JPH04104014A - Electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To decrease the fluctuation of a zero point and to improve the accuracy in flow-rate measurement by computing a correcting value for the zero point corresponding to each frequency, and correcting the zero point by using the correcting value corresponding to the frequency with respect to each output signal. CONSTITUTION:The output signal of an exciting current If corresponding to each frequency is measured. The average values E1, E2 and E3 of the output signals for the individual frequencies are computed in average-value operating circuits 18 - 20. The average values E1, E2 and E3 are outputted into a zero- correction computing circuit 21. In the circuit 21, zero-correcting values DELTAe01, DELTAe02 and DELTAe03 are computed by using these data and outputted into a flow-rate operating circuit 22. In the circuit 22, correction is performed by using the zero correcting values DELTAe01, DELTAe02 and DELTAe03 with respect to the output signals corresponding to the frequencies of a sampling circuit 17. The flow rate signals without the zero-point errors are outputted through an output terminal 23. In this way, the fluctuation of the zero point at the high frequencies can be decreased, and the effect of the external noises can be made small.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an electromagnetic flowmeter that is excited at a relatively high frequency, and particularly to an electromagnetic flowmeter that estimates the zero point of the electromagnetic flowmeter without stopping the flow of the measured fluid. This invention relates to an improved electromagnetic flowmeter that can perform zero correction using this zero point.

<Prior art> Electromagnetic flowmeters that are excited at commercial frequencies have a relatively high excitation frequency, so they are less susceptible to zero point fluctuations caused by fluctuations in DC voltage at the detection south pole, and have the advantage of fast response speed. It has been used since ancient times.

However, on the contrary, the high excitation frequency causes a considerably large electromagnetic induction in the fluid to be measured or in the signal circuit, which causes the zero point to fluctuate and reduce the accuracy of flow rate measurement.

Therefore, in order to reduce the influence of this electromagnetic induction, a low frequency excitation type electromagnetic flowmeter that excites at a low frequency lower than the commercial frequency has been developed and put into practical use.

<Problem to be solved by the invention> However, since the influence of electromagnetic induction is reduced in low-frequency excitation type electromagnetic flowmeters that are excited at low frequencies, the long-term stability of the zero point is improved. However, since the excitation frequency has become considerably lower, the zero point tends to fluctuate due to fluctuations in the DC potential caused by the detection electrode coming into contact with the fluid to be measured, and the output response to changes in the flow rate of the fluid to be measured becomes slower. This problem has arisen.

Means for Solving the Problems> In order to solve the above problems, the present invention provides an excitation means that sends an excitation current in which a plurality of frequencies are arranged in time series to an excitation coil, and an excitation current that corresponds to each frequency. average value calculation means for calculating the average value of each output signal generated at each frequency;
Zero correction calculation means for calculating a zero point correction value corresponding to each frequency using these average values, and zero point correction for each output signal using the correction value corresponding to these frequencies. and a flow rate calculation means for outputting a flow rate signal using the excitation means. The excitation means sends an excitation current in which a plurality of frequencies are arranged in time series to the excitation coil, and the average value calculation means calculates an excitation current corresponding to each frequency. The average value of each output signal generated is calculated for each frequency.

Furthermore, the zero correction calculation means uses these average values to calculate the zero point correction value corresponding to each frequency, and the flow rate calculation means uses the correction values corresponding to these frequencies for each output signal. to correct the zero point and output the flow rate signal.

<Examples> Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention.

10 is a non-magnetic conduit such as stainless steel;
A lining is placed on this inner surface for insulation. Furthermore, a pair of detection electrodes 11.1 are insulated from this conduit 10.
2 is fixed.

In addition, in order to ground the measurement fluid Q, the wetted $ pole 13 is connected to the common potential point COM.

An excitation coil 14 is fixed to the outside of the conduit 10,
The excitation current amount f is supplied here from the excitation circuit 15. The excitation current amount f is controlled by the control signal CT1, and the peak value is constant as shown in FIG.
, . . . are switched in time series and supplied to the excitation coil 14.

On the other hand, the detection electrodes 11.12 are connected to each input terminal of the differential amplifier 16 (for simplicity, the amplification degree is assumed to be 1), and each of the frequencies f1, f2 generated at the detection electrodes 11.12,
The output signals e1, ef, and e3 corresponding to f3 are outputted to the sampling circuit 17 after common mode noise and the like are removed here.

The sampling circuit 17 includes a sampling switch 5Wo-
It is composed of a hold capacitor C and a sofa amplifier Qa, etc., and the output signals et, ef, and e3 of the differential amplifier 16 are sampled and held in the hold capacitor C according to the sampling signal T1.

The held output signals el, ef, and e3 are applied to one ends of the switches SW1, SWa, and SWs. These switches SW, -SW2, SW3 are operated at the frequency f1 of the excitation current amount f by the timing signal T2.
, f2, f3, and the switch S
The hold voltages corresponding to each frequency from the other ends of W 5 , SW 2 , SW are respectively average value calculation circuits 18.1.
The average values E1, E2, and E of the hold voltages corresponding to each frequency are calculated here.

The calculated average values El, E2, and E3 of each hold voltage are output to the zero correction calculation circuit 21.

