JP6830862B2 - Electromagnetic flow meter - Google Patents

Description

The present invention relates to an electromagnetic flow meter that measures the flow rate of a conductive fluid.

Conventionally, an electromagnetic flowmeter applies a magnetic field perpendicular to the flow direction of a fluid flowing in a measuring tube, detects an electromotive force proportional to the flow velocity of the fluid, and measures the flow rate of the fluid based on the detected electromotive force. It is designed to do. Since the electromotive force detected by the electromagnetic flowmeter is very small, some conventional electromagnetic flowmeters perform damping processing, which is a type of filtering processing, in order to stabilize the detected value (for example, patent). Reference 1). In particular, when the flow rate of the fluid in the measuring tube becomes low, the noise component becomes large and the stability of the electromotive force detected by the electromagnetic flow meter decreases. Therefore, in the electromagnetic flow meter of Patent Document 1, when the flow rate of the fluid is small, the damping time constant is increased to reduce the wobbling near the zero point and to stabilize the detected value.

By the way, in the electromagnetic flowmeter, the fall when the flow rate decreases, depending on whether the input signal before the damping process is used or the output signal after the damping process is used to determine the flow rate of the fluid when determining the damping time constant. There is a difference between the processing time at the time and the processing time at the start-up when the flow rate increases. That is, if the flow rate is determined based on the input signal before the damping process, it takes longer to fall than to rise. On the other hand, when the flow rate is determined based on the output signal after the damping process, it takes longer to rise than to fall.

JP-A-2010-2321

However, in a conventional electromagnetic flowmeter such as Patent Document 1, the magnitude of the flow rate of the fluid is uniformly determined based on the output signal after the damping process regardless of whether the flow rate is falling or rising. ing. Therefore, in the conventional electromagnetic flowmeter, since the rise is slower than the fall, there is a problem that an error occurs in the integrated value of the flow rate and the integration accuracy of the flow rate is lowered.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an electromagnetic flow meter that suppresses an error in the integrated value of the flow rate and improves the accuracy of integrating the flow rate.

The electromagnetic flowmeter according to the present invention includes a detector that detects an electromotive force according to the flow rate of the fluid flowing in the measuring tube, and a converter that obtains a fluid flow rate based on the electromotive force detected by the detector. The converter acquires an input signal and an output signal for each sampling time, and a damping processing unit that performs damping processing on the input signal based on the electromotive force to generate an output signal, and the value of the input signal is the output signal. If it is smaller than the value of, the damping time constant is obtained based on the value of the output signal, and if the value of the input signal is larger than the value of the output signal, the damping time constant is obtained based on the value of the input signal. The damping processing unit performs damping processing using the damping time constant obtained by the determination processing unit.

In the present invention, since the damping time constant is obtained based on the magnitude relationship between the input signal based on the electromotive force and the output signal after the damping process, the fall time and the rise time correspond to the increase and decrease of the fluid flow rate. The balance with time can be adjusted. Therefore, it is possible to suppress an error in the integrated value of the flow rate and improve the accuracy of integrating the flow rate.

It is a block diagram which shows schematic structure of the electromagnetic flowmeter which concerns on embodiment of this invention. It is explanatory drawing about the determination processing when the input signal to the damping processing part of FIG. 1 is in a falling state. It is explanatory drawing concerning the determination processing when the input signal to the damping processing part of FIG. 1 is in a rising state. It is a table which exemplifies the time constant table which the time constant determination part of FIG. 1 refers to when finding a damping time constant. It is explanatory drawing which illustrated the state of the damping process when the time constant determination part of FIG. 1 obtained the damping time constant using only an input signal or only an output signal. It is explanatory drawing which illustrated the state of the damping process when the time constant determination part of FIG. 1 obtained the damping time constant using the flow rate value from the flow rate determination part. It is a flowchart which shows the operation of the electromagnetic flowmeter of FIG. The damping process when the time constant determination unit of the electromagnetic flow meter according to the modification of the embodiment of the present invention obtains the damping time constant using only the input signal or only the output signal and initializes the damping input / output buffer. It is explanatory drawing which illustrated the situation. A state of damping processing when the time constant determination unit of the electromagnetic flow meter according to the modified example of the embodiment of the present invention obtains the damping time constant using the flow rate value from the flow rate determination unit and initializes the damping input / output buffer. It is explanatory drawing which illustrated.

