JP2810895B2 - Compensation method for volumetric flow meter - Google Patents

Description

Description: TECHNICAL FIELD [0001] The present invention relates to a method for correcting an instrumental difference in a positive displacement flowmeter.

[Prior Art] Fluids generally used in plants often have a low viscosity index, a large change in viscosity with temperature, and errors are inevitable even when a highly accurate instrument is used. Although a high degree of technology is required to perform temperature control precisely, even a slight change in temperature is accompanied by a change in viscosity, which causes an error in accuracy.
Positive displacement flowmeters are known for their precision in metering, especially dual-rotor gear flow meters are said to have high reliability.However, due to the mechanical structure, the clearance in the measuring chamber is reduced due to the mechanical wear of the rotating parts. The weighing function is reduced by the increase. The rotating bodies and the both end faces, which perform the measuring function of the twin rotor type flow meter, are provided with a small gap between them and the wall surface of the measuring chamber, and are rotatably housed. One end face of the rotator rotates while being in contact with the inner wall surface of the casing, thereby increasing rotation resistance, and further increasing the gap between the other end surface inside the measurement wall surface and increasing the amount of leakage, resulting in a large instrumental difference value. Become. Therefore, it is preferable that the gap between the both end faces of the rotating body is rotated while maintaining the same constant value, and it is important that the rotating body is accurately maintained at the center position in order to minimize a change in instrumental performance. . In the conventional horizontal axis type, since the rotating body can move freely in the horizontal direction, the clearance value at both ends is not kept constant with the flow of fluid, so the moment of inertia due to the rotation speed of the non-circular rotating body is With the change, the amount leaking from the minute gap, that is, the instrumental difference value changes, and there is a disadvantage that an accurate flow rate display cannot be obtained. The electronic instrument difference correction microcomputer demonstrates extremely precise arithmetic functions,
If the instrument difference performance changes due to wear deformation of the measuring element of the instrument main body and fluctuation of the rotational position, such correction becomes meaningless.

Positive displacement flowmeters that have excellent performance as a measuring function for electrically insulating fluids have a mechanical structure as described above, and as the operating time elapses, the performance decreases due to wear deformation of the rotating element that performs the measuring function. It is essential to have a configuration with excellent durability.However, it is possible to maintain the measurement accuracy by accurately maintaining the position of the rotating element in the measuring chamber. The performance of the flow meter can be further enhanced. That is, since the internal leakage of the positive displacement flowmeter does not change with the elapse of the operation time, and if a constant value is maintained, the instrumental error characteristic is constant, the volume expansion of the fluid correlated with the temperature of the fluid. In addition, it is possible to make the error close to zero by correcting the viscosity and the instrument difference characteristic inherent to the instrument.

However, the flow rate cannot be corrected and converted correctly unless the value that changes with the temperature change of the instrumental error characteristic of the instrument body is corrected, and the rotation of the rotating element installed in the weighing chamber with a small clear rinse is not possible. If it is possible to rotate at the correct center position without causing positional deviation, it is difficult to obtain a measurement value in which such an error is close to zero. In order to keep this rotating body at the center position in the measuring chamber, a fixed shaft type uses a method of maintaining side clearance of the rotating body via a thrust ring, or a shaft integrated type that integrally forms the rotating body and the shaft. Thus, a complicated configuration for adjusting the shaft end by a fine adjustment screw mechanism was required.

[Problems to be Solved by the Invention] An object of the present invention is to provide a method for measuring a change in viscosity and a volume due to a temperature change of a fluid to be measured between an indicated flow rate indicated by a rotational movement of a measuring element of a flow meter and an actually measured value. An object of the present invention is to provide an accurate flow rate instruction by eliminating an error caused by expansion and an instrumental difference characteristic of an instrument body.

