JP2750550B2 - Remote seal type differential pressure / pressure transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a remote seal type differential pressure / pressure having at least one pressure measuring end facing a pressure measuring portion at an extended end of a capillary tube led out of a detecting portion body. about the transmitter.

[0002]

2. Description of the Related Art A remote seal type differential pressure or pressure transmitter used to measure the pressure of various process fluids is a process having strong corrosiveness, high viscosity, condensability, high temperature, metal deposition, and the like. It is effective for measuring fluid, and has a seal diaphragm for process liquid contact at two points on the pressure-measured part side, which is remote from the detector body that detects pressure on the transmitter body side. Alternatively, a liquid sealing structure is provided in which the pressure measuring end and the detection unit body are connected by a capillary tube, and a sealing liquid such as silicon oil is sealed therein as a pressure transmission medium. This kind of remote seal type differential pressure or pressure transmitter is used to determine the differential pressure at the upper and lower positions or the tank internal pressure in a closed tank such as a high-temperature reaction tower in an oil refining plant by the pressure difference from the atmospheric pressure. The detection is used for measuring the liquid level or measuring the tank internal pressure.

In such a remote seal type differential pressure or pressure transmitter, for example, a schematic configuration of a differential pressure transmitter will be described with reference to FIG. A detection unit body 4 including a pair of pressure receiving spaces 2A and 2B therein and a pressure detection sensor 3 for detecting a pressure difference between the pressure receiving spaces 2A and 2B;
Capillary tubes 5A, 5B in each pressure receiving space 2A, 2B
B, high and low pressure outlets 7 having seal diaphragms 6A and 6B as pressure measuring ends connected via
A, 7B. In addition, each of these pressure extraction sections 7
A silicone oil is used as a pressure transmission medium in the space from the inner chamber formed by the seal diaphragms 6A, 6B of the A, 7B to the corresponding pressure receiving spaces 2A, 2B of the detecting section body 4 which are continuous via the capillary tubes 5A, 5B. And the like. Each of the pressure extracting portions 7A and 7B of the differential pressure transmitter 1 described above is provided with a high and low pressure pressure extracting hole 9 provided in a tank 9 as a measured portion.
A, 9B, the seal diaphragms 6A, 6B as pressure receiving elements face the inside of the tank 9, and the high-pressure side seal diaphragm 6 that faces the internal fluid below the tank 9.
A, the head pressure based on the liquid level height h is measured, and the tank pressure inside the tank 9 is measured by the diaphragm 6B on the low pressure side facing the tank inner chamber above the tank 9, and the liquid level position (high H) is measured. Although not specifically shown in FIG. 10, the capillary tubes 5A and 5B on the high and low pressure sides are formed to have the same length, and the pressure transmission in both pressure measurement systems becomes equal. It is set as follows. Therefore, the capillary tube 5A on the high pressure side is placed on the installation surface close to the tank 9 or the differential pressure transmitter 1 in a state wound, for example, in a spiral shape.

In the pressure transmitter 1A, FIG.
As is clear from FIG.
One of 2B (pressure receiving space 2A) is an atmospheric pressure chamber,
The capillary tube 5A is open to the atmosphere. The other capillary tube 5B is provided with a pressure extracting portion 7B having a seal diaphragm 6B as a pressure measuring end, and a pressure extracting hole 9B formed in a part of the tank 9 is provided so as to be able to measure the tank internal pressure. The internal pressure of the tank is measured by a pressure difference from the atmospheric pressure.