Embodiment.
FIG. 1 is a block diagram schematically showing a configuration of an electromagnetic flowmeter according to an embodiment of the present invention. The electromagnetic flow meter 100 measures the flow rate of a conductive fluid. As shown in FIG. 1, the electromagnetic flowmeter 100 includes a detector 10 and a converter 20. The detector 10 has a measuring tube 11, an exciting coil 12, an electrode 13a, and an electrode 13b.

The measuring tube 11 is formed in a pipe shape and allows a fluid to pass through. The electromagnetic flowmeter 100 is arranged so that a conductive fluid flows through the measuring tube 11. The exciting coil 12 generates a magnetic field in the measuring tube 11 and applies the magnetic field to the fluid flowing in the measuring tube 11. The exciting coil 12 is arranged so that the direction in which the magnetic field is generated is perpendicular to the flow direction of the fluid flowing in the measuring tube 11.

The electrodes 13a and 13b are arranged in the measuring tube 11 so that the straight line connecting the electrodes 13a and 13b is orthogonal to the flow direction of the fluid flowing in the measuring tube 11 and the direction of the magnetic field generated by the exciting coil 12. It is arranged in a pair of electrodes to form a pair of electrodes. The electrodes 13a and 13b detect the electromotive force generated by the flow of fluid in the magnetic field generated by the exciting coil 12, and output an electromotive force signal indicating the detected electromotive force to the converter 20.

The converter 20 includes an amplification processing circuit 30, an A / D converter 40, a control unit 50, and an excitation unit 80. The amplification processing circuit 30 amplifies the electromotive force signals output from the electrodes 13a and 13b. The amplifier processing circuit 30 can be configured to include, for example, an AC amplifier circuit, a sample hold circuit, and a DC amplifier circuit. The AC amplifier circuit amplifies the difference between the electromotive force signal from the electrode 13a and the electromotive force signal from the electrode 13b. The sample hold circuit holds the voltage of the electromotive force signal when the exciting current Iex is positive or negative. The DC amplifier circuit amplifies the difference between the voltage of the electromotive force signal when the exciting current Iex is positive and the voltage of the electromotive force signal when the exciting current Iex is negative. The A / D converter 40 converts the analog electromotive force signal amplified in the amplification processing circuit 30 into a digital electromotive force signal, and outputs the converted electromotive force signal to the control unit 50.

The control unit 50 includes an arithmetic processing unit 60 and a storage unit 70. The arithmetic processing unit 60 includes an excitation control unit 61, a damping processing unit 62, a determination processing unit 63, a flow rate arithmetic processing unit 64, and an output processing unit 65.

The operation program of the arithmetic processing unit 60 is stored in the storage unit 70. For example, the storage unit 70 stores an initial time constant that is a damping time constant used by the damping processing unit 62 in the initial state. Further, the storage unit 70 stores time constant information in which the flow rate value corresponding to the input signal and the output signal, which will be described later, and the damping time constant are associated with each other. In the time constant information, the flow rate value and the damping time constant are related so that the damping time constant decreases as the flow rate value increases. The excitation control unit 61 instructs the excitation unit 80 to generate the exciting current Iex.

The damping processing unit 62 applies damping processing to the electromotive force signal output from the A / D converter 40, and outputs the electromotive force signal after the damping processing to the flow rate calculation processing unit 64. Here, the damping process is a filter process based on a digital filter with a first-order lag. Hereinafter, the electromotive force signal output from the A / D converter 40 and input to the damping processing unit 62 is also referred to as an “input signal”, and the electromotive force signal output by the damping processing unit 62 after the damping process is referred to as an “output signal”. Also called.

That is, the damping processing unit 62 performs damping processing on the input signal based on the electromotive force detected by the detector 10 to generate an output signal. More specifically, the damping processing unit 62 prevents the electromotive force signal from fluctuating by performing a calculation of a digital filter with a designated time delay on the input signal. In the present embodiment, the damping processing unit 62 executes the damping processing based on the following formula (1).

In the equation (1), KF is a coefficient in the digital filter having a first-order lag, and has a relation of "KF = TS / (TS + TK)". TS is a preset sampling time, and TK is a damping time constant. Further, n indicates a sampling timing. That is, X _n is the value of the input signal sampled at the current timing, Y _n is the value of the output signal generated at the current timing, and Y _n-1 is the timing immediately before Y _n. It is the value of the output signal generated in.

The determination processing unit 63 acquires an input signal and an output signal for each sampling time TS. Then, when the value of the input signal is smaller than the value of the output signal, the determination processing unit 63 obtains the damping time constant based on the value of the output signal. Further, when the value of the input signal is larger than the value of the output signal, the determination processing unit 63 obtains the damping time constant based on the value of the input signal.

