JP3357583B2 - Electromagnetic flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic flow meter, and more particularly, to a method of applying a magnetic field to a fluid in a pipe by a predetermined AC exciting current and sampling a detection signal including a signal electromotive force of the fluid obtained from an electrode. The present invention relates to an electromagnetic flow meter that obtains a measured flow rate by performing signal processing.

[0002]

2. Description of the Related Art Generally, in this type of electromagnetic flow meter, FIG.
The configuration is as shown in FIG. In the figure, 10 is a detector that applies a magnetic field to the fluid in the tube based on a predetermined AC exciting current and detects and outputs a signal electromotive force generated in the fluid as a detection signal. This converter outputs an AC exciting current and calculates and outputs the flow rate in the pipe by performing signal processing on a detection signal from the detector 10.

The exciting unit 8 outputs an AC exciting current having a predetermined frequency of a rectangular wave based on the exciting signal 9B from the switching unit 9. The excitation coil 10D of the detector 10 is
The tube 10 is excited by an AC exciting current from the exciting unit 8.
A predetermined magnetic field is applied to the fluid flowing in C. As a result, a signal electromotive force having an amplitude corresponding to the flow velocity of the fluid is generated. This signal electromotive force is detected by electrodes 10A and 10B provided at opposing positions on the inner wall of tube 10C, and is output to converter 11 as a detection signal.

[0004] In the converter 11, in the AC amplifier 1,
The output from the detector 10 is AC-amplified and output as an AC flow signal 2. The AC amplifier 1 is provided with a high-pass filter (HPF) that attenuates low-frequency components of the detection signal obtained from the detector 10 to attenuate low-frequency noise mixed into the detection signal. I have.

In the sample and hold section 3, the switches 3A and 3B are controlled based on the switching signal 9A from the switching section 9 so that the positive and negative sides of the AC flow signal 2 from the AC amplifying section 1 are changed. Each is sampled and output as a DC flow signal 4. The arithmetic processing unit 6 captures the DC flow signal 4 from the sample hold unit 3 as digital information via the AD conversion unit 5,
A desired measurement flow rate value is calculated by executing a predetermined calculation process, and is converted into a predetermined signal by the output unit 7 and output.

FIG. 9 is a timing chart showing a conventional sampling operation. 9B is an excitation signal from the switching section 9, and 2 is an AC flow signal input to the sample and hold section 3. Reference numerals 3A and 3B denote switches that operate based on the sampling signal 9A from the switching unit 9, and define a sampling period (shaded area) of the AC flow signal 2.

In this case, the sampling period is provided near the trailing edge of each pulse of the excitation signal 9B (AC flow signal 2) because of its waveform stability. 3B are short-circuited to integrate the AC flow signal 2 and output as a DC flow signal 4. When the AC flow signal 2 is on the positive side, only the switch 3A is short-circuited, and when the AC flow signal 2 is on the negative side, only the switch 3B is short-circuited.

[0008] VA and VB are sample and hold units 3
VA is a holding output signal obtained by sampling operation on the positive side of the AC flow signal 2, and VB is a holding output signal obtained by sampling operation on the negative side of the AC flow signal 2. The signal is shown. In this case, a relatively small time constant is generally used as the sampling time constant of the sample-and-hold unit 3 with emphasis on the response of the flow rate measurement.

The spike noise 2N is applied to the AC flow signal 2.
Is mixed, the noise 2N is sampled by the operation of the switches 3A and 3B, and the held output signals VA and VB
Is generated. Further, the hold output signals VA and VB are
The absolute values of the held output signals VA and VB are added to the non-inverting input and the inverting input of the operational amplifier, and are output from the sample and hold unit 3 as the DC flow signal 4.

[0010]

However, in such a conventional electromagnetic flow meter, the fluid to be measured is excited by an AC exciting current having a predetermined frequency consisting of a rectangular wave, and the obtained AC flow signal 2 is output at a predetermined time. Sample hold unit 3 having a constant
Since the DC flow signal 4 indicating the potential corresponding to the flow rate is obtained by sampling in the above, when the time constant of the sample and hold unit 3 is set relatively small with emphasis on the response of the flow rate measurement, In a measurement environment where spike-like or step-like noise is likely to be mixed into the AC flow signal, there is a problem that these noises are output as measurement outputs.

