JPH0695031B2 - Electromagnetic flow meter - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electromagnetic flow meter, and more particularly to improvement of an excitation circuit.

(B) Prior Art FIG. 2 shows an exciting circuit of a conventional electromagnetic flowmeter. In the figure, an AC voltage generated in the secondary side of the power transformer 1 diodes d _1, d _2, d _3, d DC voltages V ₁ at configured rectifier circuit 2 from the bridge circuit and a smoothing capacitor C ₁ of ₄ Is converted to. Transistors Tr ₁ , Tr ₂ , Tr ₃ , Tr
₄ is a switching transistor for turning on / off the exciting coil L, and diodes D ₁ , D ₂ , D ₃ and D ₄ for surge voltage protection are connected in parallel to the respective transistors. . Transistors Tr ₁ and Tr ₂ are complementary transistors with their collectors connected, and transistors Tr ₃ and Tr ₄ are also complementary transistors with their collectors commonly connected and these transistors Tr ₁ , Tr ₂
An exciting coil L is connected between the collector of and the collectors of the transistors Tr ₃ and Tr ₄ .

The emitters of these transistors Tr ₁ and Tr ₃ are commonly connected,
The emitters of the transistors Tr ₂ and Tr ₄ are commonly connected, and the output V ₁ of the rectifier circuit 2 is supplied between the emitters of the transistors Tr ₁ and Tr _{3 and} the emitters of the transistors Tr ₂ and Tr ₄ . The signal from the transistor _{Tr 1, Tr 2, Tr 3} , Tr 4 the control unit 3, the transistor Tr _1, Tr ₂ are mutually turned on / off, the transistor Tr _3, Tr ₄ also mutually ON /
Turned off. Then, as shown in FIG. 3, in the coil L, a positive direction excitation, that is, a case where an exciting current flows in the direction from a to b, and a negative direction exciting current in which a current flows in the direction from b to a contrary to the rest cycle. Are designed to flow sequentially in a cycle. That is, from the control unit 3 to the transistor Tr ₁
And a signal to turn on the transistor Tr ₄ are added, and the transistor Tr ₁ , point a, exciting coil L, point b, transistor T
A positive direction exciting current flows through r _4, and during the rest period, all of the transistors Tr ₁ , Tr ₂ , Tr ₃ , Tr ₄ are turned off, no current flows in the exciting coil L, and then the negative direction exciting current. In Case of,
Tr ₃ and Tr ₂ are turned on, and a current flows through the transistor Tr ₃ , point b, exciting coil L, point a, and transistor Tr ₂ .

In the rest cycle after the positive direction excitation, the current due to the counter electromotive force flows from the point b to the point a via the diode D ₃ , the capacitor C ₁ and the diode D ₂ . Further, in the next rest cycle of the negative direction excitation, the current due to the counter electromotive force generated in the coil L flows from a through the diode D ₁ , the capacitor C ₁ , and the diode D ₄ to the point b.

(C) Problem to be Solved by the Invention In order to speed up the response of the electromagnetic flow meter, it is necessary for the exciting current to rise quickly. The rising time of the current at the start of excitation is proportional to the voltage applied to the coil L. In order to accelerate the rise from V ₁ , it is necessary to transiently increase V ₁ only at the start of excitation. Therefore, conventionally, a means for temporarily switching the voltage is provided on the output side of the capacitor C ₁ , that is, a portion A, and in the case of a switching regulator, a means for temporarily increasing the voltage on the temporary side of the transformer is provided. Although measures have been taken to increase the response speed, the use of such a circuit has a problem that a complicated circuit configuration cannot be avoided. Further, the energy stored in the coil L during excitation becomes counter electromotive force generated at the time of suspension of excitation and is discharged through the diode, and is consumed as heat on the circuit due to the resistance. There was also the problem of being consumed by.

The present invention has been made in view of the above-mentioned problems, and is an electromagnetic flow meter that accelerates the start-up at the start of excitation with a simple circuit configuration and that consumes less back electromotive force without waste. Is intended to provide.

