Computer cable installation workflow
First, the signal classification
The reasonable layout of the cable can effectively reduce the interference of the external environment on the signal and the mutual interference between various cables, and improve the stability of the operation of the DCS system.
The signals are classified as follows:
1. Class I signals: low-level signals such as thermal resistance signals, thermocouple signals, millivolt signals, and strain signals.
2, class II signal: 0 ~ 5V, 1 ~ 5V, 4 ~ 20mA, 0 ~ 10mA analog input signal; 4 ~ 20mA, 0 ~ 10mA analog output signal; level switch input signal; contact switch
Input signal; pulse input signal; resistive load switch output signal with 24VDC less than 50mA.
3. Class III signal: Switching output signal of 24V~48VDC inductive load or resistive load with current greater than 50mA.
4. Class IV signal: 110VAC or 220VAC switch output signal, the feeder of such signal can be regarded as the problem of power line processing wiring. Among them, Class I signals are easily interfered, Class II signals are easily interfered, and Class III and IV signals become strong sources of interference at the moment of switching action, interfering with nearby signal lines through the space environment.
Second, the overall principle of signal cable deployment
1. For Class I signal cables, shielded cables must be used. When conditions are available, shielded twisted pair cables are used.
2. For class II signals, shielded cables should be used as much as possible. In the class II signals, the analog injection signals for the control and interlocking, and the input signals must be shielded cables.
Twisted pair cable.
3. It is strictly forbidden to bundle the I and II signals together with the Class IV signal. It should be handled as a 220V power cable and routed with the power cable. It is recommended to use shielded twisted pair cable when conditions permit.
4. For Class III signals, it is allowed to be routed together with the 220V power line (ie, the same as the Class IV signal), or it can be routed together with the I and II signals. However, in the latter case, Class III signals must be shielded.
Cable, Zui is good for shielded twisted pair cable, and is more than 15cm away from I and II type signal cables.
In order to ensure stable, reliable and safe operation of the system, the signal cable connected to the DCS system must also ensure:
1. The millivolt signal and strain signal in the class I signal should be shielded twisted pair cable, which can greatly reduce electromagnetic interference and static interference.
2. When the conditions permit, the shielded cable (or shielded twisted pair cable) should be used as much as possible for the I to IV signals. It should also ensure that the shield is only grounded at one point and should be grounded well.
3. It is absolutely forbidden to bundle the high-power switch output signal line, power line, power line and other cables in parallel with the I and II type signal cables that directly enter the DCS system.
4. It is absolutely forbidden to use part of the core wire of a multi-core cable to transmit Class I or Class II signals, and some core wires are used to transmit Class III or Class IV signals.
5. It is forbidden to distribute several core wires of the same signal in different cables (such as three-wire thermal resistance).
Therefore, in field cable laying, we must effectively separate cables that are prone to interference, such as Class III and IV signal cables and power cables, so that they are kept at a certain level with the I and II signal cables laid on site.
The safety distance (such as 15cm) or more.
Third, several provisions of the field cable layout
For the convenience of description, we refer to class I and II signal cables as signal cables, and class III and IV signal cables and field power cables as power cables. Signal cable and power supply when conditions permit
Cables should be routed in different cable troughs. When entering the DCS equipment room (or cabinet), they should be as far apart as possible. When these two cables fail to meet the separate wiring requirements, they must all use shielded cables.
(or shielded twisted pair cable) and meet the following requirements:
1. If the distance between the signal cable and the power cable is less than 15cm, a metal partition for shielding must be placed between the signal cable and the power cable, and the partition should be grounded. See Figure 1 (omitted) for details.
2. When the signal cable and the power cable are installed separately in the vertical or horizontal direction, the distance between the signal cable and the power cable should be greater than 15cm.
For some applications with particularly high interference, such as 220VAC on the power cable, inductive load above 10A, and the power cable without shield, then it is required to signal
The distance between the cables in the vertical direction must be above 60 cm.
3. When the two sets of cables intersect perpendicularly, if the power cable does not have a shielding layer as shown by the dotted line in the figure, the iron plate covers the intersection with a thickness of 1.6 mm or more.
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