JPH0477852B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a liningless electromagnetic flowmeter that does not provide an insulating lining on the inner surface of a conductive pipe through which a fluid to be measured flows, and particularly relates to a liningless electromagnetic flowmeter that does not provide an insulating lining on the inner surface of a conductive pipe through which a fluid to be measured flows. Concerning the improvement of tube potential formation on the tube wall of a tract.

<Prior art> Electromagnetic flowmeters generally use an insulating lining material on the inner surface of the conductive pipe to prevent the signal voltage generated in the conductive pipe in response to the flow rate from being short-circuited by the conductive pipe. It is lined.

However, recently, electromagnetic flowmeters without linings have been proposed to prevent accidents caused by deformation of the lining material. The configuration of such a conventional electromagnetic flowmeter is shown in FIG.

In FIG. 1, a fluid to be measured 2 is connected to a conductive conduit 1.
is filled, and a magnetic field B is applied to the fluid to be measured 2 by the excitation coil 3 across the conductive conduit 1 . The conductive conduit 1 has a cylindrical shape in a direction perpendicular to the plane of the paper, and the figure shows its central cross section. When the fluid to be measured 2 flows, a flow rate signal is generated between the measurement electrodes 4a and 4b. The flow rate signal is applied to the input end of the amplifier 5 and amplified. On the other hand, in the vicinity of the measurement electrodes 4a and 4b of the conductive conduit 1, the conductive conduit 1 in the vicinity
Tube potential electrodes 6a and 6b are provided to detect the potential of the tube, and the tube potential voltage at both ends thereof is applied to the input end of an amplifier 7 and amplified. The respective outputs of the amplifiers 5 and 6 are applied to the input terminal of the deviation amplifier 8, and the difference between them is taken and amplified. The output of the deviation amplifier 8 is given to the feed amplifier 9, and its output current _IW is applied to the ground electrode G of the tube potential electrodes 6a and 6b of the conductive conduit 1.
A power supply electrode 10a fixed to the side conductive conduit 1,
10b to form a potential distribution in the conductive conduit 1.

Measuring electrode 4 for potential distribution formed in this way
Potentials near a and 4b are detected by tube potential electrodes 6a and 6b and fed back to deviation amplifier 8 via amplifier 7, and are stabilized in a balanced state.

By configuring as above, the measured fluid 2
Since almost the same potential distribution as that caused by the flow rate signal generated near the inner peripheral surface of the conductive pipe 1 occurs in the conductive pipe 1, the relationship between the fluid 2 to be measured and the conductive pipe 1 is There is no current flowing in and out between them, and it is equivalent to applying an insulating lining.

On the other hand, the flow rate signal is applied from the measurement electrodes 4a, 4b to the converting section 11, where it is converted into, for example, a current output, and is obtained at the output end 12 as a current output. Conversion part 1
1 also supplies an excitation current for exciting the excitation coil 3 via excitation lines 13a and 13b.

As can be seen from the above explanation, the power supply electrodes 10a, 1
Conductive conduit 1 due to the output current I _W supplied from 0b
The potential distribution formed therein needs to be the same as the potential distribution in the vicinity of the inner peripheral surface when the inner surface of the conductive conduit 1 of the fluid to be measured 2 is insulated.

However, in the electromagnetic flowmeter, in addition to the flow rate signal, the measurement electrodes 4a and 4b have noise generated because the interfacial potential between the measurement electrodes 4a and 4b and the fluid to be measured 2 changes as the fluid to be measured 2 flows. (Hereinafter referred to as flow noise.) Fluid to be measured 2 and measurement electrode 4
Noise such as DC potential fluctuation noise due to temporal fluctuations in electrode potential occurring between electrodes a and 4b is superimposed. Therefore, these noise voltages are also detected at the measurement electrode at the same time, and the output current is determined based on this.
Since I _W is fed back, a potential is formed in the conductive conduit 1 including a noise voltage. The potential distribution in the conductive conduit must correspond to the flow rate signal, but since the noise distribution in the conductive conduit and the potential distribution of the flow rate signal are generally different, the voltage including the noise voltage must be formed. If feedback is applied, the noise component will be overcompensated, and the noise component detected between the measurement electrodes will increase. Therefore, the signal-to-noise ratio (S/
N ratio) decreases, causing output fluctuations and output fluctuations of the converter 11. Furthermore, since the current for the noise component is also passed through the conductive conduit through the power supply electrode, there is a drawback that power consumption increases.

