one side of which is directly exposed to the fluid. The foil is preferably metallic having a surface, e.g., a polished surface, to reflect light. However, the foil may also be a

composite of any material (such as a polymeric material or laminate thereof) having sufficient strength to withstand the pressure to which the foil is to be exposed and a surface which is mirrored or otherwise reflective to light. On the other side of foil 7 is enclosure 9, defining a

chamber whose internal pressure is selected such that the default condition of foil 7 is flat. Of

course, if enclosure 9 leaves the chamber open to the atmosphere, the internal pressure is that of

the atmosphere. Inside enclosure 9 are light source 11 and light-detecting device 13. Light

source 11 may operate in the visible, infrared or ultraviolet range and be a laser diode or the like.

Light-detecting device 13 outputs a signal to computing device 15 indicating the position, intensity or both at which the light is incident on light-detecting device 13.

In the absence of pressure, light from light source 11 is incident at a predetermined point

of incidence p_x on foil 7 at a predetermined angle θ_{ to normal vector ή, of foil 7 at point of

incidence p_x. The light is reflected at angle θ, and is incident on light-detecting device 13 at

position P_x and intensity /,, both of which can be determined before device 1 is put into use. Fig. 2 shows device 1 under pressure. As a result of the pressure, foil 7 is bowed (upward

in the drawing, though it is to be understood that the pressure measuring device may be oriented

other than vertical and thus may be bowed in directions other than upward). The light from light source 11 is incident at a point of incidence p₂ which is displaced by the bowing from point of

incidence ?,. Also, the curvature of foil 7 results in a new normal vector ή₂ which is different

from n,. Thus, the light from light source 11 is incident at a different angle θ₂ to new normal

vector ή₂, and the reflected light is incident on light-detecting device at a different position P₂,

a different intensity I₂ or both.

Measurement of the new position P₂, the new intensity I₂ or both allows a determination

by computing device 15 of the extent to which foil 7 is bowed and thus of the pressure.

Computing device 15 can determine the pressure by doing the necessary calculations on the fly,

by using a look-up table, or by some combination of the two techniques.

If position P₂ is to be measured, light-detecting device 13 can be a one- or two-

dimensional photodetector array, such as a linear array or a CCD array. In such an array, P₂ can be determined by determining on which pixel or pixels the light is incident. Fig. 1 shows a portion of light-detecting device 13 divided into pixels 14. If only I₂ is to be measured, light-

detecting device 13 can have a single photodetector element.

Foil 7 is a reflective, preferably metallic foil. It is preferably of a material whose response

to pressure is known, so that the amount of bowing can be calculated. Alternatively, if a foil is

used whose response to pressure is not a priori known, the device 1 can be calibrated

experimentally.

Computing device 15 can include a display to provide a visual or other local indication

(digital or analog) of the pressure. Alternatively, it can include a transmitter to inform a remote

operator of the pressure. The pressure measuring device can be used alone or in conjunction with another pressure measuring device in order to provide the differential pressure calibrations necessary to monitor modern pipelines. Alternatively, differential pressures can be sequentially monitored by sequentially exposing one side of foil 7 to sources of high/low pressure.

While a preferred embodiment of the invention has been set forth, those skilled in the art who have reviewed this disclosure will appreciate the other embodiments can be realized within the scope of the invention. Also, modifications disclosed separately can be combined.

Therefore, the invention should be construed as limited only by the appended claims.

Claims

I claim:

1. A device for measuring a pressure of a fluid, the device comprising:

a flexible, light-reflective foil having one side for being exposed to a fluid under pressure so as to deform the foil under an influence of the pressure of the fluid;

a light source for emitting light and causing the light to be incident on a surface

of the foil opposite said side exposed to said fluid and reflected by the said surface of said foil; a detector for receiving and detecting the light reflected by said surface of said foil

and for outputting a signal representing a condition of the light reflected by said surface of said foil and received by the detector; and

computing means for receiving the signal and determining the pressure in

accordance with the signal.

2. A device as in claim 1, wherein the condition of the light is intensity.

3. A device as in claim 1, wherein the condition of the light is a position at which

the light is incident on the detector.

4. A device as in claim 3, wherein: the detector comprises a plurality of detecting elements; and

the signal identifies one or more of the plurality of detecting elements on which

the light is incident.

5. A device as in claim 1 , wherein the foil is a metallic foil.

6. The device of claim 1 wherein the foil is a composite, said surface of which is

light reflective.

7. The device of claim 6 wherein the surface is mirrored.

8. The device of claim 1 wherein the light reflective surface of the foil is polished

metal.

9. A method for measuring a pressure of a fluid, the method comprising:

(a) exposing one side of a flexible, light-reflective foil to a pressured fluid so as to deform the foil under an influence of the pressure of the fluid;

(b) emitting light and causing the light to be incident on a surface of the foil opposite said one side and reflected by the foil;

(c) receiving and detecting the light reflected by the foil and outputting a signal representing a condition of the light reflected by the foil and received; and

(d) receiving the signal and determining the pressure in accordance with the

signal.

10. A method as in claim 9, wherein the condition of the light is intensity.

11. A method as in claim 9, wherein the condition of the light is a position at which

the light is received.

12. A method as in claim 11 , wherein: step (c) comprises receiving and detecting the light by use of a detector which

comprises a plurality of detecting elements; and the signal identifies one or more of the plurality of detecting elements on which

the light is incident.

13. A method as in claim 9, wherein the foil is a metallic foil.

14. The method of claim 9, wherein said exposing step is performed at least twice

with pressurized fluids of different pressure.