In the remote seal type differential pressure or pressure transmitter 1, 1A having the above-described configuration, the pressure measuring end (7
A, 7B or 7B) and the capillary tubes 5A and 5B connecting the transmitter-side detection unit body 4 are made of stainless steel or the like. It is thermally contracted, and the silicone oil or the like as the filling liquid 8 enclosed therein also undergoes thermal expansion or contraction. If the above-mentioned thermal expansion or the like occurs even partially, the volume in the capillary tube 5A, 5B or 5B changes, and even if the amount of expansion on the side of the sealed liquid 8 is taken into consideration, the pressure transmission will not occur. This causes a problem that the output of the measured value cannot be obtained because the rate changes. For this reason, conventionally, various measures for temperature correction such as adding a temperature compensation circuit have been taken in this type of differential pressure / pressure transmitters 1 and 1A. (7A, 7B or 7
B), the entire apparatus including the capillary tubes 5A, 5B or 5B and the detection unit body 4 is performed.
Ri and was not able to correct the partial temperature effects of the pressure transmitting system described above. That is, in the above-described remote seal type differential pressure or pressure transmitter 1, 1A, the capillary tube 5A,
5B; 5B is often as long as about 5 to 10 m or more, and in such a case, the capillary tube 5
A and 5B were often heated by receiving partial sunlight. And, with the above-described conventional configuration,
It is practically difficult to correct such a partial thermal effect, and it is desired to take some correction means with a simpler configuration. In particular, such a problem involves a pair of capillary tubes 5A and 5B formed by the same length as in the differential pressure transmitter 1 described above.
When one of them is affected by heat due to partial heating or the like due to direct sunlight, etc., imbalance occurs in pressure change at both pressure measuring ends (7A, 7B), and it is not possible to secure appropriate output accuracy. Was remarkable. Even if the pressure transmitter 1A is used, the capillary tube 5B having a considerable length
If this is thermally affected by partial heating or the like due to direct sunlight, etc., the pressure change will be unbalanced with the atmospheric pressure side, and appropriate output accuracy will be obtained. If it could not be secured, it was inevitable.

Therefore, in the above-described remote seal type differential pressure / pressure transmitter 1, 1A, for example,
According to Japanese Patent No. 88931 and Japanese Utility Model Application Laid-Open No. 62-88930, a capillary tube 5A, which constitutes a pressure transmission system, is used as a temperature correcting means for the above-mentioned temperature effects.
5B; In contrast to 5B, the counterpart pressure transmission system (5B, 5A;
5A) A dummy capillary tube drawn out from the side is attached alongside, thereby eliminating imbalance of pressure transmission due to the influence of heat on the sealed liquid between the pressure transmission systems on both sides to make the pressure transmission systems substantially equal. A device that performs temperature correction so that pressure measurement can be performed accurately has been previously proposed.

[0007]

However, in such a conventional temperature correction method, in addition to a capillary tube as an original pressure transmission system, a dummy capillary tube also exists in an overlapping manner. However, it is necessary to enclose a sealing liquid for pressure transmission in a capillary tube twice as large as that of a conventional capillary tube, and the enclosing operation is very difficult and difficult to realize. In addition, in the whole transmitter 1, 1A
In order to increase the total amount of sealed liquid, restrictions on the diaphragm etc. to be used increase, and the degree of freedom in design and the conditions of use arise, and this also poses a problem. It is desired to take a temperature correction method that can be realized more easily. Further, in the remote seal type differential pressure / pressure transmitters 1 and 1A as described above, the detection unit body 4 and the capillary tubes 5A and 5B; 5A are affected by ambient temperature due to direct sunlight, heat radiation from a furnace or a tank, and the like. The temperature rises up to a temperature of about 110 ° C. at the maximum.
In A, 7B and 7A, the fluid temperature in the tank on the pressure measurement side is directly received and the temperature rises to a maximum of about 310 ° C. In consideration of such a temperature influence at the pressure measurement end portion, etc. Therefore, it is necessary to take some measures for performing appropriate temperature correction.

[0008]

SUMMARY OF THE INVENTION In order to meet the above-mentioned demands, a remote seal type differential pressure / pressure transmitter according to the present invention is provided with a pair of sensors formed in a detection unit body having pressure detection means and mutually defined. An outer periphery of a capillary tube extending from at least one of the pressure receiving spaces and an outer portion of a pressure measuring end having a seal diaphragm connected to an extended end thereof and facing a portion to be measured , for example, an anti-seal diaphragm
The temperature-sensitive resistance line is extended along with the temperature-sensitive surface, and a processing part for calculating the temperature-sensitive resistance value by the temperature-sensitive resistance line is provided to reduce the temperature error due to the thermal expansion of the sealed liquid at the capillary tube and the measuring end. It is configured to correct.

