The design parameters of the differential amplifier can avoid the influence due to electrode pollution (increased impedance). Well-known brands of electromagnetic flowmeters can achieve this technical indicator, so in the water supply industry, electrode pollution is not a problem that should be paid attention to in the application of electromagnetic flowmeters.

　　9 System lightning protection

　　There are two main types of lightning: one is the discharge between different charged clouds, and the other is the discharge of clouds to the ground. The latter is the main source of lightning damage. Direct lightning strikes, lightning electrostatic induction and electromagnetic induction are the main causes of instrument damage. factor. The purpose of instrument lightning protection is not to avoid lightning strikes, but to protect the instrument from being damaged by lightning waves.

　　When the manufacturer designed the electromagnetic flowmeter product, it took certain protection measures into consideration for the lightning protection and anti-interference of the flowmeter system. For example: the power supply part is equipped with a transient suppression diode or a discharge tube; the power supply and signal input / output are electrically isolated; the digital communication interface uses lightning protection devices; the signal connection cable between the sensor and the converter uses triple shielding; the flow meter is required The system is well grounded. However, in areas where lightning is frequent and intense, users should take further measures:

　　加 Install a 1: 1 transformer and lightning arrester at the power input end to prevent the power supply from being punctured.

　　加 Add lightning arrester to the signal analog output.

　　⑶ The flowmeter system must be well grounded, and ensure that the liquid-wet ground is well connected to the ground to prevent the lightning current conducted by the pipeline and fluid medium from flowing through the meter body.

　　references:

　　1 Industry Standard · JB / T 9248-1999 "Electromagnetic Flowmeter"

　　2 Kaifeng Instrument Factory · E-mag Electromagnetic Flowmeter Instruction Manual

　　3 ABB LtdCalMaster Operating Instructions

　　4 Cai Wuchang · Flow measurement methods and instrument selection · Beijing: Chemical Industry Press, 2001.3.