JP2004037307A - Remote sealed differential pressure transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid level detecting remote sealed differential pressure transmitter for detecting an accurate liquid level without a bad influence received from a surrounding environment of an installed location. <P>SOLUTION: The liquid level detecting remote sealed differential pressure transmitter is provided with a first diaphragm 11 displaced in response to received pressure, a first capillary tube 21 connected hermetically to the first diaphragm and internally filled with a sealing liquid, a second diaphragm 12 having a pressure reception face exposed to the air, a second capillary tube 22 hermetically connected to the second diaphragm and internally filled with the sealing liquid and a differential pressure sensor 23 for detecting a pressure difference between the sealing liquids of the first and second capillary tubes. Since the first and second capillary tubes are adjacently routed, the influence received from the surrounding environment of the installed location is canceled and an accurate output is obtained. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a remote seal type differential pressure transmitter suitable for detecting a liquid level in a tank, for example.
[0002]
[Prior art]
Conventionally, a differential pressure transmitter has been generally used for detecting a liquid level in a tank. Then, instead of the structure in which the pressure guide tube is directly disposed from the upper part of the tank to the differential pressure transmitter, a remote seal type differential pressure transmitter is often used from the viewpoint of cost reduction.
[0003]
FIG. 4 shows a case where such a remote seal type differential pressure sensor is used for detecting the liquid level in a tank. In this configuration, a liquid pressure measurement side capillary tube 51 and an atmospheric pressure measurement side capillary tube 52 are connected to a differential pressure transmitter, and a liquid to be detected and a pressure receiving surface are provided at an end of the liquid pressure measurement side capillary tube 51. Is provided with a diaphragm 53 for detecting hydraulic pressure. On the other hand, the end of the capillary tube 52 on the atmospheric pressure measurement side is connected to an atmospheric pressure measurement diaphragm 54 installed above the tank to measure the atmospheric pressure near the tank.
[0004]
Each capillary tube is filled with a filling liquid (not shown) made of silicon oil, and the pressure received by each of the diaphragms 53 and 54 is transmitted to the differential pressure sensor 55 via the filling liquid.
[0005]
The differential pressure sensor 55 is composed of a piezoresistive semiconductor pressure sensor or a capacitive pressure sensor, and detects the liquid level of the liquid according to the above-mentioned pressure difference between the sealed liquids.
[0006]
[Problems to be solved by the invention]
In the above-described structure for detecting the liquid level in the tank, the pressure receiving diaphragm 54 for measuring the atmospheric pressure is provided at the upper part of the tank, and the diaphragm 53 for measuring the liquid pressure is provided at the lower part of the tank. Becomes longer. Therefore, the volume of the sealed liquid sealed in each capillary tube also increases, and the degree of thermal expansion varies depending on the temperature in the vicinity of the capillary tubes, which causes an output error of the differential pressure sensor 55.
[0007]
Specifically, in the structure shown in FIG. 4, one of the capillary tubes 52 is routed in a place exposed to direct sunlight (see an arrow in the figure), and the other capillary tube 51 is placed in a place not exposed to direct sunlight such as shade. In this case, the temperature difference between the two capillary tubes becomes large, and accordingly the amount of expansion of the sealed liquid also differs, causing the output of the differential pressure sensor 55 to shift. Error).
[0008]
On the other hand, a configuration is also conceivable in which the atmospheric pressure measurement portion of the differential pressure sensor 55 is directly connected to the diaphragm 54 on the open-to-atmosphere side without using a capillary tube. However, according to this configuration, the capillary tube 51 is connected only to the diaphragm 53 on the hydraulic pressure measurement side, and the volume change due to the temperature change of the sealed liquid in the capillary tube is provided with the above-described two capillary tubes. It cannot be offset like a differential pressure transmitter of a different type. Therefore, this type also causes an output error due to a temperature change.
[0009]
An object of the present invention is to provide a remote seal type differential pressure transmitter for detecting a liquid level, which is suitable for detecting an accurate liquid level without being adversely affected by the surrounding environment of the installation place.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problems, a remote seal type differential pressure transmitter according to the present invention includes a first diaphragm that is displaced in accordance with a pressure to be received, and is hermetically connected to the first diaphragm, and is filled with a sealed liquid. A first capillary tube, a second diaphragm having a pressure-receiving surface open to the atmosphere, a second capillary tube hermetically connected to the second diaphragm and filled with a sealed liquid, and a first capillary tube. And a differential pressure sensor for detecting a pressure difference between the respective sealed liquids of the second capillary tube.
[0011]
Then, the first capillary tube and the second capillary tube are arranged close to each other.
