JPH02122221A - Exciting circuit for electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To quicken the rise and to conserve energy obtained by counter electromotive force by providing an excitation energy conserving circuit consisting of a diode and a capacitor between the output side of a rectifying circuit and a switching element. CONSTITUTION:A conserving circuit 4 consisting of a diode D5 and a capacitor C2 is provided between an output terminal of a capacitor C1 of a rectifying circuit 2 and power source supply terminals of switching use transistors TR1 - TR4. In this state, counter electromotive force generated in an exciting coil L is charged to the capacitor C2 of the circuit 4 in a dormant cycle of the switching element. In this case, a larger voltage than a voltage inputted in the next exciting cycle exists in both ends V2 of the capacitor C2, therefore, by this voltage, a rise of a current flowing to the coil L can be quickened. Moreover, energy of the coil L obtained by counter electromotive force in the dormant cycle is charged to the capacitor C2, therefore, it is used usefully.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to an electromagnetic flowmeter, and particularly to an improvement in an excitation circuit.

(b) Prior Art The excitation circuit of a conventional electromagnetic flowmeter is shown in FIG. In the figure, an alternating current voltage generated on the secondary side of a power transformer 1 is converted into a direct current voltage (1) by a rectifier circuit 2 consisting of a bribing circuit consisting of diodes d+, dz, d3, and d4 and a smoothing capacitor C. transistor Tr,
, Tr2, Tr, , Tra are switching transistors for turning on/off the excitation coil ■7, and diodes D1, D2, D3, and D4 for surge voltage protection are connected in parallel to each transistor. It is connected. The I transistors Tr and Tr2 are complementary transistors whose collectors are connected, and the transistors Tr and Tr2 are also complementary transistors whose collectors are commonly connected and whose collectors are connected to each other.
r IXT r z collector and transistor Tr,
, an excitation coil L is connected between the collectors of the Tr4.

The emitters of the transistors T++ and Tr:+ are commonly connected, the emitters of the transistors Trz and Tr are commonly connected, and the rectifier circuit 2 is connected between the emitters of the transistors Tr, Tr3 and the emitters of the transistors Tr2 and Tra. The output ■1 is supplied. Transistor Tr.

Trz, Tr3, and Tra are controlled by signals from the control unit 3.
The transistors Tr, Tr, Trz are mutually turned on/off, and the transistors T'r3, 'Tr4 are also mutually turned on/off. As shown in Fig. 3, the coil L has two currents: positive direction excitation, that is, when the excitation current flows from direction a to b, and negative direction excitation, when the current flows from b to a, contrary to the rest cycle. are arranged to flow sequentially in a cyclical manner. That is, a signal is applied from the control unit 3 to turn on the transistors Tr and Tr4, and a positive excitation current flows through the transistor Tr1, point a, excitation coil L, point b, and transistor Tr4, and during the rest period,
Transistors Tr+, Tr2, Tr3, and Tr4 are all turned off, and no current flows through the excitation coil.Next, in the case of negative direction excitation, Tr3 and Tr2 are turned on, and transistor Tr3, point b, and excitation coil L are turned on. , a current flows through the transistor Tr2 at point a.

In addition, in the rest cycle after forward excitation, a current due to a back electromotive force flows from point b to point a via diode D3, capacitor +C1, and diode D2. In addition, in the next pause cycle of negative excitation, the current due to the back electromotive force generated in the coil flows from a to diode D1 to capacitor C.
I flows to point b via diode D4.

(c) Problem to be solved by the invention In order to speed up the response of an electromagnetic flowmeter, it is necessary for the excitation current to rise quickly, but the rise time of the current at the start of excitation is proportional to the voltage applied to the coil L. In order to speed up the rise from 1 to 2, it is necessary to make 1 transiently high only at the start of excitation.

To do this, conventionally, a means for temporarily switching the voltage was provided on the output side of the capacitor C1, or in the case of a spin inverter regulator, a means was provided for temporarily increasing the voltage on the temporary side of the transformer. Although measures have been taken to speed up the response speed, the use of such circuits has the problem of unavoidable complicated circuit configurations.

In addition, the energy stored in the coil L during excitation becomes the back electromotive force generated when the excitation is stopped and is discharged through the diode, and is consumed as heat due to the resistance on the circuit, so that energy is wasted. There was also the problem that it was consumed.

