The use of microprocessors and regulations units allows complex tasks to be carried out without loss of operating flexibility and supervision. As the variety of tasks gets larger and measuring accuracy becomes more critical, however, susceptibility to interference similarly increases.
VDE 0843 provides a European standard for the electromagnetic compatibility (EMC) of measuring, control and regulation devices for industrial process technology. Among other things, this standard lays down the interference levels which a device can be expected to tolerate.
For the trouble-free operation of an installation, the interference should be well below guidelines. It is well-known, however, that far higher interference levels may occur in industrial practice where sources of interference cannot be completely eliminated. An unsuppressed contactor can easily generate interference-voltage impulses of 3 kV.
Interference can be spread through wiring or via electro-magnetic radiation. The effects most damaging to control systems are normally the result of wire-borne interference. Possible sources of interference are:
Some basic principles must be observed for the installation of processor controlled regulation systems:
The mains power to consumers switched by the controller must never be supplied from the controller side of the mains filter.
All measures taken to suppress interference will also prolong the life of the components and consequently that of the plant. RC filters reduce contact erosion and increase contactor life.
These instructions are only suggestions and they are not complete. If you want further information please contact the manufacturers of switching elements. Usually, these manufacturers also sell units for interference suppression. You may also contact manufacturers of interference suppression devices:
The filter should always be adapted to the inductivity. The following typical component is available and recommended: RC filter, 50 R + 0,1 µF, 115/230 V~
Order no.: 900089.008
Mains filter with slip-on terminal, 230 V~
Order no.: 900089.002
Cleaning the front foil common commercial cleaners (e.g. detergents) are to be used. Organic solvents (e.g. kerosene or spirits) and high pressure cleaners are to be avoided.