In order to give an accurate flow rate instruction, it is necessary to eliminate the effect on volumetric expansion due to the change in the temperature of the fluid to be measured and the effect on the instrumental difference due to the correlation between temperature and viscosity. Different instrument-specific corrections are required depending on the temperature of the amount leaking from the gap between the mutual engagement part and the casing, and these error corrections of the fluid to be measured due to the temperature change of the process are accompanied by expansion and contraction of the instrument-specific components due to the temperature. A precise flow rate is obtained by correcting the instrumental error value caused by the above.

The various conditions of the flow state of the fluid to be measured in the process in the plant are correlated with the temperature, and it is difficult to directly measure these change factors. However, these changes are grasped in real time to obtain the reduced flow rate. Since it is possible to precisely measure the changing temperature instantaneously, it is possible to obtain a high-resolution correction value by the precise measurement of the temperature, and to obtain a more accurate flow rate instruction. Since such an electronic correction device having a high resolution gives an extremely precise correction value, it is essential to combine it with a flowmeter main body having a stable metering function, thereby achieving error measurement.

As shown in FIG. 1, there is a certain relationship with the instrumental difference-rotor rotation speed curve (B) measured with respect to the theoretical line (A).
That is, the instrumental difference value (E) that increases in the low-speed rotation range and the high-speed rotation range of the rotor is added to the reduced flow rate calculated by the rotation of the rotating body so as to become zero, and the instrumental difference due to the individual difference is corrected. Addition by the device indicates the correct flow rate. Next, even in the case of the same specification, since the specific gravity and the viscosity of the fluid to be measured change with a slight temperature change, a correction value must be added to the flow rate calculated and displayed based on the rotation speed of the rotating body. Second
The line (A) in the figure shows the relationship between the instrumental difference and the flow rate, and the curves (C) and (D) show the actual difference between the instrumental difference and the flow rate curve. Shows the case of high temperature.
Thus, the experimental results show that the deviations of the peaks X1 and X2 of the curves (C) and (D) with respect to the temperature change and the low-speed rotation ranges Y1 and Y
2, and the divergence from the high-speed rotation ranges Z1 and Z2 are not proportional, and each show a specific change amount. Further, the instrument difference-flow rate curve wets a specific shape depending on the liquid type of the fluid to be measured, and the value increases with a low-viscosity fluid. Thus, when the measurement reference temperature is set to 20 ° C., if the curve (C) or the curve (D) is corrected with a condition correction value with a condition correction value for eliminating the influence of the viscosity, the instrumental difference-flow rate curve (B) at 20 ° C. ) Is drawn.

As a result, the error is removed by the correction method shown in FIG. 1 and a theoretical curve (A) is obtained, and an accurate flow rate is calculated.
Therefore, a correct flow rate can be obtained by correcting the flow rate, that is, the instrumental difference value corresponding to the rotor rotation speed, in accordance with the instrumental error and the characteristic curve determined by the specifications of the instrument body. FIG. 3 shows a QE curve as shown in the figure when the fluid has a low viscosity and when the clearance between the rotors of the flow meter is large, since the amount of internal leakage is large.

FIG. 4 shows an instrumental difference characteristic curve in a case where the distance between the rotating bodies and the gap between the rotating body and the measuring chamber are made small. The instrumental difference becomes small, but there is a disadvantage that foreign matter is more likely to be caught and stopped by a small gap. is there.

However, since a gap is provided for the rotating body to rotate, the linearity of the instrumental error curve is inferior, but free rotation is given and the metering function is exhibited, so that internal leakage is inevitable. By adding a means for correcting the internal leakage, it is possible to increase the weighing accuracy.

The rotating body rotates at the center of the shaft by rotating the rotating body while keeping the clearances at both ends equally at the both ends during rotation by the configuration in which the rotating body is supported at both ends with the short axis of the shape gradually reduced to the shaft diameter of the end face. On the other hand, the above-mentioned problem can be solved by providing a function of centripetal rotation, and an accurate flow rate can be displayed while maintaining a constant weighing function when the rotating body rotates. However, if such a QE curve is stable without change even after long-time operation, an accurate flow rate display can be performed by the electronic correction device.

There is a relationship between the rotor speed-instrument and the temperature change-instrument in relation to the ideal instrument error-flow rate curve, which are indicated as errors, and are corrected with a specific ratio. To display accurate values.