When the time constant of the sample and hold section 3 is set to be relatively large, even if the change in the flow rate is gradual, a delay occurs until the actual change in the flow rate is output as the measurement data, and the response is reduced. In addition, there is a problem that it takes time for the output disturbed by the noise to return to the original state. An object of the present invention is to solve such a problem, and an object of the present invention is to provide an electromagnetic flowmeter that can reduce spike-like or step-like noise without lowering responsiveness during actual measurement.

[0012]

In order to achieve the above object, an electromagnetic flow meter according to the present invention sequentially samples a predetermined period of a positive-side pulse of an AC flow signal, and immediately samples the AC pulse signal.
Sampled value and a new sample
The sampling time constant corresponding to a change amount of the ring sampling values, the newly sampled San
First sampling means for holding and outputting the pulling value ;
In the AC flow signal, a predetermined period of the negative pulse is sequentially sampled, and the immediately preceding sampled value is sampled.
The new sampling time constant corresponding to a change amount of the sampled sampled values, the newly sampled
Second sampling means for holding and outputting the sampled sampling values, and synthesizing means for adding the absolute values of the outputs from the first and second sampling means and outputting the sum as a DC flow signal.

Therefore, the predetermined period of the positive pulse of the AC flow signal is sampled sequentially, and the sampling time constant according to the obtained change amount of the sampling value is obtained by
The sampled value is sampled, held and output, and a predetermined period of the negative pulse of the AC flow rate signal is sampled sequentially, and the sampled value is sampled by a sampling time constant according to a change amount of the obtained sampled value. The output is held and output, and the absolute values of these outputs are added and output as a DC flow signal.

Further, the first and second sampling means set a sampling time constant according to a difference output between the first sampled value sampled immediately before and the second sampled value newly sampled. A time-constant determining unit that determines the signal; and a signal-selecting and holding unit that samples and holds and outputs the second sampling value based on the sampling time constant determined by the time-constant determining unit. Therefore, the first sampled value sampled immediately before and the newly sampled second sampled value
The sampling time constant is determined in accordance with the magnitude of the difference output from the sampling value of the second sampling value, and the second sampling value is sampled and held and output based on the sampling time constant.

The time constant determining section outputs a control signal indicating a sampling period as a sampling time constant corresponding to the magnitude of the difference output, and the signal selection holding section outputs the second signal only during the sampling period indicated by the control signal. Is sampled. Therefore, a control signal indicating the sampling period is output as a sampling time constant according to the magnitude of the difference output, and the second sampling value is sampled only during the sampling period indicated by the control signal. The time constant determining unit outputs a control signal indicating a sampling frequency as a sampling time constant according to the magnitude of the difference output, and the signal selection holding unit outputs a second sampling value based on the sampling frequency indicated by the control signal. Is sampled. Therefore, a control signal indicating the sampling frequency is output as a sampling time constant according to the magnitude of the difference output, and the second sampling value is sampled at the sampling frequency indicated by the control signal.

Further, the time constant determining section selects a relatively small sampling time constant when the difference output is small, and selects a relatively large sampling time constant when the difference output is large. It is. Therefore, a relatively small sampling time constant is selected in the normal case where the AC flow signal is stable and the difference output between the immediately preceding sampling value and the new sampling value is small,
When spike-like or step-like noise is mixed in the AC flow signal and the difference output between the immediately preceding sampling value and the new sampling value is large, a relatively large sampling time constant is selected.

[0017]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of an electromagnetic flow meter according to an embodiment of the present invention. In FIG. 1, the same or equivalent parts as those described above (see FIG. 8) are denoted by the same reference numerals. In FIG. 1, reference numeral 10 denotes a detector that applies a magnetic field to a fluid in a pipe based on a predetermined AC exciting current and detects and outputs a signal electromotive force generated in the fluid as a detection signal. This converter outputs an AC exciting current and calculates and outputs the flow rate in the pipe by performing signal processing on a detection signal from the detector 10.

In the detector 10, the electrodes 10A, 10B
Is disposed opposite to the inner wall of the tube 10C through which the fluid to be measured flows, and is an electrode for detecting the signal electromotive force generated in the fluid. The excitation coil 10D is excited based on the AC excitation current from the converter 11, and Coil that applies a magnetic field to the fluid. In the converter 11, the switching unit 9 is a circuit unit that generates and outputs a switching signal 9A and an excitation signal 9B described later based on a predetermined clock, and the excitation unit 8 is a rectangular wave based on the excitation signal 9B from the switching unit 9. This is a circuit section that outputs an AC exciting current of a predetermined frequency.