[0009]

According to the present invention, a capillary tube and a measuring tube are provided.
The temperature-sensitive resistance wire is attached to圧端, the error in pressure detection means caused by the temperature distribution difference in sensing the temperature conditions in each pressure transmission systems, which both sides of the pressure transmission systems, electrical processing , And an output error due to a partial temperature change does not occur .

[0010]

1 shows a remote seal type differential pressure sensor according to the present invention.
An embodiment to which a pressure transmitter is applied is shown, and the same or corresponding portions in FIG. 10 as those in FIG. 10 described above are denoted by the same reference numerals and description thereof is omitted. Here, in this embodiment,
A case where the present invention is applied to a differential pressure transmitter among differential pressure / pressure transmitters will be described. According to the remote seal type differential pressure transmitter 1 according to the present invention, the pair of pressure receiving spaces 2 defined and formed in the detection unit body 4 having the pressure detection sensor 3.
Capillary tubes 5A and 5B derived from A and 2B
Seal diaphragms 6A, 6A, which are connected to the outer periphery of the
Outer portions of the high pressure side (PH) and low pressure side (PL) pressure measuring ends 7A and 7B having a pressure gauge 6B , for example, an anti-sealing diaphragm
The temperature-sensitive resistance wires 20A and 20B are extended and attached along the ram surface, and a processing part 21 for calculating the temperature-sensitive resistance value by the temperature-sensitive resistance wires 20A and 20B is provided. It is characterized in that it is configured to correct a temperature error due to thermal expansion of the sealed liquid 8 at each of the pressure measuring ends 7A and 7B . Here, the temperature-sensitive resistance wires 20A, 2A to the capillary tubes 5A, 5B described above are used.
As a method of attaching 0B, for example, a resistance wire is bonded and fixed to the tube side with an adhesive such as silicon RTV,
As shown in FIG. 2, an appropriate portion is tightened with a tightening band 22 to be assembled, or as shown in FIG.
It is conceivable that the thermosensitive resistance wires 20A, 20B are placed along the wires A, 5B, and a thermoplastic pipe 23 is fitted on the outside of the wires to cover them, thereby integrating them. In addition, the above-mentioned temperature-sensitive resistance wires 20A, 20B are provided on the back side of the flange-shaped portions of the pressure extraction portions 7A, 7B as pressure measuring ends.
Is preferably provided in such a manner as to be spirally wound, so that the temperature condition at the pressure measuring end can be detected uniformly, appropriately and reliably over the entire area. In particular, in such pressure extraction sections 7A and 7B, the temperature rises considerably more than the capillary tubes 5A and 5B that are thermally affected by direct sunlight or the like due to the direct thermal influence from the pressure measurement section such as a tank. This is a major cause of error, and the temperature change in this part is spirally wound as described above .
The effect provided by the temperature-sensitive resistance wires 20A and 20B attached is large. In the present embodiment, a pair of pressure receiving spaces 2A and 2B formed in the detection unit body 4 are defined by the center diaphragm 13, and the capillary diaphragms 5A and 5B are also defined by seal diaphragms 14A and 14B. In this case, only the pressure transmission is performed. However, the seal diaphragms 14A and 14B in the detection unit body 4 are not always required, and may be omitted . And
According to such a configuration, the capillary tubes 5A, 5A
Outer and measuring圧端(7A, 7B) of the B and outer portions (for the
For example , a temperature sensing resistance line 20A, 20B attached along the anti-seal diaphragm surface) senses the temperature condition in each pressure transmission system, and detects this by a temperature distribution difference between the pressure transmission systems on both sides. 3 can be corrected by electrical arithmetic processing so that an output error due to a partial temperature change does not occur. That is, according to the above-described configuration, the capillary tubes 5A, 5B connecting between the pair of pressure measuring ends 7A, 7B and the detection unit body 4 are provided.
At least one of the tubes is partially heated, and even if the internal sealed liquid 8 and the tubes 5A and 5B themselves are affected by thermal expansion or the like due to the thermal effect, the temperature condition is set to the temperature-sensitive resistor 20A, 20B . An arithmetic circuit (corresponding to a CPU denoted by 21 in FIG. 4) calculates the temperature of the pressure signal from the pressure detection sensor 3 based on the resistance value difference, and outputs an error due to a partial temperature change. Is not generated. here,
In FIG. 4, reference numeral 24 denotes the above-mentioned temperature-sensitive resistors 20A and 20A.
A pair of resistors 25A, 25A
B is a bridge circuit composed of
6. Introduced to the CPU 21 as an arithmetic circuit via the A / D converter 27 and the I / O interface 28, the signal from the pressure detection sensor 3 is also introduced. Can be output from. Such a temperature correction procedure is as shown in FIG. 5, in which the resistance value difference is measured in step 101, the measurement from the pressure detection sensor 3 is performed in step 102, and these are compared and calculated by the CPU 21 in step 103. By that
It will be easily understood that the pressure signal can be appropriately and reliably corrected by the resistance value difference.