As a result, it can be used for ultra-precision flow measurement and process control, especially in the field of precision chemical industry. By adding an electronic correction mechanism to a positive displacement flow meter, extremely high accuracy of ± 0.1% or less can be achieved. can get.

[Means for Solving the Problems] The means of the present invention obtains an error correction value of a volume change and a viscosity change of a fluid, which is an error factor of a positive displacement flow meter, and an error correction value of a characteristic change peculiar to an instrument in real time. The purpose of this method is to convert to a reference value with a correction value by means of high resolution through viscosity measurement using a temperature sensor, and to perform correction, especially changes in fluid viscosity and specific gravity due to minute temperature changes during the process, and temperature changes in the meter body. Correction method to display the accurate flow rate with an electronic correction device equipped with a ROM that inputs the data of the specific instrumental change due to the change, and to support the rotating body of the twin-rotor positive displacement flowmeter with a tapered shaft. With the above-mentioned electronic correction method, it is possible to obtain an ultra-high-precision weighing function by using the electronic correction method. And there.

A microcomputer that measures the period of the pulse indicating the flow rate obtained at each rotation of the rotating body, reads one pulse indicating the flow rate corresponding to the period from the data of the period previously stored in the ROM and the corrected flow rate, and converts it. use.
A rotation sensor for outputting a pulse signal indicating the flow rate for each rotation of the rotor, a temperature sensor for measuring the temperature of the fluid, and a microcomputer are provided. The cycle of the flow rate pulse signal is measured, and a temperature correction coefficient is read out in real time from the specific gravity of each temperature stored in the ROM in advance and the indicated temperature correction data to correct the flow rate of each pulse. Further, the corrected flow rate is obtained from the correction coefficient data indicating the viscosity for each temperature stored in the ROM in advance, and a correction value is obtained from a correction coefficient obtained from a correlation between the viscosity and the instrumental difference with respect to the temperature. Modify by adding a correction value.

[Embodiment of the Invention] An explanation will be given with reference to an example shown in FIGS. Reference numeral 1 denotes a twin rotor type positive displacement flowmeter. Reference numeral 5 denotes a temperature sensor provided in the measuring chamber or in a connected pipe.

The signal of the temperature sensor 5 is connected to the control device 100 via the A / D converter 101 by wiring. 6 shows the case of a viscosity sensor. A signal transmitted from an arithmetic unit in the control device 100 activates the display 103.

FIG. 6 is an explanatory diagram of an internal electric circuit of the control device 100 and connected devices.

The pulse signal from the rotation detection sensor 7 for transmitting the rotation of the rotating body of the flow meter is input to the input interface 108 and input to the terminal of the central control unit CPU (I) 112.

The central control unit CPU (I) 112 receives this signal,
Input / output interface 10
Confirm by checking steps 8 and 109, and proceed to integration.
The time between this pulse input and the previous pulse input, that is, the pulse interval, is used to determine the flow rate per pulse according to the pulse interval.
(I) The temperature is read from the correction data of the instrumental difference stored in advance in 111, and the temperature obtained by converting it into a digital value by the A / D converter 101 is read, and the volume is obtained from the temperature-specific gravity data by the ROM (I) 111. The electric signal converted into the flow rate at the corrected reference temperature is further input to the input / output interface 109 and simultaneously to the CPU (II) 115. ROM114 from read temperature signal guided by temperature sensor bypass
Is converted into the corrected flow rate at the reference temperature from the condition correction value obtained from the correlation of the internal leakage amount of the temperature-viscosity change, which is written in advance, and the converted flow rate or the instantaneous flow rate is displayed on the display 103, or the counter 105 is operated. Let it.

