JPS5824813A - Exciting circuit for electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To use one exciting circuit in common for current driving and voltage driving, by connecting voltage driving rectifier to a circuit comprising a diode bridge, a reference voltage signal generating circuit, an amplifier, and an active element, through circuit switching elements. CONSTITUTION:When only a switch J3 of switches J1-J7 is turned OFF, a current driving type exciting circuit is formed, and an exciting coil L is driven by the current through terminals Ix1 and Ix2. In the meantime, when only the circuit switch J3 is turned ON, capacitors C1 and C2, a diode D2 for protecting a reverse voltage, and a current limiting element Q2 are excluded from the circuit constitution, and the voltage driving rectifier 2 is incorporated into the circuit. Thus a voltage driving type exciting circuit is formed. Then the exciting coil L is driven by the voltage through output terminals Ex1 and Ex2 of the rectifier 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an excitation circuit for driving an oscillator of an electromagnetic current meter, and more particularly to an excitation circuit capable of both current drive and voltage drive.

In conventional electromagnetic flowmeters, an excitation current is generated from a voltage source in a converter, and the current is passed through an excitation coil of a transmitter, and the flow rate signal is divided by a signal proportional to the excitation current, that is, a comparison signal. The voltage excitation method eliminates output errors due to current fluctuations, and the current method uses a constant current source to generate an excitation current within the converter, allowing a constant amplitude excitation current to flow through the excitation coil of the transmitter regardless of the load. There is an excitation method. The former excitation method has the advantage of being completely compatible with the transmitter and converter of the electromagnetic flowmeter since it takes a comparison signal. This advantage does not exist in the latter excitation method, and although there is the inconvenience of setting the meter factor for each oscillator, there is an advantage that the oscillator and converter can be freely coupled because a comparison signal circuit is not required.

Therefore, many electromagnetic flowmeters using the two types of excitation methods described above are already in use, but the excitation circuits in the converters are completely different dedicated circuits, one for voltage drive and one for current drive, based on the excitation method.

However, it is desirable that future excitation circuits be compatible with both voltage drive and current drive. Furthermore, it is desirable that many of the elements constituting the circuit can be used in common for both voltage drive and current drive.

An object of the present invention is to provide an electromagnetic flowmeter excitation circuit that meets the above-mentioned needs.

First, the present invention will be explained in detail with reference to FIGS. 1 to 4. The first protrusion shows a conventional voltage-driven excitation circuit, and when the switch SW is turned on and off with respect to the commercial power supply 1 at the timing shown in Fig. 2(a), the power supply line to the diode grid 2 is connected between the power lines shown in Fig. 2(a). A voltage waveform shown in (b) appears, and a full-wave rectified voltage is applied to the excitation coil L as shown in (e) of the same figure. This switch SW uses a thyristor to turn on and off the alternating current, and the on/off timing is given from the timing circuit 3 of the converter. In Figure 1, 4 is a circuit that generates the comparison signal Vref, 4a is a current transformer that detects the rectified input current, 4b and 4c are diodes and current transformers that detect the continuous current of the excitation coil, and 4d is both current transformers. 4a is a rectifier that combines and rectifies the outputs of 4a, and 4e is a terminating resistor.

On the other hand, Fig. 3 shows a current drive type excitation circuit according to the invention filed as *a No. 10107/1982, which includes a power transformer 5, a diode glitch 6, and a smoothing capacitor CI.
,c! A DC voltage source is created by combining two active elements, one current-limiting element Qs=Q, and an amplifier Q3,
The excitation coil L is current-driven by a constant current circuit comprising a current detection resistor Rref for negative feedback and a reference voltage signal generation circuit 7 having a waveform similar to the excitation current. In other words, Figure 4 (
When a voltage of 10E of the reference voltage signal shown in a) is applied to the non-inverting input terminal of the amplifier Q, Ql is in the active region and Q is turned off, and the excitation coil L is supplied in the order of Q1 → Rref → L. Excitation current Iex flows. Furthermore, when a voltage of -E is applied to the non-inverting input terminal of amplifier Q3, Ql is in the active region and Q is turned off, and the excitation current Iex is increased in the order of L→Rref-+Q1.
flows. At this time, the detection voltage Rr of the resistor Rref
e? Since Iex is applied to the inverting input terminal of amplifier Q3, the current limiting elements of Ql and Qt are controlled by amplifier Q so as to balance Rref·Iex == E, and as a result, as shown in FIG. ) A current-driven excitation current flows as shown in ().

