JPH06331426A - Instrument difference correction device - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides a flow meter instrument difference test device configured to perform more precise instrument difference correction and to enable highly accurate flow rate measurement in a wide range from a low flow rate region to a high flow rate region. The purpose is to do. [Constitution] The control circuit 17 has a flow rate measuring means and a device difference correcting means, calculates the flow rate based on the flow rate signal output from the magnetic sensor 14, and uses the temperature signal from the temperature sensor 16 to calculate the flow rate. The volume change and the viscosity are obtained, and the instrumental error is corrected based on the volume change and the integrated display 18 displays the measured flow rate. The control circuit 17 includes the measurement unit calculator 1
9, an instantaneous flow rate calculation unit 20, a measured fluid viscosity calculation unit 21, a viscosity correction calculation unit 22, a rotor expansion correction calculation unit 23, a fluid expansion correction calculation unit 24, a device difference correction calculation unit 25, and a data storage unit 26. .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device difference correction device, and more particularly to a device difference correction device configured to accurately correct a device error of a flow meter to improve measurement accuracy.

[0002]

2. Description of the Related Art For example, one of the flowmeters has a pair of rotors formed in the shape of an elliptical gear or an eyebrow that delivers a fixed amount per one rotation, and detects the number of rotations according to the flow rate of this rotor. There is a positive displacement flow meter that measures the flow rate. This type of volumetric flowmeter has high measurement accuracy and generally has an instrumental error of ± 0.5%.
Each part is machined to a certain extent. Furthermore, in a positive displacement flow meter, it is possible to measure the flow rate while suppressing the instrumental error to about ± 0.2%, but in that case, there is a tendency to have a negative instrumental error in the low flow rate region, so the low flow rate region Cannot be measured and the measurable range of flow rate becomes narrow.

Therefore, conventionally, the flow rate measurement value measured by the positive displacement flow meter is corrected by the instrumental error correction device. That is, conventionally, in a factory, a just-assembled flow meter is subjected to a device difference test, and a flow rate existing in the flow meter is flowed to measure the actual device difference of the flow meter at several flow rates. Then, after the flow meter was attached to the pipeline at the site, the flow rate measurement value of the fluid to be measured, which was measured by the flow meter, was corrected by the device difference correction device based on the device difference measured in the factory in advance. As a result, the flow meter was able to measure the flow rate with high accuracy over a wide range.

Further, conventionally, a flow rate measurement is performed by providing a temperature correction device different from the instrumental error correction device, by which the temperature of the fluid to be measured is detected and the volume change due to the temperature of the fluid to be measured is corrected. The accuracy was improved.

[0005]

However, the instrumental error of the flow meter changes depending on the viscosity of the fluid to be measured, the temperature expansion of the rotor, and the flow rate (rotational speed of the rotor). In particular, the effect of viscosity is shown in FIG. As shown, the low-viscosity instrumental difference (L) has a larger drop in the low flow rate region than the high-viscosity instrumental difference (H). That is, the variation amount ΔE of the instrumental error due to the viscosity is not constant in the entire flow rate range and tends to increase in the low flow rate range.

Further, the conventional instrumental difference correction device is adapted to correct the instrumental error curve at a constant viscosity to a straight line of ± 0%. Further, regarding the temperature correction, the volume change in which the fluid expands and contracts due to the temperature change is corrected. On the other hand, as described above, the viscosity of the fluid also changes with temperature changes, and the instrumental difference of the flowmeter is affected by the viscosity. Therefore, the instrumental error is about ± 0.1% or less at any flow rate from the low flow rate region to the high flow rate region. It was difficult to measure with the above high accuracy, and it was difficult to expand the flow rate measurement range.

Therefore, an object of the present invention is to provide a device difference correction device that solves the above problems.

