Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
1999-07-19
2003-08-12
McCall, Eric S. (Department: 2855)
Measuring and testing
Fluid pressure gauge
Diaphragm
C073S705000
Reexamination Certificate
active
06604427
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to pressure sensors and, more specifically, to an Improved Bellows-Type Pressure Sensor.
2. Description of Related Art
The bellows-type pressure sensor is widely used in high sensitivity applications. Essentially, what is involved is a very small bellow that is configured to reflect light onto a detector. When the bellow stretches or contracts in response to a pressure change, the detector will sense a corresponding change in the light intensity.
FIG. 1
is a perspective view of a prior art bellow assembly
10
. As can be seen, from its outer dimensions, the bellow assembly
10
comprises a stem
12
from which extends the bellow section
14
which terminates in the head
16
. The bellow section
14
is formed somewhat like an accordion, such that the bellow assembly
10
can stretch and shrink in response to changes in external forces. If we now turn to
FIG. 2
, we can examine the details of how this bellow assembly
10
functions to detect pressure.
FIG. 2
is a partial cutaway side view of the bellow assembly
10
of FIG.
1
. Again we can see that the bellow section
14
extends from the stem
12
and terminates in the head
16
. In this current embodiment the head
16
comprises a reflector
18
formed on its inner surface. Within the bellow section
14
is conventionally located a light detector
20
mounted on a stand
22
. Also found within the bellow section
14
is a light emitter
24
. The light emitter is configured to transmit light to the reflector
18
where it is in turn reflected towards the light detector
20
. In a conventional bellow assembly pressure detector
10
, the light detector
20
is sensitive enough to detect a change in light intensity in response to a change in bellow light
26
. It should be noticed that in this conventional design, the reflector
18
has always been substantially flat. As such, the reflective light does not converge in any sort of focal point but instead essentially reflects outward in a Boolean distribution and is spread into a wide area at the depth of the receiver
20
; when the reflector moves towards the receiver
20
, reflected areas become smaller (in effect focusing the signal). If one imagines that the bellow assembly
10
has an internal pressure
1
and the bellow assembly
10
is located within another area at a unknown pressure P
X
, as P
X
is changed, the bellow length
26
will also change until P
X
and P
l
regain equilibrium. It is this bellow length change
26
that is detected by the detector
20
and converted into an electrical signal for display to the user.
FIG. 3
depicts further information about this prior art device.
FIG. 3
is a partial cutaway side view of a conventional bellow-type pressure sensor
30
of the present invention. As can be seen, bellow assembly
10
is typically located within a chamber
28
. If we imagine that the bellow assembly
10
is isolated from the chamber
28
and that the chamber
28
includes a sensor tube
32
for sensing an external pressure, we can appreciate that when the sensor tube
32
is placed in a location such that the pressure P
X
changes from some reference pressure, and the bellows
10
later extend or contract while the internal pressure P
1
seeks to reach equilibrium with the sensed or unknown pressure P
X
. If we now turn to
FIGS. 4A through 4C
we can discuss the operation of the prior device more fully.
FIG. 4A
is a depiction of the signal path of the bellow assembly
10
of
FIGS. 1
,
2
and
3
. In this simplified drawing, the reflector
18
is shown at a distance L
X1
from the detector
20
. We will assume at this point that L
X1
defines the at rest condition of the bellow
10
. As can be seen, the transmitted light
34
from the transmitter (not shown) strikes the reflector
18
and is reflected back as reflected light
36
. As discussed above, it should be understood that substantially all of the transmitted light
34
is returned along the identical path of its arrival
36
. Some light however, will scatter as a result of surface irregularities on the reflector
18
and it is this light that is most likely received by the detector
20
. If we turn to
FIG. 4B
we can see that when the sensed pressure changes, the distance between the reflector
18
and the detector
20
changes to L
X2
.
FIG. 4B
is a depiction of the device of
FIG. 4A
after a pressure change has occurred. It should be casually apparent that the reflected light
36
is not substantially changed by the change in the location of the reflector
18
. In fact, in order to sense this changed distance, detector
20
must be extremely sensitive (and therefore expensive). Even still, this design will provide a fairly responsive and sensitive pressure detector having a dynamic range in the area of 2 dB. If we now turn to
FIG. 4C
we can see yet another limitation of the prior sensor.
FIG. 4C
is a depiction of the device of
FIGS. 4A and 4B
when the device is experiencing off-axis deflection. As can well be imagined, the bellow
10
in order to be sensitive, is formed from very thin-walled material. As such, it is affected by external forces including vibrations, gravity and other acceleration and it is common for these external forces to result in an off-axis deflection &thgr;y. As can be seen here, while the transmitted light
34
has not changed, when a theoretical deflection &thgr;y is caused in the bellow
10
, the reflected light
36
tends to be directed away from the detector
20
. As such, where the sensor is experiencing vibrations they might actually be sensed as pressure changes but in fact this is not necessarily the case. This, again, adds expense because the detector must be isolated for many external acceleration-type forces.
What is needed therefore, is an improved bellow-type pressure sensor that will increase responsiveness of the detector while reducing the need for an extremely sensitive detector. It would further be desirable if the improved sensor was less sensitive to off-axis deflection.
SUMMARY OF THE INVENTION
In light of the aforementioned problems associated with the prior devices, it is an object of the present invention to provide an Improved Bellow-Type Pressure Sensing Apparatus. It is an object that the improved apparatus provide increased pressure sensitivity without added cost and complexity in the electronic detector circuitry. It is a further object that the apparatus be less sensitive to gravity, vibrations or other external influences. It is a still further object that the apparatus be available with either concave or convex reflective surfaces, or a lens. It is a further object that the signal strength be increased.
REFERENCES:
patent: 4276776 (1981-07-01), Lapeyre
patent: 4329017 (1982-05-01), Kapany et al.
patent: 4408123 (1983-10-01), Sichling et al.
patent: 4665747 (1987-05-01), Muscatell
patent: 4768381 (1988-09-01), Sugimoto
patent: 4924870 (1990-05-01), Wlodarczyk et al.
patent: 5065010 (1991-11-01), Knute
patent: 5107847 (1992-04-01), Knute et al.
patent: 5514153 (1996-05-01), Bonutti
patent: 6277136 (2001-08-01), Bonutti
McCall Eric S.
Steins & Associates, P.C.
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