JPH06174513A - Emptiness detection circuit of electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To enable emptiness to be detected in the case of empty state by providing an emptiness detection circuit between one of a pair of electrodes of the measuring pipe and a ground terminal for liquid-contacting only the electrode without the emptiness detection circuit. CONSTITUTION:AC content of voltage between a ground terminal 5-1 and an electrode 1-2 and that between the ground terminal 1-5 and an electrode 1-3 are fed to an addition circuit 3-1 via a DC capacitor 1-6 and a DC cut capacitor 1-7, respectively, for addition. The addition signal is amplifier by a non-inversion amplifier circuit 3-2, is rectified by a smoothing circuit 3-3 and them smoothed, and is compared with a comparison reference voltage 3-4-6 by a comparator 3-4, thus obtaining an emptiness detection signal 3a which is H in an empty state and L in a full state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an empty space in a measuring tube in a detector of an electromagnetic flow meter using Faraday's law that a voltage proportional to the speed of a conductive fluid is induced when the fluid flows in a magnetic field. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for detecting a state, and more particularly to an electromagnetic flow meter empty detection circuit capable of reliably detecting an empty state while maintaining accuracy of a flow rate signal output from an electromagnetic flow meter converter.

In the following figures, the same reference numerals indicate the same or corresponding parts.

[0003]

2. Description of the Related Art As an empty detection circuit of this kind for an electromagnetic flow meter, the applicant of the present application has filed a prior application, Japanese Patent Laid-Open No. 63-006420.
No., "Electromagnetic flowmeter empty water detection circuit". According to the invention of this prior application, the magnitude of the alternating current component in the voltage generated at any one of the two electrodes in the measuring tube in the electromagnetic flowmeter detection unit is in the liquid contact state and the empty water state. However, since the AC component is amplified, the AC component is converted into DC, and the DC voltage obtained as a result is compared with a reference voltage to detect the empty water state.

[0004]

FIG. 3 shows an example of a liquid contact state which should be judged to be an empty state of the measuring tube in the detector. In the figure, 1-1 is a measuring tube, 1-2 and 1-3 are electrodes, and 8 is a measuring fluid. By the way, the sky detection circuit of the above-mentioned prior application has two electrodes 1-2, 1-3 within the measuring tube 1-1 in the detection section.
Only one of the electrodes is connected to the empty detection circuit.
Now, when the measurement fluid 8 is present in the measurement tube 1-1 as shown in FIG. 3, the empty detection cannot be performed unless the empty detection circuit is connected to the electrode 1-2 which is in contact with the liquid. Occurs. Therefore, it is an object of the present invention to provide an empty detection circuit for an electromagnetic flow meter that can solve this problem.

[0005]

In order to solve the above-mentioned problems, the empty detection circuit according to claim 1 has a pair of electrodes in a detector of an electromagnetic flow meter (such as the measuring tube 1-1 of the detection section 1). AC that outputs the addition AC signal corresponding to this sum by extracting the sum of the AC components of the respective voltages generated between (1-2, 1-3, etc.) and the ground (ground terminal 1-5, etc.) Minute addition extraction means (adding circuit 3-1, non-inverting amplifier circuit 3-2, etc.), DC conversion means (smoothing circuit 3-3, etc.) for converting the added AC signal into a DC signal, and the DC signal as a reference And a comparison means (comparator 3-4 etc.) for comparing the signal (comparison reference voltage 3-4-6 etc.) and outputting a signal according to the comparison result, and the output signal of the comparison means (empty detection signal 3
(a) or the like) is used to detect an empty state in the detector.

According to a second aspect of the empty detection circuit of the present invention,
In the empty detection circuit described in (1), the DC signal has an amplification degree variably set by at least a first variable resistor (3-2-3, etc.) (non-inverting amplification circuit 3-2, etc.).
Be obtained through. Further, in the sky detection circuit according to claim 3, in the sky detection circuit according to claim 1 or 2, the reference signal is the second variable resistor (3
-4-5, etc.).

[0007]

In the present invention, by extracting the sum of the AC signals generated between the pair of electrodes in the measuring tube and the ground,
The above problems are solved. The AC signal extracted here is mainly commercial frequency noise, but its magnitude varies depending on the diameter of the measuring pipe and the grounding state of the pipe. Therefore, the amplification factor is made variable to easily obtain the optimum amplification degree. However, there are cases where the variable range of the amplification degree is restricted due to restrictions on circuit constants. In that case, the comparison reference voltage of the comparator is made variable to obtain the same effect.

[0008]

Embodiments of the present invention will be described below with reference to FIGS. FIG. 2 is an overall configuration diagram of an electromagnetic flowmeter as an embodiment of the present invention. In the figure, 5 is a microcomputer for controlling the entire electromagnetic flow meter, 1-1 is a measuring tube of the electromagnetic flow meter through which the measuring fluid 8 described in FIG. 3 flows,
1-5 is a ground terminal provided on the measuring tube 1-1, 1-2, 1
Reference numeral -3 is an electrode, 1-6 and 1-7 are capacitors for cutting a direct current component, and 1 is a detector of an electromagnetic flowmeter including the above-mentioned parts, an exciting coil 1-4 and a core not shown.

