Eurotherm 3204i, User Manual

Page: 24 / 140

22 Part number HA029005. Issue 2.0 May-06.
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)
For equipment on nominal 230V supply, the maximum
rated impulse voltage 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 indicator 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;
•
the controller failing with its heating output
constantly on
•
an external valve or contactor sticking in the
heating condition
•
the controller setpoint set too high.
Where damage or injury is possible, we recommend
fitting a separate over-temperature protection unit,