[0008]

According to the present invention, there is provided temperature detecting means for detecting the temperature of a fluid to be measured, and viscosity calculating means for calculating the viscosity of the fluid to be measured based on the temperature detected by the temperature detecting means. And volume calculation means for calculating the volume of the fluid to be measured at the reference temperature based on the temperature detected by the temperature detection means, and the upper and lower limits of the viscosity range converted by the specified temperature range of the flowmeter are exceeded. High viscosity fluid
Data storage means for storing the instrumental error when measuring a low-viscosity fluid, and viscosity correction based on the current viscosity of the fluid to be measured from the viscosity calculating means and the instrumental error and viscosity stored in the data storage means. A viscosity correction calculation means for calculating a value, and a device difference correction means for performing a device error correction of a flow rate measurement value based on a volume change of the fluid to be measured from the volume calculation means and a viscosity correction value from the viscosity correction calculation means. , And consists of.

[0009]

[Function] The correction value due to the change in the viscosity of the fluid to be measured or the temperature expansion is obtained from the temperature change of the fluid to be measured, and based on these, the measurable range can be widened and the measurement accuracy can be increased by correcting the flow rate measurement value by instrumental error. It is possible to achieve higher precision.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 to 3 show a volumetric flowmeter and an embodiment of the instrument difference correction device according to the present invention.

In both figures, a positive displacement flow meter 1 is provided with a pair of rotors 4 and 5 in a measuring chamber 3 of a casing 2. The casing 2 has an inflow path 6 located upstream of the weighing chamber 3 and an outflow path 7 located downstream of the weighing chamber 3. The inflow path 6 and the outflow path 7 open to the measuring chamber 3 from the upper side and the downstream side, respectively, and communicate with each other through the measuring chamber 3.

The rotors 4 and 5 are formed of elliptical gears and are supported by the rotating shafts 8 and 9 in a state of being meshed with each other. On the upper surface of one rotor 4, magnets 10 and 11 for rotation detection are
They are buried at 80 ° intervals.

When the fluid to be measured is supplied from the inflow path 6 into the measuring chamber 3, the pair of rotors 4 and 5 rotate about the rotating shafts 8 and 9 due to the pressure of the fluid. The fluid from the inflow passage 6 is introduced into the space 13 between the rotors 4 and 5 and the inner wall 12 of the measuring chamber 3 as the rotors 4 and 5 rotate, and the fluid corresponding to the volume of the space 13 flows to the outflow passage 7. Is discharged.

In this way, the rotors 4 and 5 rotate at a rotation speed proportional to the flow rate, and the rotation is detected by the magnetic sensor 14 for detecting rotation. The magnetic sensor 14 is embedded in a lid 15 that closes the weighing chamber 3 of the casing 2 so as to be located above a path through which the magnets 10 and 11 embedded in the upper surface of the rotor 4 pass.

A rod-shaped temperature sensor 16 for detecting the temperature of the fluid to be measured is inserted in the inflow passage 6 of the casing 2. The temperature signal detected by the temperature sensor 16 and the flow rate signal output from the magnetic sensor 14 are supplied to the control circuit 17. The mounting position of the temperature sensor 16 may be such that the temperature sensor 16 is inserted into the casing 2 as in the present embodiment, or the temperature sensor 16 may be installed in a conduit connected to the inflow path 6 or the outflow path 7 of the casing 2. It may be provided.

The control circuit 17 integrates the flow rate pulses output from the magnetic sensor 14 to calculate a flow rate measurement value, and the flow rate measurement value calculated by the flow rate measurement means 17A is 0.1. And an instrumental-difference correcting means 17B as an instrumental-difference correcting device for performing correction so that
The flow rate is calculated based on the flow rate signal output from the magnetic sensor 14, and the instrumental difference due to viscosity and temperature expansion is corrected based on the temperature signal from the temperature sensor 16 and is corrected by the integrating display 18 as described later. Display the flow rate.

Specifically, the control circuit 17 has a configuration as shown in FIG. 3, and has a measurement unit calculating section 19, an instantaneous flow rate calculating section 20, a measured fluid viscosity calculating section 21, and a viscosity correction calculating section 2.
2, rotor expansion correction calculation unit 23, fluid expansion correction calculation unit 2
4, an instrumental error correction calculation unit 25, and a data storage unit 26.

