JPH0789070B2 - Electromagnetic flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) [0001] The present invention relates to an electromagnetic flow meter, and it is possible to accurately remove a noise component generated in a detection unit and perform accurate flow rate measurement. It is a thing.

(Prior Art) An electromagnetic flow meter is an application of Faraday's law of electromagnetic induction. A magnetic field in a direction orthogonal to the flow direction is added to a conductive fluid to be measured, and the measured fluid is measured according to its flow velocity. The electromotive force generated in the fluid is detected by a pair of electrodes provided in the fluid to be measured to obtain a flow rate signal.

By the way, in this electromagnetic flowmeter, the electrode for electromotive force detection is
Since the fluid to be measured is in direct contact with the fluid to be measured, if the fluid to be measured contains, for example, an adherent substance, the adherent substance adheres to the electrode or peels off from the electrode, and the flow rate signal is transmitted to the electrode. There is a case where an electric potential unrelated to is generated.

This potential is extracted from the electrode as a noise component together with the flow 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.

As a conventional electromagnetic flowmeter with this improvement, for example, there is one disclosed in Japanese Patent Laid-Open No. 60-207006 (hereinafter referred to as a first conventional example).

The first conventional example adopts an AC excitation method in which the fluid to be measured is excited with an AC, and a bipolar flow rate signal is taken out from a detector provided with electrodes.

A converter that processes the flow rate signal is connected to the next stage of the detector, and an A / D converter that operates with a flow rate signal of both polarities and the A / D converter are used in the converter. A microprocessor is provided for performing required arithmetic processing on the flow rate data by the following functions.

That is, in the microprocessor, of the flow rate data read from the A / D converter, a pair of continuous bipolar polarity flow rate data is used as the flow rate data of each pair, and the flow rate data of this pair A data check unit is provided which compares absolute values and determines whether or not the difference is within a predetermined value.

Then, the absolute value of the flow rate data of the pair created by the data pair creation section is compared by the data check section, and if the difference is within a predetermined value, the flow rate data is within the variation due to noise below the allowable level. Judge that it is normal data,
If it is a predetermined value or more, the noise component is removed by processing such as discarding the flow rate data of the pair.

By the way, the fluid to be measured includes a slurry fluid containing a solid substance and the like, and when measuring such a fluid, a noise component having a large polarity may continuously occur.

However, in the first conventional example, the data pair creating unit creates a pair of continuous bipolar flow rate data as the flow rate data of the pair. Therefore, if a large noise component of the same polarity is generated continuously, In some cases, it is impossible to create the flow rate data, and in such a case, there is a problem that the flow rate measurement becomes impossible.

Also, as a second conventional example which has been improved to remove noise components, there is one disclosed in Japanese Patent Laid-Open No. 61-66123.

The second conventional example adopts 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 elimination circuit having the following configuration is arranged in the converter.

That is, the noise elimination circuit holds the flow signal levels of the square wave flow signal immediately before and after the rise and fall, respectively.
The sample-and-hold circuit of (1) comprises a delay unit that delays the square-wave input flow signal by a half cycle to generate a flow signal, and an operation circuit that takes the difference between the flow signal delayed by this half cycle and the input flow signal. ing.

Then, by taking the difference between the flow rate signal delayed by only a half cycle and the input signal in this operating circuit, noise components of frequencies other than the excitation signal frequency, for example, noise components of low frequency that can be approximated to a DC signal are removed. I am trying to do it.

By the way, when the fluid to be measured contains an adhering substance, which once adheres to the electrode and is peeled off, a sudden excessive noise is generated. Such a sudden excessive noise voltage component generally changes stepwise.

However, in the second conventional example, the differential circuit takes the difference between the flow signal delayed by a half cycle and the input signal to remove the noise component. When an excessive noise component is input, the excitation frequency component cannot be removed by the filter, so that the output of the differential circuit also changes accordingly, resulting in a measurement error.

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

In addition, the second conventional example has a problem that a measurement error occurs when a sudden excessive noise component occurs.

The present invention has been made based on the above circumstances, and it is possible to accurately remove both a continuous large noise component and a sudden excessive noise component and perform accurate diversion measurement. The purpose is to provide a flow meter.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention is designed so that the fluid to be measured flowing in the measuring pipe 1 is moved in the flow direction as shown in FIG. Exciting means 2 for exciting by applying magnetic fields in orthogonal directions
And a detection means 3 for detecting an electromotive force generated in the direction orthogonal to the magnetic field according to the flow velocity of the excited fluid to be measured and outputting the electromotive force as a flow rate signal, and a flow rate signal from the detection means 3 A filter 4 for extracting the flow signal frequency component,
Switching means 5 for selectively switching and outputting either the output signal from the detection means 3 or the filter 4, and this switching means 5
A / which converts the signal switched by
The D converter 6 and the digital signal converted by this A / D converter 6 are input, and it is determined whether the input signal is an excessive signal exceeding a predetermined value. When it is not an excessive signal, flow rate measurement is performed. An abnormal value determination means 7 that outputs a signal and discards the input signal when it is an excessive signal and outputs an abnormal value signal, and an abnormal value signal generation circuit output from this abnormal value determination means 7 are counted. The gist is to have an abnormal value determination means 8 that switches the switching means 5 to the filter 4 side when the count value per unit time exceeds a predetermined value.