[0012]
Since the first capillary tube and the second capillary tube are routed close to each other, the effects of the respective capillary tubes from the surrounding environment are the same, and these effects cancel each other out and the differential pressure This prevents an output error from occurring in the sensor.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a remote seal type differential pressure transmitter for liquid level detection according to an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, a remote seal type differential pressure transmitter for liquid level detection (hereinafter, simply referred to as a "differential pressure transmitter") 1 according to an embodiment of the present invention receives a liquid pressure in a tank. A fluid pressure measurement diaphragm (first diaphragm) 11, a fluid pressure measurement side capillary tube (first capillary tube) 21 which is hermetically connected to the fluid pressure measurement diaphragm 11 and filled with a sealed liquid, and a pressure receiving surface Is open to the atmosphere, and an atmospheric pressure measurement side capillary tube (second capillary tube) is hermetically connected to the atmospheric pressure measurement diaphragm 12 and is filled with a sealed liquid. ) 22, the measurement pressure between the diaphragms via the pressure transmitted to the respective sealed liquids of the liquid pressure measurement side capillary tube 21 and the atmospheric pressure measurement side capillary tube 22. And a differential pressure pressure sensor 23 for detecting a.
[0014]
The capillary tube 21 for measuring fluid pressure and the capillary tube 22 for measuring atmospheric pressure are arranged close to each other.
[0015]
The hydraulic pressure measurement diaphragm 11 is made of stainless steel, and is formed on one surface of a pressure receiving portion 41 fixed to an end of the cylindrical protrusion 31 as shown in FIG. A diaphragm receiving surface 41a having a surface shape corresponding to the hydraulic pressure measurement diaphragm 11 is formed in the pressure receiving portion 41, and a space A between the hydraulic pressure measurement diaphragm 11 and the diaphragm reception surface 41a is filled with silicon oil S1. ing. The sealed liquid S1 is sealed from a sealed liquid filling hole 41b formed on the peripheral surface of the pressure receiving portion 41.
[0016]
One end of a capillary tube 21 made of stainless steel is connected to a substantially central portion of the space A, and the capillary tube 21 is formed into a cylindrical shape via the inside of the protruding portion 31 and the stainless steel tube leading portion 45 formed in a disk shape. It is led out from the formed stainless steel tube leading end 47. As shown in detail in FIG. 2, the tube lead-out end 47 has a large-diameter space 47a and a small-diameter space 47b therein, and the outer peripheral end on the large-diameter space 47a side is closely fitted to the tube lead-out portion 45. A capillary holding spacer 49 is screwed into the large-diameter space 47a, and holds the capillary tube 21 firmly.
[0017]
On the other hand, an armored tube 82 is fixed to the small-diameter space 47b via a spacer holder 81 having a flange at one end, and the armored tube 82 is led out from the tube lead-out end 47. The capillary tube 21 is inserted through the inside of the armored tube 82 and is protected from the outside by the armored tube 82.
[0018]
The other end of the capillary tube 21 is connected to one pressure receiving portion 23a (FIG. 1) of a differential pressure sensor 23 composed of a piezoresistive semiconductor pressure sensor or a capacitive pressure sensor. The capillary tube 21 and the space A on the diaphragm side are electrically connected, and the inside of the capillary tube is also filled with the silicon oil S1.
[0019]
As shown in FIG. 1, a stainless steel atmospheric pressure receiving portion 42 having the same outer shape as the tube leading portion 45 is formed on the opposite side of the tube leading portion 45 with the drain ring 91 interposed therebetween. The drain ring 91 is made of stainless steel, has a literally ring shape, and has a communication hole 91a that communicates with the atmosphere on a part of its peripheral surface, and a drain adapter 92 is attached to the communication hole 91a.
[0020]
The atmospheric pressure receiving portion 42 is provided with a stainless steel atmospheric pressure measuring diaphragm 12 on the drain ring side, and a diaphragm having a surface shape corresponding to the atmospheric pressure measuring diaphragm 12 on one side surface of the atmospheric pressure receiving portion 42. A receiving surface 42a is formed. A silicone oil (filled liquid) S2 is filled in a space B between the diaphragm receiving surface 42a and the atmospheric pressure measurement diaphragm 12 through a filled liquid filling hole (not shown). A tube lead-out hole 42b is formed inside the atmospheric pressure receiving portion 42, and one end of the tube lead-out hole 42b is connected to the space and the other end is provided on the peripheral surface of the atmospheric pressure receiving portion. The capillary tube 22 led out from the outside is accommodated therein. The capillary tube 22 communicates with the space B, and the inside of the capillary tube 22 is also filled with the silicon oil S2.
[0021]
The other end of the capillary tube 22 is connected to the atmospheric pressure receiving side 23b of the differential pressure sensor 23 described above. The atmospheric pressure received by the atmospheric pressure measuring diaphragm 12 is transmitted to the differential pressure sensor 23 through the space B and the silicon oil S2 filled in the capillary tube 22.
