Super Systems 9205 Series - Manual (Page 8)

Series 9205 Operations Manual Rev A 7
Conductive pollution
Electrically conductive pollution must be excluded from the cabinet in which the controller is
mounted. For example, carbon dust is a form of electrically conductive pollution. To secure a
suitable atmosphere in conditions of conductive pollution, fit an air filter to the air intake of the
cabinet. Where condensation is likely, for example at low temperatures, include a
thermostatically controlled heater in the cabinet.
Over-temperature protection
When designing any control system it is essential to consider what will happen if any part of the
system should fail In temperature control applications the primary danger is that the heating will
remain constantly on. Apart from spoiling the product, this could damage any process machinery
being controlled, or even cause a fire. Reasons why the heating might remain constantly on
include:
• the temperature sensor becoming detached from the process;
• thermocouple wiring becoming a short circuit;
• the controller failing with its heating output constantly on;
• an external valve or contactor sticking in the heating condition;
• the controller set point set too high.
Where damage or injury is possible, we recommend fitting a separate over temperature
protection unit with an independent temperature sensor, which will isolate the heating circuit.
Please note that the alarm relays within the controller will not give protection under all failure
conditions.
Installation requirements for EMC
To ensure compliance with the European EMC directive certain installation precautions are
necessary as follows:
• When using relay or triac outputs it may be necessary to fit a filter suitable for suppressing
the emissions. The filter requirements will depend on the type of load. For typical
applications we recommend Schaffner FN321 or FN612.
Routing of wires
To minimize the pick-up of electrical noise, the wiring for low voltage dc should be routed away
from high-current power cables. Where it is impractical to do this, use shielded cables with the
shield grounded at one end.