JP4718121B2 - Temperature characteristic correction method - Google Patents

Description

The present invention relates to a remote seal-type measuring device that measures, for example, the pressure in the measuring environment via a pressure transducer that is externally attached to a measuring device body including a pressure sensor via a capillary tube and is provided in the measuring environment. The present invention relates to a temperature characteristic correction method suitable for correcting temperature characteristics in

  Various industrial measurement devices are required to have high measurement accuracy with excellent temperature characteristics and the like. Therefore, in general, the temperature characteristic is obtained by applying a predetermined temperature cycle to the measuring device using a thermostatic bath or the like in the manufacturing / shipping stage of the measuring device, and the measured value by the measuring device is obtained according to the obtained temperature characteristic. Corrections are made according to the temperature environment. Specifically, the temperature characteristic (coefficient indicating the temperature characteristic) obtained as described above is preset in a correction circuit incorporated in the measurement apparatus so that the measurement apparatus is temperature calibrated.

In particular, a measuring device main body provided with a pressure sensor and a pressure transducer connected to the measuring device main body via a capillary tube and provided in a measurement environment are provided, and the pressure applied to the pressure transducer is sealed in the capillary tube. In the so-called remote seal type pressure measuring device which is transmitted to the pressure sensor through the pressure propagation medium and measured, for example, the temperature characteristic of the pressure sensor and the temperature characteristic of the pressure transducer are obtained respectively. Temperature correction is performed on the entire measurement system (see, for example, Patent Document 1).
JP 2001-74558 A

  However, even if the temperature of the measuring device is calibrated at the time of shipping inspection at the factory as described above, the measuring device is not always used in the factory setting state at the installation site. For example, even if the measurement device is temperature calibrated assuming that the operation guarantee environment temperature is −10 ° C. to 60 ° C., if the actual measurement environment greatly exceeds the operation operation guarantee environment temperature, the measurement device is standard in advance. In some cases, a pressure transducer designed and manufactured in accordance with the measurement environment is used instead of the pressure transducer provided. In addition, a pressure transducer having a special specification may be used instead of the standard pressure transducer because chemical resistance or the like is required as the pressure transducer.

  Therefore, when the above-mentioned special pressure transducer is externally attached to a measuring device body equipped with a pressure sensor, it is impossible to effectively use the temperature characteristics measured at the corner, factory, etc. and used for temperature calibration. There is a problem to say. Incidentally, in order to calibrate the temperature of the measuring device with the special pressure transducer externally attached, it is necessary to return the measuring device to the factory, for example. It is also conceivable to calibrate the temperature of the measuring device at the installation site of the measuring device. However, in order to measure its temperature characteristics, for example, a thermostatic chamber and its temperature control device, a device that measures the output of the measurement device with high accuracy, a calculator that calculates the temperature correction formula from the measurement results, and a temperature correction formula are preset in the measurement device Therefore, it is necessary to provide a large-scale temperature calibration facility equipped with a device or the like at the installation site, which is not realistic.

The present invention has been made in consideration of such circumstances, and the purpose of the present invention is simple even at the installation site even if the measuring device has a special pressure transducer externally attached to the measuring device body equipped with the pressure sensor. Another object of the present invention is to provide a temperature characteristic correction method capable of correcting the temperature characteristic .

  In the present invention, even when a special pressure transducer is externally attached to a measuring device body equipped with a pressure sensor, the measurement environment itself in which the pressure transducer is provided is represented by various industrial processes. It is generally stable, the measuring device main body is provided in a normal temperature environment isolated from the measurement environment, and the basic temperature characteristics of the measuring device main body are temperature calibrated beforehand in a factory or the like. It is made paying attention to.