The AC amplifying unit 1 amplifies the detection signal from the detector 10 by AC, and outputs the signal as an AC flow signal 2 whose amplitude changes in accordance with the fluid flow rate. Is a circuit unit that samples the AC flow signal 2 from the AC amplifying unit 1 based on the switching signal 9A, and outputs it as a DC flow signal 4 whose DC potential changes according to the fluid flow velocity. The AC amplifying unit 1 is provided with a high-pass filter that attenuates low-frequency components of the detection signal obtained from the detector 10 to attenuate low-frequency noise mixed into the detection signal.

The A / D converter 5 integrates the DC flow signal 4 from the sample-and-hold unit 3 and converts it into digital information. The arithmetic processing unit 6 applies a predetermined value to the digital information from the A / D converter 5. The output unit 7 is a circuit unit that converts a flow rate calculated by the arithmetic processing unit 6 into a predetermined signal and outputs the signal. In particular, the sampling and holding section 3 includes a sampling circuit 31 (first sampling means) for sampling only the positive side of the input AC flow signal 2 and a sampling circuit 32 (second sampling section) for sampling only the negative side. Means) are provided.

Each of the sampling circuits 31 and 32 has a time constant determining unit 3 for determining a sampling time constant based on sampling values 31D and 32D obtained by sampling the AC flow signal 2 by the switches 31A and 32A.
Signals for sampling and holding the sampling values 31D and 32D again based on the control signals 31E and 32E indicating the sampling time constants determined by the time constant determining units 33 and 35 and outputting the holding output signals VA and VB. Selection holding units 34 and 36 are provided, and the absolute values of the held output signals VA and VB are added by an amplification calculator 37 and output as a DC flow signal 4.

Next, a first embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram showing the sample and hold unit according to the first embodiment of the present invention, and FIG. 3 is a timing chart showing the operation of the sample and hold unit in FIG. Since the sampling circuits 31 and 32 have the same configuration, the sampling circuit 3 will be described below.
1 will be described as an example.

The AC flow signal 2 sampled by the switch 31A is supplied to a capacitor 31B and a buffer 31C.
And output as a sampling value 31D. The output of the buffer 31C, that is, the new sampling value 31D is input to the time constant determining unit 33 as V + (second sampling value), and the immediately preceding sampling value V− (held by the switch 33A, the capacitor 33B, and the buffer 33C. The difference output signal Vo from the first sampling value is output from the operational amplifier 33D.

Here, as shown in FIG.
Immediately after 1A turns off, switch 33A turns on.
The AC flow signal 2 held by the buffer 31C
Is held as the immediately preceding sampling value V−. Thereafter, when the switch 31A is turned "ON", a difference between the new sampling value V + of the AC flow signal 2 and the immediately preceding sampling value V-, that is, a difference output signal Vo is output.

The VT (voltage-time) converter 33E outputs a control signal 31E indicating a sampling time constant corresponding to the difference output signal Vo to the signal selection and holder 34. In the signal selection holding unit 34, the control signal 3 from the time constant determination unit 33
The sampling value 31D of the AC flow rate signal 2 output from the buffer 31C based on the
Via the buffer 34, the sampling is performed with a sampling time constant consisting of the resistor 34B and the capacitor 34C.
D outputs a holding output signal VA.

In this case, when the difference output signal Vo is relatively large, the VT conversion unit 33E determines that spike-like or step-like noise is mixed in the AC flow signal 2 and sets a relatively large sampling time constant. Is output. If the difference output signal Vo is relatively small, it is determined that spike-like or step-like noise is not mixed in the AC flow signal 2 and a control signal 31E indicating a relatively small sampling time constant is output. .

FIG. 6 is an explanatory diagram showing the relationship between the sampling time constant and the sampling period. As shown in FIG. 6, the control signal 31E output from the VT converter 33E is instructed by the length of the period during which the AC flow signal 2 is sampled. As shown in FIG. 6A, when the same signal is sampled (integrated) for the same period ta with different time constants, the sampling output 61 having the smaller time constant outputs the voltage V.
The sampling output 62 having a large time constant as compared with rising to a increases only to a voltage Vb lower than the voltage Va.

On the other hand, as shown in FIG. 6B, when sampling is performed with the same time constant, the sampling output 61
However, the period tb required to reach the voltage Vb is the time t required to reach the voltage Va higher than the voltage Vb.
shorter than a. Therefore, by controlling the sampling period, a sampling output equivalent to the case where the sampling time constant is changed can be obtained.