The zero correction calculation circuit 21 executes calculations to estimate zero point correction values Δeo, -Δe02, and Δe03 of the output signals e1 and e3-e generated when excited at the respective frequencies f1, f2, and f3.

These zero point correction values ΔeO+, Δe02, Δe03
is output to the flow rate calculation circuit 22, and each frequency fifl, f
2, the output signal e of the sampling circuit 17 corresponding to f3
f + , ef 2 , ef ), the zero point is corrected, and the flow rate signals Qt 1 , Qt 2 ,
Output as Qt 3.

Note that 24 is a timing generation circuit, and this timing generation circuit 24 has a frequency of 1,
Control signal CT that controls the order of switching f2 and f3
I, and the sampling circuit 17 has a switch SW0.
outputs a timing signal T1 that samples the output signals generated corresponding to each frequency f1, f2, f3, and outputs a timing signal T1 for sampling the output signal generated corresponding to each frequency f1, f2, f3, and switches SW+, SW2, SW) to output signals 1, f2, f3 at each frequency sampled by the sampling circuit 17.
The output signals corresponding to the respective average value calculation circuits 18.
Timing signal T that switches and outputs every 19.20
2 at each frequency, and further outputs 1 at each frequency to the flow rate calculation circuit 22.
, f2, and f3 are outputted with a timing signal T3 that provides timing for zero correction.

Next, the operation of the embodiment configured as above will be explained using FIG. 3.

First, the output signals e+, e2, and e3 generated corresponding to 1, f2, and f3 at each frequency of the excitation current amount f are repeatedly measured during a short period when the measured flow rate 9 is considered to be constant, and these are sent to the average value calculation circuit. Stored in 18-2o.

The average value calculation circuits 18 to 20 use these output signals to calculate the average value l for each frequency for a predetermined period to calculate the average values E+ -Ea and El of the output signals.

These average values E+, E2, and El are output to the zero correction calculation circuit 21, so that the frequency f as shown in FIG.
The relationship between the average value E of the output signal and the output signal is obtained.

The zero correction calculation circuit 21 uses these data (fl, E+)
, (f2, E2), (f3, El), the correction curve Cv is extrapolated to the point where the frequency f is zero, as shown by the dotted line in Figure 3, using the least squares method, for example, and the frequency f is zero. It is determined that the average value E of the output signal at the point corresponds to the average value S of the signal voltage corresponding to the measured flow rate Q, and that the fluctuation is considered to be due to the fluctuation of the zero point.

This is because the response is good in the high frequency range f1, f2, and f3 and there is no influence of DC voltage, so if there is a fluctuation in the output signal E, it is assumed that it is due to the fluctuation of the zero point.
Moreover, if the frequency f is extrapolated to the point where it is zero, since there is no change in the cello point when f=o, the value of E at this zero frequency indicates the average value S of the signal voltage.

Therefore, the deviations Δe07, Δe02, and Δe03 between the line drawn horizontally from the point of zero in frequency and the correction curve Cv indicate the deviation of the zero point at each frequency f1, f2, and f3.

The zero correction calculation circuit 21 calculates the zero correction value Δe in this way.
01, Δeo2, and Δe03 are determined and outputted to the flow rate calculation circuit 22.

Next, the flow calculation circuit 22 corrects the output signals corresponding to the respective frequencies flf2 and f3 of the sampling circuit 17 using these zero correction values Δe07, Δe02, and Δe03, so that the flow rate is free from zero point error. Signal Qi+, Qf2-Q
f: Output to the output terminal 23 as +.

Note that the frequencies in the excitation current do not need to be arranged regularly in order of high frequency or low frequency, but may be a random arrangement, and the excitation period of each frequency does not need to be constant, but may be random.

Further, the correction curve CV does not need to be calculated by the linear least squares method, and may be calculated by any arbitrary method, for example, by a polynomial using an exponential number.

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, according to the present invention, a zero point correction value is calculated for each excitation frequency in a state of excitation with a plurality of high frequencies, and this is used to calculate the zero point correction value for each excitation frequency. Since the output signal corresponding to each frequency is corrected, it is possible to reduce the fluctuation of the zero point at high frequencies. Furthermore, the influence of external noise is reduced, so it is a low power consumption electromagnetic flowmeter with a small excitation current. becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention, FIG. 2 is a waveform diagram showing the waveform of the excitation@flow shown in FIG. 1, and FIG.
FIG. 1 is a characteristic curve diagram illustrating the operation of the upper end correction production circuit shown in FIG. 10... Conduit, 11.12... Detection electrode, 14...
- Excitation coil, 15... Excitation circuit, 17... Sampling circuit, 18-20... Average value calculation circuit, 21... Zero correction calculation circuit, 22... Flow rate calculation circuit, 24... Timing generation circuit. Figure 2 Figure 3

Claims (1)

[Claims] excitation means for sending an excitation current in which a plurality of frequencies are arranged in time series to an excitation coil; an average value calculation means for calculating an average value of each output signal generated corresponding to each frequency for each frequency; zero correction calculating means for calculating a zero point correction value corresponding to each frequency using these average values; and zero correction calculating means for calculating a zero point correction value corresponding to each frequency using these average values; An electromagnetic flowmeter characterized by comprising: a flow rate calculation means for correcting and outputting a flow rate signal.