As shown in FIG. 1, the determination processing unit 63 includes a flow rate determination unit 63a and a time constant determination unit 63b. The flow rate determination unit 63a acquires an input signal and an output signal for each sampling time TS, and compares the value of the input signal with the value of the output signal. Then, the flow rate determination unit 63a determines the magnitude of the value of the input signal and the value of the output signal, and outputs information based on the determination to the time constant determination unit 63b.

FIG. 2 is an explanatory diagram relating to a determination process when the input signal to the damping processing unit of FIG. 1 is in a falling state. FIG. 3 is an explanatory diagram relating to a determination process when the input signal to the damping processing unit of FIG. 1 is in the rising state. The determination process performed by the flow rate determination unit 63a will be specifically described with reference to FIGS. 2 and 3. Here, the falling state is a state in which the flow rate of the fluid is decreasing and the value of the input signal is changing in the direction of decreasing. The rising state is a state in which the flow rate of the fluid is increasing and the value of the input signal is changing in the direction of increasing. For convenience of explanation, FIG. 2 illustrates a case where the input signal Is decreases from 25% to 0%, and FIG. 3 illustrates a case where the input signal Is increases from 0% to 25%. Further, in FIGS. 2 and 3, time t ₀ and time t ₁ are illustrated as sampling timings.

The flow rate determination unit 63a compares the value of the input signal Is and the value of the output signal Os for each sampling time TS. At time t ₀ in FIG. 2, since the value of the input signal Is and the value of the output signal Os are equal, the flow rate determination unit 63a outputs the value of the input signal Is as the flow rate value to the time constant determination unit 63b. ing. On the other hand, it can be determined that for the time t ₁ in FIG. 2, than the value F _in the input signal Is better value F _out of the output signal Os is large, a state of falling. Therefore, the flow rate determining unit 63a, at time _{t 1,} and outputs the time constant determination section 63b the value _{F out} of the output signal Os as a flow value. That is, when the value of the output signal is larger than the value of the input signal at each sampling timing, the flow rate determination unit 63a outputs the value of the output signal as the flow rate value to the time constant determination unit 63b. ..

At time t ₀ in FIG. 3, since the value of the input signal Is and the value of the output signal Os are equal, the flow rate determination unit 63a outputs the value of the input signal Is as the flow rate value to the time constant determination unit 63b. ing. On the other hand, since at time t ₁ in FIG. 3, better value F _out of the output signal Os than the value F _in the input signal Is is small, it can be determined that the rise of the state. Therefore, the flow rate determining unit 63a, at time _{t 1,} and outputs the time constant determination section 63b the value _{F in} the input signal Is a flow value. That is, when the value of the output signal is smaller than the value of the input signal at each sampling timing, the flow rate determination unit 63a outputs the value of the input signal as the flow rate value to the time constant determination unit 63b. ..

As described above, in the present embodiment, it is determined whether the signal value is in the falling state or the rising state by determining which of the signal values before and after the damping process has the larger absolute value. The method of discrimination is adopted. However, when the value of the input signal Is and the value of the output signal Os are equal to each other, the flow rate determination unit 63a may output the value of the output signal Os as the flow rate value to the time constant determination unit 63b.

The time constant determination unit 63b obtains the damping time constant based on the flow rate value output from the flow rate determination unit 63a, and outputs the obtained damping time constant to the damping processing unit 62. The time constant determination unit 63b obtains the damping time constant by comparing the flow rate value output from the flow rate determination unit 63a with the time constant information in the storage unit 70.

FIG. 4 is a table illustrating a time constant table that the time constant determination unit of FIG. 1 refers to when obtaining a damping time constant. Here, it is assumed that the storage unit 70 stores the time constant table illustrated in FIG. 4 as the time constant information. FIG. 4 illustrates a time constant table in which the damping time constant is set in three stages. The flow rate value in FIG. 4 corresponds to an input signal and an output signal. In the time constant table, the flow rate value and the damping time constant are related so that the damping time constant decreases as the flow rate value increases. There is.

The time constant determination unit 63b determines the damping time constant to 1s when the flow rate value output from the flow rate determination unit 63a is 5% or more. Here, the damping time constant corresponding to the range of the flow rate value of 5% or more is also referred to as "basic time constant". The basic time constant may be the same as or different from the initial time constant described above.