From this, the VT converter 33E (FIG. 2)
If the difference output signal Vo is large, a relatively short sampling period corresponding to a large time constant is indicated by the control signal 31E. When the difference output signal Vo is small, a relatively long sampling period corresponding to a small time constant is indicated by the control signal 31E.

Actually, as shown in FIG. 3, when the spike-like noise 2N is mixed in the AC flow signal 2 and is sampled by the sampling circuit 31 immediately before the times T1 to T3, respectively, the voltage of the differential output signal Vo is In accordance with V1 to V3, the sampling periods t1 to t3 are indicated by the control signal 31E from the VT conversion unit 33E, and the signal selection holding unit 3
The fourth switch 34A is controlled.

In this case, the difference voltage V1 at the time T1 is high, and a short sampling period t1 is specified corresponding to the difference voltage V1, and only during this period is the switch 34A of the signal selection holding unit 34 switched on.
Turns “ON”. Further, the differential voltage V3 at the time T3 is low, and a long sampling period t3 is instructed corresponding to this, and the switch 34A is turned “ON” only during this period.

Thus, as in the prior art (see FIG. 9),
Compared to the case where the sampling time constant is fixed (see the broken line in FIG. 3 ), the noise 2N with respect to the held output signal VA
Is suppressed. Further, when the noise 2N is attenuated and the difference output signal Vo becomes small, the original relatively small sampling time constant becomes the control signal 31 from the VT conversion unit 33E.
E instructs the signal selection holding unit 34,
Good responsiveness is obtained at the time of actual measurement.

As described above, in the sampling circuit 31, the new sampling value V +
And a difference output signal Vo between the immediately preceding sampling value V−
Is sampled from the time constant determining unit 33, and the signal selection and holding unit 34 samples and holds and outputs the sampling value 31D only during this sampling period.

Similarly, in the sampling circuit 32, the sampling value 32D is sampled and held and output for a sampling period corresponding to the difference output signal Vo between the new sampling value V + and the immediately preceding sampling value V-. You. Therefore, the DC flow signal 4 obtained by adding the absolute values of the held output signals VA and VB from the sampling circuits 31 and 32 is not affected by the noise 2N and the noise 2N is not generated. Good responsiveness is obtained during the period, that is, at the time of actual measurement.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a block diagram showing a sample and hold unit according to the second embodiment of the present invention, and FIG. 5 is a timing chart showing the operation of the sample and hold unit in FIG. 3, which are the same as those described above (see FIGS. 2 and 3). Or, equivalent parts are denoted by the same reference numerals. Since the sampling circuits 31 and 32 have the same configuration,
Hereinafter, the sampling circuit 31 will be described as an example.

In the above-described first embodiment, the sampling period is controlled based on the sampling time constant according to the difference output signal Vo. In the second embodiment, however, the signal selection and holding unit 34 A switched capacitor (a switch 34E and a capacitor 34F) for sampling the sampling value 31D at an arbitrary frequency is provided, and based on a sampling time constant corresponding to the difference output signal Vo obtained by the time constant determining unit 33, a signal selection holding unit The sampling frequency at 34 is controlled.

The VF (voltage-frequency) conversion section 33F outputs a control signal 31E indicating a sampling time constant corresponding to the difference output signal Vo to the signal selection holding section 34. In the signal selection holding unit 34, the sampling value 31 D of the AC flow signal 2 output from the buffer 31 C based on the control signal 31 E from the time constant
The signal is sampled by the capacitor 34C via the switched capacitor composed of the capacitor E and the capacitor 34F, and the held output signal VA is output from the buffer 34D.

The switched capacitor is a capacitor that gradually charges the potential of the sampling value 31D to the capacitor 34C by switching and connecting the switch 34E using the capacitor 34F having a relatively small capacity as a bridge. In this case, the charging speed is determined by the capacitance ratio between the capacitor 34C and the capacitor 34F. However, since the time constant of the capacitor 34C is zero, the charging ratio to the capacitor 34C is controlled by the frequency at which the switch 34E is switched. it can.

In this case, if the difference output signal Vo is relatively large, the VF conversion unit 33F determines that spike-like or step-like noise has mixed into the AC flow signal 2 and sets a relatively large sampling time constant. Is output. If the difference output signal Vo is relatively small, it is determined that spike-like or step-like noise is not mixed in the AC flow signal 2 and a control signal 31E indicating a relatively small sampling time constant is output. .

