JPS6383613A - Electromagnetic flow meter - Google Patents

Abstract

PURPOSE:To reduce the power consumption of an electromagnetic flow meter by winding coils for excitation around a core which has large residual magnetic flux density and small coercive force and supplying an exciting current to the coil in a period much smaller than a cycle. CONSTITUTION:This flow meter has a couple of electrodes 2 and 3 provided on the internal wall surface of a tube 1 where fluid to be measured flows. Further, coils 4 and 5 are provided outside the tube 1 and the exciting current is supplied from an exciting circuit 6 to lead a signal corresponding to the flow rate out of the electrodes 2 and 3 through an amplifier 7. The coils 4 and 5 are wound around the core 8 made of a material which has large residual magnetic flux density Ba and small coercive force Hc and the current supplied from the circuit 6 to the coils 4 and 5 is much shorter than a cycle T and momentary. Thus, the coercive force Hc of the core 8 is small, so inversion is easily caused by magnetic fields of the coils 4 and 5 and the high magnetic flux density can be maintained even if the magnetic fields are ceased by ceasing the current of the coils 4 and 5 because the residual magnetic flux density Ba is large. Thus, the exciting current is made momentary and the magnetic flux in the tube 1 becomes sufficient for measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to an electromagnetic flowmeter, and particularly to an electromagnetic flowmeter with reduced power consumption.

(B) Prior art As shown in FIG. 4, a conventional electromagnetic flowmeter has a pair of electrodes 4 facing each other on the inner wall surface of a pipe 41 through which a fluid to be measured flows.
2.43 is provided, while a coil 44.45 is provided outside the tube.
A low-frequency excitation current is passed through the excitation circuit 46, a magnetic field perpendicular to the axis of the tube 41 and the direction of the electrodes 42, 43 is applied, and a signal corresponding to the flow rate is derived from the electrodes 42, 43 via the amplifier 47. . The excitation coils 44, 45 are either air-core or have a core, and are made of iron plate or silicon steel. In addition, the excitation circuit 4
6 to the coil 44.45 is as shown in Fig. 5 (a
), most of them were intermittently excited, or had no rest period, as shown in Fig. 6(a).

FIG. 5 (bl) and FIG. 6 (bl) are the magnetic fluxes generated in the tube through which the fluid flows in response to the respective excitation currents.

(c) Problems to be solved by the invention In the conventional electromagnetic flowmeter described above, regardless of whether the excitation is intermittent or non-intermittent, the excitation current is passed through the coil during the period when magnetic flux is applied to the tube. It was impossible to realize a so-called two-wire electromagnetic flowmeter because of the power consumption.

In view of the above, it is an object of the present invention to provide an electromagnetic flowmeter that uses an excitation current for a shorter period than the magnetic flux input period to the tube, and further reduces power consumption.

(d) Means and action for solving the problems In order to solve the above problems, the electromagnetic flowmeter of the present invention has an excitation coil made of a material with a large residual magnetic flux density and a small coercive force. The coil is wound around the core, and the excitation current is caused to flow through the coil for a period sufficiently small compared to the positive and negative cycles of the excitation signal.

In this electromagnetic flowmeter, the excitation coil is wound around a core made of a material with high residual magnetic flux density and low coercive force, so the magnetic flux in the core is easily reversed by the magnetic field generated by the coil itself, and the magnetic flux generated by the coil Even if it is set to O, a high magnetic flux density can be maintained. Therefore, the necessary magnetic flux can be generated within the tube by only passing an excitation current through the coil for a very short period of time.

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

FIG. 1 is a circuit diagram of an electromagnetic flowmeter showing an embodiment of the present invention. This electromagnetic flowmeter, like the conventional one, has a pair of electrodes 2 facing each other on the inner wall surface of a pipe 1 through which the fluid to be measured flows.
．． There are 3. Further, a coil 4.5 is provided outside the tube 1, and a low-frequency excitation current is passed from an excitation circuit 6 to apply a magnetic field orthogonal to the axis of the tube 1 and the direction of the electrodes 2.3. Electrode 2
．． 3 through an amplifier 7, a signal corresponding to the flow rate is derived.

The feature of this electromagnetic flowmeter is that the excitation coil 4.5 has a core 8 made of a material with a large residual magnetic flux density Ba and a small coercive force Hc, as shown in the BH characteristics in Fig. 2. The current flowing from the excitation circuit 6 to the coil 4.5 is instantaneous and has a very small period compared to the period T, as shown in FIG. 3(a).

Since the coercive force Hc of the core 8 is small, it is easily reversed by the magnetic field of the coil 4.5, and the residual magnetic flux density Ba is large, so even if the current of the coil 4.5 is set to 0 and the magnetic field is 0, the magnetic field remains high. Can maintain magnetic flux density. Therefore, Figure 3 (a
), even if the excitation current flowing through the coil 4.5 is instantaneous, the magnetic flux inside the tube 1 will be as shown in Figure 3 (1)), which is sufficient for measurement. .

Note that the excitation current flowing through the coil 4.5 does not need to be a constant current, and may be any value as long as it is equal to or greater than the magnitude at which the magnetic flux density within the core 8 is saturated.

Accordingly, the configuration of the excitation circuit 6 can be simplified. Also, tube 1
A magnetic sensor 9 is attached to the tube 1, and the magnetic sensor 9 detects the density of magnetic flux generated in the tube 1 via the core 8, and the density of the magnetic flux generated in the tube 1 is detected by the downstream arithmetic circuit and used to correct changes in the magnetic flux.

Further, since changes in the saturation magnetic flux density depend on temperature, a temperature sensor may be attached to the core instead of the magnetic sensor described above, and magnetic flux changes may be corrected in accordance with the temperature sensor output.

(f) Effects of the invention According to this invention, the excitation coil has a high residual magnetic flux density.
Since the coil is wound around the core of the coercive coil and the excitation current is passed through the coil during a sufficiently small period compared to the period, power consumption can be significantly reduced compared to the conventional method. Therefore, a two-wire electromagnetic flowmeter can also be realized.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an electromagnetic flowmeter showing an embodiment of the present invention, Fig. 2 is a diagram showing the BH characteristics of the core used in the electromagnetic flowmeter, and Fig. 3 (al (bl is Figure 4 is a diagram showing the waveforms of the exciting current and generated magnetic field of the electromagnetic flowmeter, and Figure 4 is a circuit diagram showing a conventional electromagnetic flowmeter, Figures 5(a), (b), and 6(a) (bl is , is a waveform diagram for explaining the operation of a conventional electromagnetic flowmeter. 1: Tube, 2 and 3: Electrodes, 4 and 5: Excitation coil, 6: Excitation circuit, 8: Ko7゜Patent applicant Shimadzu Corporation Agent
Patent Attorney Shigeru Nakamura Figure 1 8. Core figure 4

Claims (1)

[Claims] (1) A pair of electrodes are provided on the inner wall of the tube through which the fluid to be measured is guided, and a coil is installed outside the tube to apply a magnetic field in directions perpendicular to the flow direction of the fluid to be measured and the direction of the pair of electrodes. In an electromagnetic flowmeter, the excitation coil is connected to a residual magnetic flux density in which a signal of both positive and negative polarities is applied to the coil to cause an excitation current to flow, and a signal corresponding to the flow rate of the fluid to be measured is derived from the two electrodes. The coil is wound around a core made of a material having a large coercive force and a small coercive force, and the excitation current is caused to flow through the coil only for a sufficiently small period compared to the positive and negative cycles of the excitation signal. Electromagnetic flowmeter.