JP2751152B2 - Electromagnetic flow meter - Google Patents

Description

The present invention relates to an electromagnetic flow meter, and more particularly to an electromagnetic flow meter 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 and 43, on the other hand, a low-frequency excitation current is passed from the excitation circuit 46 to the coils 44 and 45 provided outside the tube, and the shaft and electrode of the tube 41 are provided.
A magnetic field perpendicular to the directions 42 and 43 is applied, and a signal corresponding to the flow rate is derived from the electrodes 42 and 43 via the amplifier 47. The exciting coils 44 and 45 may have an air core or a core, but may be made of an iron plate or a silicon steel material. Excitation currents flowing from the excitation circuit 46 to the coils 44 and 45 are mostly intermittent excitation as shown in FIG. 5 (a) or have no pause as shown in FIG. 6 (a). . FIGS. 5 (b) and 6 (b) show the magnetic flux generated in the pipe through which the fluid flows in response to the respective exciting currents. (C) Problems to be Solved by the Invention In the above-mentioned conventional electromagnetic flowmeter, regardless of intermittent excitation or non-intermittent excitation, the exciting current flows through the coil during the period of applying the magnetic flux to the tube. Therefore, it is impossible to realize a so-called two-wire type electromagnetic flow meter. SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide an electromagnetic flowmeter which uses an exciting current for a period shorter than a magnetic flux input period to a tube and consumes less power. (D) Means and Action for Solving the Problems In order to solve the above problems, the electromagnetic flowmeter of the present invention has a high magnetic flux as the core for winding the exciting coil, even if the exciting current is set to zero. The residual magnetic flux density is large enough to maintain the density, the magnetic flux in the core is made of a material with a small coercive force enough to be easily reversed by the magnetic field generated by the coil, and compared to the positive and negative periods of the excitation signal. An exciting current is supplied to the coil only for a sufficiently short period. In this electromagnetic flowmeter, the coil for excitation is wound around a core made of a material having a large residual magnetic flux density and a small coercive force.
The magnetic flux in the core is easily inverted by the magnetic field generated by the coil itself, and a high magnetic flux density can be maintained even when the magnetic field generated by the coil is zero. Therefore, a necessary magnetic flux can be formed in the tube by supplying an exciting current to the coil in a very short time. (E) Examples Hereinafter, the present invention will be described in more detail with reference to examples. FIG. 1 is a circuit diagram of an electromagnetic flow meter showing one embodiment of the present invention. In this electromagnetic flow meter, a pair of electrodes 2 and 3 facing each other are provided on the inner wall surface of a tube 1 through which a fluid to be measured flows, as in the related art. Further, coils 4 and 5 are provided outside the tube 1, and a low-frequency exciting current flows from the exciting circuit 6 to apply a magnetic field orthogonal to the axis of the tube 1 and the electrodes 2 and 3. A signal corresponding to the flow rate is derived from the electrodes 2 and 3 via the amplifier 7. The feature of this electromagnetic flowmeter is that the coils 4 and 5 for excitation are
As shown by the BH characteristic in FIG. 2, the current that is wound around the core 8 made of a material having a large residual magnetic flux density Ba and a small coercive force Hc and flowing from the excitation circuit 6 to the coils 4 and 5 As shown in FIG. 3 (a), it is instantaneous for a period very small compared to the period T. Since the coercive force Hc of the core 8 is small, it is easily reversed by the magnetic field of the coils 4 and 5, and the residual magnetic flux density Ba is large. The magnetic flux density can be maintained. Therefore, even if the exciting current flowing through the coils 4 and 5 is instantaneous as shown in FIG. 3A, the magnetic flux in the tube 1 becomes as shown in FIG. There will be sufficient magnetic flux. The exciting current flowing through the coils 4 and 5 does not need to be a constant current, and may be any value as long as the magnetic flux density in the core 8 is equal to or greater than the saturation value. Exciting circuit 6
Can be simplified. Further, a magnetic sensor 9 is attached to the tube 1, and the density of the magnetic flux generated in the tube 1 via the core 8 is detected by the magnetic sensor 9, and the arithmetic circuit at the subsequent stage corrects the change in the magnetic flux. use. Further, since the change in the saturation magnetic flux density depends on the temperature, a temperature sensor may be attached to the core instead of the magnetic sensor, and the change in the magnetic flux may be corrected according to the output of the temperature sensor. (F) Effects of the Invention According to the present invention, the core around which the exciting coil is wound has a residual magnetic flux density that is large enough to maintain a high magnetic flux density even when the exciting current is zero. Is made of a material having a small coercive force such that it can be easily reversed by the magnetic field generated by the coil, and the exciting current flows through the coil for a period sufficiently small compared to the period.
Power consumption can be greatly reduced as compared with the conventional case. for that reason,
A two-wire electromagnetic flow meter can also be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of an electromagnetic flow meter showing one embodiment of the present invention, FIG. 2 is a diagram showing BH characteristics of a core used in the electromagnetic flow meter, FIG. 4A and 4B are diagrams showing the waveforms of the exciting current and the generated magnetic field of the electromagnetic flowmeter, FIG. 4 is a circuit diagram showing a conventional electromagnetic flowmeter, and FIGS. FIGS. 6 (a) and 6 (b) are waveform diagrams for explaining the operation of a conventional electromagnetic flow meter. 1: Tube, 2: 3: Electrode, 4: 5: Coil for excitation, 6: Excitation circuit, 8: Core.

Claims (1)

(57) [Claims] A pair of electrodes is provided on the inner wall of the tube through which the fluid to be measured is guided, and a coil wound around a core for applying a magnetic field in a direction perpendicular to the flow direction of the fluid to be measured and the direction of the pair of electrodes. An electromagnetic flowmeter disposed outside the tube, applying a signal of both positive and negative polarities to the coil to flow an excitation current, and deriving a signal corresponding to the flow rate of the fluid to be measured from the two electrodes, wherein the excitation coil Has a large residual magnetic flux density enough to maintain a high magnetic flux density even when the exciting current is 0, and has a small coercive force enough to allow the magnetic flux in the core to be easily reversed by the magnetic field generated by the coil. An electromagnetic flowmeter made of a material, wherein an exciting current is supplied to the coil only for a sufficiently short period as compared with the positive and negative periods of the exciting signal.