KR102616224B1 - Flowmeter resistant to environmental changes and flow measurement method - Google Patents

Abstract

An electromagnetic flowmeter that performs flow measurement may include a detection unit for detecting the flow rate, a constant voltage supply unit for supplying a constant voltage, and a control unit for determining a delta value for determining the flow rate. The control unit converts current into voltage using a current-voltage converter, controls the converted voltage to pass through the differential amplifier and the variable amplifier and is input to the VFC, and measures the frequency output for a specified time using the VFC. Determine the first count, reverse the direction of the current using a switch circuit, convert the current to voltage using the current-to-voltage converter, and the converted voltage passes through the differential amplifier and the variable amplifier to the VFC. is controlled to be input, the second count is determined by measuring the frequency output for a specified time using VFC, the difference between the first count and the second count is determined as a delta value, and based on the delta value, the flow rate and Fluid velocity can be calculated.

Description

Flowmeter resistant to environmental changes and flow measurement method using the same {FLOWMETER RESISTANT TO ENVIRONMENTAL CHANGES AND FLOW MEASUREMENT METHOD}

The present invention applies a constant voltage to the excitation coil and measures the voltage of a reference resistance connected in series with the excitation coil, so that the amount of current flowing in the excitation coil can be known, and by monitoring the change in the amount of current, it is possible to measure the voltage of the reference resistance connected in series with the excitation coil. This relates to an electromagnetic flowmeter that improves the accuracy and reproducibility of flow measurement by measuring changes in the amount of current in the excitation coil and compensating for this in flow rate calculations.

The electromagnetic flowmeter uses Faraday's principle of electromagnetic induction and measures the average flow rate of the fluid from the flow rate of the conductive fluid flowing in the pipe, the magnetic field generated up and down, and the induced electromotive force generated to the left and right, the direction of which is vertical, in proportion to the intensity. It is a measuring instrument that calculates

Electromagnetic flowmeters have no internal moving parts, so flow field disturbance and pressure loss are small, and since they measure flow rate using electrical signals, their response is very fast. Since they measure the amount of generated current, the electrical signals can be checked even at a distance from the flowmeter, so water and wastewater Of course, it has the advantage of being able to measure the flow rate of toxic fluids, radioactive fluids, and liquids containing solids.

In a typical electromagnetic flow meter, the detection unit (A) that detects the flow rate includes a power supply unit (C) that supplies power to the electromagnet (B) of the flow meter, and a signal processing unit (D) that processes the electromotive force signal generated in the detection unit (A). It is composed. The detection unit (A) consists of a conduit (E) through which fluid passes, an electromagnet (B) that forms a magnetic field, and an electrode (F) that connects the generated electromotive force signal.

A typical electromagnetic flowmeter of the prior art applies a magnetic field to the fluid flowing in the pipe (E) using an electromagnet. When a magnetic field is applied to a flowing fluid, induced electromotive force is generated in proportion to the flow speed. At this time, the electromagnetic flowmeter measures the flow rate by measuring the induced electromotive force from the electrode.

In the conventional technology, calibration is performed to ship a product to determine the K factor for flow rate calculation, but it is often known that when installed in the field, the flow rate is measured differently, because the conditions in the calibration room and field are different. This is due to changes in the installation environment. For example, there may be some difference between the flow rate values measured in summer and the flow rate values measured in winter.

When installed in the field, the flow meter according to this document monitors the impedance and current of the electromagnet to solve the problem of measuring the flow rate differently. Since changes in impedance and current affect the induced electromotive force, the change in current is used to calculate the flow rate. The purpose is to provide an electromagnetic flowmeter that improves flow measurement precision and reproducibility through compensation.

This document systematically analyzes the operating principle of the system consisting of the detection unit (A), power supply unit (C), and signal processing unit (D), along with a detailed explanation of the technical characteristics and advantages of the electromagnetic flow meter. In addition, methods for correcting measurement errors that may occur in previous electromagnetic flow meters were examined in depth, and research results on the effects of changes in the installation environment in the field were presented. Through this, the purpose is to propose the use of a highly reliable electromagnetic flowmeter that can be used to measure the flow rate of various fluids, including toxic fluids, radioactive fluids, and solid materials, as well as water and sewage treatment. In addition, the electromagnetic flow meter according to this document has the purpose of providing useful information for technological improvement and application related to flow measurement in industrial sites.

