JP3161307B2 - 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 flowmeter which converts a flow rate of a measurement fluid into an electric signal and outputs a flow rate signal corresponding to the flow rate via a detection electrode, and particularly relates to an excitation and a circuit operation. The present invention relates to an electromagnetic flowmeter improved so as to improve S / N while reducing energy.

[0002]

2. Description of the Related Art There are several examples of a conventional electromagnetic flow meter for intermittently supplying an exciting current to an exciting coil to reduce the exciting energy, as described below. First, there is an electromagnetic flowmeter disclosed in Japanese Patent Application Laid-Open No. 54-115163, entitled "Electromagnetic Flowmeter." This relates to an electromagnetic flowmeter of low frequency excitation, in which the excitation period is made shorter than the non-excitation period so as to reduce the average power as a whole.

Second, there is an electromagnetic flow meter disclosed in Japanese Patent Application Laid-Open No. 55-33685, entitled "Title of the Invention: Electromagnetic Flow Meter."
This is because power is transmitted as current signals from the DC power source on the load side to the transmitter side via two transmission lines, and this power covers all the power on the transmitter side. A two-wire electromagnetic flowmeter that transmits a current signal to a load side via a wire is disclosed.

Third, there is an electromagnetic flow meter disclosed in Japanese Patent Application Laid-Open No. 55-76912, entitled "Title of the Invention: Electromagnetic Flow Meter."
In this method, a change in an external signal, for example, the electrode potential is monitored, and excitation is performed only when there is a change, thereby reducing the excitation power as a whole.

[0005] Fourth, there is an electromagnetic flow meter disclosed in Japanese Patent Application Laid-Open No. 62-1113019 "Title of Invention: Electromagnetic flow meter". This means that pulse-like positive and negative exciting currents are supplied to the exciting coil, the signal is sampled during the time until the differential noise disappears including each excitation period, the differential noise is removed, and the voltage between the positive and negative excitation levels is removed. A flow signal is obtained from the difference by synchronous rectification.

However, the above-mentioned first conventional electromagnetic flow meter executes signal sampling after the differential noise caused by the rise of the excitation disappears, so that the excitation ON period τ _ON becomes longer, Accordingly, if a predetermined repetition cycle is to be maintained, the excitation cycle becomes longer, and the response becomes slower.

The conventional second electromagnetic flow meter basically has the following configuration.
Although the power consumption is low as a whole as in the first prior art, there is a problem that the power at the time of excitation becomes large and the response becomes slow.

In addition, the third conventional electromagnetic flow meter samples a signal when the steady value is reached, so that the time required to reach the steady value becomes longer as in the first prior art, and the excitation time is reduced. However, there is a disadvantage that the electric power of the power supply becomes large.

Further, the fourth conventional electromagnetic flow meter cannot uniquely determine the attenuation of the differential noise. For example, if the sampling period is made sufficiently long, the noise in this period increases and the S / N becomes worse. If the sampling period is made short, the influence of differential noise appears. Then, since synchronous rectification is performed, signal processing in a low frequency region is required.

In addition, since it is necessary to calculate synchronous rectification based on sample values during the excitation period and the non-excitation period and to calculate the difference between them, there is a problem in that the hardware and software configurations are complicated. In order to solve this problem, the present applicant has made the following proposal in Japanese Patent Application No. 7-42972 titled "Title of Invention: Electromagnetic Flowmeter".

FIG. 5 is a block diagram showing the configuration of the electromagnetic flow meter proposed in this proposal. Reference numeral 10 denotes an insulating conduit through which the conductive measurement fluid Q flows. First, a description will be given based on a capacitance type electromagnetic flow meter for detecting the flow rate of a measurement fluid via a capacitance.

The detection electrodes 11a and 11b are fixed to the conduit 10 while being insulated from the measurement fluid Q, and are coupled to the measurement fluid Q via capacitances C _a and C _b . The ground electrode 11c that is in contact with the liquid is connected to the common potential point COM.