The analog-to-digital converter 101 converts the specific resistance of the temperature sensor 5 provided in the flow meter 1 into a digital value, and reads the temperature. From the temperature-specific gravity data stored in the ROM (I) 112 in advance, the flow rate per pulse is converted to a reference temperature, for example, a flow rate at 20 ° C. The converted flow rate is further fed back to the input / output interface 108.109. Next, the flow rate per pulse from the rotation detection sensor 7 is read from the instrumental difference correction data stored in the ROM (II) 114, and the signal of the temperature sensor 5 provided in the flow meter is converted into a digital value. A correction value is obtained from the instrumental error correction data based on the obtained temperature-viscosity change,
The flow rate is converted into a flow rate at a reference temperature. Then driver
The integrated flow rate range is displayed on the display 103 via the 104 to display the instantaneous flow rate or the counter 105 is operated. Reference numeral 6 denotes a sensor for continuous viscosity measurement, which can be used for a wide range of liquid types by using it alone or in combination with a temperature sensor. However, it is impossible to display the viscosity accurately, and for the purpose of showing it as reference data. used.

Guaranteed accuracy 0.05% NO accuracy is
It means an error within 1/2000, and it is important that the rotor, bearing, thrust ring, and other rotating parts that serve as the measuring function of the mechanical type positive displacement flowmeter have no wear and deformation. For example, if the tooth profile of the rotating body of the non-circular gear type flow meter has a shape that does not cause a trapping phenomenon and does not cause deformation of the meshing tooth surface, it is possible to exert a precise flow rate correction effect by the microcomputer device. .

In addition, because of the mechanical structure, it is desirable that the operating conditions are not severe. It is important that the rotating speed of the rotating body in the measured flow rate range is low and the rotating speed in the minute flow rate is low. That is, a lightweight rotating body having a large discharge rate (ratio of the discharge amount per rotation to the rotation volume) satisfies this requirement. Since there is a characteristic that the instrument difference increases in the low-speed rotation range, the means for correcting the characteristic error peculiar to the instrument is effective.

Next, the flow rate is converted into an accurate flow rate at the reference temperature using the electronic correction mechanism, and the error is corrected and displayed. However, it is important that the rotor and the bearing, which perform the measuring function of the instrument body, are not deformed due to mechanical wear. Since the deformation of these rotating elements changes the clearance value of the flowmeter main body, the instrument error curve changes, and the instrument error correction conversion value must be corrected. Therefore, a rotor that does not cause confinement, such as a cycloid tooth, is used for the rotor. Such gears are excellent in durability while producing scoring flaws. Furthermore, the rotation resistance is small and the weighing function is excellent.

The non-circular gear type flow meter has high volumetric efficiency and thus high measurement accuracy, but the greater the flatness of the rotating body, the greater the discharge rate, the better the instrumental difference characteristics, and the advantage of a smaller instrument body. However, a pair of gear rotors that mesh with each other rotate while repeatedly accelerating and decelerating with each other. Therefore, as the rotation speed increases, the vibration and noise increase, and the braking force of the rotating body increases. Many leaks.

FIG. 7 shows a signal input from a rotation detection sensor for correcting an error of a characteristic curve with respect to an ideal QE curve between a temperature sensor, a flow meter equipped with a rotation sensor, and a control device. 1 shows a circuit diagram of an embodiment incorporating a control device for inputting.

The controller 100 explained in FIG. 6 corrects the instrumental difference based on the correlation between the fluid volume change and the temperature-viscosity, and at the same time, the error of the instrument specific characteristic with respect to the ideal QE curve stored in the ROM (III) 117. FIG. 5 is an electric circuit diagram for reading and correcting data for correcting the error. Pulse signals from the rotary magnetic sensor 7 for transmitting the rotation of the rotating body of the flow meter 1 and the temperature sensor 5 are input to the input interface 108, and the central control unit CPU (III) 118 receives a pulse input by this signal input. This is confirmed by checking the signal input from the input / output interface 108, and from the time interval between this pulse input and the previous pulse input, the flow rate per pulse is stored in the ROM (III). The data is read from the correction data of the body speed and the instrument-specific instrumental difference, and the instrument-specific error correction in each flow rate range is performed. Then, the controller 100 explained with reference to FIG. Is calculated.

