JPS6358114A - Electromagnetic flow meter - Google Patents

Abstract

PURPOSE:To enable highly accurate measurement of flow rate, by discarding the flow rate signals containing a large noise or removing the noise with a filter. CONSTITUTION:A magnetic field 2 is applied to a fluid to be measured flowing through a tube 1, an electromotive force corresponding to the flow velocity thereof is detected 3 and then a flow rate signal is outputted from a detection means 3. The flow rate signal is A/D-converted 6 to be read into an abnormality value decision means 7 and when it is decided to be an excessive signal beyond a specified value, the digital signal is discarded while an abnormality signal is outputted. In this manner, the outputting of accidental excessive noise component is blocked to prevent the generation of measuring errors. Then, the frequency of occurrence of the abnormality signals is counted with an abnormal value frequency decision means 8 and when counts per unit time exceed a specified value, a switching means 5 is turned to the filter 4 side. This allows a flow rate signal to be inputted into the converter 6 after being passed through the filter 4 to block the outputting of excessive noise components frequency generated, excluding the normal frequency components of flow rate signals, thereby preventing the generation of errors and the disabling of measurement.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to an electromagnetic flowmeter, and is capable of accurately removing noise components generated in a detection section to perform accurate flow measurement. It is something.

(Prior art) An electromagnetic flowmeter is an application of Faraday's method of electromagnetic induction n11, in which a magnetic field is applied to a conductive fluid to be measured in a direction perpendicular to its flow direction, and the flow rate of the fluid to be measured is adjusted according to the flow velocity. The electromotive force generated in the fluid is detected by a pair of electrodes placed in the fluid to be measured to generate a flow signal.

By the way, in this electromagnetic flow cutting, the electrode for detecting electromotive force is
Since it is in direct contact with the fluid to be measured, if the fluid to be measured contains, for example, an adhesive substance, the f1 adhesive substance may adhere to the electrode or peel off from the electrode, causing the electrode to receive a flow rate signal. Potentials unrelated to the current may occur.

This potential is extracted from the electrode as a noise component along with the flow rate signal. Therefore, this noise component causes a measurement error.

In response to this, various improvements have been made in this type of electromagnetic flowmeter to remove this noise component.

An example of a conventional electromagnetic flowmeter with this improvement is the one disclosed in Japanese Unexamined Patent Publication No. 60-207006 (hereinafter referred to as the first conventional example).
An alternating current excitation method is adopted in which the fluid to be measured is excited with alternating current, and a bipolar flow rate signal is extracted from a detector provided with electrodes.

A converter that processes the flow rate signal is connected to the next stage of the detector, and inside the converter is an A/D that operates with bipolar flow signals.
A microprocessor is provided for performing necessary arithmetic processing on the flow rate data taken in through the converter and the A/D converter using the following functions.

That is, the microprocessor includes a data pair creation unit that generates a pair of continuous bipolar flow rate data from among the flow rate data read from the A/D converter, and a data pair generator that generates a pair of flow rate data. A data check unit is provided that compares the absolute values and determines whether the difference is within a predetermined value.

Then, the absolute value of the pair of flow rate data created by the data bear creation part is compared in the data denic part, and if the difference is within a predetermined value, the flow data is within the variation due to noise below the allowable level. It is determined that the data is normal.
If it is above a predetermined value, the noise component is removed by processing such as discarding the pair of flow rate data.

However, some of the fluids to be measured include slurry fluids that contain solids, and when measuring such fluids, large noise components of the same polarity may continuously appear. .

However, in the first conventional example, since a pair of continuous bipolar flow rate data is created as a pair of flow rate data in the data bear creation section, large noise components of the same polarity f1 occur continuously. , it may become impossible to create a pair of flow rate data, and in such a case, there is a problem in that flow rate measurement becomes impossible.

Further, a second conventional example in which improvements have been made to remove noise components is disclosed in Japanese Patent Application Laid-Open No. 61-66123.

The second conventional example employs a square wave excitation method in which the fluid to be measured is excited with a square wave, and a square wave flow rate signal is extracted from the detector.

A converter for processing a square wave flow rate signal is connected to the next stage of the detector, and a noise removal circuit having the following configuration is disposed within this converter.

In other words, the noise removal circuit uses the first and second sample and hold circuits that hold the flow rate signal level immediately before the rise and fall of the square wave flow rate signal to process the square wave input flow rate signal for half a cycle. (It is composed of a delay means for producing a delayed flow rate signal, and a differential circuit that takes the difference between this half-cycle or delayed flow rate signal and the input flow rate signal.)

