How to determine whether the shield of a signal cable is grounded at two points or at multiple points?

In accordance with specifications and relevant design manuals, the shielding layer of the signal cable should be grounded at one point on the control room side, while on the field side the shielding layer must be insulated to prevent it from coming into contact with grounded metal parts.

Two-point or multi-point grounding of the signal line shielding layer can lead to uncertainty in interference; the standards require single-point grounding.

The shielding on both sides of the cable is elevated, and then its insulation is tested relative to ground; if it can be tested successfully, there is no problem； If it can’t be lifted, there must be something in contact with the ground, or there’s an issue with the insulation.

Haha, this is simple – disconnect the ground point and use a meter to check whether it is insulated from ground! If not, then it’s two or more points of grounding.

It cannot be tested with a megohmmeter, as this can lead to problems. Unplug one end of the shielded wire that is grounded, and use a multimeter to check whether there is conductivity to ground; if there is no conductivity, it should be normal. If it is conductive, then there must be multiple ground connections. Personal opinion!

There are two types of grounding: one is electrical grounding, which requires multiple grounding points and strict standards, and the electrical grounding is connected to the metal structures within the factory building. Another aspect is the grounding of the instruments; according to the design specifications, instruments must have a separate grounding connection, with the grounding resistance not exceeding 4 ohms. If the installation of your instruments complies with the standards, then the shielding ground connection should be disconnected. Next, check whether the separate ground connection for the instrument’s shielding is active; if it isn’t, that means there is only one ground connection. It’s also necessary to check whether the ground connection for the electrical equipment is active. If the standards are not met and the instruments and electrical equipment share a single ground connection, then the ground connection can be disconnected, after which the resistance between the shielding and any other ground connection can be measured