The preamplifier 12 includes a buffer amplifier 12a,
12b and a differential amplifier 12, and the detection electrodes 11a and 11b are connected to the buffer amplifier 12 of the preamplifier 12.
a and 12b are connected to the input terminals of the differential amplifier 12c.

The output terminal of the differential amplifier 12c is connected to a high-pass filter 13 functioning as AC coupling means. The high-pass filter 13 is selected so as to have a sufficient pass band for the excitation waveform.

Further, the high-pass filter 13 comprises a capacitor 13a and a resistor 13b.
Is connected to the output terminal of the differential amplifier 12c, and the other terminal is connected to the common potential point COM via the resistor 13b.

The connection point of the capacitor 13a and the resistor 13b is connected to the common potential point COM through a switch SW ₁ which opening and closing is controlled by the control signals S ₁ is connected to an input terminal of Baffua amplifier 14 .

The output terminal of the buffer amplifier 14 receives a control signal S
Closing at ₂ is connected to a hold circuit 15 via the switch SW ₂ is controlled. The hold circuit 15 includes a resistor 15a and a capacitor 15b.
One end of 5a is connected to the switch SW ₂ and the other end thereof is connected to the common potential point COM through the capacitor 15b.

The connection point between the resistor 15a and the capacitor 15b are connected to a common potential point COM through a switch SW ₃ the opening and closing is controlled by the control signal S ₃ is connected to an input terminal of Baffua amplifier 16 .

The output terminal of the buffer amplifier 16 is connected to a signal processing unit 17. The signal processing unit 17 incorporates an analog / digital converter, a microprocessor, a memory, and the like, calculates a flow signal, and outputs the flow signal to an output terminal 18.

Reference numeral 19 denotes a timing circuit, and a switch S
W ₁ , SW ₂ , SW ₃ , signal processing unit 17, excitation circuit 20
Output control signals S ₁ , S ₂ , S ₃ , S ₄ , S ₅ to control the opening and closing of these signals.

The switching timing of the excitation circuit 20 is controlled by the control signal S ₅ , for example, the excitation coil 2
The waveform of the exciting current _If flowing in 1 is controlled to a triangular wave, and the switching repetition cycle is controlled.

The excitation circuit 20 is, for example, shown in FIG.
As shown in, the DC power supply 20a, the switch SW _5, which is constituted by a diode 20b, the switch SW
_A pseudo triangular wave is generated by controlling the opening / closing of ₅ by a control signal S ₅ and supplied to the exciting coil 21.

In this case, the DC power supply 20a may be constituted by, for example, a non-charging type or a charging type battery. And this DC power supply 20a
For example, a switching power supply circuit may be used to perform voltage conversion, and this may be used as a circuit power supply.

Next, the operation of the configuration shown in FIG. 5 will be described with reference to the waveform diagrams shown in FIGS. The timing circuit 19 sends a control signal S ₅ to repeat the exciting period T _1, as shown in FIG. 7 (a) to the excitation circuit 20 non-excitation period T _2.

The control signal S ₅ controls the switch SW ₅ shown in FIG. 6 to be turned on during the excitation period T ₁ and turned off during the non-excitation period T ₂ . When the switch SW ₅ is turned on, the excitation from the DC power supply 20a to the exciting coil 21 coil 2
The excitation current _If increases with the time constant determined by the resistance R _f and the inductance L _f of ₁ during the excitation period T ₁ as shown in FIG.

[0026] However, after a lapse of the energizing period T _1, the switch SW ₅ is so turned off, the supply of energy from the DC power supply 20a is stopped, the energy stored in the exciting coil 21 is discharged through the diode 20b , FIG.
The excitation current _If decreases as shown in FIG. Switch SW ₅ again after a lapse of the non-excitation period T ₂ is turned on, it is the energy or supplied to the excitation coil 21 from the DC power source 20a.

Thereafter, by repeating this, a pseudo triangular wave can be supplied to the exciting coil 21 to the exciting coil 21. FIG. 7B shows the triangular-wave-like exciting current _If obtained in this manner.

