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How to prevent interference from electromagnetic flowmeter

Electromagnetic interference refers to the various electromagnetic effects that cause the performance of control system equipment, transmission channels, or systems to degrade.

The whole process of interference formation is that the interference signal from the interference source passes through the coupling channel to the interfered device. The three links of interference are called the three elements of the interference system, namely the interference source, the interference propagation path and the interfered device.

1 Classification of electromagnetic interference

In the industrial measurement and control system, the interference of the electromagnetic flowmeter is an important problem affecting the normal operation. The generation may exist inside the system, that is, it may be affected by the interference generated by itself, or may be from the outside of the system, that is, affected by external interference. In the analysis of electromagnetic interference, the system refers to the electrical equipment or electronic equipment that people design, manage and control.

1.1 Internal interference

The interference sources inside the system can be divided into:

(1) Power supply interference. Power supply interference is mainly from the power supply and power leads immersed in the system.

(2) Ground interference. The ground line interference is caused by sharing a ground line in the system. When the current of each part of the circuit in the system flows through the common ground line, a voltage drop will be generated on the ground line to form noise that affects each other.

(3) Coupling interference of signal channels. If the signal requires a long transmission line, the signal is easily interfered during transmission, resulting in distortion or distortion of the transmitted signal. The interference generated mainly includes electromagnetic induction interference of the electromagnetic field around the transmission line to the transmission line: when two or When two or more signal lines whose signal strengths are different are close to each other, the inter-line interference formed by the capacitance and mutual inductance between the lines is the line-to-line crosstalk of the transmission line.

1.2 External interference

The sources of interference outside the system can be divided into:

(1) Natural interference. Natural disturbances include lightning and electric field changes in the atmosphere. Light energy generates high-frequency surge voltages of high amplitude on the transmission line, which interferes with the system.

(2) Power interference. As more and more electronic devices are connected to the power backbone, some potential interference will occur in the system. These disturbances include power line disturbances, electrical fast transients, surges, voltage changes, lightning transients, and power line harmonics.

(3) Power frequency interference. Both the power supply equipment and the output line generate power frequency interference. If the signal transmission line has a section parallel to the power supply line, the low frequency interference will be coupled to the signal line to become interference.

(4) Radio frequency interference. Communication equipment, radio, television, radar, etc. transmit strong electric waves through the antenna.

(5) Electrostatic discharge. With modern chip technology, components have become very dense in small geometries. These high-speed, multi-million transistors are highly sensitive and can be easily damaged by external electrostatic discharge.

(6) Car clutter. The car generates clutter from very high frequency to very high frequency band during the working process.

(7) Discharge interference. Partial discharge can be divided into three types: positive corona discharge, negative corona discharge and spark discharge.

(8) Glow discharge. Glow discharge is a gas discharge.

(9) Arc discharge. Arc discharge is metal fog discharge. The most typical arc discharge is metal arc welding.

2 Transmission path of electromagnetic interference

Electromagnetic interference can be divided into two categories according to the transmission route: conducted interference, mainly because the interference signals generated by electronic devices generate interference through conductive media or public power lines; radiation interference refers to the interference signals generated by electronic devices are transmitted to another through space. An electrical network or electronic device. From the perspective of disturbed sensors, interference coupling can be divided into two types: conduction coupling and radiation coupling.

3 Methods for suppressing electromagnetic interference

For the three elements of electromagnetic interference, the following three methods for solving electromagnetic interference problems are proposed:

(1) Suppress electromagnetic interference generated by interference sources

1 shield

Shielding is the use of a shield between two spatial regions to control the induction and radiation of electric, magnetic and electromagnetic waves from one region to another.

2 filtering

Filtering refers to the classification and control of the various types of signals by their frequency characteristics. It is a technique that provides transmission poles for signals in certain frequency points and transmission zeros for signals in other frequency points.

3 grounding

The ground wire is the implementation of grounding, that is, connecting certain ground potentials in the circuit with necessary metal conductors or wires according to certain requirements, or connecting a certain part of the electronic and electrical equipment to the earth.

4 wiring

Different types of signals are transmitted by different cables, and the signal lines and power cables should be prevented from being laid close to each other to reduce electromagnetic interference.

(2) Cut off the transmission route of interference.

(3) Improve the ability of sensitive equipment to resist electromagnetic interference (reduce sensitivity to interference).

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