Numeral 2 amplifies the voltage signal appearing between the two electrodes 1-2 and 1-3 via the capacitors 1-6 and 1-7, and performs a predetermined process on the amplified signal to make a measurement tube 1-.
1 is an amplification / signal conversion circuit that outputs a flow rate signal 2a corresponding to the flow rate of the measurement fluid 8 passing through 1 to the microcomputer 5. In addition, 3 inputs the voltage signal appearing between the electrodes 1-2 and 1-3 and the earth terminal 1-5 via the capacitors 1-6 and 1-7, respectively, and the inside of the measuring tube 1-1 is described later. Is an empty detection circuit that outputs an empty detection signal 3a indicating whether it is an empty state or a liquid contact state (full water state), and is the main subject of the present invention.

Reference numeral 4 is an AC power source 7 which, via a timing pulse generating circuit 6 described below, generates an alternating current pulse of a predetermined level and a predetermined time width in synchronization with the power source 7, and excites the exciting coils 1-4. The timing pulse generation circuit 6 has a role of inputting the voltage of the AC power supply 7 to generate a timing pulse of a time width designated by the microcomputer 5 and giving it to the excitation circuit 4.

FIG. 1 shows a detailed structure of the sky detection circuit 3 of FIG. The detection circuit 3 is roughly composed of an adder circuit 3-1, a non-inverting amplifier circuit 3-2, a smoothing circuit 3-3, and a comparator 3-4.
It consists of Both electrodes 1-2 and 1 of the measuring tube 1-1
-3 and the voltage generated between the earth terminal 1-5 pass through the capacitors 1-6 and 1-7, respectively, and the resistors 3-1-3 and 3-3.
-1-4, operational amplifier 3-1-5, resistor 3-1-6,
The addition circuit 3-1 composed of 3-1-7 is added and added. The AC signal extracted by the adder circuit 3-1 is amplified by the non-inverting amplifier circuit 3-2 including the operational amplifier 3-2-1, the resistor 3-2-2, and the variable resistor 3-2-3. . The amplification degree of the amplifier circuit 3-2 can be made variable by using the variable resistor 3-2-3. This is because the inner diameter of the measuring tube 1-1 causes the electrodes 1-2,
This is because the magnitude of the noise voltage extracted between 1-3 and the ground terminal 1-5 is different, so that the amplification degree suitable for the magnitude is obtained. Next, the signal amplified by the non-inverting amplifier circuit 3-2 is rectified by a rectifier 3-3-1 and a capacitor 3-.
It is converted into a DC signal by a smoothing circuit 3-3 composed of 3-2 and resistors 3-3-3. This DC signal is the operational amplifier 3
It is compared with the comparison reference voltage 3-4-6 by the comparator 3-4 composed of 4-1 and the like, and is output as the sky detection signal 3a at the High or Low level and sent to the microcomputer 5.

The sky detection signal 3a is identified as an empty state when it is at a high level and a liquid contact (full water) state when it is at a low level. The comparison reference voltage 3-4-6 used in the comparator 3-4 is given by the ratio of the resistor 3-4-2 and the variable resistor 3-4-5, and this ratio is Determined by the degree of amplification. In other words, the voltage value V _H is a relationship as that following referred (1) when the output pressure value V _L and the empty state of the smoothing circuit 3-3 when the measuring tube is filled with the measurement fluid the comparison reference voltage (V _S) 3-4-6 may be set as.

[0013]

[Equation 1] V _L <V _S <V _H ………… (1)

[0014]

According to the present invention, the summing circuit 3 adds the sum of the AC signals generated between the pair of electrodes 1-2 and 1-3 in the measuring tube 1-1 and the ground terminal 1-5. Since the empty state is detected by extracting with -1, the empty state can be surely detected even if the measuring fluid 8 exists in the measuring pipe 1-1 as shown in FIG.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a sky detection circuit as an embodiment of the present invention.

FIG. 2 is a block circuit diagram showing the overall configuration of the same electromagnetic flowmeter.

FIG. 3 is a diagram showing a liquid contact state in which a conventional empty detection circuit causes a malfunction.

[Explanation of symbols]

 1 Detection Unit 1-1 Measuring Tube 1-2 Electrode 1-3 Electrode 1-4 Excitation Coil 1-5 Earth Terminal 1-6 DC Cut Capacitor 1-7 DC Cut Capacitor 2 Amplification / Signal Conversion Circuit 2a Flow Signal 3 Empty Detection Circuit 3a Empty detection signal 3-1 Adder circuit 3-2 Non-inverting amplifier circuit 3-2-3 Variable resistor 3-3 Smoothing circuit 3-4 Comparator 3-4-5 Variable resistor 3-4-6 Comparison reference voltage 4 Excitation circuit 5 Microcomputer 6 Timing pulse generation circuit 7 AC power supply

Claims (3)

[Claims] 1. An AC component addition for extracting a sum of AC components of respective voltages generated between a pair of electrodes and a ground in a detector of an electromagnetic flow meter and outputting an addition AC signal according to the sum. An output signal of the comparison means, which comprises an extraction means, a DC conversion means for converting the added AC signal into a DC signal, and a comparison means for comparing the DC signal with a reference signal and outputting a signal according to a comparison result, An empty detection circuit for an electromagnetic flow meter, which detects an empty state in the detector based on the above. 2. The electromagnetic wave detection circuit according to claim 1, wherein the DC signal is obtained through at least an amplifying means whose amplification degree is variably set by a first variable resistor. Flow meter empty detection circuit. 3. The empty detection circuit according to claim 1 or 2, wherein the reference signal is variably set by a second variable resistor. .