An electromagnetic flowmeter that performs flow measurement may include a detection unit for detecting the flow rate, a constant voltage supply unit for supplying a constant voltage, and a control unit for determining a delta value for determining the flow rate. The control unit converts current into voltage using a current-voltage converter, controls the converted voltage to pass through the differential amplifier and the variable amplifier and is input to the VFC, and measures the frequency output for a specified time using the VFC. Determine the first count, reverse the direction of the current using a switch circuit, convert the current to voltage using the current-to-voltage converter, and the converted voltage passes through the differential amplifier and the variable amplifier to the VFC. is controlled to be input, the second count is determined by measuring the frequency output for a specified time using VFC, the difference between the first count and the second count is determined as a delta value, and based on the delta value, the flow rate and Fluid velocity can be calculated.

When installed in the field, the flow meter according to this document monitors the impedance and current of the electromagnet to solve the problem of measuring the flow rate differently. Since changes in impedance and current affect the induced electromotive force, the change in current is used to calculate the flow rate. By compensating, it is possible to provide an electromagnetic flowmeter with improved flow measurement precision and reproducibility.

Figure 1 shows the configuration of an electromagnetic flowmeter according to a comparative example.
Figure 2 shows the configuration of an electromagnetic flowmeter according to various embodiments of this document.
Figure 3 illustrates a process for determining delta values according to various embodiments.
Figure 4a is a graph showing delta values before and after compensation, respectively.
Figure 4b shows graphically the fluid velocity values before and after compensation, respectively.
Figure 5 is a flow chart showing a flow measurement method of an electromagnetic flow meter according to various embodiments.

Figure 1 shows the configuration of an electromagnetic flowmeter according to a comparative example.

The electromagnetic flowmeter is based on Faraday's electromagnetic induction principle and can accurately measure the average flow rate of the fluid according to the flow rate of the conductive fluid flowing inside the pipe and the strength of the magnetic field generated in the vertical direction.

Electromagnetic flowmeters have high stability because they have no moving parts, so there is little flow field disturbance and pressure loss, and because they measure flow rate using electrical signals, they have the advantage of quick response and the ability to check electrical signals even from remote locations. Due to these characteristics of electromagnetic flow meters, they can be used to measure the flow rate of various fluids, including toxic fluids, radioactive fluids, and solid materials, as well as water and sewage treatment.

As shown in Figure 1, the main components of the electromagnetic flowmeter may include a detection unit (A), a power supply unit (C), and a signal processing unit (D). The detection unit (A) may be composed of an electromagnet (B) that forms a magnetic field within the conduit (E) through which fluid flows, and an electrode (F) that processes the generated electromotive force signal.

The electromagnetic flow meter according to the comparative example generates an induced electromotive force proportional to the flow rate by generating a magnetic field using an electromagnet in the fluid in the pipe (E), and can calculate the flow rate by measuring this from the electrode. However, certain errors may occur in flow measurement due to changes in the installation environment in the field, and calibration before shipment may be necessary to correct this. For example, the flow rate values measured in summer and winter may differ slightly due to the influence of the installation environment. To compensate for this difference, it is necessary to correct the delta value based on the measured voltage and current values. Below, the process for correcting the difference that occurs when measuring flow rate due to the influence of the installation environment will be explained.

Figure 2 shows the configuration of an electromagnetic flowmeter according to various embodiments of this document.

The electromagnetic flowmeter according to various embodiments of this document includes a detection unit 210 for detecting the flow rate, a constant voltage supply unit 222 for supplying a constant voltage, and a current voltage that converts the current, which is an electromotive force signal generated by the detection unit 210, into voltage. Converter 220, differential amplifier 224 to amplify the voltage difference between the two electrodes, variable amplifier 226 controlled by a digital serial interface to fit the VFC input range, VFC (Voltage- Frequency-Converter (228) and a control unit (230) for determining the DELTA for determining the flow rate, a switch circuit (232) for switching a predetermined electromagnetic generation in the upward and downward directions, and an electromagnet coil are connected in series to form an impedance, It may include a reference resistance (e.g. 0.5 ohm) 234 for measuring current. Additionally, the electromagnetic flowmeter may include a level converter 236, an amplifier 238, and an ADC 240.