(Operation) When a magnetic field is applied to the fluid to be measured flowing in the measuring tube 1 by the exciting means 2, the electromotive force corresponding to the flow velocity is detected by the detecting means 3, and the flow rate signal is output from the detecting means 3.

The flow rate signal from the detection means 3 is sent to the A / D via the switching means 5.
It is input to the converter 6, converted into a digital signal and read by the abnormal value determination means 7.

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

On the other hand, when it is determined that the signal is excessive, the input digital signal is discarded and an abnormal value signal is output.

By discarding the excessive signal in this manner, it is possible to prevent a sudden excessive noise component from being output and prevent a measurement error from occurring.

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

By 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 an excessively large noise component other than the flow rate signal frequency component is output. Are prevented, and errors and measurement failures are prevented.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 2 and 3.

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

2 that are the same as or equivalent to the devices or members in FIG. 1 are designated by the same reference numerals.

First, the configuration will be explained. Electromagnetic flow meters are roughly classified into detectors.
It is composed of 10 and a converter 20.

The detector 10 has a measuring tube 1 through which the fluid to be measured flows, exciting coils 11a and 11b for applying a magnetic field orthogonal to the flow direction to the fluid to be measured through the measuring tube 1, and the velocity of the excited fluid to be measured. Is provided with a pair of electrodes 12a, 12b for detecting an electromotive force generated in a direction orthogonal to the magnetic field.

The converter 20 is also provided 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 of a predetermined level.

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

14 is an exciting circuit, and from this exciting circuit 14, exciting coils 11a, 1
An alternating excitation current of the required frequency is supplied to 1b.

Thus, the exciting circuit 2 and the exciting coils 11a and 11b constitute the exciting means 2.

A filter 4 removes noise components other than the flow signal frequency component and extracts only the flow signal frequency component.

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

Either the flow rate signal from the amplifier 13 or the flow rate signal filtered by the filter 4 is selectively switched by the changeover switch 5 and input to the A / D converter 6.

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

The function of the microprocessor 15 constitutes the abnormal value judging means 7 and the abnormal value number judging means 8 shown in FIG.

The abnormal value determination means 7 inputs the digital signal converted by the A / D converter 6, and the A / D converter 6 determines whether the input digital signal is an excessive signal exceeding a predetermined value. If it is not an excessive signal, a signal corresponding to that digital signal is output as a flow rate measurement signal.If it is an excessive signal, the input digital signal is discarded and an abnormal value signal is output. It is what is output.

The abnormal value number judging means 8 inputs this abnormal value signal,
The number of occurrences of the abnormal value signal is counted, and when the counted value per unit time exceeds a predetermined value, the changeover switch 5 is controlled to be switched to the filter 4 side.

Reference numeral 16 is an output circuit, 17 is an output terminal, and the output circuit appropriately outputs an analog flow rate measurement signal or a digital flow rate measurement signal in accordance with the digital flow rate signal output from the microprocessor 15. It is output from the terminal 17.

Next, the operation will be described with reference to the flowchart of FIG.

The changeover switch 5 is initially switched to the a-contact side, and is initially set so that the flow rate signal from the amplifier 13 is digitally converted and input to the microprocessor 15.

An electromotive force corresponding to the flow velocity of the fluid to be measured is detected by the electrodes 12a and 12b, and a flow rate 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 in step 24 through the a-contact side of the changeover switch 5 and is analog-digital converted, and then the microprocessor.
Read in 15.

The microprocessor 15 first determines whether or not the digital signal read in step 25 is an excessive signal exceeding a predetermined value. Whether the signal is an excessive signal is determined by whether the A / D converter 6 has exceeded a predetermined value.

If the result of the determination in step 25 is negative (No) and it is not an excessive signal, in step 26 it is converted into an analog flow rate measurement signal or a digital flow rate measurement signal as appropriate according to the read digital signal and is output terminal. It is output from 17.

When the determination result of step 25 is affirmative (Yes) and the signal is an excessive signal, the input digital signal is discarded and an abnormal value signal is output at the same time. As described above, the A / D converter 6 discards the excessive signal exceeding the predetermined value, so that the output of the sudden excessive noise component is prevented and the measurement error is prevented from occurring.