As described above, when the triangular excitation current _If flows through the excitation coil 21, the measurement fluid Q
The magnetic field having a magnetic flux density B of substantially the same shape as the triangular waveform is applied, the signal voltage e _s having the same waveform in the measurement fluid Q is generated.

[0029] During the detection electrodes 11a and 11b, in addition to the signal voltage e _s, the detection electrodes 11a, since 11b preamplifier 12 and a loop magnetic flux density B is interlinked signal line connecting the magnetic flux The differential noise N generated based on the change in the density B appears superimposed. The waveform of the differential noise N is as shown by a solid line in FIG.

As shown in FIG. 5, in the configuration in which the detection electrodes 11a and 11b detect the signal voltage via the capacitances C _a and C _b , the electrode capacitance is usually very small, several tens to several thousand pF. The charging / discharging time constant of the electrode impedance due to the eddy current generated in the measurement fluid Q becomes sufficiently small, and the differential noise N is substantially proportional to the time derivative of the exciting current.
Only the components shown by the solid lines.

On the other hand, the waveform shown by a broken line in FIG. 7C shows the case of a liquid-contact type electromagnetic flow meter.
In the configuration in which the detection electrode is in contact with the liquid, the electrode capacitance formed by the detection electrode and the measurement fluid also exists as about 0.1 to 10 μF,
Further, since the electrochemical surface state of the detection electrode is unstable, the influence of the eddy current flowing in the measurement fluid is caused by the influence shown in FIG.
The waveform has a long tail as shown by the broken line in FIG.

As described above, the detection electrodes 11a and 11a
b, the voltage (e _s + N) generated during preamplifier 12,
The signal is output to the buffer amplifier 14 via the high-pass filter 13.

The voltage appearing at the output terminal of Baffua amplifier 14 7 corresponding to the signal voltage e _s of _{(e s + N) (e} )
The output voltage V _S shown in FIG.
₂ is integrated in the hold circuit 15 the switch SW ₂ as on for a predetermined time T ₃ by (FIG. 7 (g)) is sampled and held. The predetermined time T ₃ is it is sufficient to have the time width of an extent that the differential noise N disappears as shown in FIG. 7 (c).

The high pass in this case, prior to sampling the output voltage V _S of the switch SW ₂ as on the hold circuit 15, the switch SW ₁ as ON by the control signals S ₁ as shown in FIG. 7 (d) Filter 13
Is reset and this is fixed to the reference potential.

[0035] By such a reset operation, the detection electrodes 11a, 11b, or even if there is fluctuation of the DC voltage, such as a preamplifier 12, a signal voltage generated in response to the excitation period T ₁ is As shown in FIG. 7E, the operation accurately starts from the reference potential at the common potential point COM.

Therefore, the output voltage V _S shown in FIG. 7E is integrated into the hold circuit 15 during the fixed time T ₃ shown in FIG. 7G, so that a voltage that is accurately proportional to the flow rate is obtained. At the same time, the differential noise N shown in FIG. 7 (c) does not affect the output because the positive and negative components are canceled to zero.

The switch SW ₃ is turned on by the control signal S ₃ shown in FIG. 7 (h) to release the charge of the capacitor 15b, and the hold circuit 15 is prepared for the next signal processing.
The sampling voltage thus obtained is output to the signal processing unit 17 via the buffer amplifier 16.

The signal processing unit 17 obtains, via the control signal S ₄ , information on the control of the exciting current output from the timing circuit 19 to the exciting circuit 20 via the control signal S _4. And outputs it to the output terminal 18. It is also possible to correct the span determined the ratio of the excitation circuit 20 to obtain the value of the exciting current I _f signal value and the exciting current value in the flow rate calculation.

It should be noted, the high-pass filter to the point when the electromagnetic flowmeter not reset operation by the switch SW ₁ is the upper and lower portions of the DC potential indicated by oblique lines resulting from such pre-amplifier 13 FIG 7 (f) to balance It changes with a time constant of 13. The amount ε remaining in signal polarity opposite this case is dependent on the magnitude of the signal voltage e _s, simply becomes an error factor than sampled signals during a fixed time T _3.

