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Key points of measuring low conductivity medium with electromagnetic flowmeter

Author: Release date: March 31, 2017 09:23:30 Source: Shanghai Cixi View: 125
The electromagnetic flowmeter is simple in structure and convenient in measurement and use. Although there are certain requirements for the conductivity of the medium, accurate measurement can be achieved through some processing even when the conductivity is relatively low. We will briefly introduce it with you.

1. Measuring tube: it is mainly used to let the measured conductive liquid pass through.

In terms of materials, it is mainly made of non-magnetic, low conductivity, low thermal conductivity and mechanical strength materials. The commonly used materials are glass fiber reinforced plastics, high-strength plastics, stainless steel, aluminum, etc.

2. Magnetic circuit system: generate uniform DC or AC magnetic field in use. The DC magnetic circuit is realized by permanent magnet.

Its advantages are simple structure, less interference by AC magnetic field, but it is easy to polarize the electrolyte liquid in the measuring tube, so that the positive electrode is surrounded by negative ions, and the negative electrode is surrounded by positive ions, which is the polarization phenomenon of the electrode, and causes the internal resistance of the two electrodes to increase, thus seriously affecting the normal operation of the instrument. When the pipe diameter is large, the permanent magnet is also large, bulky and uneconomical. Therefore, the electromagnetic flowmeter generally adopts alternating magnetic field, which is generated by the excitation of 50 Hz power supply.

3. Lining: there is a layer of complete electrical insulation lining on the inner side of measuring pipe and flange sealing surface.

The lining directly contacts with the measured liquid, its function is to increase the corrosion resistance of the measuring tube, and prevent the induced potential from being short circuited by the metal measuring tube wall. The lining materials are mostly corrosion-resistant, high-temperature resistant and wear-resistant polytetrafluoroethylene plastic and ceramics.

4. Electrode: lead out the induced potential signal which is proportional to the measured value.

The electrodes are generally made of non magnetic stainless steel and are required to be flush with the lining so that the flow of fluid is not obstructed. It should be installed in the vertical direction of the pipeline. In order to prevent the deposition on it and affect the measurement accuracy.

5. Converter: work with electrode.

The induced electromotive force (EMF) signal generated by liquid flow is very weak, which is greatly affected by various disturbance factors. The function of the converter is to amplify and transform the induced potential signal into a unified standard signal and suppress the main interference signal. Its task is to amplify the induced potential signal detected by the electrode into a unified standard DC signal.

6. Shell: protect electromagnetic flowmeter.

It is made of ferromagnetic material, which is the outer cover of the distribution system excitation coil and insulates the interference of external magnetic field.

Generally speaking, electromagnetic flowmeter has conductive requirements for the measured medium. This is because when the conductivity of the measured medium is very low, the contact resistance between the electrode and the liquid will increase, which will increase the internal resistance of the transmitter. Moreover, the influence of the distributed capacitance in the signal transmission area will also increase, which will cause signal attenuation and phase shift. At the same time, the interference potential is due to the decrease of conductivity This is mainly caused by electrostatic induction. Therefore, for the liquid with low conductivity, the following measures are usually adopted:

Firstly, the internal resistance of the transmitter can be reduced; the internal resistance of the transmitter can be reduced by using large area electrode or three electrode structure to reduce the contact resistance between electrode and liquid. At the same time, a low noise preamplifier is set inside the transmitter to make the transmitter output with low impedance and high noise ratio. On the premise of ensuring the measurement accuracy, in order to measure the liquid flow with low conductivity and extend the length of the signal transmission line. Secondly, the input impedance of the converter can be increased. Finally, we can shield the driving circuit.

Electromagnetic flowmeter is rarely affected by the physical characteristics of the medium in use, so it is a good choice for users. But before using it, it is suggested that we should have a basic understanding of it, so as to get better effect in use.

The above is the introduction of Shanghai Cixi on electromagnetic flowmeter measuring low conductivity medium points, hope to help you, if you still have related product problems, you can call the page for consultation! The company provides 24-hour service!

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