Grounding issues at the site and in the control room
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Is there a situation where a certain instrument on-site requires grounding, while the signal wires on the control room side are grounded together? So, the shielding layer of the signal cable is grounded in the control room, and grounding is also required at the site; therefore, a junction box must be used to separate them, with the shielding layer being disconnected at the junction box. Is such a meter available? Is that the requirement for electromagnetic flowmeters? Should most instruments that require on-site power supply have their ground wires connected separately, with the shielding layers grounded only in the control room?
Shielding it as single-ended grounded helps prevent interference with the instrument’s power supply and transmission signals, such as from high-voltage cable trays above； For the on-site grounding of electromagnetic flowmeters, flange grounding is often sufficient
To avoid interference, it is generally required to ground the ground wire separately and at a single point, with grounding being more common in control rooms.
The cable shielding layer is grounded at one end in the DCS system. For instruments that use a voltage of over 36 V, the gauge usually has a grounding terminal that is connected to the site’s grounding electrode, serving to protect human safety.