JPH03186716A - Electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To execute the dead detection even when wetting resistances of measuring electrodes become both larger and its value approaches by calculating the sum and a difference of DC voltages generated in each measuring electrode, respectively, and executing the dead detection by using OR of dead detecting signals detected by comparing with a threshold, respectively. CONSTITUTION:In an area in which a dead detection can be executed by a dead detecting signal Ve2 related to a difference voltage obtained in the output of a dead detecting circuit 19, when a difference between values of a wetting resistance Ra and Rb is in a dead zone beta which enters in width of a first threshold voltage VR1, whether it is dead or not cannot be decided by the signal Ve2. However, when a dead detecting signal Ve3 related to a sum voltage obtained in the output of a dead detecting circuit 23 is used, an area surrounded by a longitudinal line can also be brought to dead detection. Therefore, by an OR gate 25, OR of the signal Ve2 and Ve3 is calculated and outputted as a dead detecting signal Ve4. By this signal Ve4, the dead detection of part of the wetting resistance being larger than a boundary shown by a straight line for connecting delta and delta is executed and the part of the dead zone beta of this area is eliminated.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an electromagnetic flowmeter that detects when a measuring fluid in a conduit is empty, and particularly relates to an electromagnetic flowmeter that detects when a measuring fluid in a conduit is empty. This invention relates to an electromagnetic flowmeter that has been improved so that there is no area in which complete detection cannot be performed even if the flowmeter becomes larger.

<Prior Art> FIG. 5 is a block diagram showing the configuration of a conventional electromagnetic flowmeter having all detection functions.

Reference numeral 10 denotes a conduit whose inner surface is insulated and allows the measurement fluid Q to flow therein. A pair of measurement electrodes 11a and 11b which are in contact with the measurement fluid Q are fixed to this conduit 10 and are insulated from the conduit 10. The wetted electrode 11c that grounds Q is connected to the ground point G.

A wJ magnetic cocoil 12 for applying a magnetic field to the measurement fluid Q is arranged close to the conduit 10, and an excitation current If is passed through the excitation coil 12 from an excitation circuit 13.

And these conduits 10. A detector 14 is configured by an excitation coil 12 and the like.

Further, a preamplifier 15 is connected to the measurement electrodes 11a, 11b, and this preamplifier 15 includes a buffer amplifier 15a whose input end is connected to the measurement electrodes 11a, llb,
15b and a differential amplifier 15c whose output ends are connected to the input ends. Furthermore, the cathodes of diodes D + and D 2 are connected to these measurement electrodes 11a and 11b. These diodes DI, D
The anodes of 2 are connected to the negative power supply -■, respectively, and the constant current circuit 16 is connected by the diodes D+, D2 and the negative power supply -■.
(16a, 16b) are formed.

A series circuit in which Zener diodes I)zt and D22 are connected in series with opposite polarities is connected between the output terminal of the buffer amplifier 15b and the common potential point COM.

The output end of the differential amplifier 15c is connected to the input end of the signal processing circuit 17, and the signal processing circuit 17 uses the measured voltage VM+ appearing at this output end to calculate the flow rate signal V(l) and outputs it to the output end 18. do.

In addition, the entire detection circuit 19 is connected to the measurement voltage th of the measurement voltage V gate 1.
The difference voltage Ed+ corresponding to the difference between the DC voltages Ea and Eb appearing at the poles 11a and llb is compared with the first dark value voltage VR+ from the reference voltage source 20, and the entire detection signal Ve is outputted to the output terminal 21.
, outputs.

Next, the operation of the electromagnetic flowmeter configured as above will be explained.

For example, a rectangular-wave excitation current If is passed from the excitation circuit 13 to the excitation coil 12, thereby applying a rectangular-wave magnetic field to the measurement fluid Q. Along with this, the measurement electrode 11a
, llb is impedance-converted by the preamplifier 15, and the measured voltage vr'++ is output to the output terminal of the preamplifier 15.
is output as

The signal processing circuit 17 at the next stage uses this measured voltage VM1 to calculate the flow rate and outputs it to the output terminal 18 as a flow rate signal VQ.

On the other hand, the anodes of the measurement electrodes 11a and llb are connected to the negative power source.
Since the diodes D+ and D2 connected to
When the wetted resistances Ra and Rh between the electrodes 11a and 11b become larger, the DC voltages Ea and Bb of the measurement electrodes 11a and 11b become larger.

The differential amplifier 15c calculates the difference between these DC voltages Ea and Eb and outputs a differential voltage Ed+ to its output terminal. When the differential voltage Ed+ exceeds the threshold voltage VR+, the total detection circuit 19 determines that the inside of the conduit 10 is empty and outputs, for example, a negative total detection signal Ve+ to its output terminal 21.