The number of occurrences of the abnormal value signal is counted (incremented) in step 27, and it is determined whether or not the count value per unit time exceeds a predetermined value.

When the determination result is negative (No) and the predetermined value is not exceeded, the changeover switch 5 remains switched to the a contact side (step 28).

On the other hand, when the determination result of step 27 is affirmative (Yes) and the count value per unit time exceeds the predetermined value, the changeover switch 5 is switched to the b contact side (step 29).

Therefore, when a large noise component is continuously generated, the flow rate signal that has passed through the filter 4 is input to the A / D converter 6, and a frequently occurring excessive noise component other than the flow rate signal frequency component is output. It is prevented that the error is caused and the measurement becomes impossible.

Also, when the normal flow rate measurement signal is output in step 26, the abnormal value number determination processing in step 27 is performed.
In this case, the stored value which is determined as an abnormal value and is counted is decremented. By this decrement processing, even if the number of abnormal values once exceeds the predetermined value and the changeover switch 5 is switched to the b contact side, if the stored count value falls below the predetermined value, the changeover switch 5 is changed to the a contact side. Will be restored.

Note that in a normal electromagnetic flowmeter, the reading of the flow rate signal into the converter 20 is performed at regular time intervals, so the value obtained by the increase / decrease process of the abnormal value generation circuit performed each time the flow rate signal is read is used. However, this is equivalent to determining the number of abnormal values based on the count value per unit time.

Therefore, depending on the nature of the noise generated in the detector 10, a method for removing the noise component by an optimum means is a microprocessor 15
Is discriminated, and a noise component of any property is accurately removed.

In the above-described embodiment, the hardware changeover switch 5 is provided as means for selectively switching and inputting either the output signal from the amplifier 13 or the filter 4 to the A / D converter 6, but instead of this, A / D converter amplifier 1
A dedicated one for 3 and a dedicated one for the filter 4 are provided respectively, and each digital signal from these two A / D converters is read by the microprocessor 15, and these are read by a software switch in the microprocessor 15. It is also possible to adopt any of the digital signals.

Further, the switching selection of the output signal from the amplifier 13 and the output signal from the filter 4 is made by the judgment signal from the abnormal value number judging means 8, but the kind of the fluid to be measured is limited to a specific one. In some cases, the measurement can be performed before the measurement by executing a preset program corresponding to the type of the fluid to be measured regardless of the determination signal.

As described above, according to the configuration of the present invention, the abnormal value determination means determines whether the digital signal corresponding to the flow rate signal is an excessive signal exceeding a predetermined value, and the excessive signal is detected. When it is not, the flow rate measurement signal corresponding to the input digital signal is output, and when it is an excessive signal, the input digital signal is discarded and an abnormal value signal is output together with it. Since the excessive signal is discarded in this manner, the output of a sudden excessive noise component is prevented and the occurrence of a measurement error is prevented.

When the number of occurrences of an abnormal value signal is counted by the abnormal value number determination means and the count 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 switched. Input to the A / D converter. Therefore, it is possible to prevent output of a frequent excessive noise component other than the frequency component of the flow rate signal, thereby preventing an error from occurring and becoming impossible to measure.

As described above, both the sudden and excessive noise components and the frequent and excessive noise components can be accurately removed, so that the flow rate can be measured with high accuracy and the measurement is prevented from becoming impossible. .

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a basic configuration of an electromagnetic flowmeter according to the present invention, FIG. 2 is a configuration diagram showing an embodiment of the present invention, and FIG. 3 is a flow chart for explaining the operation of the embodiment. Is. 1: Measuring tube, 2: Excitation means, 3: Detection means, 4: 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.

Claims (1)

[Claims] 1. An exciting means for exciting a fluid to be measured flowing in a measuring pipe by applying a magnetic field in a direction orthogonal to the flow direction, and an exciting means generated in a direction orthogonal to the magnetic field according to a flow velocity of the excited fluid to be measured. Detection means for detecting electromotive force and outputting it as a flow rate signal, a filter for extracting the flow rate signal frequency component by inputting the flow rate signal from the detection means, and selecting either the detection means or the output signal from the filter Inputting the digital signal converted by the A / D converter and the A / D converter for analog-digital converting the signal switched by the switching means, and the input signal is It is determined whether the signal is an excessive signal that exceeds a specified value.If it is not an excessive signal, it is output as a flow rate measurement signal, and if it is an excessive signal, the input signal is discarded and an abnormal value signal is sent. And the number of occurrences of the abnormal value signal output from the abnormal value determination means is counted, and when the counted value per unit time exceeds a predetermined value, the switching means is set to the filter side. An electromagnetic flowmeter, comprising: means for determining the number of abnormal values for switching to.