Then, by taking the difference between the flow rate signal delayed by half a period and the input signal using this differential circuit, noise components at frequencies other than the excitation signal frequency, such as noise components at a low frequency that can be approximated to a DC signal, are removed. I try to do that.

By the way, when the fluid to be measured contains an adhesive substance, which once adheres to the electrode and then peels off, sudden excessive noise is generated. Such sudden excessive noise voltage components generally change stepwise.

However, in the second conventional example, the noise component is removed by taking the difference between the flow rate signal delayed by half a cycle and the input signal in a differential circuit, so that the noise changes in a stepwise manner as described above. If a sudden excessive noise component is input, the excitation frequency component cannot be removed by a filter, so the output of the differential circuit will change accordingly, causing a problem in that this will cause a measurement error. Ta.

(Problems to be Solved by the Invention) In the first conventional example, there is a problem in that if large noise components occur continuously, flow measurement may become impossible.

81; Furthermore, in the second conventional example, there is a problem in that a measurement error occurs when a sudden excessive noise component occurs.

This invention was made based on two conditions, and it is possible to accurately remove both continuous large noise components and sudden excessive noise components, and to measure J:current h1 with accuracy. The purpose of this invention is to provide an electromagnetic flowmeter that can perform the following functions.

[Structure 1 of the Invention (Means for Solving Problems 1-1)] In order to solve the above-mentioned problems, the present invention, as shown in FIG. excitation means 2 that excites by applying a magnetic field perpendicular to the direction; and detection means that detects an electromotive force generated in a direction perpendicular to the magnetic field according to the flow velocity of the excited fluid to be measured, and outputs this as a flow rate signal. 3, a filter 4 for inputting the flow rate signal from the detection means 3 and extracting the frequency component of the flow rate signal, a switching means 5 for selectively switching and outputting either the output signal from the detection means 3 or the filter 4; An analog/digital converter for the signal switched by this switching means 5
A digital signal converted by the D converter 6 and this A/D converter is input, and it is determined whether or not the input signal is an excessive signal exceeding a predetermined value, and if it is not an excessive signal, the flow rate is An abnormal value determining means 7 which outputs a measurement signal and discards the input signal when the signal is excessive and outputs an abnormal value signal, and a circuit for generating an abnormal value signal output from this abnormal value determining means 7 is counted. , and abnormal value frequency determination means 8 which switches the switching means 5 to the filter 4 side when the count value per unit time exceeds a predetermined value.

(Function) When an If field is applied by the exciting means 2 to the fluid to be measured flowing in the measuring tube 1, an electromotive force corresponding to the flow velocity is generated by the detecting means 3.
The detection means 3 outputs a flow rate signal.

The flow rate signal from the detection means 3 is changed to C△/ through the switching means 5.
I) Input to converter 6, converted to digital signal 1.3, and read into abnormal value determination means 7.

The abnormal value determining means 7 determines whether the read digital signal is an excessive signal exceeding a predetermined value. When the signal is not excessive, it is output as a flow rate measurement signal corresponding to the input digital signal.

-h, if it is determined to be an excessive signal, the input digital signal is discarded and 5'l! %'
; (ll'l signal is output.

By discarding the excessive Iha issue like this! 2′
This prevents the output of one tone component that exceeds IF within 2 (measurement error Z- is prevented from occurring).

The number of occurrences of the abnormal value signal is counted by the abnormal value frequency determination means 8, and when the counted value per unit time exceeds a predetermined value, the switching means 5 is switched to the filter 4 side.

Due to this switching process to the filter 4 side, the flow rate signal that has passed through the filter 4 is input to the A/D converter 6, and excessive noise components that frequently occur other than the frequency components of the flow rate signal are output. This prevents errors from occurring and making it impossible to measure.

(Example) An example of the present invention will be described below based on FIGS. 2 and 3.

FIG. 2 is an overall configuration diagram, and FIG. 3 is a flowchart for explaining the operation.

In FIG. 2, the same or equivalent equipment or members as shown in FIG. 1 are designated by the same reference numerals.

First, to explain the configuration, the electromagnetic flowmeter is roughly divided into a detector 10 and a converter 2o.