FIG. 7 is an explanatory diagram showing the relationship between the sampling time constant in the selection signal holding unit and the sampling frequency. In the selection signal holding unit 34 shown in FIG. 7A, a circuit portion including the capacitor C1 and the switch SW sets the frequency at which the switch SW is turned on and off to fs.
Then, as shown in FIG. 7B, R = 1 / (fs · C1) can be equivalently expressed.

Therefore, the time constant of the selection signal holding unit 34 can be expressed as follows: C · R = C / (fs · C1) When the sampling time constant is changed by controlling the sampling frequency fs. And the same sampling output can be obtained.

From this, the VF converter 33F (FIG. 2)
If the difference output signal Vo is large, a relatively low frequency signal corresponding to a large time constant is transmitted to the control signal 31E.
Instruct. When the difference output signal Vo is small, a relatively high frequency signal corresponding to a small time constant is indicated by the control signal 31E.

Actually, as shown in FIG. 5, when the spike noise 2N is mixed in the AC flow signal 2 and is sampled by the sampling circuit 31 immediately before the times T1 to T3, respectively, the voltage of the differential output signal Vo is In accordance with V1 to V3, the sampling frequencies f1 to f3 are changed to the VF converter 33F.
, And the switch 34A of the signal selection holding unit 34 is controlled.

In this case, the difference voltage V1 at the time T1 is high, and a low sampling frequency f1 is instructed correspondingly, and the switch 34E of the signal selection holding unit 34 is turned "ON" according to this frequency. Further, the difference voltage V3 at the time T3 is low, and the sampling voltage f corresponding to this is high.
3 is instructed, and the switch 34E is turned "ON" according to this frequency.

Thus, as in the prior art (see FIG. 9),
Compared with the case where the positive and negative pulses of the AC flow signal 2 are sampled and their absolute values are simply added (see the broken line in FIG. 5), the effect of the noise 2N on the holding output signal VA is suppressed. When the noise 2N is attenuated and the difference output signal Vo is reduced, the sampling frequency corresponding to the original relatively small sampling time constant is changed to the VF conversion unit 33.
The signal is instructed to the signal selection holding unit 34 by the control signal 31E from F, and good responsiveness is obtained at the time of actual measurement.

As described above, in the sampling circuit 31, a new sampling value V +
And a difference output signal Vo between the immediately preceding sampling value V−
Is designated by the time constant determining unit 33, and the signal selection and holding unit 34 samples and holds and outputs the sampling value 31D at this sampling frequency.

Similarly, in the sampling circuit 32, the sampling value 32D is sampled at the sampling frequency corresponding to the difference output signal Vo between the new sampling value V + and the immediately preceding sampling value V-, and is held and output. You. Therefore, the DC flow signal 4 obtained by adding the absolute values of the held output signals VA and VB from the sampling circuits 31 and 32 has a noise of 2N.
Is suppressed, and good responsiveness can be obtained during the period when the noise 2N is not generated, that is, during actual measurement.

In the above description, the case where the sample-and-hold unit 3 is constituted by circuit components has been described as an example. However, the present invention is not limited to this. For example, the AC flow signal 2 is obtained by AD conversion. The digital information may be arithmetically processed by a time constant determining unit and a signal selecting unit constituted by an arithmetic processing unit (CPU), and the same operation and effect as described above can be obtained.

[0049]

As described above, according to the present invention, the predetermined periods of the positive and negative pulses of the AC flow rate signal are separately and sequentially sampled, and the sampled immediately before is sampled.
Sampling values and newly sampled sampling
The sampling time constant according to the amount of change from the value
The newly sampled values are held and output, and the absolute values of the sampled values obtained from these positive and negative pulses are added and output as a DC flow signal. Therefore, when the amount of change in the sampling value is large, the sampling time constant is increased to compare the positive and negative pulses of the AC flow signal with those obtained by simply adding the absolute values as in the conventional case. The noise 2N with respect to the held output signal VA.
Is suppressed. In addition, when the amount of change in the sampling value is small, such as in a normal state where the flow rate is stable or in a normal flow rate change, a good response can be obtained at the time of actual measurement by reducing the sampling time constant.

Also, a control signal indicating a sampling period is output as a sampling time constant according to the magnitude of the difference output, and a sampling value is sampled only during the sampling period indicated by the control signal. Also, a control signal indicating a sampling frequency is output as a sampling time constant according to the magnitude of the difference output, and a sampling value is sampled at the sampling frequency indicated by the control signal. Therefore, the sampling time constant can be changed without changing the constants of the circuit components, and an inexpensive and good temperature characteristic can be obtained as compared with the case where a variable resistor or a trimmer is used. Further, accurate adjustment of the sampling time constant can be easily performed.