<Object of the Invention> In view of the above-mentioned prior art, an object of the present invention is to provide an electromagnetic flowmeter that reduces the influence of noise voltage detected by measurement electrodes and has less output fluctuation.

<Configuration of the present invention> The configuration of the present invention that achieves this object relates to an electromagnetic flowmeter, and includes an amplifying means for amplifying the voltage from the measuring electrode, and rectifying and smoothing at least an output related to the output of the amplifying means. A conductive device comprising a rectifying and smoothing means and a converting means for converting the output of the rectifying and smoothing means into an alternating current voltage synchronized with excitation, and causing a current related to the output of the converting means to flow through a power supply electrode to cause the fluid to be measured to flow. The present invention is characterized in that a potential distribution similar to the potential generated near the inner surface of the conduit is formed in the conductive conduit.

<Example> Hereinafter, an example of the present invention will be described based on the drawings. Note that parts having the same functions as those in the prior art are denoted by the same reference numerals, and redundant explanations will be omitted.

FIG. 2 is a block diagram showing a first embodiment of the present invention. The difference from the conventional technology shown in Fig. 1 is that
The output of the amplifier 5, which receives the flow rate signal, is input to the synchronous rectifier circuit 14 to which a comparison voltage V _r corresponding to the excitation current is applied, where it is converted into direct current, smoothed by the smoothing circuit 15, and this output is converted into the comparison voltage V _r The DC/AC conversion circuit 16 converts the AC signal into an AC signal corresponding to the AC signal, which is used as a non-inverting input of the deviation amplifier 8. With such a configuration, high frequency noise etc. are removed and the output current I _W is supplied to the power supply electrode so that the deviation between the voltage corresponding to the flow rate signal and the tube potential voltage becomes zero.

The operation of the embodiment shown in FIG. 2 will be described below using the waveform diagram shown in FIG. Excitation coil 3
The conversion unit 11 outputs +, 0, as shown in FIG. 3a.
An excitation current If having three values of - and ₀ is supplied. When the excitation current I _f is supplied to the excitation coil 3 and the fluid 2 to be measured flows, a voltage including a flow rate signal is obtained between the measurement electrodes 4a and 4b. This voltage is sampled at each time point t ₁ , t ₂ , t ₃ , t ₄ shown in FIG. 3b by a converter 11 which converts it into a current output or the like. The converting unit 11 performs a calculation to remove noise using each of the sampled values, and outputs a current. As shown in Fig. 3c, the voltage obtained between the measurement electrodes 3a and 3b is a flow signal synchronized with the excitation current (Fig. 3a) and a voltage having a high frequency component of flow noise superimposed thereon. . This voltage is amplified by an amplifier 5, and synchronously rectified by a synchronous rectifier circuit 14 to which a comparison voltage corresponding to the excitation current is applied.
The voltage has the waveform shown in Figure d. The smoothing circuit 15 smoothes the voltage having the waveform shown in FIG.
Obtain a voltage waveform from which flow noise including high frequency components has been removed, as shown in . The output voltage of the smoothing circuit 15 is
The DC/AC conversion circuit 16 applies the voltage to the non-inverting input terminal of the deviation amplifier 8 as a voltage (FIG. 3f) with a polarity corresponding to the excitation current. The tube potential voltage of the tube potential electrodes 6a and 6b is applied to the inverting input terminal of the deviation amplifier 8, and the output current _IW is applied to the feeding electrode from the feeding amplifier 9 so that the voltage difference between both input terminals of the deviation amplifier 8 becomes zero. 1
0a and 10b. In this way, flow noise, DC potential fluctuation noise, etc. are removed, and a potential distribution corresponding to the flow rate signal is formed in the conductive conduit 1.

FIG. 4 is a circuit diagram showing another embodiment of the synchronous rectifier circuit in FIG. 2. FIG. 5 is a waveform diagram illustrating the operation of the circuit shown in FIG. 4.