Here, the temperature-sensitive resistor 20 as described above is used.
The point that the temperature can be corrected by A and 20B will be described below with reference to FIG. First, the points of the sealed liquid in the capillary tubes 5A and 5B accompanying the temperature change will be examined. Here, L: length of the entire tube T (x): change from temperature To at position x [° C.] A: cross-sectional area of capillary α: expansion coefficient of sealed liquid (silicon oil) The volume of the portion cut out by dx is (A · dx), and d in the temperature change T (x)
The volume expansion of the x portion is dv = αT (x) · A · dx ‥‥ (1), and the volume expansion of the entire capillary tube is expressed by the following equation (2).

[0012]

(Equation 1)

From the equation (2), the capillary tubes 5A, 5A for transmitting pressure on the high pressure side PH and the low pressure side PL are obtained.
The volume changes ΔVcH and ΔVcL of the sealed liquid 8 at B are represented by the following equations (3) and (4).

[0014]

(Equation 2)

[0015]

(Equation 3)

The change ΔP of the differential pressure , which is an error due to the difference in the liquid amount between them, is given by Φ = diaphragm compliance.

[0017]

(Equation 4)

## EQU1 ## Next, the capillary tube 5A,
The temperature-sensitive resistance wires 20A and 20B creeped along 5B will be described below with reference to FIG. The resistance value at the dx portion of the temperature-sensitive resistance lines 20A and 20B is (ρdx). And the temperature change T
The resistance increase dR at the dx portion in (x) is dR = βT (x) · ρdx ‥‥ (6), and the total resistance change ΔRc is:

[0019]

(Equation 5)

From the equation (7), the resistance change of the temperature-sensitive resistance wires 20A and 20B on the high-pressure side PH and the low-pressure side PL is obtained.
ΔRcH and ΔRcL are expressed by the following equations (8) and (9).

[0021]

(Equation 6)

[0022]

(Equation 7)

The difference between the equations (8) and (9)
Taking (ΔRc) ,

[0024]

(Equation 8)

[0025]

(Equation 9)

Therefore, the temperature-sensitive resistance wires 20A, 20B on the side of the capillary tubes 5A, 5B are expressed by the equation (5).
Substituting equation (11) on the side,

[0027]

(Equation 10)

Is derived and the measurement result of the resistance change ΔRc
Thus, ΔPc can be obtained by the equation (12).