[Brief description of the drawings]

FIG. 1 is a block diagram of an electromagnetic flow meter according to an embodiment of the present invention.

FIG. 2 is a block diagram of a sample and hold unit according to the first embodiment of the present invention.

FIG. 3 is a timing chart showing the operation of each unit in FIG. 2;

FIG. 4 is a block diagram of a sample and hold unit according to a second embodiment of the present invention.

FIG. 5 is a timing chart showing the operation of each unit in FIG.

FIG. 6 is an explanatory diagram showing a relationship between a sampling time constant and a sampling period.

FIG. 7 is an explanatory diagram showing a relationship between a sampling time constant and a sampling frequency.

FIG. 8 is a block diagram of a conventional electromagnetic flow meter.

FIG. 9 is a timing chart showing the operation of each unit in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... AC amplification part, 2 ... AC flow signal, 3 ... Sample hold part, 31, 32 ... Sampling circuit, 31A, 32
A: switch, 31B, 32B: capacitor, 31C,
32C: buffer, 31D, 32D: sampling value,
31E, 32E: control signal, 33, 35: time constant determining unit, 33A, 35A: switch, 33B, 35B: capacitor, 33C, 35C: buffer, 33D, 35D ...
Operational amplifier, 33E, 35E ... VT converter, 33F, 3
5F: VF converter, V +, V-: sampling value, Vo
... Difference output signal, 34, 36 ... Signal selection holding unit, 34
A, 36A: switch, 34B, 36B: resistor, 34
C, 36C: condenser, 34D, 36D: buffer,
34E, 36E: switch, 34F, 36F: capacitor, VA, VB: hold output signal, 37: operational amplifier, 4
... DC flow signal, 5 ... A / D converter, 6 ... Calculator,
7 output section, 8 excitation section, 9 switching section, 9A ...
Sampling signal, 9B excitation signal, 10 detector, 1
0A, 10B ... electrodes, 10C ... tubes, 10D ... excitation coils, 11 ... converters.

Claims (5)

(57) [Claims] 1. A magnetic field is applied to a fluid in a tube by a predetermined AC exciting current, an AC flow signal including a signal electromotive force of the fluid obtained from an electrode is sampled, and a DC flow signal obtained by the sampling is subjected to signal processing. In the electromagnetic flow meter that obtains the measured flow rate by performing the above, the predetermined period of the positive side pulse of the AC flow rate signal is sequentially sampled, and the sampled value sampled immediately before
The new sampling time constant corresponding to a change amount of the sampled sampled values, the newly sampled
First sampling means for holding and outputting the sampled sampling value, and sequentially sampling a predetermined period of the negative pulse of the AC flow signal, and
The new sampling time constant corresponding to a change amount of the sampled sampled values, the newly sampled
A second sampling means for holding and outputting the sampled sampling value; and a synthesizing means for adding the absolute values of the outputs from the first and second sampling means and outputting the sum as a DC flow signal. Flowmeter. 2. The electromagnetic flow meter according to claim 1, wherein the first and second sampling means output a difference between a first sampling value sampled immediately before and a second sampling value newly sampled. A time constant determining unit that determines a sampling time constant according to the magnitude of the signal, and a signal selection and holding unit that samples, holds, and outputs a second sampling value based on the sampling time constant determined by the time constant determining unit. An electromagnetic flowmeter comprising: 3. The electromagnetic flow meter according to claim 2, wherein the time constant determining unit outputs a control signal indicating a sampling period as a sampling time constant according to the magnitude of the difference output. An electromagnetic flowmeter for sampling a second sampling value only during a sampling period indicated by a signal. 4. The electromagnetic flow meter according to claim 2, wherein the time constant determining unit outputs a control signal indicating a sampling frequency as a sampling time constant according to the magnitude of the difference output, and the signal selection holding unit controls The second is determined by the sampling frequency indicated by the signal.
An electromagnetic flowmeter characterized by sampling a sampling value of the above. 5. The electromagnetic flow meter according to claim 2, wherein the time constant determining unit selects a relatively small sampling time constant when the difference output is small, and compares the sampling time constant when the difference output is large. An electromagnetic flowmeter characterized by selecting an extremely large sampling time constant.