33 - General Measures When Using Electronic Control Systems - Liscarroll Engineering LE-200 Installation And Operating Instructions Manual

General measures
when using electronic
control systems
32
Other Information
So that even complicated regulatory tasks can be presented to the user in a
manner which is clear and simple and ensures high measurement accuracy, today's
electronic control systems make increasing use of microprocessors. However,
the benefits of these systems are countered by the disadvantage that increased
measurement accuracy is accompanied by sensitivity to interference. In order to
minimise the effect which interference may have
must take account of a number of points when installing a new regulator.
Assistance here is provided by standard DIN VDE 0843 on the electromagnetic
compatibility (EMC) of measurement, control and regulatory devices in industrial
process technology. The following table shows, for example, the maximum
interference levels to which (according to the standard), an appliance may be
exposed.
Degree of Environment
Severity Class
1 Well-protected
Environment
2 Protected
Environment
3 Typica Industrial
Environment
4 Industrial Environment
with very high
interference level
As the values given in the table are maximum values, operational values should
remain well below them. However, in practice this is possible only with difficulty, as
even a normal contactor without interference suppression produces interference
pulses of up to 3.0 kV. For this reason we recommend that the following principles
be taken into account during installation:
a.
Try to eliminate all sources of interference by carrying out interference suppression
and minimising the interference level. Radio interference suppression is required
under VDE 0875 and confirmed by VDE 0874. In principle the interference must
be eliminated at source. The nearer the interference suppresser is to the source of
interference the greater its effect.
Interference spreads through wires or by electromagnetic radiation. It is usually the
former which interferes most seriously with regulation systems.
Possible interference sources (to name a few) include:
• bouncing contacts when switching loads
• switching off inductive loads (contactors, motors, solenoid valves, etc.)
• unsatisfactory routing of wires, too small cross-sections
• loose contacts
• rhythmically changing power stages (power converters)
• power breakers
• high-frequency generators
on the regulator the user also
Test Voltage Test Voltage
Power Supply Signal/Control Line
0.5 kV 0.25 kV
1.0 kV 0.5 kV
2.0 kV 1.25 kV
4.0 kV 2.0 kV