On the other hand, the sealed liquid sealed by the seal diaphragms 6A and 6B on the pressure measuring ends 7A and 7B side and the temperature-sensitive resistance wires 20A and 20B attached to this part will be described below with reference to FIG. . First, when the sealed liquid at the pressure measuring end is regarded as the same as the thick and thin flange-shaped capillary tube at this part, from the above-mentioned equation (5),

[0030]

[Equation 11]

## EQU1 ## Here, [Delta] P _F is flanged Haka圧
Change in differential pressure resulting in error due to difference in liquid volume between ends 7A and 7B
The pressure receiving area of a minute, also A 'is measured flanged 圧端, 1
Is its thickness. Then, in this case, (A '/ A) =
If κ,

[0032]

(Equation 12)

## EQU1 ## Next, the feeling at the flange-shaped
The temperature resistance wires 20A and 20B are perpendicular to the central axis of the lateral pressure end.
It is considered that the capillary tube exists on the surface by the area ratio κ times.
If so, from the above (11),

[0034]

(Equation 13) Becomes Therefore, the capillary tube and the measuring end
All differences pressure change amount [Delta] P _T in the total change in resistance [Delta] R _T is below (16), becomes (17), [Delta] P _T from both these formulas
And ΔR _T is (18).

[Equation 14]

[0036]

(Equation 15)

[0037]

(Equation 16) That is, the differential pressure change is calculated by measuring the resistance change.
Obviously, temperature correction can be performed.

FIG. 9 shows an embodiment in which the present invention is applied to a remote seal type pressure transmitter 1A. In the drawing, the same or corresponding parts as those in the above-described embodiment and the like are denoted by the same reference numerals. Is omitted. In this embodiment, in the remote seal type pressure transmitter 1A, the pressure-measured part (9)
Measuring end (7B) having a seal diaphragm 6B facing the front
And a pressure receiving space 2A in which a pressure transmitting medium (8) communicating with the pressure transmitting medium 8 via the capillary tube 5B is sealed, and the internal pressure thereof is detected by a pressure difference between the pressure receiving space 2A and the second pressure receiving space 2B to which atmospheric pressure is applied. A detection unit body 4 having means (3) is provided, and the temperature-sensitive resistance wire 20B is provided between the detection unit body 4 and the pressure measuring end 6B on the anti-seal diaphragm surface of the capillary tube 5B and the side pressure end 6B. Is shown. In such a configuration, the temperature-sensitive resistance line 20 of the bridge circuit 24 in FIG.
If a bridge is constructed using A as a dummy, the temperature-sensitive resistance line 2
It will be easily understood that the temperature change at 0B can be obtained from the resistance value difference, and the temperature correction can be performed in the same manner as described above. Here, in FIG. 9, reference numeral 30 denotes a pair of pressure receiving spaces 2A and 2B formed in the detection unit body 4 defined by the pressure detection sensor 3 and an atmospheric pressure side (reference pressure side) defined by the seal diaphragm 30. Although the case of a liquid-sealed space is shown, there is no difference from the configuration as a pressure transmission system.

The present invention is not limited to the structure of the above-described embodiment, but includes the detecting unit body 4 and the measuring units 7A, 7B;
Capillary tubes 5A and 5B on the pressure measurement side connected to B;
5B, the shape and structure of each part including the pressure transmission system on the atmospheric pressure (reference pressure) side, etc.
It is free to change. Further, the remote seal type differential pressure / pressure transmitter according to the present invention is not limited to the liquid level gauge in the above-described embodiment, and is used for measuring the differential pressure / pressure in various devices and apparatuses in various fields. The effect can be exhibited.