According to one embodiment, the control unit 230 converts the current into voltage using the current-to-voltage converter 220, and the converted voltage passes through the differential amplifier 224 and the variable amplifier 226 to the VFC (228). It is controlled to be input, and the first count can be determined by measuring the frequency output for a specified time using the VFC 228. The control unit 230 reverses the direction of the current using the switch circuit 232, converts the current into voltage using the current-to-voltage converter 220, and the converted voltage is transmitted to the differential amplifier 224 and the It is controlled to pass through the variable amplifier 226 and input to the VFC 228, and the second count is determined by measuring the frequency output for a specified time using the VFC 228, and the difference between the first count and the second count is determined. The difference can be determined as a delta value, and flow rates and fluid velocities can be calculated based on the delta value.

According to one embodiment, the control unit 230 measures the voltage applied to the reference resistance 234 located between the plurality of coils when a specific voltage is supplied between the plurality of coils on the constant voltage supply unit, and measures the measured voltage and the reference resistance. Using the size of (234), the size of the current flowing between the plurality of coils is determined as the first value, the voltage applied to the reference resistance located between the plurality of coils is measured when the actual flow rate is detected, and the measured The size of the current flowing between the plurality of coils is determined as a second value using the voltage and the size of the reference resistance 234, and the time zone in which the flow rate is detected is classified into specific time units, and the first Based on the difference between this value and the second value, the magnitude of the delta value that must be compensated to match the theoretical value when the actual flow rate is detected can be determined.

According to one embodiment, the control unit 230 determines the difference between the first value and the second value, determines this as the amount of change in the initial current, and determines the size of the delta value to be compensated based on the amount of change in the initial current. , and the rate of change (K_rate) of the delta value that needs to be compensated can be determined by Equation 1.

: At constant flow rate , DELTA change rate between liver

: Flow rate proportionality constant

: Voltage measured at the reference resistance when the first value is measured

: Current measured at the reference resistance when the first value is measured

: Voltage measured at the reference resistance when the second value is measured

: Current measured at the reference resistance when the second value is measured

Q: Flow rate, V: Fluid velocity, A: Measurement tube cross-sectional area, Kf: Proportionality constant that determines the flow velocity

[Equation 1] will be explained in FIG. 4A.

According to one embodiment, the control unit 230 determines a specific time period when the first value and the second value differ by exceeding a specified level, and adjusts the constant voltage based on a change in the voltage supplied from the constant voltage supply unit at the specific time period. It is determined that the supply voltage of the supply part was the factor that caused the error with the actual flow rate value, and based on the fact that the temperature of the fluid changed beyond the specified level at a certain time, the change in impedance of the coil due to the change in temperature of the fluid was the actual flow rate value. It can be determined that this was the factor that caused the error.

According to one embodiment, the control unit 230 warms up the electromagnetic flow meter based on the fact that the voltage supplied from the constant voltage supply unit does not change in a specific time period and the temperature of the fluid does not change beyond a specified level in the specific time period. It can be determined that less warming up was the factor that caused the error with the actual flow rate value.

Figure 3 illustrates a process for determining delta values according to various embodiments.

The signal that generates electromagnetism by supplying a constant voltage and controls the direction of the electromagnetism consists of an upward control signal and a downward control signal. The control unit (e.g., the control unit 230 in FIG. 2) can control the upward control signal to ON and the downward control signal to OFF to generate an upward magnetic field from the lower coil to the upper coil. Alternatively, the control unit 230 may use a switch circuit ( 232), conversely, the upward control signal can be controlled to OFF and the downward control signal to be ON, thereby generating a downward magnetic field from the upper coil to the lower coil.