When the contact potential difference between the measurement electrodes 4a and 4b fluctuates slowly over time compared to the excitation period, in order to remove this fluctuation at the same time, for example, a sample synchronous rectifier circuit 17 shown in FIG. amplifier 5
It is effective to configure it by connecting it to the output end of the One ends of the switches SW ₁ and SW ₂ are connected to the output end of the amplifier 5, and the other ends are connected to the non-inverting input end and the inverting input end of the amplifier 18 via resistors, respectively. When the voltage obtained between the measurement electrodes 4a and 4b in response to the excitation current shown in FIG. 5a is superimposed with flow noise and slowly fluctuates almost linearly as shown in FIG. 5b, as shown in FIG. Timing t ₁ ~ shown by c and d
When the voltage obtained between the measurement electrodes is sampled at t ₄ , the calculation shown in the following equation is performed as a result, and the influence of the slowly fluctuating contact potential difference is removed.

e _S =e ₁ −e ₂ −e ₃ +e ₄ (1) Here, e ₁ to e ₄ represent voltages sampled corresponding to timings t ₁ to t ₄ shown in FIGS. 5c and 5d. Sampling timing t ₁ to _{t 4} is the conversion unit 1
₁ (not shown in FIG. ₂ ). switch
SW ₁ is closed by the sampling signal S ₁ and switch SW ₂ is closed by the sampling signal S ₂ to sample the voltage between the measurement electrodes.

FIG. 6 is a block diagram showing a second embodiment of the present invention. This embodiment is an example in which a microcomputer is used. Measuring electrode 4a,
The voltage across 4b is amplified by an amplifier 5, sampled by a sampling circuit ₂₀ using a sampling signal S3 from a microcomputer 19, and taken into an analog-to-digital converter (hereinafter referred to as an A/D converter) 21. The captured data is processed by a microprocessor (hereinafter abbreviated as CPU)
22 is stored in a predetermined location in the memory (ROM/RAM) 24 designated via the address bus 23 via the data bus 26 via the input/output port (I/O port) 25. The data stored in the memory 24 is subjected to processing such as the calculation shown in equation (1), smoothing, and DC/AC conversion synchronized with the excitation current I _f according to the calculation procedure stored in advance in the ROM of the memory 24. , flow noise, DC potential fluctuation noise, slow fluctuations in contact potential difference, etc. are removed.
The voltage corresponding to the flow rate signal from which noise has been removed by performing such calculations is applied to the non-inverting input terminal of the deviation amplifier 8 via the digital-to-analog converter (D/A converter) 27, The tube potential voltage of the tube potential electrodes 6a, 6b is applied to the ends via an amplifier 7, and a feed amplifier 9 is applied to the feed electrodes 10a, 10b so that the potential difference between these input ends becomes zero.
An output current _IW is caused to flow through the conductive pipe 1, and a potential distribution corresponding to the flow rate signal is formed in the conductive conduit 1. In addition,
The excitation coil 3 is connected to the I/O port 2 under the control of the CPU 22 so that the waveform shown in FIG.
The switches SW ₃ to SW ₆ are switched by the excitation switching signal S ₄ applied via the constant current source 28, and the excitation current _If is supplied from the constant current source 28. On the other hand, the voltage corresponding to the flow rate signal is output via the D/A converter 29 as, for example, a unified current signal.

FIG. 7 is a block diagram showing a third embodiment of the present invention. The voltage between the measurement electrodes 4a and 4b is received by the amplifier 5, and its output is input to the non-inverting input terminal of the deviation amplifier 29. The output of the deviation amplifier 29 is synchronously rectified by a synchronous rectifier circuit 14 which uses a comparison voltage V _r having the same waveform as the excitation current I _f as a comparison voltage.
After being smoothed by the comparison voltage V _r , it is multiplied by the multiplier 30 and input to the inverting input terminal of the deviation amplifier 29 . When the deviation amplifier 29 is in a balanced state, the output circuit 31 outputs a ratio between the flow rate signal and the comparison voltage, and as a result, a voltage divided by the excitation current _If is obtained. In this case, the multiplier 30 corresponds to, for example, the AC/DC conversion circuit 16 in FIG. 2, and also has the function of modulating the excitation current to the same phase. On the other hand, after the tube potential voltage is received by the deviation amplifier 8,
This becomes the inverting input of the deviation amplifier 8, and its non-inverting input is inputted with the output of the multiplier 30.
An output current _IW is supplied to a and 10b, and a potential distribution corresponding to the flow rate signal is formed in the conductive conduit 1.
Note that an excitation _current If is supplied to the excitation coil 3 from an excitation circuit 32 via a resistor r.

