JPH0583137B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention transmits the pressure of a measuring fluid to a sealed liquid in a diaphragm seal, and the resulting displacement of a measuring diaphragm is applied to a gap between an opposing fixed electrode. Regarding the differential pressure detector that detects capacitance changes due to displacement, in more detail, the diaphragm seal has a double structure, and it is possible to fill the space between the two diaphragm seals with a secondary filling liquid or introduce a calibration fluid. , relates to a double diaphragm seal type differential pressure detector that allows calibration without drawing out the fluid to be measured.

[Prior Art] A differential pressure detector of a type that detects the displacement of a measuring diaphragm as a capacitance change due to a gap displacement between the measuring diaphragm and a fixed electrode facing the diaphragm is conventionally known. In this case, the space between the measurement diaphragm and the fixed electrode needs to be filled with a highly insulating fluid with a known dielectric constant, so a diaphragm seal method is used that transmits pressure through the sealed liquid without directly introducing the measurement fluid. There are many things.

Such differential pressure detectors are used in pressure tube nuclear reactors that use heavy water as a moderator, chemical plants, and other lines that use hazardous substances.

FIG. 2 shows an example of a conventional differential pressure detector and an example in which it is incorporated into heavy water system instrumentation piping in a pressure tube nuclear reactor. The differential pressure detector 10 includes a measuring diaphragm 12 located at the center, fixed electrodes 14a, 14b provided on both sides of the measuring diaphragm 12, and diaphragm seals 16a, 16b provided outside of these electrodes.
It has a symmetrical structure with respect to the central measuring diaphragm 12 and is incorporated into a housing 18 .

The fixed electrodes 14a and 14b are metal coatings formed on the inner spherical surface of a block 20 made of glass, for example. A sealing liquid 22a, 22b such as silicone oil is filled between the measuring diaphragm 12 and the diaphragm seals 16a, 16b. The measuring fluid is configured to be introduced from the outside of the diaphragm seals 16a and 16b. Further, lead wires from the measurement diaphragm 12 and fixed electrodes 14a, 14b are guided to a transmission section 24 to generate an output signal. Plugs 26a and 26b for meter calibration are provided at both ends of the housing 18, respectively.

In normal operating conditions, the low-pressure side process valve 28 and the high-pressure side process valve 30 are open, and the pressure difference between the pressure of heavy water contained in the heavy water tank 32 and the pressure measured by the reference level gauge 34 is detected. do.

Calibration of instruments is performed in the following steps. The low pressure side process main valve 28 and the high pressure side process main valve 30 are closed. A helium cylinder (not shown) is connected to the drain pressurizing port 36. Then, open the low pressure side vent valve 38a and the high pressure side vent valve 38b,
Low pressure side drain source valve 40a and high pressure side drain source valve 40
Let b be open. It is pressurized with helium gas from a helium cylinder, and the drain pressure source valve 42 is opened to discharge the heavy water in the differential pressure detector 10 to the heavy water drain tank 44. After discharging, the drain pressure source valve 42 is closed. Furthermore, the vent source valves 38a, 3 on the low pressure side and high pressure side
8b and drain source valves 40a, 40b are closed.

And calibration plugs 26 on the low pressure side and high pressure side
a, 26b are opened, a pressure pump and a digital manometer (both not shown) are connected to the high pressure side plug opening, and calibration is started. Calibration is zero calibration and span calibration of the differential pressure detector, and is usually performed at five points.

After the calibration is completed, the low-pressure side and high-pressure side calibration plugs 26a and 26b are restored. Then, the low-pressure side process main valve 28 and the high-pressure side process main valve 30 are opened, and the vent main valves 38a and 38b are sequentially opened to perform degassing and water filling work. At this time, the vent-drain communication valve 46 is used. After water filling is completed,
Vent source valves 38a, 38b on the low pressure side and high pressure side
is closed and the recovery is completed.

[Problems to be Solved by the Invention] However, in such a differential pressure detector, when performing calibration, the measurement fluid (in this case, heavy water) must be removed from the housing 18, and as a result, the fluid to be measured (heavy water in this case) must be removed. Various problems arise. First, for calibration using air pressure, the plug is opened and exposed to the atmosphere, which poses the problem of tritium in heavy water diffusing into the air and exposing workers to tritium. Additionally, gas accumulation is likely to occur and instrument drift is likely to occur. Additionally, there is the problem that it takes a long time to calibrate one instrumentation loop.