<Invention or Problem to be Solved> However, the electromagnetic flowmeter as described above operates normally as described above when either the measurement pole 11a or llb is not in contact with liquid, but when it is in contact with liquid When the resistances Ra and Rb both become large, the differential voltage IEaBbl becomes almost zero, and even though the circuit is empty, one of the detection circuits cannot determine that it is empty. In preparation for such a case, in the conventional electromagnetic flowmeter shown in FIG. 5, a Zener diode D2 is connected between the output terminal of the buffer amplifier 15b and the common potential point COM.
1 and D22 are connected in series with opposite polarities to limit the output, so that even when both the wetted resistances Ra and Rb become large, a difference occurs between the outputs of the buffer amplifiers 15a and 15b.

However, even if such an output limiting circuit is provided, as shown in FIG. 6, there will be areas where all detection circuits 19 cannot be determined to be empty.

That is, the horizontal axis in FIG. 6 represents the wetted resistance Rh, and the vertical axis represents Ra.
, R indicates the limit voltage of the output by the Zener diode Dart and Di2, respectively. Empty detection cannot be performed in the shaded area in the figure. In particular, ■ The wetted resistance Rh increases and the DC potential of Eb increases. is limited by Zener diodes D21 and D22, empty detection cannot be performed when the wetted resistance R is within a certain width β1,
In addition, there is a problem that (2) there is a large area in which empty detection cannot be performed when the liquid contact resistances Ra and Rh increase simultaneously.

Means for Solving the Problems> In order to solve the above problems, the present invention detects a signal voltage generated in a measuring fluid with a pair of measurement electrodes, and converts this signal voltage into a signal using a signal processing means. In an electromagnetic flowmeter that performs processing and outputs it as a flow rate signal, the difference between the DC voltage generated between the constant current means that sends a constant DC current to the measuring electrode and the measuring electrode is calculated and compared with a first threshold value. a difference determining means for detecting a non-wetted state of the measuring electrode, a sum determining means for detecting a non-wetted state of the measuring electrode by calculating the sum of DC voltages generated between the measuring electrodes and comparing it with a second threshold value, and a difference determining means for detecting a non-wetted state of the measuring electrode. and calculation means for calculating the logical sum of each output of the sum determination means, and the empty state of the measurement electrode is determined based on the output of the calculation means.

Function: The constant current means passes a constant DC current to the measurement electrode, and the difference determination means compares the difference in DC voltage generated between the measurement electrodes with a first threshold value to determine the non-wetted state of the measurement electrodes. Detect.

Furthermore, the sum determination means compares the sum of the DC voltages generated between the measurement electrodes with a second threshold value to detect the non-wetted state of the measurement electrodes.

Thereafter, the calculation means calculates the logical sum of the respective outputs of the difference determination means and the sum determination means, and it is determined from this calculation result whether or not the measured fluid is empty.

<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. Note that parts having the same functions as those in the conventional configuration shown in FIG. 5 are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

A measurement electrode 11a generated at the output end of the differential amplifier 15c,
The measured voltage V corresponding to the difference in the measured voltages measured at llb
M2 undergoes signal processing in a signal processing circuit 17 and outputs a flow rate signal vQ to its output terminal 18.

On the other hand, this measurement voltage vbar2 is applied to one input terminal of the entire detection circuit 19, and the first threshold voltage VR+ from the voltage source 20 is applied to the other input terminal. F! ! 619 compares the DC difference voltage Ed2 included in the measurement voltage VM2 and the first threshold voltage vR, and outputs the entire detection signal Ve2 to its output terminal.

Also, the measurement electrode 1 appearing at the output of the buffer amplifier 15a
The measurement voltage measured at 1a and the measurement pressure measured at the measurement electrode 11b appearing at the output of the buffer amplifier 15b are added by a summing amplifier 22 via resistors R1 and R2, and the measurement electrode 11a, A measurement voltage vM3 is generated for the sum of the measurement voltages measured at llb.

This measurement voltage V gate 3 is connected to one input terminal of the entire detection circuit 23.
However, the second threshold Vi from the reference voltage source 24 is applied to the other input terminal.
``Although the X voltage VR2 is applied to each, the total detection circuit 23 compares the DC sum voltage Es2 included in the measurement voltage VM3 with the second threshold voltage VR2, and outputs the total detection signal Ve3 to its output terminal. In this case, the value of the second threshold voltage VR2 is set to about 3 to 4 times the first threshold voltage VR+.

25 is an OR gate, and this OR gate 25 calculates the logical sum of all detection signals Ve2 and Ve3 and outputs the output terminal 26.
It is outputted as a total detection signal Ve4.

Next, the sky detection operation of the embodiment configured as above will be explained using the characteristic diagram shown in FIG. 2.