Further, the time constant determination unit 63b determines the damping time constant to 10s when the flow rate value output from the flow rate determination unit 63a is 1% or more and less than 5%. Further, the time constant determination unit 63b determines the damping time constant to 20s when the flow rate value output from the flow rate determination unit 63a is less than 1%. Then, the time constant determination unit 63b outputs the determined damping time constant to the damping processing unit 62.

FIG. 5 is an explanatory diagram illustrating a state of damping processing when the time constant determining unit of FIG. 1 obtains a damping time constant using only an input signal or only an output signal. FIG. 6 is an explanatory diagram illustrating a state of damping processing when the time constant determination unit of FIG. 1 obtains a damping time constant using the flow rate value from the flow rate determination unit. For convenience of explanation, FIGS. 5 and 6 show waveforms after low flow cut when a rectangular wave of 0% to 25% is input. Here, FIG. 5 shows the damping process in the comparative example of the present embodiment, and FIG. 6 shows the damping process in the present embodiment. The damping process in the present embodiment will be described with reference to FIGS. 4 to 6.

Figure. 5 (a) shows an output signal O _in after dumping process when determined the damping time constant based on the input signal in both the falling condition and the rising condition. FIG. 5B shows the output signal _Out after the damping process when the damping time constant is obtained based on the output signal in both the falling state and the rising state. In FIG. 5A, time t ₂ is illustrated as the sampling timing immediately after the start of the fall, and time t ₃ is exemplified as the sampling timing immediately after the start of the rise. In FIG. 5 (b), falling immediately after the start of the sampling timing, and the arbitrary sampling timing later, the time t _4, the time t _5, illustrates a time t _6. Further, in FIG. 5 (b), the immediately following rising start sampling timing, and the arbitrary sampling timing later, the time t _7, the time t _8, illustrates the time t _9. In addition, in FIG. 5A and FIG. 5B, the rectangular wave-shaped input signal Is is shown by a broken line. The same applies to FIGS. 6, 8 and 9, which will be described later.

Here, it is assumed that the time constant determination unit 63b uses the time constant table of FIG.
If Figure 5 (a), when constant determining unit 63b, since the value of the input signal Is at time t ₂ is 0%, to determine the damping time constant 20s immediately after start falling. Further, the time constant determination unit 63b, since the value of the input signal Is at time t ₃ is 25%, determines the damping time constant immediately after the rise start to 1s. Therefore, the output signal O _in after dumping process by damping processor 62 takes time to fall than rise. As a result, in the case of FIG. 5A, there is a large difference between the region D _{in at the} falling edge and the region U _{in at} the rising edge between the input signal Is and the output signal O _in , which is accurate. The flow rate value cannot be obtained, and the integration accuracy of the flow rate is lowered.

For FIG. 5 (b), the time constant determining unit 63b, since the value of the output signal O _out at time t ₄ is greater than 5%, to determine the damping time constant 1s immediately after start falling. The time constant determination unit 63b, since the value of the output signal _{O out} at time _{t 5} is less than 5% 1% or more, to determine the damping time constant to 10s. The time constant determination unit 63b, since the value of the output signal _{O out} at time _{t 6} is less than 1%, to determine the damping time constant to 20s. Further, the time constant determination unit 63b, since the value of the output signal _{O out} at time _{t 7} is less than 1%, to determine the damping time constant immediately after the rise start to 20s. The time constant determination unit 63b, since the value of the output signal _{O out} at time _{t 8} is less than 5% 1% or more, to determine the damping time constant to 10s. Since the value of the output signal _Out at time t ₉ is 5% or more, the time constant determination unit 63b determines the damping time constant to 1s. Therefore, the output signal _Out after the damping process by the damping processing unit 62 takes longer to rise than the fall. As a result, in the case of FIG. 5B, there is a large difference between the region D _{out at the} falling edge and the region U _{out at} the rising edge between the input signal Is and the output signal O _out , which is accurate. The flow rate value cannot be obtained, and the integration accuracy of the flow rate is lowered.

On the other hand, the time constant determination unit 63b in the present embodiment is configured to obtain the damping time constant based on the flow rate value from the flow rate determination unit 63a as described above. FIG. 6 shows the output signal Os after the damping process when the damping time constant is obtained by using the output signal in the falling state and using the input signal in the rising state. In FIG. 6, a plurality of sampling timings are illustrated in association with the rising edge of FIG. 5A and the falling edge of FIG. 5B.

