Delta AH500 series Manual download pdf (Page 259)

Chapter 7 EMC Standards

7.1.2 Installation Instructions for the EMC Standards

A PLC must be installed in a control box. The control box protects the PLC, and shields off the electromagnetic

interference generated by the PLC.

(1) Control box

 Use a conductive control box.

 To ensure that an inner plate contacts the control box well, users have to mask the paint on the bolts of

the plate.

 To ensure that the control box is grounded well even if there is high-frequency noise, users have to

connect the control box with a thick wire.

 The diameter of a hole in the control box must be less than 10 millimeters, i.e. 3.94 inches. If the

diameter of the hole is larger than 10 millimeters, the radio frequency noise may be emitted.

 To prevent the radio waves from leaking through the interval between the door of the control box and

the PLC, the interval needs to be reduced. Besides, users can prevent the radio waves from leaking

by putting an EMI gasket on the painted surface.

(2) Connecting a power cable and a ground

The power cable of the PLC system and the ground are connected in a way described below.

 Provide a ground point near the power supply module. Use thick and short wires to connect the

terminals LG and FG with the ground. (The length of the wire should be less than 30 centimeters, i.e.

11.18 inches.) LG and FG function to pass the noise generated by the PLC system to the ground.

Therefore, the impedance should be as low as possible. Besides, the wires are used to relieve the

noise. They themselves carry a lot of noise. Using the short wires can prevent the wires from acting as

antennas.

 Twist the ground and the power cable. After the ground and the power cable are twisted, the noise

flowing through the power cable is passed to the ground. If a filter is installed on the power cable, the

ground and the power cable do not need to be twisted.

7.1.3 Cables

Grounding a shielded cable

Cables drawn from the control box carry high-frequency noise. When they are outside the control box, they are

like antennas emitting noise. To prevent the emission of noise, the cables connected to digital input/output

modules, analog input/output modules, temperature measurement modules, network modules, and motion

control modules should be shielded cables.

he use of shield

ed ca

bles also increases the resistance to noise. If the signal cables connected to digital

input/output modules, analog input/output modules, temperature measurement modules, network modules,

and motion control modules are shielded cables, and are grounded properly, the resistance to noise is

improved. However, the resistance to noise will not meet the specified requirement if users do not use shielded

cables or the shielded cables are not grounded correctly. If the shield of a cable is connected with the control

box, users have to make sure that the shield contacts the control box. If the control box is painted, users have

to scrape the paint. All fastening must be metal, and the shield must contact the surface of the control box. If the

surface is not even, users need to use washers to correct the unevenness, or use an abrasive to level the

surface.

If the shield of a shielded cable is grounded, it needs to be as close to a module as possible. Users have to

make sure that there is no electromagnetic induction between the cable which is grounded and other cable

which is grounded. Besides, users have to take appropriate measures so that the shield of a cable contacts the

control box.

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Delta AH500 series Manual Page 259

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Delta AH500 series Manual Page 259

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