Structure or construction for mounting a pressure detector

Details Structure or construction for mounting a pressure detector Structure or construction for mounting a pressure detector

2001-04-04

2003-08-19

Williams, Hezron (Department: 2855)

Measuring and testing

Fluid pressure gauge

Mounting and connection

Reexamination Certificate

active

06606912

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to improvements in and relating to a mounting structure or construction for mounting a pressure detector utilizing mainly a sensor chip as a pressure sensitive element.
BACKGROUND OF THE INVENTION
Diaphragm type pressure detectors utilizing a sensor chip as the pressure sensitive element or strain gauge have been widely used for the detection of fluid pressure in pipes.
FIGS. 10 and 11
illustrate diaphragm type pressure detectors as disclosed in the inventors' Japanese patent applications No. 10-82707 and 10-008841. The pressure detectors each comprise a sensor base
1
for supporting a pressure sensitive element in the form of a sensor chip
2
, a diaphragm
3
, a diaphragm base
4
, a pressure transfer medium (silicone oil)
5
, a seal ball
6
, output lead pins
7
, and a weld
8
. If a fluid pressure
10
is applied to sensor chip
2
through diaphragm
3
and pressure transfer medium
5
, voltage signals proportional to the pressure from a semiconductor pressure transducer forming the sensor chip
2
are produced at output lead pins
7
.
FIGS. 12 and 13
show the pressure detectors of
FIGS. 10 and 11
, respectively, mounted to measure pressure in a pipeline or the like.
FIG. 14
is an enlarged sectional view of a portion A of FIG.
13
.
In
FIG. 12
, a fixture main body
11
has a fluid channel
11
b
therein, the channel extending from one side of the main body to an opposite side thereof. The main body
11
is mounted between pipe line end sections
52
so that fluid may flow between the end sections via channel
11
b
. A fluid passage
22
connects with channel
11
b
and permits pressure in the channel to be applied to diaphragm
3
.
A presser member
12
rests on diaphragm base
4
and a bearing
14
rests on presser
12
. A threaded clamping element such as a clamping bolt
15
is inserted into a threaded opening in the fixture main body
11
and, as the clamp is tightened, a force acting through bearing
14
and presser
12
pushes diaphragm
4
downward against a metal gasket
17
.
In
FIG. 13
, clamping element
16
presses down on presser member
13
which in turn presses down on the sensor base
1
so that diaphragm
4
is pressed against metal gasket
17
.
In both
FIGS. 12 and 13
, the pressure applied by the presser member
12
,
13
creates an air-tight seal, via the metal gasket
17
, between the diaphragm
4
and the fixture main body
11
. The metal gasket
17
is made of a material that has a high resistance to corrosion and wear, and does not generate dust.
Diaphragm type pressure detectors constructed as shown in
FIGS. 10 and 11
can minimize the so-called dead space when mounted on a pipe line or the like. This offers practical advantages in that the gas exchangeability is high and a desired passive state film without spots, and with a uniform thickness, can be formed with relative ease on the gas-contact surface of the diaphragm
3
.
The metal gasket
17
, being made of a material having a high resistance to corrosion and not prone to generating dust, is almost free from O-ring corrosion-caused problems, unlike the mountings of diaphragm type pressure detectors using an O-ring. However, other problems exist, the most serious problem being fluctuations in measurements attributable to stress, strain or the like on the diaphragm
3
.
Diaphragm
3
is very thin, on the order of 0.05 to 0.06 mm. The diaphragm thickness is reduced to raise the pressure detection sensitivity. In such a state as shown in
FIG. 12
, therefore, stress or strain on the diaphragm
3
inevitably results at the time of tightening clamping bolt
15
when the contact surface of metal gasket
17
is brought into contact with the block lower surface
4
f
(
FIG. 10
) of the diaphragm base
4
. This changes greatly the stress applied to the sensor chip
2
through silicone oil
5
.
Experiments were conducted using a pressure detector with a diaphragm 0.05-0.06 mm thick, about 10 mm in inside diameter, and having a detection pressure range from several Torr to 7 kgf/cm
2
abs. The pressure P acting on the diaphragm
3
was high at some Ps=7 kgf/cm
2
abs, and the pressure detector was mounted on the fixture main body
11
. The output Vs (mv) and temperature characteristics ZTC (% FS/° C.) were not much different from those observed when the pressure detector was in a free state, that is, not mounted on the fixture main body
11
.
However, in the case where the pressure P applied to the diaphragm
3
was low, for example, Po=0 kfg/cm
2
abs, the output Vo changed by more than 5.2 mv when the pressure detector was mounted. (The output was 16.66 mv before the mounting of the pressure detector and 21.86 mv after the mounting.) The temperature characteristics ZTC (% FS/° C.), too, greatly fluctuated from 0.162 to 0.719. That is, as far as the output is concerned, differences in measurements are too large. In respect of temperature characteristics, too, fluctuations are too large to compensate. Thus, this pressure detector presents problems when used in practice.
On the other hand, if the peripheral portion of the diaphragm base
4
is formed as shown in
FIG. 11
, and if the pressure detector is tightened and clamped with the outer circumferential surface
4
d
of the block of the diaphragm base
4
, and the inner circumferential surface
17
d
of the gasket
17
not in contact with each other (FIG.
14
), the magnitude of change &Dgr;Vo in output before and after the mounting under pressure Po=0 kgf/cm
2
abs can be reduced to less than ± about 3.5 mv. Likewise, the temperature characteristics ZTC (% FS/° C.) will come within a range between 0.052 and 0.259. If the pressure detector is mounted on a pipe line etc., the characteristics will be well applicable in practice through a specific correction procedure.
In the mounting construction shown in
FIGS. 13 and 14
, the magnitude of the change &Dgr;Vo in output before and after mounting of the sensor will be small. This is because the gasket
17
is placed between the collar lower surface
4
c
of a collar
4
a
provided on the diaphragm base
4
and the outer circumferential surface
4
d
of the thick (about 2 mm) block
4
b
of the diaphragm base
4
, and further because the inner circumferential surface
17
d
of the metal gasket
17
and the outer circumferential surface
4
d
of the block
4
b
are not in contact with each other. Therefore, even if the presser member
13
applies downward pressure on the metal gasket
17
through the sensor base
1
and diaphragm base
4
, the upward and downward reaction forces of the metal gasket
17
are all received by the collar
4
a
of the diaphragm base
4
. In other words, almost no strain or stress, resulting from tightening, acts on the diaphragm
3
formed integrally in the block
4
b
of the diaphragm base
4
.
However, it is desirable that the change &Dgr;Vo in output before and after the mounting of the pressure detector and the temperature characteristic ZTC (%FS/° C.), be as small as possible. With the prior art construction or mounting structure shown in
FIG. 14
, the trouble is that the magnitude of &Dgr;Vo is still too large.
SUMMARY OF THE INVENTION
The main object of the present invention is to solve the above-mentioned problem encountered when the diaphragm type pressure detector having the constitution shown in
FIGS. 10
to
14
is actually applied to the pipe line or the like. That is, an object of the invention is to solve the problem of lowered measurement precision, resulting from large changes in output and temperature characteristics caused by differences in stress or strain on the diaphragm, that arise when the pressure detector is mounted in the fixture main body. This object is achieved by improvements in the structure or construction for mounting the pressure detector on the pressure detector fixture main body so that (1) when the pressure detector is fixed in the fixture main body the output and temperature characteristics will be hardly different from those observed when the

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