[0040] If the capacity of the drive power source is small, the easy change of the exciting current I _f is generated, the ratio of the signal voltage using the reference voltage takes in the reference voltage corresponding to the exciting current I _f at a predetermined cycle The configuration shown in FIG. 9 for calculating and correcting the span variation is used.

Hereinafter, a specific description will be given. Note that the same reference numerals as those shown in FIG. 5 denote the same parts, and a description thereof will be omitted as appropriate. In this case, the reference resistance r is connected in series to the exciting coil 21 to the configuration shown in FIG. 5, it is applied to the other switch end switch SW ₁₀ is taken out reference voltage V _r from the opposite ends.

[0042] Then, typically, is sampling the connection has been provided and hold circuit 15 to the signal voltage e _s to one common end switch end of the switch SW ₁₀ by a control signal S ₆ output from the timing circuit 22.

[0043] The switch SW by a control signal S ₆ with less cycles than the sampling period of the signal voltage e _s
Is switched to the other ₁₀ of the switch end, the reference voltage V _r is sampled at the hold circuit 15.

This sampling value is stored in the buffer amplifier 16.
Memo stored in the signal processing unit 17 via the
Stored in the directory. The signal processing unit 17 uses this to
Pressure e _sIs calculated as a flow rate signal at the output terminal 18.
Output. This makes it possible to compensate for span variations.
Wear.

In the description so far, for the sake of simplicity, the description has been made on the basis of a capacitance type electromagnetic flow meter. However, a liquid contact type electromagnetic flow meter in which a detection electrode is in contact with a measurement fluid may be used. If a specific condition is allowed, it can be applied similarly to the case of the capacitance type as described below.

In the case of the capacitance type, since the electrode capacity is very small, the time constant of charging and discharging of the electrode impedance due to the eddy current generated in the measuring fluid Q is sufficiently small, and the response is short with a short repetition cycle of excitation. Can also be applied when is required.

On the other hand, in the case of the liquid contact type, the electrode capacity formed by the detection electrode and the measurement fluid becomes large.
As shown by the dotted line in FIG. 7 (c), the differential noise N has a trailing shape, and it is necessary to lengthen the excitation cycle, so that a fast response cannot be expected.

However, in a case where the response may be slow, for example, a use as a water meter, the switch SW ₁ disposed at the subsequent stage of the high-pass filter 13 when the differential noise N disappears is used. By resetting at a predetermined timing, the initial value of the integration can be accurately set to zero at the beginning of the integration by the hold circuit 15, so that a good S / N can be obtained.

[Problems to be solved by the invention]

However, the configuration shown in FIG. 9 is a configuration in which the ratio between the reference voltage and the signal voltage is calculated by software operation using a microcomputer in the signal processing unit 17 to correct the span variation. In order to execute with limited electric power such as driving, the load of software calculation increases.

More specifically, the clock frequency must be increased in order to secure a predetermined operation speed, and the operation time of the microprocessor is increased. Therefore, the increase in power consumption due to these becomes a serious problem. come.

[0051]

According to the present invention, as a main structure for solving the above problems, a flow rate of a measurement fluid is converted into an electric signal, and a flow rate signal corresponding to the previous flow rate is detected via a detection electrode. In the output electromagnetic flow meter, the excitation period is shorter than the non-excitation period and the excitation current flows intermittently to apply a magnetic field to the previous measurement fluid, and the inter-electrode signal output from the previous detection electrode is exchanged. AC coupling means for coupling to obtain an AC signal, and first sample and hold means for sampling and holding the previous AC signal with a sampling signal having a sampling width including before and after the previous excitation period and outputting this as a first hold signal And a reference voltage proportional to the previous excitation current is switched by the sample switch from the previous AC signal, and is sampled and held by the previous sampling signal.
A second sample-and-hold means for outputting as a hold signal, a hardware operation means for calculating the ratio by hardware using the first and second hold signals, and a first operation using the output of the hardware operation means. Software calculation means for calculating the flow rate signal.

