First, the signal cable shielding methods are divided into the following types:

Split screen - a way to shield each core independently;

Screen - the way in which each pair of twisted pair is individually shielded;

Group screen - a way of independently shielding a group of multi-core cables;

Total screen - An external shielding mode for the whole cable.

These shielding methods can be combined.

Second, the shielding selection of the signal loop control cable of the computer monitoring system should comply with the following provisions:

1) Switch signal, can choose total shielding.

2) For high level analog signals, the total shielding of the strand core should be selected, and the separate shielding of the strand core can also be selected if necessary.

3) Low level analog signal or pulse signal, it is appropriate to choose the strand core shielding, if necessary, can also choose the strand core shielding composite total shielding.

4) In other cases, the appropriate shielding type should be selected according to the influencing factors such as electromagnetic induction, electrostatic induction and ground potential rise.

5) When the cable has steel armor and metal sleeves, its shielding function should be fully utilized. Control cables that need to reduce electrical interference can be added with a grounded spare core and should be grounded at one point on the side of the control room.


Third, the grounding method of the metal shield of the control cable shall comply with the following provisions:

1) The computer monitoring system of analog signal loop control cable shielding layer, shall not constitute two points or multi-point grounding, should be centralized ground.

2) The cable shielding layer of integrated circuit and microcomputer protection of current, voltage and signal should be grounded simultaneously in the switch placement place and the control room.

3) In addition to the above cases, the control cable shield layer, when the interference of electromagnetic induction is large, it is appropriate to use two-point grounding; When the interference of electrostatic induction is large, one point grounding can be used. Dual shielding or composite total shielding should be grounded at one point and two points respectively for internal and external shielding.

4) The choice of two-point grounding should also be shielded from melting under the action of transient current.

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