A signal that controls the direction of electromagnetism (e.g., UpDown_Control signal) may require a relatively high voltage from the constant voltage supply unit 222. On the other hand, since the control unit 230 operates with a relatively small voltage, switching the signal level may be necessary.

When an upward magnetic field is generated, a current proportional to the flow speed flows from the right electrode to the left electrode, is converted to voltage through the current-voltage converter 220, and passes through the differential amplifier 224 and the variable amplifier 226. This is input to the VFC (Voltage-Freuency-Converter) 228, and the control device counts the frequency output by the VFC (228) to determine the average voltage for a certain period of time (50 msec). As shown in the figure below, this count number is called COUNT1 (first count). Similarly, when a downward magnetic field is generated by adjusting the UpDownControl signal, a current flows from the left electrode to the right electrode, and the VFC (228) generates a frequency proportional to the input voltage, and the control device counts the frequency for a certain period of time (50 msec). This value is called COUNT2 (second count) and the difference is called DELTA.

DELTA = COUNT1 - COUNT2

This DELTA value is proportional to the velocity of the fluid.

In the figure above, channel 1 (yellow) measures one line of the switch circuit connected to the coil, and channel 2 represents the input signal of VFC.

The electromagnetic flowmeter determines the Kf value using flow test equipment.

V=DELTA*K_f

Q=V*A

Q: Flow rate, V: Fluid velocity, A: Measurement tube cross-sectional area, Kf: Proportionality constant that determines the flow velocity

Figure 4a is a graph showing delta values before and after compensation, respectively.

The current flowing through the upper and lower coils flows through a reference resistance connected in series, and by measuring this voltage, the impedance of the coil and the current flowing into the coil can be determined. When DC15V is provided from the constant voltage supply, the current flowing in inverse proportion to the impedance of the two coils is determined, and a constant current flows through the reference resistance of 0.5 Ohm, generating voltage. Since this signal is a small value, if the amplifier amplifies it 5.7 times and the voltage measured with the ADC is 850 mV, the current can be measured as follows.

Both the upper and lower coils may have the same current value.

If the electromagnetic flowmeter is less warmed up or there is a change in the external environment such that the temperature of the fluid increases or decreases, the impedance of the upper and lower coils may change. This change in impedance can be determined by measuring the change in current flowing through the two coils and the voltage applied to the reference resistance.

If the reference voltage changes, the amount of current flowing through the coil changes and the magnetic field changes, and DELTA, which counts the output of the VFC (228) from the electrode, may be affected.

Figure 4a is a diagram showing the DELTA (blue) and the reference resistance voltage Vcoil (orange) of an electromagnetic flowmeter that is not stabilized because it is warming up. It can be seen that the flow rate value in the cold state at the beginning of the measurement appears to be approximately 8% larger than the flow rate value measured in the stabilized state.

If the initially measured reference voltage is 890 mV while the flow temperature is cold,

In this way, a change of 14 mA in the initial current was measured, and the size of the magnetic field can also be expanded by this amount.

This also means that the total impedance of the upper and lower coils is lowered, and the DELTA value increases proportionally.

This can be formalized as follows.

: At constant flow rate , DELTA change rate between liver

: Flow rate proportionality constant

: Voltage measured from reference resistance in a stable state

: Current measured from reference resistance in a stable state

: Voltage measured from reference resistance in measurement state

: Current measured from reference resistance in measurement state

Figure 4b shows graphically the fluid velocity values before and after compensation, respectively.

In Figure 4b, blue represents the fluid velocity before compensation, and orange represents the fluid velocity after compensation. The K-Rate value can be determined by reflecting this difference in fluid velocity. By compensating for the determined K-Rate value, the accurate flow rate can be measured without being affected by environmental changes. Additionally, the electromagnetic flowmeter according to this document can provide excellent reproducibility.

Figure 5 is a flow chart showing a flow measurement method of an electromagnetic flow meter according to various embodiments.

