JPH052828Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field This invention relates to an electromagnetic flowmeter, particularly an electromagnetic flowmeter that can detect whether a fluid in a conduit is empty or empty.

(B) Prior Art As shown in Fig. 2, a generally well-known electromagnetic flowmeter is equipped with a pair of electrodes 2 and 3 on the inner wall of a conduit 1 through which the fluid to be measured flows, and a pair of electrodes 2 and 3 on the outer periphery of the conduit 1. , excitation coils 4 and 5 that apply a magnetic field B in directions orthogonal to the axial direction of the conduit 1 and the direction connecting the pair of electrodes 2 and 3 are provided, and if fluid flows in the tube at a velocity v, the electrodes 2 and 3 to e=Blv(l:
By deriving this voltage, the fluid flow rate is measured.

(c) Problems that the invention aims to solve In the conventional electromagnetic flowmeter described above, when the fluid in the conduit becomes empty, the electrodes no longer come into contact with the fluid.
Therefore, no current flows between the two electrodes, and no output can be obtained. In this case, fluid is present in the conduit, but it cannot be distinguished from the case where the flow velocity is 0,
There was a problem that it was not possible to measure the flow rate correctly.

In view of the above, an object of this invention is to provide an electromagnetic flowmeter that can determine whether a fluid in a conduit is empty or empty.

(d) Means and action for solving the problems The electromagnetic flowmeter of this invention has a pair of electrodes that are provided facing the wall inside the conduit through which fluid flows, and a direction that connects the pair of electrodes in the axial direction of the conduit. In a device that includes an excitation coil that applies a magnetic field in a direction orthogonal to each, and a circuit that derives the voltage obtained between the electrodes, the magnetic field is generated in a direction that intersects the plane that includes the magnetic field direction of the electrodes and the excitation coil. a sub-excitation coil disposed in the sub-excitation coil, an AC signal source that excites the sub-excitation coil, and leads from the pair of electrodes that are wired along the conduit wall in a plane including the magnetic field direction of the electrode and the excitation coil. It is equipped with a line.

In this electromagnetic flowmeter, when the conduit is filled with stationary fluid (liquid), the magnetic field of the auxiliary excitation coil caused by the AC signal source interlinks with the closed loop connecting the lead wire and the electrodes, so there is a gap between the electrodes. A constant electromotive force is obtained, confirming that the fluid is filled. However, if the fluid is not filled, the pair of electrodes will be exposed to the outside of the fluid, the closed loop will be open, and no electromotive force will be generated between the electrodes. This confirms that the conduit is not filled with fluid.

(e) Examples This invention will be explained in more detail below using examples.

FIG. 1 is a schematic diagram of an electromagnetic flowmeter showing an embodiment of this invention.

This electromagnetic flowmeter has a pair of electrodes 2 and 3 provided horizontally on the inner wall of a conduit 1, and a magnetic field B is generated in a direction perpendicular to both the direction of the electrodes 2 and 3 and the axial direction of the conduit 1. Excitation coils 4 and 5 are provided. Note that the excitation coils 4 and 5 are configured to be excited by an excitation circuit 6. These points are no different from the conventional one. Further, the electrodes 2 and 3 are connected to an amplifier 9 through lead wires 7 and 8, respectively, and the amplifier 9 is connected to a signal processing circuit 10. The lead wires 7 and 8 are wired along the outer peripheral surface of the conduit 1 in a plane that includes the electrodes 2 and 3 and the magnetic field B.

Further, sub-excitation coils 11 and 12 are provided near the excitation coils 4 and 5. These sub-excitation coils 11 and 12 are AC excitation circuit (AC signal source) 13
The magnetic field generated intersects the plane including the electrodes 2 and 3 and the lead wires 7 and 8. The excitation circuit 6, the AC excitation circuit 13, and the signal processing circuit 10 are connected to the control circuit 1.
4.

Next, the operation of this electromagnetic flowmeter will be explained.

In operation, the control circuit 14 repeats empty detection mode and measurement mode. The sky detection mode may be performed, for example, once every few minutes, and the measurement mode may be set during that time.

In the empty detection mode, the AC excitation circuit 13 excites the sub-excitation coils 11 and 12. If conduit 1
When the inside is filled with fluid, an alternating magnetic field intersects the closed loop consisting of the lead wire 7, electrode 2, fluid, electrode 3, and lead wire 8, and an electromotive force is induced between the electrodes 2 and 3. The signal is led out to a signal processing circuit 10 through an amplifier 9. This electromotive force confirms the fluid filling state.

On the other hand, when the fluid in the conduit 1 is empty, the electrodes 2 and 3 are disconnected, so the sub-excitation coil 1
Even when the electrodes 1 and 12 are excited, no electromotive force is generated in the electrodes 2 and 3, and no alternating current signal is input to the signal processing circuit 10 via the amplifier 9. This confirms that the conduit 1 is empty.

In the measurement mode, the operation of the AC excitation circuit 13 is stopped, and the excitation circuit 6 is operated to excite the excitation coils 4 and 5. This generates a magnetic field B. If the fluid is flowing at a velocity of v, the voltage according to Faraday's law will be applied to the electrodes 2 and 2.
It is induced between 3 and 3. This voltage is also taken into the signal processing circuit 10 via the amplifier 9, and the flow rate is measured.

(f) Effects of the invention According to this invention, the emptyness of fluid in a conduit can be detected with a simple configuration that includes a sub-excitation coil in addition to the excitation coil, and an AC signal source that excites the sub-excitation coil. and be able to take correct measurements.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an electromagnetic flowmeter showing an embodiment of this invention, and FIG. 2 is a diagram for explaining a conventional electromagnetic flowmeter. 1... Conduit, 2, 3... Electrode, 4, 5... Excitation coil, 7, 8... Lead wire, 11, 12... Sub-excitation coil, 13... AC excitation circuit.

Claims (1)

[Claims for Utility Model Registration] A pair of electrodes provided facing the wall inside a conduit through which fluid flows, and an excitation coil that applies a magnetic field in directions orthogonal to the axial direction of the conduit and the direction connecting the pair of electrodes. and a circuit for deriving the voltage obtained between the electrodes, the electromagnetic flowmeter comprising: a sub-excitation coil arranged to generate a magnetic field in a direction intersecting a plane including the magnetic field directions of the electrodes and the excitation coil; , comprising: an AC signal source that excites the sub-excitation coil; and lead wires from the pair of electrodes that are wired along the conduit wall in a plane that includes the magnetic field direction of the electrodes and the excitation coil; An electromagnetic flowmeter that detects whether or not a conduit is full or empty based on the presence or absence of an output signal from the lead wire when the sub-excitation coil is excited by a signal source.