JPH0726662Y2 - Power circuit of electromagnetic flowmeter - Google Patents

Description

[Detailed Description of the Invention] <Industrial field of application> The present invention relates to a power supply circuit of an electromagnetic flow meter, and in particular, even if power is supplied to an exciting circuit with large load fluctuation, the flow rate output is stable with an inexpensive configuration. The present invention relates to a power supply circuit improved.

<Prior Art> FIG. 3 is a block diagram showing a configuration of a conventional electromagnetic flowmeter.

The signal voltage Vs detected by the detection unit 10 that detects the measured flow rate is input to the signal processing unit 11 where a predetermined calculation is executed and the flow rate signal is output via the output unit 12 that converts the result of this calculation into a current output. It is output to the output terminal 13 as Vq.

The excitation voltage Vf is supplied to the detection unit 10 from the power supply circuit 14 via terminals T1 and T2, and the circuit voltages Vc1 and Vf are supplied to the signal processing unit 11 and the output unit 12.
c ₂ and Vc 3 are supplied respectively.

Next, the power supply circuit 14 functioning as a switching regulator will be described in detail.

The alternating-current power supply e1 outputs a direct-current voltage E1 to its output end via a double-wave rectifier circuit 15 and a capacitor C1 connected in parallel with this.

This DC voltage E1 is applied to one end of the input winding n1 of the transformer 16, and the other end is connected to the common potential point COM via the switch SW1. A diode is placed across the input winding n1.
When the switch SW1 is turned off by connecting the series circuit of D1 and the capacitor C2, the energy held in the input winding n1 is released.

The output winding n2 has a midpoint tap, a series circuit of a diode D2 and a capacitor C3 is provided between one end of the output winding n2 and the midpoint, and the other end of the output winding n1 is A series circuit of a diode D3 and a capacitor C4 is connected between the middle point and each of them, and circuit voltages Vc1 and Vc2 are obtained between both ends of the capacitor C3 and C4, respectively.

Further, a series circuit of a diode D4 and a capacitor C5 is connected to both ends of the output winding n3, and a circuit voltage Vc3 is obtained at both ends of the capacitor C5 to energize the output unit 12.

A series circuit of a diode D5 and a capacitor C6 is connected to both ends of the output winding n4, an exciting circuit 17 is connected to both ends of the capacitor C6, and an exciting voltage Vf is obtained at both ends of the exciting circuit 17.

A series circuit of a diode D6 and a capacitor C7 is connected to both ends of the feedback winding n5, and a feedback voltage Vk1 is obtained across the capacitor C7.

The control circuit 18 has a circuit voltage Vc1 to Vc3, and a reference voltage Er1 that sets the magnitude of the excitation voltage Vf. The reference voltage Er1 and the feedback voltage Vk1 are compared by a comparator 19 and a switching pulse is output from the output terminal. Output Sp1 to switch SW1 and switch SW
Open and close 1.

In the above configuration, the control circuit 18 compares the feedback voltage Vk1 with the reference voltage Er1 and controls the feedback voltage Vk1 to be equal to the reference voltage Er1 by switching the switch SW1 according to the magnitude of the feedback voltage Vk1 and the reference voltage Er1. Voltage Vc1 to Vc3 and excitation voltage
It controls the size of Vf.

By the way, the electromagnetic flowmeter generates an exciting current as shown in FIG. 4 in the exciting circuit 17 in order to separate the polarization voltage and the signal voltage generated by the contact of the electrode of the detection unit 10 with the fluid to be measured. It is applied to the excitation coil. FIG. 4 (a) shows the case of binary low-frequency excitation having a predetermined value of + and-, (b) the other three-valued low-frequency excitation having a zero value, and (c) commercial. The cases of dual-frequency excitation having a waveform in which a low frequency having a frequency lower than the frequency and a high frequency having a frequency higher than this are combined are shown. Both
It is an exciting current that fluctuates intermittently, and has a considerably large current value compared to the signal voltage.

Then, the signal processing unit 11 takes out a signal voltage indicating a change corresponding to the change of the exciting current, and uses this as a flow rate signal Vq.

