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Electromagnetic flowmeter electrode type and maintenance instructions

General-purpose products and special-type instruments on the market are classified as follows from different angles. The electromagnetic flowmeter is divided according to the excitation current mode, and has DC excitation, AC (power frequency or other frequency) excitation, low frequency rectangular wave excitation and dual-frequency rectangular wave excitation. The waveforms of several excitation methods are shown on the right. According to the classification of the output signal connection and the excitation (or power) connection, there are four-wire and two-wire systems. Classified by converter and sensor assembly, there are separate and integrated models. Classified by flow sensor and pipe connection, flange type, clamp type (clamp type electromagnetic flowmeter), sanitary type (hygienic electromagnetic flowmeter), plug-in type (plug-in electromagnetic flowmeter), threaded connection (oil) Any connected high-voltage electromagnetic flowmeter). Note: According to whether the flow sensor electrode is in contact with the liquid to be tested, there are contact type and non-contact type. Classified by flow sensor structure, there are short tube type and plug type (plug-in electromagnetic flowmeter). Classified by use, there are general-purpose, explosion-proof, hygienic, anti-intrusion type and submersible (open channel flowmeter) for open channel flow measurement. First, the electromagnetic flowmeter is classified according to the excitation current method. (1) DC excitation The electromagnetic excitation electromagnetic flowmeter is used to measure the flow rate of liquid metal, such as mercury at room temperature and liquid, lithium and potassium at high temperature. In the fast neutron proliferating nuclear reactor *** secondary loop used to measure the molten nanoflow of 500 degrees Celsius, I have seen reports on the DN300mm pipeline instrument. The dry method verifies the flow value and has an accuracy of 3% compared to the wet (solid flow) test. In addition to the secondary field generated by the electromagnet value excitation, a higher aperture sensor with a magnetic field of the magnet is also used. The application of this type of instrument in China's general process industry is still a high-exploration. In the 1960s and 1970s, it was successfully used to measure the flow rate of the normal temperature pump in the electrolytic cell; the non-ferrous metallurgical industry also tried to measure the flow of molten zinc, due to the zinc liquid. It was not used successfully in measuring the fouling of the inner wall of the tube and zinc oxide. (2), AC excitation early electromagnetic flowmeter is used for 50Hz power frequency mains excitation, which produces sinusoidal alternating magnetic field; the reason for using AC excitation is to avoid the phenomenon of electromagnetic surface generation when using DC excitation, but because of the vulnerability The superposition caused by the electric lock with the flow signal and the corresponding various induced noises, forming characteristic drift, etc., has now been gradually replaced by low frequency rectangular wave excitation. These superimposed induced noises are caused by the following reasons. 1) The eddy current in the liquid generates the same phase noise as the flow signal, and the noise and characteristic drift caused by the electrode pollution; 2) The iron loss in the magnetic circuit shifts the phase between the excitation current and the magnetic field, so that the transformer effect is formed in the signal loop. Orthogonal (90°) noise phase shift, producing the same noise; 3) Static induction noise between the excitation coil and the signal line and between the excitation coil and the fluid.
Electromagnetic flowmeter will cause fouling of the electrode after long-term use, which will not only reduce the measurement accuracy but also damage the instrument. Therefore, if the electrode is found to be dirty, we must clean it in time to ensure the accuracy of the measurement. .
The methods for cleaning the electrodes generally include the following:
Electrochemical method
2. Mechanical removal method, which is to install a special machine on the electrode to remove. There are currently two forms, mechanical scrapers, which are stable in performance and easy to operate. The other is to install a wire brush for removing dirt in the tubular electrode. This method requires pulling the wire brush to clean the electrode, so the operation is not very convenient.
3. Ultrasonic cleaning method is mainly to concentrate the energy of the ultrasonic wave on the contact surface between the electrode and the medium, and crush the dirt to achieve the purpose of cleaning.
4. Electrical breakdown method, that is, using AC high voltage electricity to periodically add between the electrode and the medium, the attachment is broken down, and then washed away by the fluid.
The above is the method of electrode cleaning of electromagnetic flowmeter, I hope to help everyone.

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