Here, it is assumed that the time constant determination unit 63b uses the time constant table of FIG.
The time constant determination unit 63b, since the value of the output signal Os at time t ₄ is greater than 5%, to determine the damping time constant 1s immediately after start falling. The time constant determination unit 63b, since the value of the output signal _{O out} at time _{t 5} is less than 5% 1% or more, to determine the damping time constant to 10s. The time constant determination unit 63b, since the value of the output signal _{O out} at time _{t 6} is less than 1%, to determine the damping time constant to 20s. Further, the time constant determination unit 63b, since the value of the input signal Is at time t ₃ is 25%, determines the damping time constant in rising to 1s. Therefore, in the output signal Os after the damping process by the damping processing unit 62, the falling time and the rising time are about the same. As a result, the difference between the region D _{out at the} falling edge and the region U _{in at} the rising edge between the input signal Is and the output signal Os can be reduced, so that an accurate flow rate value can be obtained. , It is possible to improve the integration accuracy of the flow rate.

The flow rate calculation processing unit 64 obtains the current flow rate of the fluid flowing in the measuring tube 11 based on the output signal from the damping processing unit 62, and outputs the obtained flow rate information to the output processing unit 65. Is. The flow rate calculation processing unit 64 may have a function of calculating the amount of heat of the fluid flowing in the measuring tube 11. The output processing unit 65 outputs the flow rate information obtained by the flow rate calculation processing unit 64 to an external device or the like. Here, when the converter 20 has a display unit including a liquid crystal display (LCD: liquid crystal display), a 7-segment type display unit, or the like, the output processing unit 65 determines the flow rate obtained by the flow rate calculation processing unit 64. The information may be displayed on the display unit.

The exciting unit 80 supplies the exciting coil 12 with an exciting current Iex having an exciting frequency nex whose polarity changes alternately in response to an instruction from the exciting control unit 61. That is, in this embodiment, as shown in FIG. 1, a rectangular wave excitation method is adopted.

The arithmetic processing unit 60 can be configured by an arithmetic unit such as a CPU (Central Processing Unit) or a DSP (Digital Signal Processor), and an operation program that realizes the above-mentioned various functions in cooperation with such an arithmetic unit. The storage unit 70 can be configured by a RAM (Random Access Memory) and a ROM (Read Only Memory), a PROM (Programmable ROM) such as a flash memory, an HDD (Hard Disk Drive), or the like.

FIG. 7 is a flowchart showing the operation of the electromagnetic flowmeter of FIG. The processing contents of the control unit 50 will be described with reference to FIG. 7.

The damping processing unit 62 acquires an electromotive force signal from the detector 10 as an input signal via the amplification processing circuit 30 and the A / D converter 40. Next, the damping processing unit 62 performs a damping process based on the equation (1) on the input signal using the initial time constant to generate an output signal. At that time, the damping processing unit 62 starts the damping process by first setting “Y _n = Y _n-1 = X _n ” in the equation (1). Then, the damping processing unit 62 outputs the generated output signal to the flow rate calculation processing unit 64 (step S101).

The flow rate determination unit 63a acquires an input signal input to the damping processing unit 62 and an output signal output from the damping processing unit 62 (step S102). Next, the flow rate determination unit 63a compares the magnitude of the value of the input signal and the value of the output signal, and determines whether or not the value of the input signal is smaller than the value of the output signal (step S103).

If the value of the input signal is smaller than the value of the output signal (step S103 / Yes), the flow rate determination unit 63a can determine that the state is in the falling state, so that the value of the output signal is used as the flow rate value as a time constant. Output to the determination unit 63b (step S104). On the other hand, if the value of the input signal is equal to or greater than the value of the output signal (step S103 / No), the flow rate determination unit 63a outputs the value of the input signal as the flow rate value to the time constant determination unit 63b. This is because if the value of the input signal is larger than the value of the output signal, it can be determined that the input signal is in the rising state. Further, when the value of the input signal and the value of the output signal are equal, either value may be transmitted. Therefore, in the present embodiment, the flow rate determination unit 63a determines the value of the input signal by the time constant determination unit 63b. It is designed to output to (step S105).

Next, the time constant determination unit 63b obtains the damping time constant by comparing the flow rate value output from the flow rate determination unit 63a with the time constant information (step S106). Then, the time constant determination unit 63b outputs the obtained damping time constant to the damping processing unit 62 (step S107). The damping processing unit 62 performs a damping process based on the equation (1) on the input signal by using the damping time constant acquired from the time constant determination unit 63b, and generates an output signal. Then, the damping processing unit 62 outputs the generated output signal to the flow rate calculation processing unit 64 (step S108). The control unit 50 repeatedly executes a series of processes of steps S102 to S108 for each sampling time TS.

