JPS597930B2 - electromagnetic flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises: a pair of electrodes that directly sandwich at least a portion of a fluid flow; , an electromagnetic flowmeter that has an excitation wire ring that excites this magnetic circuit and calculates the flow velocity based on the voltage generated between both electrodes due to the magnetic flux of the magnetic circuit and the flow of fluid, and has low power consumption. The purpose is to realize something.

Focusing only on this purpose, the use of permanent magnets is ideal as a means of obtaining a magnetic circuit, but since the voltage polarity between the two electrodes remains unchanged, contact potential and polarization voltage are generated due to electrochemical action. However, this method has the disadvantage of causing significant zero point fluctuations, making it impractical except in special cases.

When using a magnetic circuit with AC excitation, the above-mentioned difficulties are solved, but there is 90 degree noise, and the combination with the in-mode noise does not necessarily result in a 90 degree phase difference, and there may be fluctuations, so the fluid is flowing. It is difficult to confirm the zero point in between.

When using a magnetic circuit that is excited by rectangular wave currents that alternate in opposite directions, there is no problem mentioned above when using permanent magnets, and the magnetic flux can be excited from the average value while there is no change in magnetic flux in both current directions. There is an advantage that the amount of zero point fluctuation can be determined even while the fluid is flowing, and it can be corrected based on this, but in the conventional method, the excitation current was kept flowing all the time, so there was a problem in that it consumed a lot of power. Ta.

In view of this, the electromagnetic flowmeter of the present invention maintains the above-mentioned advantages by generating in the magnetic circuit a rectangular wave magnetic flux whose polarity is alternately reversed and which is intermittent but lasts for a certain amount of time each time, Moreover, as a configuration item to reduce power consumption, an excitation current is passed through the excitation wire ring intermittently, instantaneously, and alternately in the opposite direction, and the magnetic circuit retains residual energy while the excitation current is not flowing. This is an electromagnetic flowmeter that calculates flow velocity based on the voltage generated between both electrodes due to magnetic flux and fluid flow.

FIG. 1 shows a cross section perpendicular to the fluid flow of one embodiment of the invention.

The fluid conduit 1 is non-magnetic and non-conductive over a considerable length in the vicinity of this cross-section. There is a pair of electrodes 2a and 2b exposed inside the conduit 1 so as to directly sandwich at least a portion of the fluid flow and face each other. Each electrode 2a, 2b
is connected via a conductor portion that penetrates the wall of the conduit 1 in a watertight manner to a flow rate calculation device 3 that calculates the flow rate based on the voltage between both electrodes 2a and 2b. Magnetic poles 4a, 4 sandwich pipe line 1.
A magnetic circuit 4 having a magnetic field 4b is provided to generate a magnetic flux between the magnetic poles 4a and 4b that crosses both the straight line passing through the electrodes 2a and 2b and the flow of the fluid.

The material of the magnetic circuit 4 is one that has high magnetic permeability, is easily magnetized, and has a certain degree of coercive force, and in this embodiment, ordinary steel is used.

Excitation wire rings 5a, 5b for exciting the magnetic circuit 4 are wound around each magnetic pole 4a, 4b.

The wire diameter is thick and the total resistance value is small. Both excitation coils 5a and 5b are connected in series, and an excitation device 6 is connected thereto which supplies excitation current intermittently, instantaneously each time, and alternately in opposite directions.

When the strength of the magnetic field generated in the magnetic circuit 4 by this excitation current is +Hp and -Hp, the magnetic velocity density B generated between the magnetic poles 4a and 4b changes as shown by the curve in Figure 2, but the excitation current When becomes O, since the vermeance between the magnetic poles 4a and 4b is small, the magnetic field strength passes through the point of 0 and becomes stable at the point p or p' shown in the figure. The residual magnetic flux density B in this state is represented by the illustrated line segment 0b or 0b'. In order to set a large residual density, the cross section of the conduit 1 should be rectangular,
It is a good idea to narrow the gap between the magnetic poles 4a and 4b to increase permeance.