FIG. 8 is a block diagram showing a fourth embodiment of the present invention. In this embodiment, the amplifier 8 calculates the difference between the voltage between the measurement electrodes and the tube potential voltage, and the deviation amplifier 29 operates so that this difference becomes zero.
This is different from the embodiment shown in the figure.

FIG. 9 is a block diagram showing a fifth embodiment of the present invention. This embodiment is a liningless electromagnetic flow meter converter 33 by adding a servo amplifier 34 including an amplifier 7, a DC/AC conversion circuit 16, a deviation amplifier 8, and a power supply amplifier 9 to a conventional low frequency excitation type electromagnetic flowmeter converter 33. This is a configuration of a flow meter. With such a configuration, a liningless electromagnetic flowmeter can be easily obtained by simply adding the servo amplification section 34 to an existing electromagnetic flowmeter.

FIG. 10 is a configuration diagram showing a configuration in which a power supply electrode and a tube potential electrode are shared in each embodiment of the present invention. The power supply electrode 10a and tube potential electrode 6a, and the power supply electrode 10b and tube potential electrode 6b of each embodiment are each integrated into one body. The object of the present invention can be achieved even with such a simple configuration.

In each embodiment, the case where the synchronous rectifier circuit 14, the smoothing circuit 15, the DC/AC conversion circuit 16, etc. are installed on the measurement electrodes 4a, 4b side has been described, but these can be installed on the tube potential electrodes 6a, 4b as necessary. 6b
You can also put it on the side.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, noises such as flow noise and DC potential fluctuation noise that appear in liningless electromagnetic flowmeters are removed, and only the flow signal component is detected. Since a potential distribution is formed in the conductive conduit, fluctuations in the flow rate output can be reduced, and the output current can also be reduced by the amount caused by noise components, so a potential distribution is formed in the conductive conduit. The power required for this can be reduced.

This effect is particularly effective when the conductivity of the fluid to be measured is low and the influence of flow noise and DC potential fluctuation noise is large.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of a conventional electromagnetic flowmeter, Fig. 2 is a block diagram showing the first embodiment of the present invention, and Fig. 3 is a waveform showing waveforms of various parts of the embodiment of Fig. 2. 4 is a circuit diagram showing another embodiment of the synchronous rectifier circuit in FIG. 2, FIG. 5 is a waveform diagram explaining the operation of the circuit in FIG. 4, and FIG. FIG. 7 is a block diagram showing a third embodiment of the present invention, FIG. 8 is a block diagram showing a fourth embodiment of the present invention, and FIG. 9 is a block diagram showing a fifth embodiment of the present invention. FIG. 10 is a block diagram showing an embodiment of the present invention, and FIG. 10 is a configuration diagram showing a configuration when a power supply electrode and a tube potential electrode are shared in each embodiment of the present invention. 1... Conductive pipe line, 2... Fluid to be measured, 4a, 4b
... Measuring electrode, 6a, 6b... Tube potential electrode, 8... Deviation amplifier, 9... Feeding amplifier, 10a, 10b... Feeding electrode, 11... Conversion section, 14, 17... Synchronous rectifier circuit, 15... Smoothing circuit, 16... DC /AC conversion circuit,
19...Microcomputer, 20...Sample circuit, 21...A/D converter, 22...CPU, 24...
Memory, 25...I/O port, 27, 29...D/
A converter, 30... Multiplier, 31... Output circuit, 32
...excitation circuit.

Claims (1)

[Claims] 1 amplification means for amplifying the voltage from the measurement electrode;
It comprises at least a rectifying and smoothing means for rectifying and smoothing an output related to the output of the amplifying means, and a converting means for converting the output of the rectifying and smoothing means into an alternating current voltage synchronized with the excitation, and the output of the converting means An electromagnetic flow rate characterized in that a potential distribution similar to a potential generated near the inner surface of the conductive conduit through which the fluid to be measured flows is formed in the conductive conduit by passing a current related to the flow through the feeding electrode. Total.