The data storage unit 26 is preliminarily input with each data necessary for the instrumental error correction and functions as a memory. The data storage unit 26 stores, for example, the viscosity of the high-viscosity fluid in the pre-factory test (μ ₁ ), the viscosity of the low-viscosity fluid in the pre-factory test (μ ₂ ), and the instrumental error of the high-viscosity fluid in the pre-factory test (E ₁ ), instrumental error (E ₂ ) of low-viscosity fluid before factory shipment test, test fluid temperature (t ′) at factory shipment test, linear expansion coefficient (β) of rotors 4 and 5, volume change Each data such as the rate (V) is stored.

The measurement unit calculation unit 19 includes the magnetic sensor 1
The detection signal output from 4 is converted into a flow rate pulse signal in integer units. In addition, the instantaneous flow rate calculation unit 20 integrates the flow rate pulse signals output from the measurement unit calculation unit 19 to calculate the instantaneous flow rate per unit time.

The measured fluid viscosity calculation unit 21 includes a temperature sensor 1
The viscosity of the fluid to be measured is calculated based on the temperature signal from 6. The viscosity correction calculation unit 22 also calculates the instantaneous flow rate output from the instantaneous flow rate calculation unit 20, the viscosity output from the measured fluid viscosity calculation unit 21, and the viscosity (μ of the high viscosity fluid read from the data storage unit 26. ₁ ), the viscosity of the low viscosity fluid (μ ₂ ), the instrumental error of the high viscosity fluid (E ₁ ) and the instrumental error of the low viscosity fluid (E ₂ ) are used to calculate the flow rate correction value based on the viscosity of the fluid to be measured.

The rotor expansion correction calculation unit 23 includes the instantaneous flow rate output from the instantaneous flow rate calculation unit 20 and the temperature sensor 16.
, The instrumental error E ′ (= E ₁ , E ₂ ) read from the data storage unit 26, the test fluid temperature (t ′),
A flow rate correction value due to the expansion of the rotors 4 and 5 is calculated from the linear expansion coefficient (β) of the rotors 4 and 5.

The fluid expansion correction calculator 24 is provided with the temperature sensor 1
A correction value due to expansion of the fluid to be measured is calculated from the temperature signal from 6 and the volume change rate (V) read from the data storage unit 26. Then, the instrument difference correction calculation unit 25, the flow rate correction value from the viscosity correction calculation unit 22, the flow rate correction value from the rotor expansion correction calculation unit 23, the flow rate correction value from the fluid expansion correction calculation unit 24, The integrated value of the flow rate pulse from the measurement unit calculation unit 19 is corrected based on the instrument error, and the corrected flow rate value is displayed on the integration display 18, the pulse output unit 27, and the analog output unit 2.
Output to 8.

In this embodiment, the fluid to be measured is ethyl alcohol as an example. The temperature of this ethyl alcohol shall change in the range of 0 to 40 ° C. The viscosity of the fluid to be measured is obtained as a function of temperature. For ethyl alcohol, 1.78 cP at 0 ° C and 0.
It becomes 825 cP.

Therefore, the difference between the high-viscosity fluid and the low-viscosity fluid outside this viscosity range will be determined in advance. In that case, for example, the instrumental difference is measured for gasoline of about 0.5 cP and light oil of about 2 cP. The fluid temperature and viscosity at this time must be accurately measured.

Therefore, the data storage unit 26 stores the relationship between the temperature and the viscosity of ethyl alcohol and the instrumental difference between gasoline and light oil. The viscosity is obtained from the temperature of the ethyl alcohol input from the temperature sensor 16, and the instrumental error at this time is obtained by the interpolation method according to the following equation to correct the flow rate measurement value. In E = viscosity of _{{E 2 + (E 1 -E} 2) · μ 1 (μ-μ 2)} / μ (μ 1 -μ 2) ... (1) where, E is ethyl alcohol (object to be measured on the fluid) Instrument error (%), E ₁ is instrumental error (%) of light oil (high viscosity fluid), E ₂ is instrumental error (%) of gasoline (low viscosity fluid),
μ is the viscosity cP of ethyl alcohol (fluid to be measured) calculated from the measured temperature, μ ₁ is the viscosity cP of light oil (high viscosity fluid), and μ ₂ is the viscosity cP of gasoline (low viscosity fluid).

