Interference in the 4-20mA signal feedback from on-site instruments (causes and solutions)
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Hello everyone! Please share your views on the interference issues related to the 4-20mA signal feedback from field instruments (the causes and solutions)
The most common type of interference is electromagnetic interference; therefore, we use shielded twisted pair cables to prevent such interference. Moreover, our field testing instruments are generally equipped with grounding wires
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It is mainly caused by electromagnetic interference, poor shielding, inadequate grounding, incorrect selection of grounding points, and multiple grounding points. The solution is to follow standard procedures and implement the relevant standards strictly.
The main source of interference for the 4-20mA signals from instruments is electromagnetic interference.
Grounding refers to whether the field instruments are grounded directly, or whether it is better to achieve grounding by adding an additional wire.
The shielding layer of the on-site instruments should be grounded.
The electromagnetic interference mentioned upstairs is the correct answer. A proper grounding solution is also the correct answer. Another point to consider is that cable routing must be standardized: it is necessary to maintain a specified distance from heat sources, and the cables should be arranged in layers, with power cables and signal/control cables placed in separate layers. Third is distance; the distance from the field instruments to the control room or signal acquisition/analysis equipment should not be too great. The pressure drop also has a certain impact on the instrument output.
The answer on the 9th floor was quite comprehensive! Cabling has a significant impact, especially in applications where frequency converters are used; interferences such as harmonics can affect the proper transmission of signals, and even proper shielding and grounding cannot eliminate these interferences!
The measures to mitigate interference now consist of using shielded cables, maintaining a certain distance from power cables, and ensuring proper grounding. But I found that if the PLC uses analog signals, it works much better when you connect the common terminals together. If they aren’t connected, the interference is extremely severe! But I will also explain the principle clearly!