Chapter 4 Electrical Installation Shenzhen Hpmont Technology Co., Ltd
―40― HD5L Series Controller User Manual
Function of EMI filter
1. The EMI filter ensures the equipment not only can satisfy the conducting emission and
conducting sensitivity in EMC standard but also can suppress the radiation of the equipment.
2. It can prevent the EMI generated by equipment from entering the power cable and the EMI
generated by power cable from entering equipment.
Common mistakes in using EMI filter
1. Too long the power cable is between the EMI filter and the controller
The filter inside the cabinet should be located near to the input power source. The length of the
power cables should be as short as possible.
2. Too close the input and output cables of the EMI filter
The distance between input and output cables of the filter should be as far apart as possible.
Otherwise the high-frequency noise may be coupled between the cables and bypass the filter.
Thus, the filter will become ineffective.
3. Bad earthing of the EMI filter
The EMI filter’s enclosure must be earthed properly to the metal case of the controller. In order to
achieve better earthing effect, make use of a special earthing terminal on the filter’s enclosure. If
you use one cable to connect the filter to the case, the earthing is useless for high frequency
interference. When the frequency is high, so is the impedance of cable, hence there is little
bypass effect.
The correct installation: The filter should be mounted on the enclosure of equipment. Ensure to
clear away the insulation paint between the filter case and the enclosure for good earthing
contact.
4.7.6 Conduction, Radiation and Radio Frequency Interference
Countermeasures
EMI of the controller
The controller’s operating theory means that some EMI is unavoidable. The controller is usually
installed in a metal cabinet which normally little affects the instruments outside the metal cabinet.
The cables are the main EMI source. If connect the cables according to this manual, the EMI can
be suppressed effectively.
If the controller and other control equipment are installed in one cabinet, the area rule must be
observed. Pay attention to the isolation between different areas, cable layout and shielding.
Reducing conducted interference
Please add a noise filter to suppress conducted interference on the output side. Additionally,
conducted interference can be efficiently reduced by threading all the output cables through a
grounded metal tube. And conducted interference can be dramatically decreased when the
distance between the output cables and the signal cables is above 0.3m.
RF interference clearing
The I/O cables and the controller produce radio frequency interference. A noise filter can be
installed both on the input side and output side, and shield them with iron utensil to reduce RF
interference.
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