[0052]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of the present invention. Components having the same functions as those shown in FIGS. 5 to 9 are denoted by the corresponding reference numerals, and the description thereof is omitted.

The excitation current _If is _calculated by the reference resistance r and the reference voltage _Vr.
Is detected as the reference voltage V _r is held in the hold circuit 26 via the switch SW ₁₁ for sampling which is controlled by a control signal S ₈ output from the timing circuit 25, it is taken out through the Baffua amplifier 27.

In the voltage / frequency conversion circuit 28 functioning as hardware operation means, the resistors R _S and R _r and the non-inverting input terminal (+) are connected to the common potential point COM and the inverting input terminal (−) is used.
Operational amplifier 29 but connected to the output terminal by a capacitor C _f
In an integrator 30 configured, comparator 31, one-shot circuit 32, which is constituted by a switch SW _12, executes the dividing Thus such hardware.

[0055] Then, the output of Baffua amplifier 16 and 27, the inverting input of the operational amplifier 29, respectively via a resistor R _S and R _r and switch SW ₁₂ - is applied to the ().
The output of the operational amplifier 29 is supplied to the non-inverting input terminal (+) of the comparator 31 whose inverting input terminal (-) is connected to the common potential point COM.
, And its output is output to the counter 33 and also to the one-shot circuit 32.

[0056] switch SW ₁₂ by the pulse P _L that is output from the one-shot circuit 32 is set to on for a predetermined time. The contents of the counter 33 are periodically read by the microcomputer 34 functioning as software operation means.

In the above configuration, the flow signal is represented by the resistance R _S
While being integrated by the integrator 30 via this integration output pulse P _L of a predetermined time width τ from the one-shot circuit 32 comparator 31 operates Upon reaching a predetermined level is output.

The pulse P _L is supplied by turning on the switch SW ₁₂ for a predetermined time τ, thereby inputting a reference voltage V _r having a polarity opposite to that of the flow signal to the integrator 30 via the resistor R _r . 30 and the comparator 31 are reset.

By operating as described above, the comparator
The frequency f occurring at the output of V.31 is V _SPHold circuit 1
Hold voltage held at 5, V_rPThe hold circuit
Assuming the hold voltage held at 26,  f = (R_rV_SP/ R_SV_rP) And the frequency signal f is integrated by the integration capacitor C_f,as well as
The flow signal V is independent of the variation of the operating voltage of the circuit._S
And reference voltage V_rObtain as a signal proportional to the ratio
Can be.

The control signal S ₈ samples the reference voltage at the same timing as the control signal S ₆ by turning on the switch SW ₁₁ in an arbitrary period during which the control signal S ₂ is not turned on. The microcomputer 34 periodically reads the count value corresponding to the ratio between the flow voltage of the counter 33 and the reference voltage, and calculates the flow rate.

Since the configuration shown in FIG. 1 is a configuration in which the calculation of the ratio between the flow signal and the reference voltage is executed by hardware, the load on the software of the microcomputer 34 is reduced as compared with the software processing method shown in FIG. can do.

For example, the microcomputer 34 consumes a current of about 10 μA even in the sleep mode added to the recent low power consumption type, and generally consumes a current of 50 μA or more in the active mode. In general, the operational amplifier 29 and the like can generally operate at about 1 μA.

Therefore, when burdening the ratio calculation on the hardware, the microcomputer 34 can be operated in the sleep mode during this calculation. In this operation mode, the microcomputer 34 generates the timing signal and the counter 33. The operation time in this low power consumption mode is lengthened because the operation of reading data from the memory is sufficient, and the power consumption is reduced to 1/5 to 1/2 compared to, for example, the case where all are processed by software. Can be done.

FIG. 2 is a configuration showing another embodiment of the present invention.
FIG. This configuration corresponds to the output side of the buffer amplifier 14.
Switch SW₁₃And the flow signal V_SAnd reference voltage V_rWhen
And switch SW₁₃At the common end of
Switch SW₁₆And resistance R _iAnd capacitor C_iProduct with
The output circuit is connected to one end of a hold circuit.
Switch SW connected to 15₁₄The other end of the
Switch SW connected to the field circuit 26_FifteenAt the other end of it
Each is connected.