Therefore, in order to achieve the above-described object, the temperature characteristic correction method according to the present invention includes a pressure transducer provided in a measurement environment where the temperature is stable , and a normal temperature environment isolated from the measurement environment. and a measuring device main body and temperature sensors are provided, the pressure transducer transmits a fluid pressure generated according to the state of the measurement object to the differential pressure sensor, the measurement from the fluid pressure applied to the differential pressure sensor In the measurement device that measures the pressure state of the measurement object in the environment, as described in claim 1, when correcting the temperature characteristic,
<a> Temperature calibration is performed in advance on the input / output characteristics of the differential pressure sensor in the measuring device body,
<b> After that, the measurement device body with the pressure transducer externally attached is provided in a normal temperature environment isolated from the measurement environment in which the pressure transducer is installed,
<c> Maintaining the pressure and temperature of the measurement environment constant, applying a constant differential pressure to the differential pressure sensor, and applying a temperature cycle to the measurement device body due to a daily temperature difference in the installation environment of the measurement device body ,
<d> respectively determined at different temperatures and measured values by said differential pressure sensor of the temperature applied to the differential pressure sensor and its time,
<e> A temperature correction equation for the input / output characteristics of the pressure sensor calibrated in advance is obtained from the correlation between the temperature and the measured value, and the measured value by the differential pressure sensor is corrected.

Incidentally, with respect to the temperature applied to the pressure sensor and the measurement value by the pressure sensor at that time, in the state where a temperature cycle is applied to the measuring device main body, for example, at the highest temperature, at the lowest temperature, at the start of measurement, or at the measurement What is necessary is just to respectively obtain | require as data in standard temperature time, such as the time of completion | finish (Claim 2) .

  According to the temperature characteristic correction method for a measuring apparatus according to the present invention, a predetermined temperature cycle is applied to the measuring apparatus main body while maintaining the measurement environment provided with the pressure transducer in a constant state, for example, within the temperature cycle condition. Each temperature value at the maximum temperature, the minimum temperature, and the standard temperature and the measured value measured by the pressure sensor via the pressure transducer are obtained, and the pressure transducer is determined from the correlation between the temperature and the measured value. Since the temperature characteristics of the entire measurement system in the externally attached state can be obtained, a temperature correction formula for the measurement value (pressure sensor output) measured by the pressure sensor is obtained from this temperature characteristic, and the temperature correction is performed. It can be applied with high accuracy.

  In particular, a measurement environment provided with a pressure transducer, in particular, only a temperature cycle is applied to the measurement device main body while keeping the pressure converted by the pressure transducer constant. If the temperature difference is given as a daily temperature difference, the temperature characteristics of the entire measurement system can be easily and effectively corrected without using a large-scale temperature calibration facility provided in a factory or the like.

Hereinafter, a temperature characteristic correcting method and a measuring apparatus according to an embodiment of the present invention will be described with reference to the drawings, taking a remote seal type pressure measuring apparatus as an example.
FIG. 1 is a schematic configuration diagram of a main part of a remote seal type pressure measuring device (measuring device). The pressure measuring device includes a measuring device body 10 having a pressure sensor and a first externally attached to the measuring device 10. And a pressure transducer 11. The pressure sensor includes, for example, a semiconductor type differential pressure sensor 1 and a pair of diaphragms 13 and 16 for introducing pressure into the differential pressure sensor 1. The first pressure transducer 11 includes a diaphragm that receives a pressure Px of the measurement environment and generates a bend. A pressure propagation medium (silicone oil or the like) is provided between the diaphragm and one diaphragm 13 of the pressure sensor. Are connected to the measuring apparatus main body 10 by connecting them through a capillary tube 12 enclosing the pressure oil. Similarly, a second pressure transducer 14 for introducing a reference pressure (for example, atmospheric pressure) Po through a capillary tube 15 is connected to the other diaphragm 16 of the pressure sensor.