By the calculation of the above equation (1), the instrumental error at a certain viscosity of the fluid to be measured can be calculated based on the instrumental error of the fluid having a higher viscosity and the fluid having a lower viscosity than that of the fluid to be measured. It is possible to calculate the instrumental error of the fluid to be measured in a wide range from to high flow rate range. Therefore, as shown in FIG. 4, the correction due to the change in the flow rate can be performed at any flow rate in the entire flow rate range by approximating a straight line between two measured flow rates which are two measurement points.

Further, when the temperature of the fluid to be measured changes, the rotors 4 and 5 expand or contract, and the discharge amount of the rotors 4 and 5 per rotation changes, so that the instrumental error changes. Therefore, the instrumental error measured in advance, the fluid temperature at this time, and the linear expansion coefficient of the rotors 4 and 5 are stored in the data storage unit 26, and the measured fluid temperature input from the temperature sensor 16 is used. By obtaining the instrumental error during measurement from the following equation, the measurement value input from the measurement unit conversion unit 19 is corrected, and highly accurate measurement becomes possible. _{E = E 1 -3β (t 1} -t 2) ... (2) where, E is instrumental error in the measured fluid measurement (%), E ₁ is instrumental error instrumental error of the test (%), t ₁ is Fluid temperature (° C) at instrument difference test, t ₂ is temperature of measured fluid (° C), β is linear expansion coefficient of rotor (% / ° C) The volume change due to the temperature change of the fluid and the instrumental difference due to the expansion and contraction of the rotors 4 and 5 can be calculated.

The processing executed by the control circuit 17 will be described with reference to FIG. The process shown in FIG. 5 is repeatedly executed at a predetermined time interval (for example, every 0.05 msec), and the control circuit 17 sequentially performs instrumental error correction according to the temperature of the fluid to be measured, which changes every moment. There is.

In FIG. 5, in step S1 (hereinafter, "step" is omitted), the pulse signal output from the magnetic sensor 14, that is, the rotation detection signals of the rotors 4 and 5 that rotate in proportion to the flow rate is an integer. Is converted to the unit of measurement (for example, an integer corresponding to liter).

In the next S2, the instantaneous flow rate is converted from the numerical value converted in S1.

Next, the instrumental difference which has been tested before shipment from the factory at the instantaneous flow rate stored in the data storage section 26 in advance,
The viscosity of the test fluid at the time of the test (in this embodiment, the viscosities of light oil and gasoline μ ₁ , μ ₂ ) is read (S3). The test fluid must be a fluid having two types of physical properties, high viscosity and low viscosity with respect to the viscosity (μ) of ethyl alcohol, which is the fluid to be measured.

In step S4, the viscosity of the fluid to be measured is calculated based on the temperature of the fluid to be measured input from the temperature sensor 16. The correlation between the temperature and the viscosity is a physical property unique to the fluid to be measured and is stored in the data storage unit 26 in advance.

Subsequently, the data obtained in the above S3 and S4, that is, the viscosity (μ ₁ , μ ₂ ) of the test fluid and the viscosity (μ) of the fluid to be measured are substituted into the above equation (1) to obtain the current value. The instrumental difference E in viscosity and flow rate is obtained (S5).

Further, the instantaneous flow rate, the instrumental error due to the test before factory shipment, the temperature and the linear expansion coefficient β of the rotors 4 and 5 are read (S6). Then, the input temperature from the temperature sensor 16 and the data read in the above S6 are used to obtain the equation (2) described above.
By substituting into (4) to obtain the instrumental difference due to the temperature expansion of the rotors 4 and 5 (S7).

Then, the volume change rate V of the fluid to be measured, which is stored in advance, is read (S8). The volume change rate V is a physical property peculiar to the fluid to be measured, and is defined by the JIS standard in the case of petroleum, for example.

In the next step S9, the volume at the reference temperature is obtained from the input temperature from the temperature sensor and the volume change rate V, and the instrumental difference due to the temperature expansion of the fluid to be measured is calculated. Then, the flow rate measurement value converted into the integer measurement unit in S1 described above is calculated as the current viscosity and the instrumental difference E in the flow rate calculated in S5, and S
It is corrected by the instrumental difference due to the temperature expansion of the rotors 4 and 5 calculated in 7 and the instrumental difference due to the temperature expansion of the fluid to be measured (S1).
0).