Here, in the above description, the case where the time constant determination unit 63b outputs the obtained damping time constant to the damping processing unit 62 has been illustrated, but the present invention is not limited to this. For example, the time constant determination unit 63b may store the obtained damping time constant in the storage unit 70. Then, the damping processing unit 62 may read the damping time constant stored in the storage unit 70 at each sampling timing by the time constant determination unit 63b and perform the damping process.

As described above, the electromagnetic flowmeter 100 in the present embodiment obtains the damping time constant based on the magnitude relationship between the input signal based on the electromotive force and the output signal after the damping process. Therefore, the balance between the falling time and the rising time can be adjusted in correspondence with the increase or decrease of the fluid flow rate, so that the error of the integrated value of the flow rate can be suppressed and the integrated accuracy of the flow rate can be improved. Can be done.

By the way, the waveform of the signal input to the damping processing unit 62 is not constant, and it is not known what kind of waveform signal is actually input to the damping processing unit 62. In this regard, in the present embodiment, paying attention to the fact that the output signal after the damping process is delayed more than the input signal, a method of determining which of the signal values before and after the damping process has the larger absolute value. Is adopted. That is, in the electromagnetic flowmeter 100, if the input signal is in the falling state, "input signal value <output signal value", and if the input signal is in the rising state, "input signal value> output signal value". It is designed to determine whether it is in the falling state or the rising state by utilizing the fact that. Therefore, according to the electromagnetic flow meter 100, it is possible to automatically perform the process of using the output signal for the falling edge and the input signal for the rising edge, so that accurate flow rate measurement can be realized.

Further, the storage unit 70 stores a time constant table in which the range of the flow rate value and the damping time constant are stepwise associated with each other. Then, the determination processing unit 63 compares the value of the input signal or the value of the output signal with the time constant table to obtain the damping time constant. Therefore, the damping time constant switching process can be performed accurately based on the threshold value of the flow rate value (1% and 5% in the example of FIG. 4). That is, according to the electromagnetic flow meter 100, as shown in the example of FIG. 6, the damping process using the basic time constant can be performed in both the falling state and the falling state, so that the flow rate is integrated. The error in the value can be reduced.

Further, since the electromagnetic flow meter 100 of the present embodiment does not initialize when the damping time constant changes, the output signal is output even when the flow rate value changes across the threshold value and the damping time constant is switched. Since the change is smooth, the flow rate of the fluid can be measured accurately.

Here, the time constant information is not limited to the table information as shown in FIG. 4, but may be information such as a graph in which the flow rate and the damping time constant are related so that the damping time constant decreases as the flow rate increases. Good. In this case, the time constant information may be configured so that the damping time constant becomes constant when the flow rate exceeds a certain value. Even in this case, since the electromagnetic flowmeter 100 of the present embodiment does not initialize when the damping time constant changes, the output signal suddenly changes when the damping time constant is switched. Since it does not occur, the flow rate of the fluid can be measured accurately.

<Modification example>
FIG. 8 shows a case where the time constant determination unit of the electromagnetic flow meter according to the modified example of the embodiment of the present invention obtains the damping time constant using only the input signal or only the output signal and initializes the damping input / output buffer. It is explanatory drawing which illustrated the state of the damping process of. FIG. 9 shows a case where the time constant determination unit of the electromagnetic flow meter according to the modified example of the embodiment of the present invention obtains the damping time constant using the flow rate value from the flow rate determination unit and initializes the damping input / output buffer. It is explanatory drawing which illustrated the state of the damping process. The electromagnetic flowmeter of this modified example is characterized in that it is initialized when the damping time constant changes, but since it is configured in the same manner as the example of FIG. 1, the same reference numerals are given to the equivalent constituent members. The description will be omitted using.

The damping processing unit 62 of this modification performs initialization when the damping time constant obtained by the determination processing unit 63 changes from the damping time constant obtained by the determination processing unit 63 at the previous sampling timing. It is configured in. In this modification, when the damping time constant is changed, the damping processing unit 62 initializes by setting “Y _n = Y _n-1 = X _n ” in the equation (1) and executes the damping process. It is designed to do.

For convenience of explanation, FIGS. 8 and 9 show waveforms after low flow cut when a rectangular wave of 0% to 25% is input. Here, FIG. 8 shows the damping process in the comparative example of the present modification, and FIG. 9 shows the damping process in the present modification. The damping process in this modification will be described with reference to FIGS. 4, 8 and 9.