  Such a remote seal type pressure measuring device, as disclosed in Patent Document 1 described above, applies a pressure Px applied to a first pressure transducer 11 provided in a measurement environment to a diaphragm via a capillary tube 12. 13, the pressure is applied to the differential pressure sensor 1 through the diaphragm 13, and the pressure Po applied to the second pressure transducer 14 provided in the normal environment is applied to the differential pressure sensor 1 through the diaphragm 16. In addition, the pressure in the measurement environment in which the pressure transducer 11 is provided is measured as the difference (Px−Po) between these pressures Px and Po.

  In addition, the measurement device main body 10 to which the pressure transducer 11 is externally provided is provided with a temperature sensor 2 for measuring the temperature T of the installation environment of the measurement device 10 and is measured by the differential pressure sensor 1. A microprocessor 3 is provided that takes in values and executes a temperature correction process and the like described later. Further, the measuring device main body 10 includes a switch 4 for prompting the microprocessor 3 to perform measurement processing and temperature characteristic calculation processing, which will be described later, necessary for correcting the temperature characteristics, and the temperature T and the measurement at the temperature T. A memory 5 for storing the value PV in association with each other, an output circuit 6 for outputting the measurement data to the outside, and the like are provided.

In particular, when the microprocessor 3 is instructed to perform temperature calibration processing via the switch 4, for example, the temperature at which the temperature difference (daily temperature difference) in the installation environment of the measurement apparatus body 10 is applied to the measurement apparatus body 10. As a cycle, the temperature T detected by the temperature sensor 2 is monitored to detect the maximum temperature Tmax and the minimum temperature Tmin, and the standard temperature Tstd at the start and end of the temperature characteristic measurement process, respectively. Detected. The microprocessor 3 detects the outputs (measured values) PV _Tmax , PV _Tmin , and PV _Tstd of the differential pressure sensor 1 at the time when the respective temperatures Tmax, Tmin, and Tstd are detected. , Tstd are sequentially written in the memory 5.

Note that only the measured values at two different temperature points may be written in the memory 5, and conversely, the measured values at four or more temperature points are respectively obtained, and all of these measured values are stored in the memory 5. You may make it write in the memory 5. FIG .

The temperature characteristic correction process for the measurement apparatus having such a function is executed as follows, for example. That is, as shown in FIG. 2 showing a schematic processing procedure, first, the measurement environment provided with the first pressure transducer 11 is made constant [step S1]. In this embodiment, the measurement environment is made constant because the pressure of the measurement environment is a measurement target. For example, the measurement environment is opened, and thereby the atmospheric pressure is applied to each of the first and second pressure transducers 11 and 14. It is realized by adding only. In this state, the switch 4 is turned on to start temperature characteristic measurement processing. And add temperature cycles before Symbol measuring unit 10 by using the temperature difference between the date of the above-described Step S2].

Next, as described above, the temperature T detected by the temperature sensor 2 is set as described above under the condition that the measurement environment by the first pressure transducer 11 is made constant and at the same time the temperature cycle is applied to the measurement apparatus main body 10. The maximum temperature Tmax and the minimum temperature Tmin are detected while monitoring, and the outputs (measured values) PV _Tmax and PV _Tmin of the differential pressure sensor 1 at the time when these temperatures Tmax and Tmin are detected are obtained to obtain the above-mentioned temperatures. Write to the memory 5 in association with Tmax and Tmin. Further, at the start and end of the temperature characteristic measurement process, the standard temperature Tstd is detected, and the output (measured value) PV _Tstd of the differential pressure sensor 1 at that time is detected to obtain the standard temperature Tstd. Write in association with the memory 5 [step S3].

If the temperatures Tmax, Tmin, Tstd and the outputs (measured values) PV _Tmax , PV _Tmin , PV _Tstd of the differential pressure sensor 1 at these temperature points are sequentially written in the memory 5 as described above, Next, temperature characteristics of the measurement system are obtained based on these temperatures and measured values [Step S4]. Specifically, assuming that the output (measured value) PV of the differential pressure sensor 1 with respect to the change of the temperature T is approximated by a quadratic expression, the temperature characteristic is expressed as PV (T) = aT ² + bT + c
Represent as Then, the temperatures Tmax, Tmin, Tstd and the measured values PV _Tmax , PV _Tmin , PV _Tstd stored in the memory 5 are substituted into this approximate expression (temperature characteristics), and the coefficients a, b, c are calculated. [Step S4].