Furthermore, if dust or the like gets caught on the seat surface of the instrumentation valve, the seat surface may be damaged and measurement may become impossible, and if the instrumentation valve has a seat pass, it may cause calibration failure. It becomes possible.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a differential pressure detector having a structure that allows easy calibration without removing a measuring fluid such as system heavy water from the detector. .

[Means for Solving the Problems] The present invention includes a measuring diaphragm located at the center, fixed electrodes provided on both sides of the measuring diaphragm, and diaphragm seals provided further outside of the measuring diaphragm. This is based on a capacitive diaphragm type differential pressure detector configured to fill a sealed liquid between the diaphragm seal and introduce the measuring fluid from the outside of the diaphragm seal.

In the present invention, which can achieve the above objects, the diaphragm seals each have a first
It has a double structure of a diaphragm seal and a second diaphragm seal, and the space between the measurement diaphragm and the first diaphragm seal is filled with a primary liquid, and communicates with the space between the first and second diaphragm seals. Flow ports with plugs are provided at the upper and lower parts of the space, respectively, to enable filling and discharging of the secondary filled liquid and introduction and discharging of the calibration fluid, and the measurement fluid is placed outside the second diaphragm seal. It is configured to be installed from

[Operation] In a normal differential pressure measurement state, a secondary sealed liquid is filled between the first diaphragm seal and the second diaphragm seal. The pressure of the measuring fluid is then transmitted to the secondary filled liquid via the second diaphragm seal, and further transmitted to the primary filled liquid via the first diaphragm seal, thereby displacing the measuring diaphragm. This causes a change in capacitance with the fixed electrode, and by detecting this change, the differential pressure can be determined.

When calibrating the instrument, the secondary fill liquid is drained from the space between the first diaphragm seal and the second diaphragm seal, and a calibration fluid is introduced. One of the calibration fluids may be atmospheric air. There is no need to draw the measuring fluid out of the detector. Since it is the secondary sealed liquid that is extracted, even if the measured fluid is heavy water used in nuclear reactors, it will not be released into the atmosphere.

In this way, in the present invention, calibration can be performed without drawing out the fluid to be measured, which not only improves work efficiency, but also greatly reduces the possibility of contamination even if the fluid to be measured contains harmful substances.

[Embodiment] FIG. 1 is a sectional view showing an embodiment of a double diaphragm seal type differential pressure detector according to the present invention. This differential pressure detector 50 has a measuring diaphragm 52 located at the center and fixed electrodes 54a and 54b provided on both sides of the measuring diaphragm 52. In the present invention, the diaphragm seals provided further outside the fixed electrodes 54a, 54b are the first diaphragm seals 56a, 56b and the second diaphragm seal 58.
It has a double structure with a and 58b. This point is one of the outstanding features of the present invention.

The fixed electrodes 54a and 54b are metal coatings formed on the inner spherical surface of the ceramic block 60,
The ceramic block 60 is supported within a housing 64 by a support member 62 which also serves as a partition at the center. Lead wires are drawn out from the measurement diaphragm 52 and the fixed electrodes 54a and 54b, respectively, and a detection signal is outputted to the outside via the transmission section 65. Areas separated by the measuring diaphragm 52 and the first diaphragm seals 56a, 56b are filled with primary liquids 66a, 66b made of silicone oil or the like.

Outer housings 68a and 68b are attached to the outsides of the second diaphragm seals 58a and 58b, respectively, and process piping 70a and 70b for introducing the measurement fluid are connected to the centers of the outer housings 68a and 68b, respectively. Instrument main valves 72a, 72b
is installed.

In the present invention, the first diaphragm seal 56
a, 56b and a second diaphragm seal 58a,
Each space divided by 58b is provided with a communication port with a plug to communicate therewith,
This allows filling, introducing, and discharging fluid into the space. This point is also a feature of the present invention.

In this embodiment, air bleed pipes 74a, 74b and air bleed plugs 76a, 76b for closing the spaces are provided above the space, and drain pipes 78a, 78b and drain plugs 80a, 80b are provided below, respectively. It is provided.