In this case, the switches SW ₁₃ , SW ₁₄ ,
The switching timing of SW ₁₅ and SW ₁₆ is controlled by control signals S ₉ , S ₁₀ , S ₁₁ and S ₁₂ output from the timing circuit 36.

Next, the operation of the circuit shown in FIG. 2 will be described with reference to the operation timing charts shown in FIGS. FIG. 3 (a) control signal S ₅ to control the timing of switching of the excitation, the timing of the integration operation in FIG. 3 (b) integrating circuit 35, FIG. 3 (c) control shown a timing for sampling a signal FIG. 3D shows a signal S ₁₀ (S ₁₁ ), and FIG. 3D shows a control signal S ₁₂ for controlling the reset operation of the integrating circuit 35.
Figure 3 (e) shows a control signal S ₉ indicating timing for switching between the reference voltage and the flow rate signal.

FIG. 3B showing the timing of the integration operation of the integration circuit 35 is a timing operation corresponding to the complementary operation <S ₁₂ > of the control signal S ₁₂ for controlling the reset operation of the integration circuit 35. .

The switch SW ₁₃ switches between the flow signal V _S side and the reference voltage V _r side by the control signal S ₉ shown in FIG. Normally, the flow rate signal V _S is switched to the flow rate signal V _S and the flow rate signal V _S is read into the integration circuit 35. However, the reference voltage V _r with little fluctuation is several times or several times with respect to the reading cycle of the flow rate signal V _S. The reference voltage _Vr is switched to the reference voltage _Vr side at a cycle of one in ten times and is read into the integration circuit 35.

[0069] First, a state where the switch SW ₁₃ is switched to the flow rate signal V _S side (FIG. 3 (e)) will be described. Integration shown in FIG. 3 (d) to the control signal S ₁₂ state the integrating circuit 35 the reset state has been canceled for indicating is initiated.

The integration time T _i of the integration circuit 35 (FIG. 3)
In (b)), the integration constant R _i C _i and its timing are selected so as to include the rise time T _st of the excitation timing (FIG. 3A) and the time necessary for eliminating the differential noise. Accordingly, the integration circuit 35 at the end of the integration time T _i (FIG. 3B) does not include the differential noise.

At the end of the integration time T _i (FIG. 3B), as shown in FIG. 3C, the switch SW ₁₄ is closed for the sampling time T _s by the control signal S ₁₀ and the flow rate is supplied to the hold circuit 15. signal V _s is the sample-and-hold.

Accordingly, a DC voltage proportional to the flow signal without noise is obtained at the output of the buffer amplifier 16. After the lapse of the integration time T _i (FIG. 3B), the switch SW ₁₆ is closed by the control signal S ₁₂ (FIG. 3D), and the integration circuit 35 is reset.

Next, the flow rate signal V _S several times to several tens times to once the control signal S ₉ by the switch SW ₁₃ is the reference voltage V as shown in FIG. 3 (e) in a proportion of relative reading cycle of _The reference voltage _Vr is read into the integration circuit 35 by switching to the _r side.

[0074] The integration time T _i (FIG. 3 (b)) control signal S _{1 1} and between the switch SW ₁₅ of the sampling time T _s is closed by the hold circuit 26 as shown in FIG. 3 (c) at the end of The reference voltage _Vr is sampled and held.

In this manner, the hold circuits 15 and 26
The flow signal V _S and the reference voltage V _r held at
The ratio is output to a frequency conversion circuit 28, where these ratios are calculated by hardware, read by a microcomputer 34 via a counter 33, a predetermined flow rate calculation is executed by software, and output to the output terminal 18. Is done.

According to the configuration shown in FIG. 2, since the linear integration circuit 35 is introduced for removing the differential noise, the capability of removing the differential noise is improved. Further, since the same integration circuit 35 is used for both the flow signal and the reference voltage, it is possible to eliminate an error due to the fluctuation of the integration circuit 35.

