4.3
Bypassing Cascade Control
This applies where the Control Thermocouple is a removal probe (e.g. in a tube
furnace), or where for other reasons it may be required to operate the furnace or oven
directly from the Element Loop.
To operate without Cascade Control the load thermocouple has to remain connected at
all time; or a link has to be made across the thermocouple input connections.
4.4
3508P1 Element Loop (Loop 2)
In these circumstances the Element Controller is configured with the local/remote
parameter, accessible in level 2 (Refer to instrument operating instructions).
To switch cascade control on or off. In Level 2, press Scroll until the display shows
.
Using the up
down
set:
= cascade control on
= cascade control off
The top left hand side of the screen will show
X when
is enabled. The instrument
operates as an independent Programmer/Controller when
is set to
. To return to
cascade control, change the
parameter to
. Also note that cooling at low
temperatures takes longer per degree than it does at high temperatures.
4.5
Caution
If the Load Thermocouple is removable, leave it in the furnace or oven
chamber whenever possible. Operating with the Cascade Control active
and with the Load Thermocouple in an unheated position (such as lying
on the work bench) may cause the furnace or oven to heat up to its
maximum temperature, wasting power and possibly shortening element
life.
4.6
Over-Temperature Control
Where over-temperature control is fitted, it normally protects against failure of the
control system or of a component such as a power control relay. The over-temperature
controller must be set at a level higher than the greatest element temperature, typically
15 °C above maximum.
If the working temperature is less than the maximum temperature, then it may be
possible to set the over-temperature limit as follows:
working tempe (maximum temperature x FF/100) + 15 °C
where FF is the Feed Forward percent parameter value (e.g. 10)
Example: for working at 800 °C in a 1200 °C product, the over-temperature limit could
be set to 800+120+15=935.
41
4.0 3508 Dual Loop Cascade