The detector 10 includes a measuring tube 1 through which a fluid to be measured flows, excitation coils 11a and 11b that apply a magnetic field perpendicular to the flow direction of the fluid to be measured through the measuring tube 1, and excited coils to be measured. A pair of electrodes 12a112b are provided to detect an electromotive force generated in a direction orthogonal to the magnetic field depending on the flow velocity of the fluid.

In addition, the converter 20 is equipped with an amplifier 13 that amplifies the electromotive force detected by the electrodes 12a and 12b to a predetermined level. The amplifier 13 outputs a flow rate signal at a predetermined level.

Thus, the electrodes 12a, 12b and the amplifier 13 constitute the detection means 3.

14 is an excitation circuit, and the excitation coil 1 is connected from this excitation circuit 14.
An alternating current excitation vA current having a required frequency is supplied to 1a and 11b.

Therefore, this excitation circuit 14 and excitation coils 11a, 1
1b constitutes an excitation means 2.

Reference numeral 4 denotes a filter, which removes noise components other than the frequency component of the flow rate signal and extracts only the frequency component of the flow rate signal.

One of the output terminals of the amplifier 13 is directly connected to the fixed contact a of the changeover switch (switching means) 5, and the other is connected to the fixed contact a of the filter 4 via the filter 4.

The changeover switch 5 selectively switches either the flow rate signal from the amplifier 13 or the flow rate signal filtered by the filter 4 and inputs it to the A/D converter 6 .

The output terminal of the A/D converter 6 is connected to a microprocessor 15 for performing necessary arithmetic processing.

The functions of the microprocessor 15 constitute the abnormal value determining means 7 and the abnormal value frequency determining means 8 shown in FIG.

The abnormal value determining means 7 inputs the digital signal converted by the Δ/D converter 6, and the A/D converter 6 determines whether the input digital signal is an excessive signal exceeding a predetermined value. It is determined based on whether the value exceeds the value of
When the signal is not an excessive signal, a signal corresponding to the digital signal is output as a constant signal on the flow rate side, and when the signal is an excessive signal, the input digital signal is discarded and an abnormal value signal is output.

The yC normal value frequency determining means 8 inputs this abnormal value signal, counts the number of occurrences of the abnormal value signal, and when the counted value per unit time exceeds a predetermined value, switches the selector switch 5 to the filter. This is to control switching to the 4th side.

1 ( ) is an output circuit, 17 is an output terminal, and the output circuit converts the digital flow signal output from the microprocessor 15 into an analog flow measurement signal or a digital flow measurement signal as appropriate. Output terminal 17
This is what is output from.

Next, the operation will be explained using flowchart 1 in FIG.

The selector switch 5 is initially switched to the a contact side, and the microprocessor 15 receives the flow rate from the amplifier 13).
The initial setting is J, which is input after digital conversion.

An electromotive force corresponding to the flow velocity of the fluid to be measured is applied to the electrodes 12a, 12.
b, and a flow signal amplified to a predetermined level is output from the amplifier 13 (step 21).

The flow rate signal from the amplifier 13 is input to the A/D converter 6 via the a contact side of the changeover switch 5 in step 24, and is read into the microprocessor 15 after being converted from analog to digital.

The microprocessor 15 first determines whether the digital signal read in step 25 is an excessive signal exceeding a predetermined value. A/
The determination is made based on whether the D converter 6 exceeds a predetermined value.

If the determination result in step 25 is negative (NO) and there is no excessive signal, in step 26, the read digital signal is converted into an analog flow rate measurement signal or a digital flow rate measurement signal as appropriate and output. terminal 1
Output from 7.

If the determination result in step 25 is affirmative (Yes) and the signal is excessive, the input digital signal is discarded and at the same time an abnormal value signal is output.

By discarding excessive signals exceeding a predetermined value in the A/D converter 6, sudden excessive noise components are prevented from being output, and measurement errors are prevented from occurring.

The number of occurrences of the abnormal value signal is incremented by 4 in step 27, and it is determined whether the 51 numerical value per unit time exceeds a predetermined value.

If the determination result is negative (NO) and the predetermined value is not exceeded, the selector switch 5 is switched to the a contact side (step 28).

On the other hand, if the determination result in step 27 is affirmative ('1'es) and the count value per unit time exceeds a predetermined value, the selector switch 5 is switched to the b contact side (step 29). .

Therefore, when large noise components occur continuously, the flow rate signal that has passed through the filter 4 is input to the Δ/D converter 6, and frequently occurring excessive noise components other than the flow rate signal frequency components are output. This prevents errors from occurring and impossibility of measurement.