(D) Means for Solving the Problems The electromagnetic flowmeter of the present invention is an on / off switch for turning on / off an exciting coil for applying a magnetic field to a fluid tube and a current flowing through the exciting coil.
A switching element for off control, and a rectifying circuit that rectifies an AC signal and supplies a power supply voltage to the switching element, wherein an excitation including a diode and a capacitor is provided between the output side of the rectifying circuit and the switching element. It is characteristically provided with an excitation circuit provided with an energy storage circuit.

(E) Action In the exciting circuit of this electromagnetic flow meter, the counter electromotive force generated in the exciting coil is charged in the capacitor of the exciting energy storage circuit in the idle cycle of the switching element and is larger than the voltage input in the next exciting cycle. Since a voltage exists across the capacitor, this voltage can speed up the rise of the current flowing in the exciting coil. Moreover, the energy of the exciting coil due to the back electromotive force in the idle cycle is charged in the capacitor, so that it is used without waste.

(F) Examples Hereinafter, the present invention will be described in more detail with reference to Examples.

FIG. 1 is a circuit diagram of an exciting circuit of an electromagnetic flowmeter showing an embodiment of the present invention.

In the figure, the same reference numerals and symbols as those of the circuit of FIG. 2 mean the same circuit elements. The feature of the excitation circuit of this embodiment is that it is added to the circuit of FIG. 2 and the output terminal of the capacitor C ₁ of the rectifier circuit 2 and the switching transistor Tr.
_The excitation energy storage circuit 4 including the diode D ₅ and the capacitor C ₂ is provided between the power supply terminals of ₁ , Tr ₂ , Tr ₃ and Tr ₄ .

Now, the energy stored in the coil L in the excitation as 1 / 2LI ^2, when the energy stored in the capacitor C ₂ and 1 / 2C ₂ V ₂ ^2, across V ₂ of capacitor C ₂ is And this voltage will be developed across capacitor C ₂ . In the above circuit, the capacitance of the capacitors C ₁ and C ₂ is C ₂ > C ₁ and the diode D ₅ is connected so that V ₂ > V ₁ .

In the exciting circuit of this embodiment, it is assumed that the transistors Tr ₁ and Tr ₄ are turned on by a signal from the control unit 3 and a current flows through the coil L from the point a to the point b. In this state, when moving to the next rest cycle, the counter electromotive force generated in the coil L is the diode D ₃ , the capacitor C ₂ , the diode from the point b.
The energy flowing to point b via D ₂ and stored in the coil L during excitation is stored in the capacitor C ₂ . And above Voltage is developed across capacitor C ₂ . This voltage V
₂ is a voltage higher than the DC voltage V ₁ .

When the transistors Tr ₂ and Tr ₃ are turned on in the next cycle, the voltage V ₂ stored in the capacitor C ₂ is first applied to the coil L. As described above, this voltage V ₂ is higher than the power supply voltage V ₁ , so that the exciting current rises faster than in the conventional configuration. Moreover, since the energy stored in the coil in the previous cycle is used at the rising of the next cycle, the energy is not wasted and the overall power consumption can be reduced.

(G) Effect of the Invention According to the present invention, the exciting energy storage circuit including the diode and the capacitor is provided between the output side of the rectifier circuit and the switching element, and the counter electromotive force generated in the coil L is generated in the capacitor of the storage circuit in the idle cycle. Energy is stored and the energy stored in the capacitor is first applied in the next power supply cycle, so the rise can be made faster by that amount, and energy due to back electromotive force in the rest cycle can also be stored, resulting in efficient power consumption. Can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an exciting circuit of an electromagnetic flowmeter showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing an exciting circuit of a conventional electromagnetic flowmeter, and FIG. 3 shows an exciting coil. It is a figure which shows the flowing current waveform. 1: power transformer, 2: rectifier circuit, 4: excitation energy storage circuit, D _5: diode, C _{2: capacitors, Tr 1 · Tr 2 · Tr} 3 · Tr 4: switching transistors,

Claims (1)

[Claims] 1. An exciting coil for applying a magnetic field to a fluid tube, a switching element for controlling ON / OFF of a current flowing through the exciting coil, an AC signal is rectified, and a power supply voltage is supplied to the switching element. An electromagnetic flowmeter comprising: a rectifier circuit for performing an excitation energy storage circuit including a diode and a capacitor between the output side of the rectification circuit and the switching element.