On the other hand, the circuit voltages Vc1 to Vc3 applied to the signal processing unit 11 and the output unit 12 consume a load that is substantially constant over time.

Therefore, the power supply circuit shown in FIG. 5 is a circuit in which an exciting circuit having a large load fluctuation is separated so that this influence does not reach the signal processing unit 11 and the output unit 12.

Hereinafter, parts having the same functions as those of the power supply circuit shown in FIG. 3 are designated by the same reference numerals, and the description thereof will be appropriately omitted.

The AC power supply e1 is rectified by the full-wave rectifier circuit 15 and converted into a DC voltage E1, and this DC voltage E1 is applied to the input winding n1 of the transformer 20. As a result, the circuit voltages Vc1 to Vc3 are obtained at the output windings n2 and n3 in the same manner as in the case shown in FIG.

On the other hand, the AC power supply e1 is rectified by the full-wave rectifier circuit 21 and converted into a DC voltage E2 via a capacitor C8 connected in parallel with this, and this DC voltage E2 is applied to one end of the input winding n6 of the transformer 22. , The other end is connected to the common potential point COM via the switch SW2. A series circuit of a diode D7 and a capacitor C9 is connected to both ends of the input winding n6 to release the energy retained in the input winding n6 when the switch SW2 is turned off.

Further, a series circuit of a diode D8 and a capacitor C10 is connected to both ends of the feedback winding n7, and a feedback voltage Vk2 is obtained across the capacitor C10.

The control circuit 23 has a circuit voltage Vc1 to Vc3, and a reference voltage Er2 that sets the magnitude of the excitation voltage Vf.The reference voltage Er2 and the feedback voltage Vk2 are compared by a comparator 24 and a switching pulse is output from the output terminal. Output Sp2 to switch SW2 and switch SW2
Open and close 2.

The voltage across the output winding n4 is controlled to a value corresponding to the reference voltage Er2, and this voltage is output to the terminals T1 and T2 as the exciting voltage Vf via the exciting circuit 17.

As described above, the switching regulator 25 that obtains the circuit voltages Vc1 to Vc3 and the switching regulator 26 that obtains the excitation voltage Vf are separated as separate circuit blocks, so that the circuit voltage is not affected by the excitation voltage Vf having large fluctuations.

<Problems to be Solved by the Invention> However, in the power supply circuit of the electromagnetic flowmeter shown in FIG. 3, particularly in the recent electromagnetic flowmeter, the power consumed for excitation is large in the total power consumption of the electromagnetic flowmeter. Since it is occupying a part, load fluctuation in the excitation circuit is the circuit voltage.
It has a drawback that it easily affects Vc1 to Vc3 as a cross regulation term.

Further, in the power supply circuit shown in FIG. 5, since the control circuit of the switching regulator has two control circuits 18 and 23, it has a drawback of being expensive.

<Means for Solving the Problems> In order to solve the above problems, the present invention provides a signal voltage corresponding to the measured flow rate generated in the detection unit, which is energized by a DC power supply that rectifies the AC voltage. In a power supply circuit of an electromagnetic flowmeter that performs calculation in a calculation processing unit and outputs the output as a flow rate signal via an output unit, a DC power supply is applied to an input winding of a first transformer having an input winding, an output winding, and a feedback winding. Is input and the predetermined reference voltage is compared with the voltage generated in the feedback winding to switch the current flowing in the input winding by the switching pulse signal, and the circuit voltage from the output winding to the arithmetic processing unit and the output unit. DC power supply is input to the primary winding of the second transformer that has a primary winding and a secondary winding, and a switching regulator that supplies the Then, a switching circuit for outputting as an exciting power source from the secondary winding to the detecting portion is provided.

<Operation> A switching regulator is an input winding of a first transformer having an input winding, an output winding, and a feedback winding by a switching pulse signal obtained by comparing a predetermined reference voltage and a voltage generated in the feedback winding. The circuit voltage is supplied from the output winding to the arithmetic processing unit and the output unit by switching the current flowing through the output winding.