This invention has been made in view of the above problems, and is an electromagnetic flowmeter with low power consumption that speeds up the start-up at the start of excitation with a simple circuit configuration, and can use back electromotive force without wasting it. The purpose is to provide an excitation circuit for

(d) Means for Solving the Problems The excitation circuit of the electromagnetic flowmeter of the present invention includes an excitation coil for applying a magnetic field to a fluid pipe, and a switching element for controlling on/off the current flowing through the excitation coil. and a rectifier circuit that rectifies an alternating current signal and supplies a power supply voltage to the switching element, characterized in that an excitation energy storage circuit comprising a diode and a capacitor is provided between the output side of the rectifier circuit and the switching element. We are prepared.

(B) Effect In the excitation circuit of this electromagnetic flowmeter, the back electromotive force generated in the excitation coil is charged to the capacitor of the excitation energy storage circuit during the rest cycle of the switching element, and is larger than the voltage input in the next excitation cycle. Since a voltage is present across the capacitor, this voltage allows the current flowing through the excitation coil to rise quickly. Furthermore, the energy of the excitation coil due to the back electromotive force during the rest cycle is charged to the capacitor, so it is used without wastage.

(f) Examples The present invention will now be explained in more detail with reference to Examples.

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

In the same description, the same numbers and symbols as those in the circuit of FIG. 2 refer to the same circuit elements. The feature of the excitation circuit of this embodiment is that in addition to the circuit shown in FIG. This is because an excitation energy storage circuit 4 consisting of a capacitor C2 is provided.

Now, the energy stored in coil L during excitation is 1/2L.
As I2, the energy stored in capacitor C2 is 1
/2C2V2'', this voltage is expressed as V2 across capacitor C2, and this voltage is generated across capacitor C2.In addition, in the above circuit, the capacitance of capacitor CC2 is C2>CI. , V2>V, a diode D is connected.

In the excitation circuit of this embodiment, assume that the transistors Tr and Tr4 are turned on by a signal from the control section 3, and current flows through the coil L from point a to point b. When the next rest cycle is started in this state, the back electromotive force generated in the coil L flows from point b to point b via diode D3, capacitor C2, and diode D2, and the energy that was in coil L during excitation is , stored in capacitor C2. Then, a voltage of 2 is generated across the capacitor C2 at the above-described voltage v2=JT-AP7. This voltage (2) is a higher voltage than the DC voltage (2).

When the transistors Tr2 and Tr3 are turned on in the next cycle, the voltage 2 stored in the capacitor C2 is first applied to the coil 7. As mentioned above, this voltage V2 is
Since it is higher than the power supply voltage V, the excitation current rises faster than in the conventional configuration. Moreover, the energy stored in the coil in the previous cycle is used at the start of the next cycle, so there is no wastage of energy.
Lower overall power consumption can be achieved.

(1.) Effects of the Invention According to this invention, an excitation energy storage circuit consisting of a diode I and a capacitor is provided between the output side of the rectifier circuit and the switching element, and during the rest cycle, the excitation energy is generated by the coil in the capacitor of the storage circuit. Since the energy from the back electromotive force is stored and the energy stored in the capacitor is first applied in the next power supply cycle, it is possible to speed up the rise by that amount, and also save the elbow caused by the back electromotive force during the rest cycle. An excitation circuit with efficient power consumption can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an excitation circuit of an electromagnetic flowmeter according to an embodiment of the present invention, Fig. 2 is a circuit diagram showing an excitation circuit of a conventional electromagnetic flowmeter, and Fig. 3 is a circuit diagram showing an excitation circuit of a conventional electromagnetic flowmeter. FIG. 3 is a diagram showing a flowing current waveform. 1: Power transformer, 2: Rectifier circuit, 4: Excitation energy storage circuit, D: Diode, C2: Capacitor, T r 1-
Transistor for Trz-Tr3/Tr4 switching, Patent applicant: Shimadzu Corporation Representative Patent attorney: Shigenobu Nakamura

Claims (1)

[Claims] (1) An excitation coil for applying a magnetic field to the fluid tube, a switching element for controlling on/off the current flowing through the excitation coil, and a rectifier that rectifies an AC signal and supplies a power supply voltage to the switching element. An excitation circuit for an electromagnetic flowmeter comprising: an excitation energy storage circuit comprising a diode and a capacitor between the output side of the rectifier circuit and the switching element.