RU2518380C1 - Flow measurement electromagnetic method - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: flow measurement electromagnetic method for electroconducting fluid passing in a electromagnetic field through a non-magnet pipe with two installed electrodes, the electromagnetic field is created by means of an electromagnet having an inductance coil through which electric energy is supplied, at that flow measurement is determined against measurement of the current passing through the inductance coil and against potential drop between the electrodes, the method is distinguished by additional measurement of voltage at terminals of the inductance coil and the flow rate value is calculated by the formula $$Q=k\frac{U}{I}\left[1-\frac{\lambda }{{\rho }_k}\left(\frac{U_k}{I}-R_k\right)\right],$$

where Q is a flow rate of the measured fluid, k is calibration factor, U is potential drop between the electrodes, I is current passing through the inductance coil, U_k is voltage at terminals of the inductance coil, R_k is electrical resistance of the inductance coil at calibration temperature of the measured fluid, λ is temperature error of the flow metre [1/°C], ρ_k is a change of the inductance coil resistance at changes in temperature of the measured fluid per one degree Celsius.

EFFECT: improvement of flow rate measurement in a wide range of changes in temperature of the measured fluid.

2 cl

Description

The present invention relates to instrumentation, and in particular to a technique for measuring the flow rate of electrically conductive liquids using an electromagnetic 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 (Faraday law), according to which in a fluid crossing a magnetic field, an EMF is proportional to the flow rate of the fluid.

Known electromagnetic flowmeter [1], containing a pipe made of non-magnetic material, the inner surface of which has an insulating coating, two electrodes inserted into the pipe channel, two induction coils located on the pipe, magnetic circuit and measuring and computing device in which there is a current source power induction coils. The control of the power source of the induction coils is performed by a measuring and computing device. In addition, using a measuring and computing device, the potential difference between the electrodes U and the supply current of the induction coils are measured I. The flow value Q is determined by the formula

$$Q=k\frac{U}{I};\left(\mathrm{one}\right)$$

where k is the calibration coefficient.

Known electromagnetic liquid metal flow meter [2], which consists of a pipe made of stainless steel without electrical insulation coating, an inductor consisting of a magnetic circuit and one induction coil, and a measuring and computing device in which there is a power source for the induction coil. The control of the power source of the induction coil, the measurement of the potential difference at the electrodes and the power supply current of the induction coil is performed by a measuring and computing device. The value of flow Q is determined by the formula (1).

The disadvantage of this method is the low accuracy of the flow measurement when the temperature of the measured liquid changes. Sources of temperature error of the flow meter can be changes in temperature of the linear dimensions of the device design, changes in the magnetic properties of the magnetic circuit, the dependence of the shunt action of the channel wall, if there is no electrical insulation coating on the inner surface of the channel, etc.

A particularly significant value of the temperature error of the flow measurement arises when measuring liquid metals, for which the working temperature of the medium being measured varies widely (for example, for liquid sodium flow meters, its working temperature varies from 200 to 525 ° C).

The present invention eliminates this disadvantage.

An electromagnetic method is proposed for measuring the flow rate of an electrically conductive fluid, based on the interaction of a moving fluid with a magnetic field, in which the voltage at the terminals of the induction coils U _k is additionally measured, and the flow rate is calculated by the formula

$$Q=k\frac{U}{I}\left[\mathrm{one}-\frac{\lambda }{{\rho }_k}\left(\frac{U_k}{I}-R_k\right)\right]\left(2\right)$$

where R _k is the electrical resistance of the induction coils at the calibration temperature of the measured medium; λ is the temperature error of the flow meter [1 / ° C]; ρ _k is the change in the electrical resistance of the induction coils caused by a change in the temperature of the medium being measured by degrees Celsius, i.e. [Ohm / ° C].

Structurally, induction coils of the magnetic field of excitation are located directly on or near the flowmeter tube. Therefore, a change in the temperature of the measured medium in one way or another affects the temperature of the induction coil itself. In the proposed method for measuring flow, an induction coil is used as a resistance thermometer. In liquid metal flowmeters, a pipe with a measured medium flowing through it is a particularly powerful source of temperature radiation to an induction coil. To ensure the reliability of liquid metal flowmeters, induction coils are made of copper wire with heat-resistant insulation, for example, type POZH, and the coil itself can be heated from the pipe to 200-250 ° C or more. For example, a flowmeter of the IRMU-1 type of liquid sodium has a normalized temperature error of λ = 1.5 · 10 ^-4 [1 / ° С]. Those. when the temperature of liquid sodium changes by 100 ° C, the temperature error will be 1.5%. In this case, the temperature of the induction coil increases by approximately 50 ° C, and its resistance changes by approximately 15-20%.

Implementation of the proposed method for measuring flow is as follows. For the particular flowmeter design under consideration, the following parameters are preliminarily calculated or experimentally determined: λ, ρ _k and R _k, since for this flowmeter design these parameters are considered as constant values. If λ, ρ _k depend on the temperature of the medium being measured, then the corresponding dependences are calculated.

The flow meter according to the invention work as follows. Due to the current flowing through the turns of the induction coils in the working volume of the channel, a magnetic field is excited, perpendicular to the plane passing through the axis of the electrodes and the axis of the channel. When an electrically conductive fluid moves along a pipe channel in its working volume, an electric field is induced according to the Faraday law, the intensity of which is proportional to the velocity of the fluid flow.

Using a measuring and computing device, the potential difference between the electrodes, the voltage at the terminals of the induction coils and the supply current of the induction coils are measured. The flow rate Q is determined by the formula (2).

In addition, the flow meter allows you to measure the temperature t of the measured medium, which is calculated by the measuring and computing device according to the formula

$$t=t_0+\frac{\mathrm{one}}{{\rho }_k}\left(\frac{U_k}{I}-R_k\right)\left(3\right)$$

where t ₀ - calibration temperature of the measured medium.

The technical result that can be obtained by carrying out the invention consists in increasing the accuracy of measuring the flow rate in a wide change in the temperature of the medium being measured.

Sources of invention

1. Kremlin P.P. Flow meters and quantity counters. Handbook, L .: Engineering, 1989, 701 p.

2. Electromagnetic flowmeter of liquid metals, patent RU No. 2431118, bull. No. 28, 2011

Claims (2)

1. An electromagnetic method for measuring the flow rate of an electrically conductive fluid flowing in a magnetic field through a non-magnetic pipe in which two electrodes are mounted, the magnetic field is created using an electromagnet having an induction coil through which an electric current is passed, and the flow rate of the fluid is determined by measuring the current flowing through the induction coil, and the potential difference between the electrodes, characterized in that, additionally measure the voltage at the terminals of the induction coil, and the value of descent calculated by the formula

where Q is the flow rate of the measured medium, k is the calibration coefficient, U is the potential difference between the electrodes, I is the current flowing through the induction coil, U _k is the voltage at the terminals of the induction coil, R _k is the electrical resistance of the induction coil at the calibration temperature of the measured medium, λ is the temperature error of the flow meter [1 / ° C], ρ _k is the change in the electrical resistance of the induction coil when the temperature of the medium is measured by degrees Celsius. 2. The method according to claim 1, characterized in that calculate the temperature t of the measured medium according to the expression

where t ₀ - calibration temperature of the measured medium.