RU2489686C2 - Electromagnetic method of flow measurement - Google Patents

Abstract

FIELD: instrument making.

SUBSTANCE: in a liquid that crosses a magnetic field, an EMF is induced, which is proportionate to speed of liquid motion. The pipeline section has the second pair of electrodes contacting with a channel wall in the same points as the first pair of electrodes, besides, if the external current is supplied to one pair of electrodes, then potentials are measured in the second pair of electrodes. At the same time measurement of voltage between potential electrodes is done twice, once when there is no external current through current electrodes, but with the connected inductor's field, and for the second time with the disconnected inductor's field, but with the external current available with a certain value.

EFFECT: possibility to measure volume flow of liquid metal with absence of a shunting pipe action.

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Description

The present invention relates to instrumentation, and in particular to a technique for measuring the flow of liquid metals using an electromagnetic measurement method, i.e. a method based on the interaction of a moving fluid with a magnetic field. This interaction obeys the law of electromagnetic induction, according to which in a fluid crossing a magnetic field, an EMF is proportional to the velocity of the fluid.

The measurement of the flow rate of liquid metals is necessary, for example, in the operation of power plants, where liquid metal is used as a coolant.

A known method of measuring the flow rate of liquid metal flowing in a magnetic field through a steel non-magnetic pipe [1]. Since the measurement is carried out, as a rule, at a high temperature of liquid metal, do not use an electrical insulation coating on the inner surface of the pipe.

The method consists in determining the flow rate of liquid metal by the potential difference between two electrodes touching the outer surface of the pipe at points diametrically opposed along a line perpendicular to the direction of the magnetic field. A disadvantage of the known measurement method is the shunting action of the pipe walls, leading to a partial loss of signal and low accuracy in determining the flow rate.

A known electromagnetic method for measuring the flow rate of liquid metal flowing in a magnetic field of an inductor through a non-magnetic steel pipe, on the outer wall of which, along a line perpendicular to the direction of the magnetic field, two pairs of electrodes are diametrically opposed, each pair of electrodes having potential and current electrodes [2]. This method of measuring the flow rate of a liquid metal involves passing through a current electrode an external current of a magnitude at which the voltage between the potential electrodes becomes equal to zero. In this case, there is no current in the pipe wall. As a measure of volumetric flow rate, the value of the external current is taken.

The disadvantage of this method [2] is the low accuracy of flow measurement, because instability of the electric voltage between the electrodes caused by the interaction of pulsations of the flow rate of the liquid metal with the magnetic field of the inductor and the appearance of an interference signal in connection with this makes it difficult to control the zero voltage between the potential electrodes and set the required external current through the current electrodes.

The present invention eliminates this disadvantage.

In it, it is proposed to measure the voltage between potential electrodes twice, once in the absence of an external current through current electrodes, but when the inductor field is turned on, and a second time when the inductor field is off, but in the presence of an external current of a certain value.

Thus, it is proposed to supply external current to the electrodes at the moment when the magnetic field of the inductor is disconnected, i.e. control the current and voltage between potential electrodes when there is no interaction of the flow rate with the magnetic field of the inductor and, therefore, there is no interference signal.

Fig. 1 and Fig. 2 explain the proposed method for measuring the flow rate of liquid metal.

Fig. 1 shows a flowmeter diagram made on this proposal. Figure 1 shows: 1 - a steel non-magnetic pipe to which two pairs of electrodes are diametrically opposed, 2-2 - potential electrodes, 3-3 - current electrodes. The flowmeter inductor consists of a magnetic field excitation coil 4 and a magnetic circuit 5. Potential electrodes are connected to the input of the measuring device 6. In addition, the measuring device has a current source to which current electrodes 3-3 and a magnetic field excitation coil 4 are connected.

Figure 2 shows a simplified electrical equivalent circuit of the flowmeter pipeline assembly. The following notation is used in the diagram: E - EMF induced in the channel as a result of the interaction of the flow velocity with the magnetic field, r - internal resistance of the EMF source (resistance of liquid metal), R - resistance of the pipe wall, U - voltage between the electrodes, j - external current .

The flow measurement process is controlled by measuring device 6. It periodically switches the current source to the inductor 4, then to the current electrodes 3-3, measures the voltages between the potential electrodes 2-2 and calculates the volumetric flow of liquid metal.

When the inductor is on, there is no external current. Then the voltage between the potential electrodes U _{1 is} described by the expression

$$U_{\mathrm{one}}=\frac{ER}{2r+R}(\mathrm{one})$$

Moreover, the EMF E is proportional to the volumetric flow rate of the liquid metal Q, i.e.

$$E=f(Q)(2)$$

When the inductor is turned off, the current to the current electrodes 3-3 is supplied by an external current from the measuring device 6. In this mode, the voltage between the electrodes U _{2 is} described by the expression

$$U_2=\frac{rRj}{2r+R}(3)$$

From a comparison of expressions (1) and (3) it follows that the EMF E can be represented by the expression

$$E=rj\frac{U_{\mathrm{one}}}{U_2}(\mathrm{four})$$

As follows from the analysis of expressions (1) and (3), the voltages U ₁ and U ₂ , each individually and equally, depend on the value of the resistance of the channel wall R, and their ratio remains constant regardless of the value of R.

It is assumed that the internal resistance of the measured medium r does not change during the operation of the device, except for its dependence on temperature. The advantage of the proposed measurement method is that it allows you to determine the flow rate in the absence of the influence of changes in the resistance of the pipe wall.

Information sources

1. Kremlin P.P. “Flow Measurement of Multiphase Flows,” ed. Engineering, Leningrad, 1982.

2. The electromagnetic method of measuring the flow rate, RF patent No. 2308685 from 12.29.2005.

Claims (1)

The electromagnetic method of measuring the flow rate of liquid metal flowing in the magnetic field of the inductor through a non-magnetic steel pipe, on the outer wall of which along the line perpendicular to the direction of the magnetic field, two pairs of electrodes are diametrically opposed, each pair of electrodes having potential and current electrodes, and the flow rate is determined according to the result of measuring the voltage between the potential electrodes and the external current flowing through the current electrodes, characterized in that the measurement of conjugation between the potential electrodes produce twice, once in the absence of external current via current electrodes, but when the field of the inductor, and a second time at the disconnected inductor field, but in the presence of external current a certain value.

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