Although the process steps, method steps, algorithms, etc. are depicted in a sequential order in the flow chart of FIG. 5, such processes, methods, and algorithms may be configured to operate in any suitable order. In other words, the steps of the processes, methods and algorithms described in various embodiments of the invention do not need to be performed in the order described herein. Additionally, although some steps are described as being performed asynchronously, in other embodiments, some such steps may be performed concurrently. Additionally, illustration of a process by depiction in the drawings is not intended to imply that the illustrated process excludes other variations and modifications thereto, and that any of the illustrated process or steps thereof may be incorporated into any of the various embodiments of the invention. It does not imply that more than one is required, nor does it imply that the illustrated process is preferred.

In operation 510, the control unit (e.g., control unit 230 in FIG. 2) may convert the current into voltage and input it to VFC. The control unit 230 converts current into voltage using a current-voltage converter, and controls the converted voltage to pass through the differential amplifier and the variable amplifier and be input to the VFC.

In operation 520, the controller 230 may determine the first count using VFC. The control unit 230 can determine the first count by measuring the frequency output during a specified time using VFC.

In operation 530, the controller 230 may switch the current direction using a switch circuit and determine the second count using VFC. The control unit 230 reverses the direction of the current using a switch circuit, converts the current to voltage using a current-voltage converter, and allows the converted voltage to pass through the differential amplifier and the variable amplifier and be input to the VFC. You can control it. The control unit 230 can determine the second count by measuring the frequency output during a specified time using VFC.

In operation 540, the controller 230 may determine the difference between the first count and the second count as a delta value.

In operation 550, the controller 230 may calculate the flow rate and fluid velocity based on the delta value.

Claims (3)

In an electromagnetic flow meter that performs flow measurement,
A detection unit for detecting flow rate;
A constant voltage supply unit for supplying constant voltage;
A current-to-voltage converter that converts the current generated by the detection unit into voltage;
A differential amplifier to amplify the voltage difference between both electrodes;
A variable amplifier controlled by a digital serial interface to fit the VFC (Voltage-Frequency-Converter) input range;
VFC (Voltage-Frequency-Converter), which converts voltage into frequency;
A control unit that determines a delta value for determining the flow rate;
a switch circuit that switches the direction of electromagnetic generation; and
It is connected in series with the electromagnet coil and includes a reference resistance for measuring impedance and current.
The control unit
Converting current to voltage using the current-voltage converter,
Controlling the converted voltage to pass through the differential amplifier and the variable amplifier and be input to the VFC,
Determine the first count by measuring the frequency output for a specified time using the VFC,
The direction of the current is reversed using the switch circuit, and the current is converted to voltage using the current-voltage converter,
Controlling the converted voltage to pass through the differential amplifier and the variable amplifier and be input to the VFC,
Determine the second count by measuring the frequency output during a specified time using the VFC,
Determine the difference between the first count and the second count as a delta value,
Calculate the flow rate and fluid velocity based on the delta value,
When a specific voltage is supplied between the plurality of coils from the constant voltage supply unit, the voltage applied to the reference resistance located between the plurality of coils is measured,
Using the measured voltage and the size of the reference resistance, the size of the current flowing between the plurality of coils is determined as a first value,
When the actual flow rate is detected, the voltage applied to the reference resistance located between the plurality of coils is measured, and the size of the current flowing between the plurality of coils is determined as the second value using the measured voltage and the size of the reference resistance. And
The time zone in which the flow rate was detected is classified into specific time units, and based on the difference between the first value and the second value for each classified section, the size of the delta value that must be compensated to match the theoretical value when the actual flow rate is detected is determined. decide
Determine the difference from the second value based on the first value, and determine this as the amount of change in the initial current,
Determines the size of delta value that must be compensated based on the amount of change in initial current,
The rate of change in delta value that must be compensated for ( ) is an electromagnetic flowmeter determined by Equation 1.
[Equation 1]






: At constant flow rate , DELTA change rate between liver
: Flow rate proportionality constant
: Voltage measured at the reference resistance when the first value is measured
: Current measured at the reference resistance when the first value is measured
: Voltage measured at the reference resistance when the second value is measured
: Current measured at the reference resistance when the second value is measured
Q: Flow rate, V: Fluid velocity, A: Measurement tube cross-sectional area, Kf: Proportionality constant that determines the flow velocity


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