Next, both the excitation device 6 and the flow rate calculation device 3 maintain a fixed relationship with each other in time by the pulses received from the control device 7 which generates a required signal based on the pulses of the oscillator 1. It operates periodically, and as a result performs a predetermined action. As shown in the circuit shown in the upper half of FIG. 3, the excitation device 6 is constructed by connecting excitation wire rings 5a and 5b in series in order to substantially eliminate the influence of changes in the copper resistance of the excitation wire rings due to temperature changes. A fixed resistor r having a sufficiently large resistance value compared to both wire rings 5a and 5b is inserted in series, and a capacitor c and a normally open instantaneous closing switch S1 are connected in series, and the polarity of both ends is reversed. It is connected to both ends of a series connection consisting of the wire rings 5a, 5b and a fixed resistor r via a switch S, and a series connection of a high resistance R and a stabilized DC power source EO is connected in parallel with a capacitor c. .

In the above, the normally open instantaneous closing switch S1 and the polarity reversing switch S2 are replaced with electronic circuits having equivalent functions in the actual circuit, and these are controlled by pulses at constant intervals emitted by the control device 7, as shown in FIG. As shown in diagrams S, , S, the connection polarity of switch S2 is reversed at regular intervals, and in the middle of each polarity maintenance period, switch S1 is closed only for a very short time and then immediately opened. Therefore, as shown in Figure 4 and Diagram 5, an excitation current of a constant magnitude flows intermittently in the excitation wire rings 5a and 5b, each time having a pointed shape and alternating in the opposite direction. As can be seen from the diagram in FIG. 2, between the magnetic poles 4a and 4b, a magnetic flux that changes in a peaked manner as shown in diagram 4 in FIG. 4 is followed by a residual magnetic flux that is almost constant.

As a result, for example, considering the case where the flow rate of the fluid in the pipe line 1 gradually decreases, the voltage generated between the electrodes 2a and 2b is
As shown in diagram 2, it changes in proportion to the product of magnetic flux and flow velocity in diagram 4.

Next, as shown in the block diagram in the lower half of FIG.
1 and transmits it to the sampling circuit SP, and the sampling circuit SP receives the signal from the control device 7 by avoiding the first half of each period of the electrode voltage in the diagram 2, where the fluctuation is large, as shown in the fourth diagram Sp. In response to sampling pulses that match only the second half, only the change in electrode voltage within the period of each sampling pulse is shown in FIG. Sample output as shown. This output is amplified by the second amplifier A2 and synchronously rectified by the synchronous rectifier SR to obtain an intermittent output that changes in proportion to the flow velocity as shown in the diagram SR in Figure 4. This is time averaged by the averaging circuit m. As a result, a smooth change as shown in diagram m in Figure 4 is obtained, and based on this, the instantaneous flow velocity is indicated. In the structure described above, by appropriately determining the frequency of the excitation current by the output pulse of the control device 7, the zero point fluctuation due to the electrochemical action on the electrodes 2a and 2b while the excitation current does not flow can be practically tolerated. It is possible to maintain the overall average flow velocity within the range and to make the overall average flow velocity substantially the same as the average flow velocity only during the sampling pulse period even if the flow velocity fluctuates during periods other than the sampling pulse period.

According to the electromagnetic flowmeter of the present invention, since the excitation current is instantaneous, the intended purpose can be achieved with extremely low power consumption.

In addition, since the voltage polarity between the electrodes 2a and 2b is reversed every time, there is no significant zero point fluctuation due to electrochemical action, and furthermore, since the measurement is performed only during a period when changes in residual magnetic flux have no practical effect, it is possible to measure the voltage while the fluid is flowing. However, it is easy to check the zero point.

This invention enables the emergence of a practical electromagnetic flowmeter that consumes less power and is powered by batteries.

[Brief explanation of drawings]

Fig. 1 is a sectional view of one embodiment of the present invention, Fig. 2 is a diagram explaining the properties of the magnetic circuit, Fig. 3 is a circuit diagram of the excitation device and a block diagram of the flow velocity calculation device, and Fig. 4 is each part. It is a line diagram showing the operation of. 2a, 2b...electrode, 4...magnetic circuit, 5a, 5b...excitation wire ring.

Claims (1)

[Claims] 1 A pair of electrodes that face each other by directly sandwiching at least a portion of the fluid flow, a magnetic circuit that generates a magnetic flux that crosses both the straight line passing through the electrodes and the flow, and an excitation wire ring that excites this magnetic circuit. With an intermittent, instantaneous and alternately opposite excitation current flowing through the excitation coil, the magnetic circuit maintains a residual magnetic flux and fluid flow while the excitation current does not flow. An electromagnetic flowmeter that calculates flow velocity based on the voltage generated between both electrodes.