The temperature characteristics of the measurement system thus obtained are assumed to be corrected by temperature calibration processing at a factory or the like in a state where a standard pressure transducer is used in advance in the measurement characteristics of the measurement apparatus body 10. For example, it can be considered that this is due to the pressure transmission system in the externally attached first pressure transducer 11 and capillary tube 12.
That is, the temperature calibration process for the measurement device main body 10 in a factory or the like is performed by, for example, the output P of the differential pressure sensor 1 at a specific reference temperature Tref (for example, 25 ° C.) and the output data PV output from the measurement device main body 10. The input / output relationship α as indicated by a broken line in FIG. 3A is, for example, PV = m · P + n
Is approximated by the following linear expression. By adjusting the slope (span) indicated by the coefficient m and the offset (zero point) indicated by the coefficient n in this approximate expression, the relationship between the output P and the output data PV is indicated by a solid line in FIG. The input / output characteristics are corrected such that the input / output characteristics β are as described above. By obtaining the measurement characteristics (input / output characteristics) represented by the above approximate expression at each temperature point in a predetermined guaranteed operating temperature range, the correction function F (P, T) for the output (measurement value) of the differential pressure sensor 1 is obtained. ) Is obtained, and the output data PV of the measuring device 10 is corrected by PV = F (P, T) by correcting the output of the differential pressure sensor 1 under this correction function F (P, T).
Will be required.

On the other hand, as described above, the relationship between the temperature T and the output data PV obtained by adding the first pressure transducer 11 and applying a temperature cycle to the measuring apparatus main body 10 is, for example, FIG. As shown in PV (T) = aT ² + bT + c
As shown. The temperature characteristic PV (T) is a state where the environment (pressure and temperature in this example) applied to the pressure transducer 11 is constant, and as described above, the basic input / output characteristics of the measuring device body 10 are as follows. It is obtained in a calibrated state. Therefore, the change in the output data PV indicated as the temperature characteristic PV (T) described above is a measurement error component newly generated due to the first pressure transducer 11 and the capillary tube 12 that are externally attached. Can be understood as That is, the correction function F (P, T) for the measuring apparatus main body 10 is obtained on the assumption that a standard pressure transducer prepared in advance is attached. Moreover, the measurement environment in which the externally attached first pressure transducer 11 is provided is usually an industrial process whose temperature is controlled with high accuracy. Therefore, if the measurement environment is kept constant, the temperature characteristic PV (T), which is an output change generated when a temperature cycle is applied to the measurement apparatus main body 10, is different from the specification of the pressure transducer and the capillary tube. It can be considered that this is due to a change in the pressure transmission characteristic via the pressure.

Therefore, in order to cancel this change (measurement error), the output data PV obtained from the measuring apparatus body 10 is obtained by PV = F (P, T) −PV (T)
= F (P, T)-[aT ² + bT + c]
If the correction formula is obtained [Step S5] and the output P of the differential pressure sensor 1 is corrected according to the temperature correction formula, measurement data PV without measurement error, that is, temperature-corrected measurement data PV can be obtained. [Step S6].

  Thus, according to the temperature characteristic correction method for correcting the temperature characteristic of the measurement system to which the first pressure transducer 11 is externally attached as described above, the temperature correction formula is easily obtained at the installation site of the measurement device. It becomes possible to correct the temperature of the measurement data. In other words, the temperature calibration can be performed at the installation site of the measurement device without returning the entire measurement device with the first pressure transducer 11 attached to the factory or the like. In addition, if a temperature cycle is added using the daily temperature difference in the installation environment of the measurement apparatus main body 10, a temperature correction formula can be obtained at least in the use environment temperature range of the measurement apparatus main body 10. Therefore, for example, even if a temperature calibration processing time of one day or more is required, it is possible to easily perform temperature calibration with a practically sufficient accuracy at the installation site of the measuring device, and its practical advantage is very large. . Moreover, even if the measurement characteristics of the measuring device change due to seasonal changes or changes over time, the temperature characteristics can be easily recorrected (calibrated) at the installation site as necessary. This also has a great practical advantage in this respect.