In FIG. 8 (a) shows an output signal O _in after dumping process when determined the damping time constant based on the input signal in both the falling condition and the rising condition. FIG. 8B shows the output signal _Out after the damping process when the damping time constant is obtained based on the output signal in both the falling state and the rising state. In FIG. 8A, time t ₂ is illustrated as the sampling timing immediately after the start of the fall, and time t ₃ is exemplified as the sampling timing immediately after the start of the rise. In FIG. 8 (b), falling immediately after the start of the sampling timing, and the arbitrary sampling timing later, the time t _4, the time t _5, illustrates a time t _6. Further, in FIG. 8 (b), immediately after the rise start sampling timing, and the arbitrary sampling timing later, the time t _7, the time t _8, illustrates the time t _9.

Here, it is assumed that the time constant determination unit 63b uses the time constant table of FIG.
If FIG. 8 (a), when constant determining unit 63b, since the value of the input signal Is at time t ₂ is 0%, to determine the damping time constant 20s immediately after start falling. Since the damping processing unit 62 of this modification performs initialization when the damping time constant is changed, as shown in FIG. 8A, skipping occurs when the damping time constant is switched, and the output signal is output. O _in is rapidly lowered.

Further, the time constant determination unit 63b, since the value of the input signal Is at time t ₃ is 25%, determines the damping time constant in rising to 1s. Since the damping processing unit 62 of this modification performs initialization when the damping time constant is changed, skipping occurs when the damping time constant is switched, as shown in FIG. 8A.

Therefore, the output signal O _in after dumping process by damping unit 62 is made faster toward the falling than rising. As a result, in the case of FIG. 8A, there is a large difference between the region D _{in at the} falling edge and the region U _{in at} the rising edge between the input signal Is and the output signal O _in , which is accurate. The flow rate value cannot be obtained, and the integration accuracy of the flow rate is lowered.

If in FIG. 8 (b), the time constant determination unit 63b, because it exceeds 5% value of the output signal _{O out} at time _{t 4,} to determine the damping time constant 1s immediately after start falling. The time constant determination unit 63b, since the value of the output signal _{O out} at time _{t 5} is less than 5% 1% or more, to determine the damping time constant to 10s. The time constant determination unit 63b, since the value of the output signal _{O out} at time _{t 6} is less than 1%, to determine the damping time constant to 20s. Since the damping processing unit 62 of this modification performs initialization when the damping time constant is changed, the output signal _Out changes when the damping time constant is switched, as compared with the case of FIG. 5B. Is getting bigger.

Further, the time constant determination unit 63b, since the value of the output signal _{O out} at time _{t 7} is less than 1%, to determine the damping time constant immediately after the rise start to 20s. The time constant determination unit 63b, since the value of the output signal _{O out} at time _{t 8} is less than 5% 1% or more, to determine the damping time constant to 10s. Since the value of the output signal _Out at time t ₉ is 5% or more, the time constant determination unit 63b determines the damping time constant to 1s. Since the damping processing unit 62 of this modification performs initialization when the damping time constant is changed, the change in the output signal _Out is larger than in the case of FIG. 5B. In particular, when the damping time constant is determined to be 20s, the output signal _Out changes rapidly.

Therefore, the output signal _Out after the damping process by the damping processing unit 62 takes longer to rise than the fall. As a result, in the case of FIG. 8B, there is a large difference between the region D _{out at the} falling edge and the region U _{out at} the rising edge between the input signal Is and the output signal O _out , which is accurate. The flow rate value cannot be obtained, and the integration accuracy of the flow rate is lowered.

On the other hand, the time constant determination unit 63b in this modification is configured to obtain the damping time constant based on the flow rate value from the flow rate determination unit 63a as described above. FIG. 9 shows the output signal Os after the damping process when the damping time constant is obtained by using the output signal in the falling state and using the input signal in the rising state. In FIG. 9, a plurality of sampling timings are illustrated in association with the rising edge of FIG. 8A and the falling edge of FIG. 8B.

Here, it is assumed that the time constant determination unit 63b uses the time constant table of FIG.
The time constant determination unit 63b, since the value of the output signal Os at time t ₄ is greater than 5%, to determine the damping time constant in fall to 1s. The time constant determination unit 63b, since the value of the output signal _{O out} at time _{t 5} is less than 5% 1% or more, to determine the damping time constant to 10s. The time constant determination unit 63b, since the value of the output signal _{O out} at time _{t 6} is less than 1%, to determine the damping time constant to 20s. Further, the time constant determination unit 63b, since the value of the input signal Is at time t ₃ is 25%, determines the damping time constant in rising to 1s. Therefore, in the output signal Os after the damping process by the damping processing unit 62, the falling time and the rising time are about the same. As a result, between the input signal Is and the output signal Os, and region D _out in the fall, it is possible to reduce the difference between the region U _in the rising, it is possible to obtain an accurate flow rate value , It is possible to improve the integration accuracy of the flow rate. However, since the damping processing unit 62 of this modification performs initialization when the damping time constant is changed, skipping occurs when the damping time constant is switched, as shown in FIG.

