Electromagnetic flowmeter easily affected by the installation environment, installation position

　　Therefore, in order to ensure the accuracy of the electromagnetic flowmeter, the installation environment and location must be carefully selected. The electromagnetic flowmeter failures caused by the environment are mainly the following.

　　1. Strong magnetic fields: During installation, people usually pay attention to keeping away from strong magnetic fields, so there is not much practical experience on the effects of strong magnetic fields.

　　2. Strong electromagnetic wave electromagnetic flowmeters should meet the requirements of electromagnetic compatibility and work normally in the specified radiated electromagnetic field environment without causing instrument performance degradation or malfunction in this environment. When the separate electromagnetic flowmeter has large common mode interference on site, the possibility of strong radio waves being the interference source should be considered when analyzing the cause of the failure. This example is a failure during the debugging period.

　　3. Pipeline stray current After the electromagnetic flowmeter is properly grounded, most of the stray current in the pipeline can be avoided. Sometimes, the flow sensor is connected with thick wires and grounded properly according to regulations, but it is still affected by stray currents, and other measures need to be taken.

　　4. Changes in ground potential Changes in ground potential will affect flow measurement. For example, voltage drops in the grounding wires of other equipment can cause changes in the ground potential of the electromagnetic flowmeter. If large common-mode interference is formed, it may affect the measurement.

　　5. Moisture immersion Electromagnetic flowmeters used in the water supply and drainage industry often place flow sensors in instrument wells below the horizon, so they are often immersed in rainwater that is not discharged in time, or even immersed in water for a long time. Even if the shell protection is IP67 (dust-tight short-term immersion) or IP68 (dust-tight continuous immersion), such accidents often occur because the sealing gasket of the terminal box cover or the cable introduction sealing ring is not tightly sealed, the ring is missing, or the ring does not match the outer diameter of the cable.

　　If the sealing gaskets of the terminal box cover of the flow sensor installed on the ground are not sealed well, they will also absorb moisture and condense into water due to the breathing effect of the steam temperature change. The terminal box cable entry device is missing a sealing ring or is not tightly sealed, and condensed water on the cable surface can easily enter the terminal box. During the construction process, the cable is intentionally or unintentionally cut and reconnected, and wrapped with tape. This hidden danger will not cause a fault in the early stage of operation, but the sealing will age over time, and moisture will be absorbed at the connection, and the cable insulation will be reduced. Water and moisture penetrate into the terminal box, reducing the insulation strength and insulation resistance. In severe cases, the flow signal circuit will have no flow signal output, and the excitation coil circuit will form a point offset or instability.

　　If necessary, silicone can be used to seal the connection. The non-airtight structure of the excitation coil protection shell inhales moisture due to breathing. If the liquid temperature is lower than the room temperature, it is easy to condense on the outer wall of the measuring tube. If it is lower than 0℃, it will frost, which will short-circuit the flow signal loop and fail. The reason is that the excitation coil loop drops to ground, which adds a larger insulation resistance and signal internal resistance to the voltage division of the excitation voltage, forming a larger common-mode interference signal, and the common-mode rejection ratio of the converter preamplifier is limited, so that the converter has no output.