In the next S11, the measured value corrected in S10 is output to the integration display 18, the pulse output section 27, and the analog output section 28.

As described above, the control circuit 17 sequentially corrects the instrumental error according to the temperature of the fluid to be measured, which changes every moment.
Since the flow rate measurement value is corrected by the instrumental difference E in the current viscosity and the flow rate, the instrumental difference due to the temperature expansion of the rotors 4 and 5, and the instrumental difference due to the temperature expansion of the fluid to be measured, a low flow rate that cannot be conventionally measured. It is possible to precisely correct not only the instrumental error in the region but also the instrumental error in the high flow rate region. Therefore, the temperature correction device used conventionally corrects the volume change of the fluid to be measured due to the temperature change.
By combining and using the instrumental error correction of the equation (2), highly accurate flow rate measurement with an instrumental error of about 0.1% is possible in a wide range from the low flow rate region to the high flow rate region.

In the above embodiment, the volumetric flowmeter in which the rotor made of an elliptical gear is incorporated is taken as an example, but the present invention is not limited to this, and the volumetric flowmeter in which, for example, a roots type rotor is incorporated. Of course, the instrumental difference may be corrected, or the invention can be applied to other types of flow meters.

Further, in the above embodiment, the control circuit 17 is configured to include the instrumental difference correction means, but the invention is not limited to this. For example, an instrumental error correction device separate from the control circuit 17 for measuring the flow rate may be provided. Of course, it may be provided.

[0041]

As described above, according to the instrumental difference correction device of the present invention, instrumental error compensation can be sequentially performed according to the temperature of the fluid to be measured, which is constantly changing, and at the present viscosity and flow rate. Since the flow rate measurement value is corrected by the instrumental error and the instrumental error due to the temperature expansion, not only the instrumental error in the low flow rate region that could not be conventionally measured but also the instrumental error in the high flow rate region can be precisely corrected. Therefore, highly accurate flow rate measurement can be performed in a wide range from low flow rate range to high flow rate range, and the measurable range can be expanded by correcting the flow rate measurement value according to the temperature change of the fluid to be measured. It has features such as higher measurement accuracy.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a positive displacement flow meter to which an embodiment of the instrument difference correction device according to the present invention is applied.

FIG. 2 is a cross-sectional view of a positive displacement flow meter.

FIG. 3 is a block diagram showing a configuration of a control circuit.

FIG. 4 is a diagram showing a relationship between a device difference calculated by a device difference correction process executed by a control circuit and a flow rate.

FIG. 5 is a flowchart for explaining instrumental difference correction processing executed by a control circuit.

FIG. 6 is a diagram showing a relationship between a device difference and a flow rate for explaining a device difference change by a conventional device difference correction device.

[Explanation of symbols]

 1 Volumetric Flowmeter 2 Casing 4,5 Rotor 14 Magnetic Sensor 16 Temperature Sensor 17 Control Circuit 19 Measurement Unit Converter 20 Instantaneous Flow Rate Calculator 21 Measured Fluid Viscosity Calculator 22 Viscosity Correction Calculator 23 Rotor Expansion Correction Calculator 24 Fluid Expansion Correction Calculation Unit 25 Instrumental Difference Correction Calculation Unit 26 Data Storage Unit

Claims (1)

[Claims] 1. A temperature detecting means for detecting the temperature of a fluid to be measured, a viscosity calculating means for calculating the viscosity of the fluid to be measured based on the temperature detected by the temperature detecting means, and a temperature detecting means for detecting the viscosity. A volume calculation means for calculating the volume of the fluid to be measured at a reference temperature based on the measured temperature, and a high-viscosity fluid / low-viscosity fluid exceeding the upper and lower limits of the viscosity range converted by the specification temperature range of the flowmeter. A data storage unit that stores the instrumental error at the time of measurement, and a viscosity correction value is calculated based on the current viscosity of the fluid to be measured from the viscosity operation unit and the instrumental error and viscosity stored in the data storage unit. A viscosity correction calculation means, and a device difference correction means for performing a device difference correction of the flow rate measurement value by the volume change of the fluid to be measured from the volume calculation means and the viscosity correction value from the viscosity correction calculation means. An instrumental error correction device characterized by the above.