Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
2003-03-28
2004-09-28
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Fluid pressure gauge
Diaphragm
C073S714000, C073S715000
Reexamination Certificate
active
06796185
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to differential pressure/pressure transmitters, and in particular to pressure transmitters used for industrial measurement, having a construction in which an overpressure, even if applied to the pressure sensing assembly, is not transferred to the sensor itself, thus preventing sensor damage.
2. Description of the Prior Art
In the past, as a characteristic index of diaphragms adopted for differential pressure/pressure transmitters, “f(&phgr;)” has been conventionally used to indicate the characteristic of diaphragm displacement volume “&Dgr;V” to pressure “P”. For this characteristic, it is desirable that the linear relationship have as uniform a slope as possible in a measuring pressure range.
A differential pressure transmitter adopting a center diaphragm having such an ideal characteristic becomes capable of obtaining output signals from the sensor proportional to the process pressures. The transmitter also enables measurement error to be extremely small, even if higher order terms in a higher order equation are neglected in signal conversion in the amplifier assembly and in corrective calculation in the CPU.
In the meantime, conventional differential pressure/pressure transmitters adopting a conventional three-diaphragm system, that is, comprising two process diaphragms on the high and low pressure sides and one center diaphragm inside the body, for a total of three diaphragms, have a construction in which the center diaphragm moves in both directions depending on the process pressures.
In such a construction, it is required to obtain the uniform linear characteristic “f(&phgr;)”. To obtain such a characteristic, it is effective to take a remedial measure such as increasing the outer diameter of the center diaphragm or making the thickness of the center diaphragm thinner.
However, the problem is mainly solved by increasing the diameter of the center diaphragm because making the thickness of the diaphragm thinner may cause greater stress to be generated.
In these differential pressure/pressure transmitters using such a three-diaphragm system, if an overpressure is applied to a process diaphragm on the high pressure side or the low pressure side, the process diaphragm on the pressure-applied side is closely pressed to the body.
This stops moving of the pressure transferring oil enclosed inside the body, then pressure transfer to the sensor assembly is lost, and the overpressure is not transferred to the sensor assembly.
As shown in FIG.
1
and
FIG. 2
, differential pressure/pressure transmitter
110
is composed of pressure detection assembly
111
that converts the pressure based on the pressure difference between high pressure and low pressure from a process and amplifier assembly
112
that comprises the electrical circuit to amplify signals generated in detection assembly
111
.
Pressure detection assembly
111
is composed of a high pressure-side flange
113
forming the high pressure introducing part that introduces high pressures from a process, a low pressure-side flange
114
forming the low pressure introducing part that introduces low pressures from a process, and pressure sensing assembly
115
that detects both high pressure from high pressure-side flange
113
and low pressure from low pressure-side flange
114
using a diaphragm. High pressure-side flange
113
and low pressure-side flange
114
are fixed with nuts
116
and bolts
117
.
Pressure sensing assembly
115
, as shown in
FIG. 2
, has body
121
whose upper middle part is formed in the shape of a slender neck, sensor assembly
123
fixed in the center position of the upper part of body
121
using ring
122
, high pressure-side diaphragm assembly
124
and low pressure-side diaphragm assembly
125
provided facing to the outside and positioned back to back to each other in the lower part of body
121
.
Further, inside body
121
, high pressure-side oil transfer hole
126
which transfers oil from high pressure-side process diaphragm assembly
124
to sensor assembly
123
and low pressure-side oil transfer hole
127
which transfers oil from low pressure-side process diaphragm assembly
125
to sensor assembly
123
are provided. Details of each part will be described below.
Sensor assembly
123
is composed of terminal
128
, differential pressure sensor
129
that detects differential pressures by applying high pressure-side pressure from the top, and low pressure-side pressure from the bottom of the differential pressure sensor, and two hermetically sealed terminals
130
a
and
130
b
which are electrically connected to differential pressure sensor
129
by wire-bonding. The two hermetically sealed terminals
130
a
and
130
b
are connected to amplifier assembly
112
shown in FIG.
1
.
There is a space between high pressure-side diaphragm assembly
124
and body
121
, in which high pressure-side oil
133
is enclosed, and this space is connected with high pressure-side conducting hole
139
which leads to the space between center diaphragm C and body
121
.
In addition, high pressure-side conducting hole
139
is connected to high pressure-side oil transfer hole
126
. These spaces and holes are filled with high pressure-side oil
133
for pressure transfer.
Similarly, there is a space between low pressure-side diaphragm assembly
125
and body
121
, in which low pressure-side oil
137
is enclosed, and this space is connected with low pressure-side conducting hole
142
which leads to the space between center diaphragm C and body
121
.
Low pressure-side conducting hole
142
is also connected to low pressure-side oil transfer hole
127
. These spaces and holes are filled with low pressure-side oil
137
.
In differential pressure/pressure transmitter
110
having the above described structure, specifically in pressure sensing assembly
115
, if high pressure-side diaphragm assembly
124
, for example, receives pressure from a high pressure-side process, that pressure is transferred to high pressure-side oil
133
and the transferred pressure of high pressure-side oil
133
is supplied to differential pressure sensor
129
in sensor assembly
123
and center diaphragm C via high pressure-side transfer hole
126
after passing through high pressure-side conducting hole
139
.
At the same time, if low pressure-side diaphragm assembly
125
receives pressure from the low pressure-side process, that pressure is transferred to low pressure-side oil
137
and the transferred pressure of low pressure-side oil
137
is supplied to differential pressure sensor
129
in sensor assembly
123
and center diaphragm C via low pressure-side transfer hole
127
after passing through low pressure-side conducting hole
142
.
In such a manner, pressures from the high pressure-side and low pressure-side are transferred using oil
133
and
137
, and their difference is detected with differential pressure sensor
129
.
In this case, if a pressure difference is generated between the high pressure side and low pressure side and, for example, the pressure on the high pressure side becomes an overpressure as a result of loss of pressure balance between the high and low pressure sides, the process diaphragm of high pressure-side diaphragm assembly
124
moves towards body
121
, and the center diaphragm C is also deflected corresponding to the volume of moved oil at that time.
Further, the low pressure-side oil also moves due to the deflection of center diaphragm C to push the process diaphragm of low pressure-side diaphragm assembly
125
towards the outside.
However, if a center diaphragm in the three-diaphragm system described in conventional techniques is employed, the stress generated in the center diaphragm becomes high and so there is a problem that a stronger material from the viewpoint of strength of material must be employed.
In addition, although it is required that the material itself has ductility for forming diaphragms, if a stress generated in the center diaphragm employed for differential pressure/pressure transmitt
Aizawa Mamoru
Kurosawa Ryou
Jenkins Jermaine
Lefkowitz Edward
Westerman Hattori Daniels & Adrian LLP
Yokogawa Electric Corporation
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