Further, the switching circuit switches a current flowing through a primary winding of a second transformer having a primary winding and a secondary winding by a switching pulse signal from the switching regulator, and separates the circuit voltage from the secondary winding. The voltage is output to the detection unit as an excitation voltage.

<Embodiment> An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention.

The switching pulse Sp1 output from the control circuit 18 of the switching regulator 25 controls the opening / closing of the switch SW1 in its duty cycle to compensate the fluctuation of the input / output of the switching regulator 25 and to maintain a constant circuit voltage Vc1 to Vc3.
To activate the signal processing unit 11 and the output unit 12.

The switching circuit 27 is a switching regulator.
Switching pulse Sp1 output from the control circuit 18 of 25
The switch SW2 is turned on / off in the duty cycle of, and the excitation voltage Vf is obtained at the terminals T1 and T2 by adding compensation for the fluctuation of the input / output of the switching regulator 25.

According to such a configuration, the circuit voltages Vc1 to Vc3 can be regarded as being substantially constant in time, so that the excitation voltage Vf becomes a substantially constant voltage despite the fluctuation of the AC voltage e1.

Therefore, a wide input range, for example, 80 V to 264 VAC, is designed by designing that 100 V and 200 V systems are shared.
The stable circuit voltages Vc1 to Vc3 and the excitation voltage Vf can be obtained over the entire range.

However, with respect to the excitation voltage Vf, it is necessary to give consideration to the excitation circuit 17 so that a desired excitation current can be stably obtained against variations in the excitation load.

FIG. 2 is a block diagram showing the configuration of another embodiment of the present invention.

In this configuration, the power supplies for the switching regulator 25 and the switching circuit 27 are obtained from the same rectifying / smoothing circuit.
This is effective when the ripple of power consumption in the switching circuit 27 is large.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, the switching circuit for obtaining the exciting voltage having a large fluctuation is separately controlled by using the switching pulse of the switching regulator having a small load fluctuation. I did so,
It is possible to obtain a stable circuit voltage and exciting voltage with a simple configuration that widely uses only one control circuit against fluctuations in AC voltage.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of one embodiment of the present invention, FIG. 2 is a block diagram showing a configuration of another embodiment of the present invention, and FIG. 3 is a configuration of a power supply circuit of a conventional electromagnetic flow meter. The block diagram shown in FIG. 4, FIG. 4 is a waveform diagram showing the waveform of the exciting current produced by the exciting circuit shown in FIG. 3, and FIG. 5 is a circuit diagram showing the configuration of another power supply circuit of the conventional electromagnetic flowmeter. 10 ... Detecting unit, 11 ... Signal processing unit, 12 ... Output unit, 14 ... Power supply circuit, 16, 20, 22 ... Transformer, 17 ... Excitation circuit, 18, 23 ... Control circuit, 25, 26 ... Switching regulator, 27 ... Switching circuit, Vc1 to Vc3 ... Circuit voltage, Vf ... Excitation voltage, Sp
1, Sp2 ... Switching pulse.

Claims (1)

[Scope of utility model registration request] 1. An arithmetic processing unit calculates a signal voltage corresponding to a measured flow rate generated in a detection unit when an AC voltage is applied and is rectified by a rectified DC power supply, and an output thereof is used as a flow rate signal via an output unit. In the power circuit of the electromagnetic flow meter that outputs,
A switching pulse obtained by inputting the DC power supply to the input winding of a first transformer having an input winding, an output winding, and a feedback winding, and comparing a predetermined reference voltage with a voltage generated in the feedback winding. A switching transformer that switches a current flowing through the input winding by a signal to supply a circuit voltage from the output winding to the arithmetic processing unit and the output unit, and a second transformer having a primary winding and a secondary winding. A switching circuit for inputting the DC power supply to the primary winding, switching the current flowing through the primary winding by the switching pulse signal, and outputting the current from the secondary winding to the detection unit as an excitation power supply. Power supply circuit of electromagnetic flowmeter characterized by.