How should the shielding layer of signal wires be grounded to achieve good interference resistance?

This post was last edited by 1111111 on 2019-4-16 23:05. Grounding has no fixed value. Sometimes when the shielding layer is left suspended and not grounded, the instrument signal is the most stable. Sometimes, grounding the shield at one end yields the most stable instrument signal. Sometimes, when the shielding layer is grounded at both ends or at multiple points, the instrument signal remains the most stable. Sometimes, whether it is grounded or not, the instrument signals remain stable or fluctuate accordingly. It’s better to do less than to do more; if the instrument signal isn’t fluctuating, then leave the shielding layer unconnected. Going through all that extra effort won’t increase production or help with weight loss, right? Generally speaking, with the exception of a few instruments that operate on the principle of electromagnetic induction and for which grounding of the instrument’s enclosure is required, the technical documentation provided by instrument manufacturers for the vast majority of low-voltage instruments does not mention anything regarding the grounding of the enclosure’s shielding layer. Only when an instrument is designed with lightning protection circuits will the manufacturer require that the instrument’s enclosure be grounded, and in such cases it is essential that the grounding resistance be less than 1Ω! Note that this 1Ω value is crucial for lightning protection grounding. If lightning protection equipment is connected to the ground in a careless manner, resulting in a high grounding resistance, it’s actually better not to connect it to the ground at all. Without such connection, in the event of a lightning strike, the power supply is the first to be damaged, thereby reducing the risk of the equipment being damaged. :lol

Those without a junction box are called single-pull cables; they usually remain suspended on one side of the meter and are grounded by being woven together at the DCS (commonly known as braiding). Those with junction boxes (oil and petrochemical companies prefer EJB and IEJB) are also mounted at the site; the terminal connections provided in the junction boxes are used to connect the branch cables coming from the site with the main cable shielding from the DCS, and the cables at the DCS end are twisted together

It needs to be handled based on the actual conditions at the site. In the cases where I have implemented on-site shielding layer grounding, one end was left suspended while the other end was connected to ground ； When applying the same treatment at another location, the signal fluctuated excessively; adding a capacitor eventually resolved the issue.

On our end, the signal wires are twisted together, while the shield wire is grounded at one end