  Furthermore, since the measuring device itself includes the temperature sensor 2 and the memory 5 and the temperature correction function set in the microprocessor 3 is used to correct the temperature of its own measurement characteristics, it is not necessary to prepare a large-scale temperature calibration facility. There are also advantages. Therefore, when using the special 1st pressure transducer 11 according to a measurement specification, when using several kinds of pressure transducers 11 selectively, a big effect is produced.

  The present invention is not limited to the embodiment described above. Here, the pressure measuring device (pressure sensor) has been described as an example. However, a remote seal type flow meter that generates pressure according to the flow rate and transmits the pressure to the measuring device main body 10 or pressure according to the liquid level is generated. Thus, the present invention can be similarly applied to a remote seal type liquid level meter transmitted to the measuring apparatus main body 10. In the embodiment, the temperature correction formula is approximated by a quadratic formula, but it is of course possible to approximate it using another function.

  Here, the measurement environment in which the first pressure transducer 11 is provided is opened to the atmosphere and the calibration process is executed. However, if the pressure of the measurement environment is constant and the pressure is known, It is also possible to execute the calibration process while maintaining the environmental conditions. Further, if the differential pressure sensor 1 itself has a large diaphragm, the fluid pressure converted by the pressure transducers 11 and 16 is directly applied to the differential pressure sensor 1 via the capillary tubes 12 and 15. You may make it add. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

The figure for demonstrating the schematic structure of the measuring device which concerns on one Embodiment of this invention, and the temperature characteristic correction method using this measuring device. The figure which shows the rough process sequence of the temperature characteristic correction method which concerns on this invention. The figure for demonstrating the input-output characteristic in a pressure measuring device, its correction principle, and a temperature correction characteristic.

Explanation of symbols

1 Differential pressure sensor (pressure sensor)
2 Temperature sensor 3 Microprocessor 5 Memory 10 Measuring device body 11 First pressure transducer (pressure transducer)
12,15 Capillary tube 13,14 Diaphragm 16 Second pressure transducer

Claims (2)

A pressure transducer provided in a measurement environment in which the temperature is stable, and a measurement device body provided in a normal temperature environment isolated from the measurement environment and provided with a differential pressure sensor and a temperature sensor . There transmits the fluid pressure generated in accordance with the state of the measurement object to the differential pressure sensor, a temperature characteristic correction method for measuring device for measuring the pressure state of the measurement object in the measurement environment from the fluid pressure applied to the differential pressure sensor In
The input / output characteristics of the differential pressure sensor in the measuring device main body are temperature calibrated in advance,
After that, the measuring device main body with the pressure transducer attached externally is provided in a normal temperature environment isolated from the measurement environment in which the pressure transducer is installed,
Applying a constant differential pressure to the differential pressure sensor while keeping the pressure and temperature of the measurement environment constant, and giving a temperature cycle to the measurement device body due to a daily temperature difference in the installation environment of the measurement device body ,
Respectively obtained at different temperatures from each other and a measurement value measured by the differential pressure sensor at that time and the applied differential pressure sensor temperature,
A temperature characteristic correction method comprising: obtaining a temperature correction formula for input / output characteristics of the pressure sensor calibrated in advance from the correlation between the temperature and the measured value, and correcting the measured value by the differential pressure sensor. The applied differential pressure sensor temperature and the measured value by the differential pressure sensor at this time, at the highest temperature, at the minimum temperature, and the temperature characteristics of claim 1 at standard temperature are those obtained respectively correcting method .

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