Electromagnetic flowmeter classification and installation requirements

1. Principle of electromagnetic flowmeter

Electromagnetic flowmeter is an instrument made by using Faraday's law of electromagnetic induction (scientific law) to measure the volume flow of conductive liquid. In addition to measuring the volume flow of general conductive liquids, sewage flow meters can also be used to measure the volume flow of highly corrosive liquids such as strong acids and alkalis, and uniform liquid-solid two-phase suspension liquids such as mud, pulp, and paper pulp. It is widely used in flow measurement in petroleum, chemical industry, metallurgy, textile, papermaking, environmental protection, food and other industrial sectors and municipal management, water conservancy construction, river dredging and other fields. In the electromagnetic flowmeter, the conductive medium (the decisive substance) in the measuring tube is equivalent to the conductive metal rod in the Faraday test. The two electromagnetic coils (winding) at the upper and lower ends produce constant characteristics: radiation of wave particles. When a conductive medium flows through, an induced voltage will be generated. This voltage is proportional to the flow rate of the fluid, and the flow value Q is obtained.

2. Classification of electromagnetic flowmeters

Electromagnetic flowmeters are divided according to the excitation current method, including DC excitation, AC (power frequency or other frequencies) excitation, low-frequency rectangular wave excitation and dual-frequency rectangular wave excitation. . According to the format of output signal connection and excitation (or power supply) connection, there are four-wire system and two-wire system. According to the combined installation method of converter and sensor, there are split type and integrated type. (Pressure transmitter) is classified according to the connection method between the flow sensor and the pipeline, including flange type, clamping type (clamping type electromagnetic flowmeter), sanitary type (sanitary electromagnetic flowmeter), and insertion type (insertion type electromagnetic flowmeter). ), threaded connection (high-pressure electromagnetic flowmeter with oil connection). According to whether the flow sensor electrode is in contact with the liquid to be measured, there are contact type and non-contact type. According to the flow (unit: cubic meters per second) sensor structure, there are short tube type and insertion type (insertion electromagnetic flowmeter). Vortex flowmeter is also called vortex flowmeter or Karman vortex flowmeter. Carefully designed products based on comprehensive absorption of advanced technologies from developed countries and summarizing years of research and production experience have achieved product intelligence, standardization, serialization, generalization, production molding, and ensured the aesthetics of product quality. Classified by use, there are general-purpose, explosion-proof, sanitary, water-intrusion-proof and submersible types (open channel flowmeters) for measuring open channel flow (unit: cubic meters per second).

3. Installation environment requirements for electromagnetic flowmeters

The protection level of the electromagnetic flow sensor housing is generally IP65 (GB4208 housing protection level - dustproof and water-proof level). The main requirements for the installation environment are: (1) Sensor It should be installed in a dry and ventilated place, avoid places that are humid and prone to water accumulation, and should also try to avoid direct sunlight and direct rainwater. (2) Avoid installing in places where the ambient temperature is too high. The electromagnetic flow meter with an integrated structure (unit: cubic meters per second) is also subject to the ambient temperature of the electronic components, which is lower. (3) There should be no strong leakage current on the pipeline where the sensor (transducer) is installed.As far as possible, stay away from equipment with strong electrical characteristics: wave particle radiation, such as large electrical machinery, large transformers, etc., to avoid causing electromagnetic field interference; (4) The pipeline or ground where the sensor is installed should not have strong vibrations, especially integrated instruments; ( 5) The location where the sensor is installed should consider the space for on-site maintenance by the staff. The function of the electromagnetic flowmeter is to generate a uniform DC or AC magnetic field. The DC magnetic circuit is implemented with magnets. Its advantage is that the structure is relatively simple and is less disturbed by the AC magnetic field. However, it easily polarizes the electrolyte liquid passing through the measurement catheter, causing the positive electrode to be surrounded by negative ions and the negative electrode to be surrounded by positive ions. , that is, the polarization phenomenon of the electrodes, and causes the internal resistance between the two electrodes to increase, thus seriously affecting the normal operation of the instrument.