FIG. 8 shows a ROM (I) 111, RO for correcting a value of an instrumental error due to a change in fluid volume and a change in viscosity due to the temperature change.
Shows an electric circuit incorporating M (II) 114 and a control device in which ROM (III) 117 is combined with a circuit for correcting characteristic errors inherent to the flow meter path, and displays instantaneous instrument error correction values. FIG. 3 is an explanatory diagram of an electronic correction device of an embodiment using means for correcting the three elements of temperature-specific gravity, temperature-viscosity, and temperature-instrument characteristic error of the present invention having a function of transmitting and transmitting.

As described above, the correction of the non-circular gear type flow meter main body by the electronic correction device has extremely fine resolution and eliminates errors, but the shape for exhibiting a stable measuring function of the rotating body is provided. As shown in FIG. Shaft 2 of non-circular gear rotating body 201
02 has a shape in which the tip is thinner than the shaft diameter of the end face as shown in the figure. The opposite shaft has a similar shape.

These shafts 202 are fitted to hole-shaped bearings on the inner wall surface in the measuring chamber for fitting. The fitting portion has a hole shape so as to form a minute clearance. The pair of rotators housed on the horizontal axis by the flow of the fluid to be measured rotate while meshing and engaging with each other, but rotate while maintaining the center position of the horizontal axis, and emit a pulse by the action of the magnet 203.

FIG. 10 shows a bearing having a perforated shape in which the shaft hole 204 of the rotating body 201 is gradually reduced in diameter to the shaft diameter of the end face. A fixed shaft having a shape to be fitted into the shaft hole is provided on a side wall surface in the measuring chamber for supporting the correction. A fixed shaft provided on the wall surface of the measuring chamber is fitted into a shaft hole having a shape gradually narrowing with respect to the shaft hole on the end face of the rotating body, and is rotatably housed. The rotator rotates while the rotational position is centripetally maintained by the flow of the fluid, as in the case shown in FIG. 9, and is moved while maintaining a constant clearance between the end surface of the rotator and the side wall surface in the measuring chamber. Therefore, there is no change in instrumental error, and accurate measurement is performed.

The internal leakage of the structure having a large gap inside the measuring chamber shown in FIG. 3 increases in the small flow rate region and the large flow rate region, and the instrumental difference value is large. In a structure with a reduced clearance, fluids of the same viscosity have relatively less leakage as shown in FIG. 4, but there is a risk of a stop accident due to the intrusion of foreign matter,
The phenomenon of internal leakage indicated by the QE curve of the positive displacement flow meter is inevitable, and by correcting with the instrumental difference value that correlates with the rotation speed of the rotating body corresponding to the QE curve for each specification, accurate flow rate can be achieved to correct.

The present invention corrects an abnormal QE curve due to internal leakage and return phenomenon in a small flow rate region due to an involute tooth shape which are inevitably caused by leakage from a design gap to allow free rotation of a rotating body. By means, a ROM that records data for correcting instrument-specific measurement errors based on the characteristics of the flow meter so that the instrumental difference value of the small flow rate and the large flow rate is corrected and a QE curve showing ideal linearity is obtained It is an object of the present invention to provide an instrumental difference correction method using an instrumental difference correction unit that shows an accurate flow rate by using a controller that incorporates a ROM for a plurality of correction functions that combine the above means, . Furthermore, non-circular gears with the shape of a rotating body formed by processing a lightweight material and the other end formed as a shaft hole to be fitted with a fixed shaft having the same shape as that of the measuring chamber also perform the same centripetal rotation. Such a configuration is also included in the gist of the invention.

[Effects of the Invention] The present invention provides an instrument based on the specific gravity and viscosity of a fluid and the characteristics of the flowmeter main body in response to a temperature change of a fluid to be measured, in order to enhance the accuracy of the indicated flow rate of a highly reliable positive displacement flowmeter. The electronic correction that displays and sends the converted flow rate with the correction value calculated by the rotation speed in real time has the effect of exhibiting the ultra-precision measurement function over a wide flow rate range and even a slight temperature change. It is characterized by equipping the control unit with an arithmetic unit that grasps and corrects a minute change due to temperature change of the measurement error peculiar to the instrument that changes in association with such a slight temperature environment change, and also reduces the weight. Error-free measurement is possible due to the stable function of the rotating element that rotates concentrically with respect to the axis center in the measuring chamber.