In the actual differential pressure measurement state, the airtight space between the first diaphragm seals 56a, 56b and the second diaphragm seals 58a, 58b (the air vent plugs 76a, 76b and the drain plugs 80a, 80b are sealed) A secondary filling liquid 82 consisting of silicone oil, fresh heavy water, etc.
a, 82b are filled, and the instrument main valves 72a,
72b in the open state, respectively, the process piping 70
The measuring fluid is introduced from ports a and 70b. The pressure of the fluid to be measured is determined by the second diaphragm seals 58a, 58.
b to the secondary fill liquid 82a, 82b, and further to the first diaphragm seals 56a, 56.
b to the primary sealed liquid 66a, 66b, and the measuring diaphragm 52 due to the differential pressure between the two.
is displaced. Along with this, the measuring diaphragm 5
The gap between the fixed electrodes 54a and 54b changes, which results in a change in capacitance, and a differential pressure is detected.

In the present invention, since the diaphragm seal has a double structure, the intermediate secondary sealed liquids 82a and 82b can be extracted without coming into contact with the measurement fluid (process side). In other words, during calibration, the instrument main valves 72a and 72b are closed, and the air bleed plug 7 is closed.
6a, 76b, and drain plug 80a,
By opening 80b, the secondary filling liquid 82a, 82
b can be drained from the drain pipes 78a and 78b. What is drained here is the secondary filling liquid 82a, 8
2b and is different from the measurement fluid, so even if the measurement fluid contains harmful substances, there is no risk of contamination by them.

In the calibration procedure, after tightening the high-pressure side air bleed plug 76b, the high-pressure side drain pipe 78b
A pressurizing pump (not shown) may be connected to the calibrator, and calibration may be performed in the same manner as in the past while supplying calibration fluid.

[Effects of the Invention] As described above, the present invention has a diaphragm seal having a double structure, filling the space between them with a secondary filling liquid,
Since it is constructed so that it can be extracted from the drain pipe, calibration can be performed without removing the measuring fluid from the detector, thereby preventing contamination even if the measuring fluid contains harmful substances. can. Therefore, especially when the fluid to be measured is heavy water used in a heavy water moderation reactor, conventional technology requires that when the heavy water is removed and the work is opened to the atmosphere, the work is carried out while preventing the diffusion of tritium using a local ventilation device. However, according to the present invention, this series of operations can be simplified and radiation exposure can be reduced.

Furthermore, according to the present invention, the number of valves for draining and venting various fluids can be reduced. For example, the conventional technology normally requires seven valves, but according to the present invention, only three valves are required, and the instrumentation rack is also small. It has the effect of making it more effective.

Furthermore, with conventional differential pressure detectors, it took a long time to drain and fill with water during calibration, but with the present invention, the work process can be significantly streamlined, making it possible to perform calibration work more efficiently. Therefore, even if the measured fluid is heavy water from a nuclear reactor, for example, it is effective in reducing external exposure.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an embodiment of the double diaphragm seal type differential pressure detector according to the present invention, and Fig. 2 shows a conventional diaphragm seal type differential pressure detector and heavy water system instrumentation piping using the same. It is an explanatory diagram. 50... Differential pressure detector, 52... Measuring diaphragm, 54a, 54b... Fixed electrode, 56a, 5
6b...first diaphragm seal, 58a, 5
8b...Second diaphragm seal, 60...Ceramic block, 66a, 66b...Primary filled liquid, 74a, 74b...Air vent piping, 76
a, 76b...Air bleeding plug, 78a, 7
8b...Drain piping, 80a, 80b...Drain plug, 82a, 82b...Secondary sealed liquid.

Claims (1)

[Claims] 1.Equipped with a measuring diaphragm located in the center, fixed electrodes provided on both sides of the measuring diaphragm, and a diaphragm seal provided on the outside thereof, a sealed liquid is filled between the measuring diaphragm and the diaphragm seal, and the diaphragm seal is In a capacitive differential pressure sensor that introduces a measuring fluid from the outside, each of the diaphragm seals has a double structure of a first diaphragm seal and a second diaphragm seal, and the measuring diaphragm and the first diaphragm seal Fill the primary filling liquid between the
A communication port with a plug that communicates with the space between the second diaphragm seal is provided at the upper and lower parts of the space, respectively, to enable the filling and discharging of the secondary filled liquid and the introduction and discharging of the calibration fluid into the space. , a double diaphragm seal type differential pressure detector, characterized in that a measuring fluid is introduced from the outside of the second diaphragm seal.