16
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.
This product has been designed to conform to
BSEN61010 installation category II, pollution degree 2.
These are defined as follows:-
Installation Category
II
(CAT
II)
The rated impulse voltage for equipment on nominal
230V supply is 2500V.
Pollution Degree 2
Normally only non conductive pollution occurs.
Occasionally, however, a temporary conductivity caused
by condensation shall be expected.
Grounding of the temperature sensor
shield
In some installations it is common practice to
replace the temperature sensor while the controller is
still powered up. Under these conditions, as
additional protection against electric shock, we
recommend that the shield of the temperature sensor
is grounded. Do not rely on grounding through the
framework of the machine.
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 short circuit;