The value of the excitation current is controlled by changing the resistance value Rref or the amplitude E of the reference voltage signal.

Therefore, after comparing and examining the circuits in Figures 1 and 3, we found that: (1) Diode glitch 6 and current limiting element Q in Figure 3.
1 or Q2 in combination, the switch SW in Figure 1
It is possible to configure an AC switch corresponding to
, C, etc., and by adding a rectifier corresponding to the diode bridge 2 in Fig. 1, it is possible to change it to a voltage-driven excitation circuit. (2) On the other hand, in Fig. 3, the two currents It has been found that it is possible to change the excitation circuit to a voltage-driven type by simply turning on and off the limiting elements Q, Q, and l, removing the capacitors C, and C, and changing the resistor Rref or the amplitude E of the reference voltage signal. .

Hereinafter, the present invention will be described in detail based on FIGS. In each figure, parts having the same functions as those in FIGS. 1 and 3 are given the same reference numerals to avoid redundant explanation.

FIG. 5 shows an embodiment of the present invention, where J7 to J7 are switches for switching circuits, and if each switch J1 to J is in the state shown, that is, only J3 is turned off, the result is equivalent to that in FIG. It becomes a current drive type excitation circuit.

The exciting coil L can be driven with current through the terminal Ix2.

On the other hand, if only the circuit changeover switch J is turned on, the reverse voltage protection diode t'Dt of one of the capacitors C, , C, , D, and the current limit of one of Q and Q2 Element Q2 is removed from the circuit configuration, and conversely, voltage-driven rectifier 2 is inserted into the circuit. This state is shown in FIG. The circuit formed by the diode glitch 6 in FIG. 6 and the current limiting element Q1 inserted between its + and one terminal is expressed isometrically as
Illustrated! Switch SW that indicates on/off of 0 and Q.

An alternating current switch is configured to turn on and off between fiA and B. In this case, the current flowing through switch SW2 is unidirectional, so Ql should be a transistor or MOS-FET? l: Any semiconductor active device can be used. In addition, in order to turn on and off Q as a switching element outside the active region, the reference voltage signal generation port wr
The amplitude E of the reference voltage signal may be increased using the potentiometer VR in I. In the circuit 7, ZD is a zener diode, SW, .

Therefore, the circuit in FIG. 6 is a voltage-driven excitation circuit equivalent to that in FIG.
The excitation coil L can be driven with voltage through. Note that you can remove the current detection resistor Rref, but if you leave it as Rref・Iex (E) as shown in the figure, the output terminal EX
Acts as a current limiter against excessive current when I and EX2 are short-circuited. When the voltage generated across resistor Rref exceeds a certain value, Q enters the active region and limits the current. Furthermore, when driving with voltage, switch J is connected as shown by the broken line in FIG.
,,J, may be used to bypass the transformer 5.

FIG. 8 shows another embodiment. In this embodiment, in both voltage drive and current drive, the excitation coil L is connected between the power transformer 5 and the midpoints of the pair of current limiters Q1-Q20, and between Ixl and IX2 in FIG. In this case, use the circuit changeover switch J. , J,1 is turned off to disconnect the capacitor C,,C,. If JIO and 511 are turned on, it becomes a current-driven excitation circuit exactly the same as that shown in FIG.

On the other hand, if JIG and 41 are turned off and the current limiting element Qt +Q2 is turned on and off as shown in Fig. 6, positive and negative voltages as shown in Fig. 9 are applied to the exciting coil L, resulting in a full wave. It is driven by voltage. Also in this embodiment, the resistor Rref for current detection is left and Rref・Iex (E
By setting it as , it is possible to limit overcurrent during voltage drive. In addition,
CT is a current transformer for obtaining a comparison signal Vref 'e, and when driving with current, switch Jl! It is best to bypass this with +J1m.