Further, even when a normal flow rate measurement signal is output in step 26, the abnormal value frequency determination process in step 27 is performed. In this case, the stored value determined to be an abnormal value and counted is decremented. With this decrement process,
- Even if the number of abnormal values exceeds a predetermined value and the changeover switch 5 is switched to the B contact side, when the number of tears stored value falls below the predetermined value, the changeover switch 5 is returned to the A contact side. .

In addition, in normal electromagnetic flow opening, the flow rate signal is read into the converter 2o at fixed time intervals, so the value obtained by the increase/decrease process of the abnormal value generation circuit performed every time the flow rate signal is read. Even if it is used, it is equivalent to determining the number of abnormal values based on the bar 1 value per unit time.

Depending on the nature of the noise generated by the detector 10, the microprocessor 15 determines the optimal method for removing the noise component, so that noise components of any nature can be removed accurately.

In the above embodiment, either the output signal from the amplifier 13 or the filter 4 is sent to the A/D converter 6.
A hardware selector switch 5 is provided as a means for selectively switching input to the Δ/D converter (one dedicated to the amplifier 13 and one dedicated to the filter 4 instead). Then, each digital signal from these two A/D converters is processed by a microprocessor 15.
A software switch in the microphone transmitter 15 can be used to select either of these digital signals.

The switching selection of the output signal from the amplifier 13 and the output signal from the filter 4 was made based on the judgment signal from the abnormal value count judgment means 8. If the measurement is limited, it may be possible to run a preset program corresponding to the type of fluid to be measured, regardless of the above judgment signal, before the measurement. can.

[Effects of the Invention] According to the configuration of the present invention, the abnormal value determining means determines whether the digital signal corresponding to the flow rate signal is an excessive signal exceeding a predetermined value. If it is not an excessive signal, a flow rate measurement signal corresponding to the manual digital signal is output, and if it is an excessive signal,
The input digital signal is discarded, and an abnormal value signal is output together with it.

Since excessive signals are discarded in this way, sudden excessive noise components are prevented from being output, and measurement errors are prevented from occurring.

Further, the number of occurrences of the abnormal value signal is counted by the abnormal value frequency determination means, and when the counted value per unit time exceeds a predetermined value, the switching means is switched to the filter side, and the flow rate signal passing through the filter is is input to the A/D converter. Therefore, frequently occurring excessive noise components other than the frequency components of the flow rate signal are prevented from being outputted, thereby preventing the occurrence of errors and failure to measure.

In this way, both sudden excessive noise components and frequent excessive noise components can be accurately removed, making it possible to perform highly accurate flow measurement, and having the advantage of preventing measurement failure. .

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the basic structure of an electromagnetic flowmeter according to the present invention, Fig. 2 is a block diagram showing an embodiment of the invention, and Fig. 3 is a flow chart for explaining the operation of the above embodiment. It is. 1: Measuring tube, 2: Excitation means, 3: Detection means, /I: Filter, 5: Changeover switch (switching means), 6: A/D converter, 7: Abnormal value determination means, 8: Abnormal value frequency determination means , 11a, 11b: excitation coil, 12a, 12b: electrode, 15: microprocessor. Agent B1, Yoshiyasu Ri, Figure 2, Figure 3

Claims (1)

[Scope of Claims] Excitation means for exciting a fluid to be measured flowing in a measurement pipe by applying a magnetic field in a direction perpendicular to the flow direction thereof; a detection means for detecting the generated electromotive force and outputting it as a flow rate signal; a filter for inputting the flow rate signal from the detection means and extracting the frequency component of the flow rate signal; and a filter for detecting the output signal from either the detection means or the filter. A switching means for selectively switching and outputting; an A/D converter for converting the signal switched by the switching means from analog to digital; and an A/D converter for inputting the digital signal converted by the A/D converter, and converting the input signal to the digital signal. Abnormal value judgment that determines whether or not the signal is an excessive signal that exceeds a predetermined value, and if it is not an excessive signal, outputs it as a flow rate measurement signal, and if it is an excessive signal, discards the input signal and outputs an abnormal value signal. and an abnormal value determination means that counts the number of occurrences of an abnormal value signal output from the abnormal value determination means and switches the switching means to the filter side when the counted value per unit time exceeds a predetermined value. An electromagnetic flowmeter characterized by having means.