For the induction noise from the commercial power supply, the integration time T _i of the integration circuit 35 is selected to be an integral multiple of the cycle of the commercial power supply at the place where the electromagnetic flow meter is installed. By doing so, the induced noise is integrated for a time that is an integral multiple of the period of the commercial power supply, so that the induced noise can be removed in principle.

When the motor is driven with a low excitation level in order to operate with low power consumption, the influence of noise mixed in by induction from the commercial frequency power supply becomes a large factor. It effectively contributes to improvement of S / N.

Although the description of FIGS. 1 and 2 has been made based on the capacitance type electromagnetic flow meter, the liquid contact type electromagnetic flow meter in which the detection electrode is in contact with the fluid to be measured is also specified. When the above condition is permissible, the present invention can be applied similarly to the case of the capacitance type as described below.

FIG. 4 shows the structure near the flow detecting unit of the electromagnetic flow meter of the liquid contact type. The detection electrode 38a, 38b in contact with the measurement fluid Q is fixed to the conduit 37, and the other configuration is basically the same as the configuration shown in FIG. 1 or FIG.

In the case of the capacitance type, since the electrode capacity is very small, the time constant of charging and discharging of the electrode impedance due to the eddy current generated in the measurement fluid Q is sufficiently small, and the response is short with a short repetition cycle of excitation. Can also be applied when is required.

On the other hand, in the case of the liquid contact type, since the electrode capacity formed by the detection electrodes 38a and 38b and the measurement fluid Q becomes large, the differential noise N as shown by the dotted line in FIG. However, it is necessary to lengthen the excitation cycle, and a fast response cannot be expected.

However, in the case where the response is slow, for example, as an integrating flow meter for a water meter or the like, when the differential noise N disappears, it is disposed at the subsequent stage of the high-pass filter 13. Switch SW
By resetting ₁ at a predetermined timing, the initial value of the integration can be accurately set to zero at the beginning of the integration by the hold circuit 15, so that a good S / N can be obtained.

Specifically, for example, when an on-off ratio of excitation is set to about 1/100 or less and the latest low-power element is used as an electromagnetic flow meter for tap water for measuring the amount of tap water used, the total consumption is reduced. An electromagnetic flowmeter with a power of about 1 mW can be realized.

With this level of power consumption, an electromagnetic flowmeter that does not require external wiring can be constructed by using a battery as a drive power source, and flow rate measurement in an area without power supply equipment is possible.

When a battery is used as a driving power source, S
Even if the output fluctuation fluctuates slightly in the measurement of the instantaneous flow rate from the level of / N, it can be realized that it can sufficiently withstand use as a water meter for measuring the integrated flow rate.

[0087]

As described above, the present invention has been specifically described with the embodiments. According to the invention described in each claim, the calculation of the ratio between the flow rate signal and the reference voltage is executed by a hardware configuration. The flow rate calculation is configured to be shared and executed by software, so the current consumption can be significantly reduced by utilizing the latest power-saving circuit elements. It is possible to effectively cope with applications in which the capacity of the drive power supply is limited.

In particular, according to the third aspect of the present invention, it is possible to apply the present invention to a capacitance type electromagnetic flow meter. It can be applied to an electromagnetic flow meter.

According to the fifth aspect of the present invention, since the built-in battery is used as the driving power source,
An electromagnetic flowmeter that does not require external wiring and is easy to instrument and maintain can be realized.

Further, according to the invention described in claim 6, since the flow signal is measured as the integrated flow rate by using the integrator, the driving current is small and the S / N is small.
Even if the output fluctuation is large in the measurement of the instantaneous flow rate when the level is poor, it is possible to cope with an application such as a water meter for measuring only the integrated flow rate.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing a modification of the embodiment shown in FIG.

FIG. 3 is a waveform chart for explaining the operation of the embodiment shown in FIG. 2;

FIG. 4 is a partial configuration diagram in which a part of the embodiment shown in FIG. 1 or FIG. 2 is changed;

FIG. 5 is a block diagram showing a configuration of a conventional electromagnetic flow meter.