[0040]

As described above, according to the remote seal type differential pressure / pressure transmitter according to the present invention, a pair of pressure receiving spaces formed so as to be mutually defined in the detecting portion body having the pressure detecting means. Outer part of the pressure measuring end having a seal diaphragm that is connected to the outer periphery of the capillary tube derived from at least one of them and an extended end thereof and faces the part to be measured.
For example , a temperature-sensitive resistance line is extended along the surface of the anti-seal diaphragm, and a processing part for calculating a temperature-sensitive resistance value by the temperature-sensitive resistance line is provided. Because it was configured to correct the temperature error due to expansion, despite the simple and inexpensive configuration,
The following excellent effects are obtained. That is, in the present invention
According to the temperature sensing resistance wires attached to the outer periphery of the capillary tube and the outer portion at the pressure measuring end, the temperature conditions in each pressure transmission system can be appropriately and reliably sensed, and thereby the temperature distribution in the pressure transmission systems on both sides can be detected. By correcting an error in the pressure detecting means caused by the difference by an electric operation process, it is possible to prevent an output error due to a partial temperature change . Thus, according to the present invention,
The pressure-measuring end that faces the pressure-measured part and is easily affected by the temperature, and at least a part of the capillary tube that connects between the pressure-measuring end and the detecting part body are partially heated, and the heat influences the inside. Even if the sealed liquid or the tube itself is affected by thermal expansion, etc., the temperature should be properly corrected so that output errors due to partial temperature changes do not occur .
Can be.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of a remote seal type differential pressure transmitter to which the present invention is applied.

FIG. 2 is a schematic view showing an example of attaching a temperature-sensitive resistance wire to a capillary tube.

FIG. 3 is a schematic view showing another example of attaching a temperature-sensitive resistance wire to a capillary tube.

FIG. 4 is a circuit diagram for temperature correction.

FIG. 5 is a flowchart for temperature correction.

FIG. 6 is a diagram for explaining a temperature change of a sealed liquid in a capillary tube.

FIG. 7 is a diagram for explaining a temperature change in a temperature-sensitive resistance wire attached to a capillary tube portion.

FIG. 8 is a diagram for explaining temperature changes of a sealed liquid and a temperature-sensitive resistance line at a pressure measuring end portion.

FIG. 9 is a schematic configuration diagram showing one embodiment of a remote seal type pressure transmitter to which the present invention is applied.

FIG. 10 is a schematic configuration diagram for explaining a conventional remote seal type differential pressure transmitter.

FIG. 11 is a schematic configuration diagram for explaining a conventional remote seal type pressure transmitter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Remote seal type differential pressure transmitter, 1A ... Remote seal type pressure transmitter, 2A ... Pressure receiving space, 2B ... Pressure receiving space, 3
... pressure detection sensor, 4 ... detection unit body, 5A ... first (pressure measurement side) capillary tube, 5B ... first (pressure measurement side) capillary tube, 6A ... pressure extraction seal diaphragm, 6B ... pressure extraction seal diaphragm , 7A: pressure extraction part (pressure measurement end), 7B: pressure extraction part (pressure measurement end), 8
... Internal sealed liquid, 9 ... Tank (measured part), 20A ... Temperature-sensitive resistance wire, 20B ... Temperature-sensitive resistance wire, 21 ... CP for arithmetic processing
U.

Claims (2)

(57) [Claims] 1. A detecting body having a pair of pressure receiving spaces defined by each other and a means for detecting a pressure difference between the pressure receiving spaces, and a pressure transmitting enclosure which is drawn out from each pressure receiving space of the detecting portion body. In a remote seal type differential pressure / pressure transmitter having a pressure measuring end having a seal diaphragm which is connected to an extended end of at least one capillary tube in which a liquid is sealed and faces a portion to be measured, the capillary tube On the outer circumference of the
Along with extending the temperature-sensitive resistance line along with the temperature-sensitive resistance value, a processing unit for calculating the temperature-sensitive resistance value by the temperature-sensitive resistance line is provided so as to correct the temperature error due to the thermal expansion of the sealed liquid at the capillary tube and the pressure measuring end. A remote seal type differential pressure / pressure transmitter characterized by comprising. 2. The remote seal type differential pressure sensor according to claim 1,
In the pressure transmitter, the resistance due to the temperature-sensitive resistance
So that the resistance is κ times the resistance of the capillary tube
Remote seal type differential pressure / pressure characterized by setting
Transmitter.