(Summary)
Here, the electromagnetic flow meter 100 according to the present embodiment will be considered with reference to FIGS. 5, 6, 8, and 9. According to the comparison between FIGS. 5 and 6 and the comparison between FIGS. 8 and 9, the method of the present application, that is, regardless of whether the damping time constant is switched, whether the damping time constant is initialized or not. It can be said that the method in which the output signal is used for the falling edge and the input signal is used for the rising edge has less error in the flow rate value. Further, when the comparison between FIGS. 5 and 9 and the comparison between FIGS. 6 and 8 are combined, the method of the present application produces only the input signal or only the output signal regardless of whether or not the initialization is performed. It can be seen that the error of the flow rate value is smaller than that of the method of obtaining the damping time constant using the method.

Here, when FIG. 6 and FIG. 9 are compared, the error of the flow rate value is larger in the modified example in which the jump occurs when the damping time constant is switched. Therefore, it can be said that the most preferable process is to obtain the damping time constant by using the output signal for the falling edge and the input signal for the rising edge, and not to perform initialization when the damping time constant is switched.

The above-described embodiment is a suitable specific example in the electromagnetic flowmeter, and the technical scope of the present invention is not limited to these embodiments. For example, in the time constant table of FIG. 4, 1% and 5% are adopted as the flow rate threshold values, but the present invention is not limited to this, and the flow rate threshold value in the time constant table can be arbitrarily changed. Further, in the time constant table of FIG. 4, 1s, 10s, and 20s are exemplified as the damping time constants, but the present invention is not limited to this, and the damping time constants in the time constant table can be arbitrarily changed. For example, the damping time constant corresponding to the flow rate of 5% or more may be 2 s. Further, FIG. 4 illustrates a time constant table in which the damping time constant is set in three stages, but the time constant table is not limited to this, and the damping time constant may be set in two stages. It may be set to four or more stages.

Here, the converter 20 may have an operation unit that accepts a user's operation. Alternatively, the control unit 50 may have a function of accepting a user's operation in cooperation with an external device. Then, the user may set and change the flow rate threshold value and the damping time constant via the operation unit or an external device.

10 Detector, 11 Measuring tube, 12 Excitation coil, 13a, 13b Electrode, 20 Converter, 30 Amplification processing circuit, 40 A / D converter, 50 Control unit, 60 Arithmetic processing unit, 61 Excitation control unit, 62 Damping processing Unit, 63 Judgment processing unit, 63a Flow rate determination unit, 63b Time constant determination unit, 64 Flow rate calculation processing unit, 65 Output processing unit, 70 Storage unit, 80 Excitation unit, 100 Electromagnetic flow meter.

Claims (4)

A detector that detects the electromotive force according to the flow rate of the fluid flowing in the measuring tube,
A converter for obtaining the flow rate of the fluid based on the electromotive force detected by the detector is provided.
The converter
A damping processing unit that generates an output signal by performing damping processing on the input signal based on the electromotive force.
The input signal and the output signal are acquired for each sampling time, and when the value of the input signal is smaller than the value of the output signal, the damping time constant is obtained based on the value of the output signal, and the input signal is obtained. When the value of is larger than the value of the output signal, it has a determination processing unit for obtaining a damping time constant based on the value of the input signal.
The damping processing unit is
An electromagnetic flowmeter that performs the damping process using the damping time constant obtained by the determination processing unit. The flow rate value corresponding to the input signal and the output signal and the damping time constant further have a storage unit for storing the time constant information associated with each other so that the damping time constant decreases as the flow rate value increases.
The determination processing unit
The electromagnetic flow meter according to claim 1, wherein the value of the input signal or the value of the output signal is compared with the time constant information to obtain a damping time constant. The time constant information is
The electromagnetic flow meter according to claim 2, which is table information in which the range of the flow rate value and the damping time constant are stepwise associated with each other. The damping processing unit is
Any one of claims 1 to 3 that initializes when the damping time constant obtained by the determination processing unit changes from the damping time constant obtained by the determination processing unit at the previous sampling timing. The electromagnetic flowmeter described in the section.

Images