[0022]
The atmospheric pressure receiving part 42, the tube lead-out part 45, and the drain ring 91 are firmly sandwiched between two carrier plates 93, 94 and bolts 95 for fastening them. In addition, a seal packing is interposed between them to ensure liquid tightness.
[0023]
One carrier plate 93 is welded and fixed to a mounting portion 96 that protrudes outward from the tank wall position detecting portion. Therefore, in FIG. 1, the diaphragm 11 for measuring the fluid pressure is mounted flush with the inner peripheral surface of the tank T via the protruding portion 31, and the sealed liquid S1 in the capillary tube is affected by the temperature R from the liquid R in the tank. Is not to receive.
[0024]
Since the remote seal type differential pressure transmitter 1 according to the present embodiment has the above configuration, the capillary tube 11 for detecting the liquid pressure and the capillary tube for detecting the atmospheric pressure, in which the filling liquids S1 and S2 are filled, respectively. 22 are both short in length and are routed close to each other. Therefore, the temperature of only one of the capillary tubes does not rise due to, for example, radiant heat due to sunlight or thermal influence from a heating element near the transmitter. Similarly, it is also bad that only one of the capillary tubes is cooled by the external atmosphere. Accordingly, a similar temperature change occurs in the sealed liquid in both capillary tubes, and the volume expansion of the sealed liquid accompanying the temperature change can be offset. Therefore, if the remote seal type differential pressure transmitter 1 of the present embodiment is used, accurate liquid level detection can always be performed regardless of the installation location.
[0025]
Note that, unlike the remote seal type differential pressure transmitter according to the above-described embodiment, as shown in FIG. 3, the atmospheric pressure receiving portion 42a is arranged near the liquid level detecting portion via the capillary tube 24 having a short overall length. A configuration may be adopted. Even in this case, the pressure received by the atmospheric pressure receiving unit is transmitted to one of the differential pressure sensors by the first filled liquid, and the pressure received by the hydraulic pressure receiving unit is changed by the second filled liquid to the differential pressure. It is transmitted to the other of the sensors. And, since the capillary tubes in which the respective liquids are filled are routed close to each other, there is no temperature difference caused by the external environment between the capillary tubes as in the above-described embodiment, and the capillary tubes are always accurate. Liquid level detection can be performed.
[0026]
【The invention's effect】
As described above, in the remote seal type differential pressure transmitter for liquid level detection according to the present invention, since the first capillary tube and the second capillary tube are routed close to each other, a space between each capillary tube is provided. The influences from the surrounding environment are the same, and these effects cancel each other to prevent an output error from occurring in the differential pressure sensor.
[Brief description of the drawings]
FIG. 1 is a partial sectional view showing a state in which a remote seal type differential pressure transmitter according to an embodiment of the present invention is attached to a tank.
FIG. 2 is an enlarged partial sectional view of a tube lead-out portion of the differential pressure transmitter shown in FIG.
FIG. 3 is a partial cross-sectional view showing a modification of the capillary tube of FIG.
FIG. 4 is a schematic view showing a state where a conventional remote seal type differential pressure transmitter is attached to a tank.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Differential pressure transmitter 11 Fluid pressure measurement diaphragm 12 Atmospheric pressure measurement diaphragm 21 Fluid pressure measurement side capillary tube 22 Atmospheric pressure measurement side capillary tube 24 Capillary tube 31 Projecting portion 41 Pressure receiving portion 41a Diaphragm receiving surface 41b Filled liquid filling hole 42 Atmospheric pressure receiving part 42a Diaphragm receiving surface 42b Tube lead-out hole 45 Tube lead-out part 45 Tube lead-out part 47 Tube lead-out end 47a Large diameter space 47b Small diameter space 81 Spacer holder 82 Armored tube 91 Drain ring 91a Communication hole 92 Drain adapter 93, 94 Carrier Plate 95 Bolt 96 Mounting part A Space B Space S1 Filled liquid S1 Silicon oil S2 Silicon oil (filled liquid)
T tank

Claims (1)

A first diaphragm that is displaced in accordance with the pressure received;
A first capillary tube hermetically connected to the first diaphragm and filled with a sealed liquid therein;
A second diaphragm having a pressure-receiving surface open to the atmosphere;
A second capillary tube hermetically connected to the second diaphragm and filled with a sealed liquid therein;
In a remote seal type differential pressure transmitter including a differential pressure sensor for detecting a pressure difference between a sealed liquid of each of the first capillary tube and the second capillary tube,
A remote seal type differential pressure transmitter, wherein the first capillary tube and the second capillary tube are arranged close to each other.

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