[Brief description of the drawings]

1, 2, 3 and 4 are explanatory diagrams showing instrumental curves of positive displacement flowmeters, FIG. 5 is an explanatory diagram showing the structure of the apparatus of the present invention, FIG. 6, FIG. FIG. 8 and FIG. 8 are circuit diagrams of a control device incorporating an electronic operation mechanism for correcting instrumental differences,
9 and 10 are views showing a non-circular gear rotating body provided with a conical rotating shaft and a bearing hole. 1: flow meter, 5: temperature sensor, 7: rotation detection sensor, 8: wiring, 100: controller, 101: converter, 103: display, 104, 106:
Driver, 105: Counter, 107: Clock, 108, 109:
I / O interface, 110, 113, 116: ROM, 118: ROM for temperature-specific instrumental difference / calculation, 112, 115, 118: CPU, 201: non-circular rotating body, 202: tapered shaft, 204: shaft hole, 203: magnet

Claims (3)

(57) [Claims] 1. A flow rate obtained by correcting a flow rate conversion value calculated from the rotation of a non-circular rotating body element of a positive displacement type flow meter by a correction value given by a correlation such as a specific gravity-instrumental difference of a fluid to be measured as a function of temperature. In order to output and display the temperature, the conductor of the temperature sensor provided in the flow path is connected to the electronic arithmetic unit of the flow meter, and the electric signal indicating the temperature change is input to the arithmetic unit. A signal from a temperature sensor is input to a central control unit equipped with a ROM in which a correction value corresponding to a change in volume expansion and contraction of a fluid to be measured corresponding to a change is input. Means for calculating and outputting an instrumental difference correction value given by the instrumental correlation,
Means for measuring and calculating the period of the pulse signal transmitted for each rotation of the rotary element, and means for outputting and displaying the flow rate corrected in real time in addition to the calculated flow rate conversion value. A memory for recording the correlation function of the volume expansion coefficient associated with the temperature of the fluid and the correlation function of the viscosity coefficient associated with the temperature of the fluid, and correcting the measurement error inherent in the meter based on the characteristics of the flow meter. The signal of the rotation detection sensor is input to the central control unit equipped with the ROM that stores the data of the data of the volume, and the instrument error of the positive displacement type flow meter using the means to correct the measurement error inherent in the instrument, which is a function of the rotation speed of the rotating body Correction method. 2. A shaft hole of a non-circular rotary element of a twin rotor type is formed to have a shape in which an inner diameter is made smaller than a diameter of an end face of the rotary element, and a fixed shaft to be fitted therein is used as a measuring chamber. The volume expansion and contraction of the fluid, which is correlated with the temperature of the positive displacement flowmeter, which is installed on the inner measuring wall and rotatably housed, the change in the instrumental error due to the change in the viscosity of the fluid, the measurement error and the temperature of the fluid 2. A method according to claim 1, wherein the measurement error caused by the correlation between the volume expansion coefficient associated with the change and the correlation between the viscosity coefficients associated with the temperature change of the fluid is corrected. . 3. A double-rotor type non-circular rotary element and a rotary shaft are integrally formed, and the rotary shaft is formed into a shape that is thinner with respect to the diameter of the end face of the rotary element, and is fitted with this. The shape of the bearing in the measuring chamber is the same as that of the measuring chamber, and it is linked to the measurement error inherent in the instrument due to the temperature change of the fluid accompanying the measurement of the positive displacement flowmeter with the rotating element rotatably housed, and the temperature change of the fluid. 2. The method according to claim 1, wherein a measurement error caused by a correlation between a volume expansion coefficient and a viscosity coefficient caused by a temperature change of a fluid is corrected.