In the case of the embodiment shown in FIG. 8, the comparison signal Vref can be generated by the circuit shown in FIG. Note that FIGS. K10 (a) and (b) show only the main parts, and the output side circuit part of the diode glitch 6 is omitted because it is the same as in FIG. 8. In other words, Fig. 10 (a
), the current transformer C with the same connection as in Fig.
The output of T is rectified by a glitch-connected rectifier 4d in the same manner as in FIG. 1 to provide a comparison signal Vref. Figure 10 (b)
In this circuit, the primary side of the current transformer CT is connected between the secondary midpoints of the power transformer 5. One end of the exciting coil L is connected to the primary center point of the current transformer CT, and the output of the current transformer CT is rectified by a rectifier 4d to provide a comparison signal Vref.

In each of the embodiments described above, a switch is used as a circuit switching element, but this may be changed depending on whether or not a jumper wire is connected.

As explained above, according to the present invention, one excitation circuit can be used in common for current drive and voltage drive.

[Brief explanation of drawings]

1 and 3 are circuit diagrams for explaining the principle of the present invention, and FIGS. 2 and 4 are waveform diagrams thereof. Figure 5 is a circuit diagram of one embodiment of the first invention of the present invention, Figure 6 is a circuit diagram when the circuit in Figure 5 is switched to voltage drive, Figure 7 is an equivalent circuit diagram of an AC switch, and Figure 8 is an equivalent circuit diagram of an AC switch. The figure is a circuit diagram of another embodiment, Figure 9 is a waveform diagram during voltage drive in Figure 8, and Figures 10 (a) and (b).
) is a circuit diagram showing another example of comparison signal creation in FIG. 8; In the drawing, L is the excitation coil 1, the commercial power supply 2 is the voltage drive rectifier 5, the power transformer 6 is the diode grid 7 is the reference voltage signal generation circuit, C1 and C2 are the capacitors Q, and Q are the capacitors Q3. are amplifiers J, ~J, and 3 are circuit changeover switches. Patent applicant: Hokushin Electric Manufacturing Co., Ltd. Agent
Patent Attorney Mitsuishi Shibu (1 other person) 2 Figure 10 6 (b) ref 67-

Claims (2)

[Claims] (1) In an excitation circuit that generates an excitation current from an AC power source to flow into an excitation coil of an electromagnetic flowmeter, a diode glitch is used.
A smoothing circuit, a reference voltage signal generation circuit, an amplifier that amplifies the reference voltage signal, a function wJ regulator that controls the load current using the output signal of this amplifier, and a load current that is detected and provides negative feedback to the amplifier. the resistor to be applied, the voltage-driven rectifier,
9, an excitation device configured to rectify alternating current power by the diode-P glitch, control its smoothed output to a current having a value according to a reference voltage signal by the active element, and send the current to the excitation coil. circuit, and among the circuit elements that make up this excitation circuit, a diode glitch, a reference voltage signal generation circuit,
An amplifier and an active element are shared, and an active element is connected between the output terminals of this diode glitch to create an AC switch that opens and closes in response to a reference voltage signal, and the AC power that has passed through this AC switch is rectified by the voltage drive rectifier. An excitation circuit for an electromagnetic flowmeter, characterized in that the excitation circuit configured to cause the current to flow through the excitation coil can be selected by the circuit switching element. (2) The electromagnetic flowmeter excitation according to claim 1, wherein the active element is a pair of active elements that operate in a bush-sol manner, and one of the active elements is shared in the configuration of an AC switch. circuit. (In addition to the excitation circuit that generates the excitation current from the AC power supply to flow into the excitation coil of the 31'it magnetic flowmeter, it also includes a diode grid that rectifies the AC power, a smoothing circuit, a reference voltage signal generation circuit, and a reference voltage signal generation circuit. It includes an amplifier for amplification, a pair of active elements of Bushsol operation for controlling the load current by the output signal of the amplifier, a resistor for detecting the load current and applying negative feedback to the amplifier, and a circuit switching element. The coil is connected between the alternating current power supply and each midpoint of the pair of active elements, and the rectified and smoothed output from the diode glitch and smoothing circuit is used to generate a current of a value corresponding to the reference voltage signal in the pair of active elements. Among the circuit elements that make up this excitation circuit, a diode glitch, a reference voltage signal generation circuit, an amplifier, and a pair of active elements are shared, and the rectified output of this diode glitch is An excitation circuit for an electromagnetic flowmeter, characterized in that an excitation circuit configured to cause a current to flow through an excitation coil by opening and closing the pair of active elements according to a reference voltage signal can be selected by the circuit switching element.