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.,
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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 px on foil 7 at a predetermined angle θ{ to normal vector ή, of foil 7 at point of
incidence px. The light is reflected at angle θ, and is incident on light-detecting device 13 at
position Px 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.