The horizontal axis in FIG. 2 shows the liquid contact resistance Rb of the measurement electrode 11b, and the vertical axis shows the liquid contact resistance 11a of the measurement electrode 11a. β is a value determined in relation to the first threshold voltage VR+, and δ is a value determined in relation to the second threshold voltage VR2.

The area where empty detection can be performed using the total detection signal ■e2 related to the differential voltage Bd2 obtained from the output of empty detection time #119 is as follows:
In this case, when the difference between the values of the wetted resistances Ra and Rb is within the dead zone β2 within the width of the first threshold voltage VR+, the entire detection signal v
It is not possible to determine whether it is empty or not based on e2.

However, the sum voltage ES3 obtained at the output of all detection circuits 23
When using the total detection signal ve3 related to , the area surrounded by the vertical line can also be sky-detected.

Therefore, the OR gate 25 calculates the logical sum of these all detection signals Ve2 and Ve3 and outputs it as an all detection signal Ve4.
2, and the dead zone β2 in this region is removed.

In other words, the empty state can be detected in all cases where the inside of the conduit 10 is empty and both the liquid contact resistances Ra and Rb become large.

FIG. 3 is a block diagram showing the main parts of the configuration of another embodiment of the present invention. This embodiment is a configuration using a microprocessor.

The measurement voltage V of the difference appearing at the output terminal of the differential amplifier 15c
M2 and the sum measurement voltage VM3 appearing at the output of the summing amplifier 22 are applied to the switching terminals of a changeover switch SW, respectively, and a switching signal is outputted to the analog/digital converter 27 from their common switching terminal.

The voltages vM2 and VM measured by the analog/digital converter 27
2 is converted into a digital signal and processed by the microprocessor 2.
8 is output. The memory of the microprocessor 28 stores data corresponding to the first threshold voltage VR+ and the first r&value voltage VR2, and all detection circuits 19 and 23 that use these data to perform empty detection. An empty detection program that executes the corresponding calculation and the calculation corresponding to the OR gate 25 is also stored. Then, the microprocessor 28 executes all detection calculations using these data according to this sky detection program and outputs @2.
An empty detection signal is output to 6. The flow rate signal is similarly calculated and the flow rate signal Vc is outputted at the output @18.

Furthermore, the microprocessor 28 sends a switching signal S, to the switch SW, to control switching of the switch SW1.

FIG. 4 is a professional diagram showing the configuration of the main parts of another embodiment of the present invention.
It is a y diagram.

In this case, the outputs of the buffer amplifiers 15a and 15b are switched by the switch SW1, and the analog/digital converter 2
7, which is converted into a digital signal and output to the microprocessor 19. Therefore, the functions of the differential amplifier 15c and the summing amplifier 22 are also realized by the microprocessor. In this case as well, the switching signal S2 for switching the switch SW is sent out by the microprocessor 29.

<Effects of the Invention> As specifically explained above with the solid line example, the present invention has the following effects:
The sum and difference of the DC voltages generated at each measurement @pole are calculated, and compared with the respective threshold values, and the empty detection is performed using the logical sum of the detected empty detection signals, so the connection between each measurement electrode is Empty detection can be easily performed even when both liquid resistances are large and these values are close to each other.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention, FIG. 2 is a characteristic diagram explaining the operation of the embodiment shown in FIG. 1, and FIG. 3 is a main part of another embodiment of the present invention. FIG. 4 is a block diagram showing the main parts of still another embodiment of the present invention, FIG. 5 is a block diagram showing the configuration of a conventional electromagnetic flowmeter, and FIG. 6 is shown in FIG. FIG. 3 is a characteristic diagram illustrating the operation of an electromagnetic flowmeter. 10- Conduit, lla, 1 l b... Measuring electrode, 11C... Wetted electrode, 14... Detector, 116a
, 16 b-- Constant current circuit, 1 path, 19.23...
All detection circuits, 2 voltage source, 22... summing amplifier, vR pressure, VR2... second threshold voltage. 5... Preamplifier, 7... Signal processing diagram 0.21... Reference,... First threshold voltage

Claims (1)

[Claims] In an electromagnetic flowmeter that detects a signal voltage generated in a measuring fluid with a pair of measuring electrodes, processes this signal voltage with a signal processing means, and outputs it as a flow rate signal, a constant DC current is applied to the measuring electrodes. a constant current means for causing a constant current to flow; a difference determining means for determining a difference in the DC voltage generated between the measurement electrodes and comparing it with a first threshold value to detect a non-wetted state of the measurement electrode; and a DC voltage generated between the measurement electrodes. a sum determining means for calculating a sum of voltages and comparing it with a second threshold value to detect a non-wetted state of the measurement electrode; and an arithmetic means for calculating a logical sum of each output of the difference determining means and the sum determining means. An electromagnetic flowmeter characterized in that the empty state of the measurement electrode is determined based on the output of the calculation means.