FIG. 6 is a circuit diagram showing a configuration of an excitation circuit of the electromagnetic flow meter shown in FIG.

FIG. 7 is a waveform chart for explaining the operation of the electromagnetic flow meter shown in FIG.

FIG. 8 is a waveform chart illustrating the operation of the excitation circuit shown in FIG.

FIG. 9 is a block diagram showing a configuration for compensating a variation in an excitation voltage with respect to the electromagnetic flow meter shown in FIG. 5;

[Explanation of symbols]

 10, 37 Conduit 11a, 11b, 38a, 38b Detection electrode 12 Preamplifier 13 High pass filter 15, 26 Hold circuit 17 Signal processing unit 19 Timing circuit 20 Excitation circuit 21 Excitation coil 22 Power supply circuit 25, 36 Timing circuit 28 Voltage / frequency Conversion circuit 33 Counter 34 Microcomputer 35 Integration circuit

Continuation of the front page (72) Inventor Seiji Tanabe 2-9-132 Nakamachi, Musashino City, Tokyo Yokogawa Electric Corporation (56) References JP-A-54-115163 (JP, A) JP-A-55-33685 (JP, A) JP-A-55-76912 (JP, A) JP-A-62-113019 (JP, A) JP-A-4-372824 (JP, A) JP-A-5-172602 (JP, A) Kaihei 5-172600 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01F 1/58-1/60

Claims (6)

(57) [Claims] 1. An electromagnetic flowmeter for converting a flow rate of a measurement fluid into an electric signal and outputting a flow rate signal corresponding to the flow rate via a detection electrode, wherein an excitation period is shorter than a non-excitation period and an excitation current is intermittently reduced. Exciting means for flowing and applying a magnetic field to the measurement fluid; AC coupling means for AC coupling an inter-electrode signal output from the detection electrode to obtain an AC signal; and sampling the AC signal including before and after the excitation period. First sample-and-hold means for sampling and holding with a sampling signal having a width and outputting this as a first hold signal; and sample-and-hold with the sampling signal by switching a reference voltage proportional to the excitation current from the AC signal by a sample switch. And a second sample-and-hold means for outputting this as a second hold signal, and using the first and second hold signals. An electromagnetic flowmeter comprising: hardware operation means for calculating these ratios by hardware; and software operation means for calculating the flow rate signal using the output of the hardware operation means. 2. An electromagnetic flowmeter which converts a flow rate of a measurement fluid into an electric signal and outputs a flow rate signal corresponding to the flow rate via a detection electrode, wherein an excitation period is shorter than a non-excitation period and an excitation current is intermittently reduced. Exciting means for flowing and applying a magnetic field to the measurement fluid; AC coupling means for AC coupling an inter-electrode signal output from the detection electrode to obtain an AC signal; and a reference voltage proportional to the AC signal and the excitation current. Switching means for switching between the switching signal and the switching signal; an integrating means for integrating an output signal of the switching means with a sampling signal having an integration time width including before and after the excitation period to output an integrated signal; A third hold means for sampling the integrated signal in the vicinity of the end of the integration time width and outputting the sampled signal as a third hold signal; And a fourth holding means for sampling the integrated signal near the end of the integration time width and outputting the sampled signal as a fourth hold signal in the state switched to the third side.
A hardware operation means for calculating the ratio by hardware using a fourth hold signal; and a software operation means for operating the flow rate signal using an output of the hardware operation means. Electromagnetic flow meter. 3. The electromagnetic flowmeter according to claim 1, wherein the detection electrode detects a flow signal via a capacitance. 4. The electromagnetic flowmeter according to claim 1, wherein the detection electrode contacts a measurement fluid to detect a flow signal. 5. The electromagnetic flowmeter according to claim 1, wherein a built-in battery is used as a drive power source for operating each unit including the exciting unit. 6. An electromagnetic flow meter according to claim 1, wherein said flow signal is measured as an integrated flow rate by an integrator.