Because the details of the customer’s cascade application (in particular the nature
of the load) are generally not known, the feed forward parameter (FF Trim) is
made easily accessible in level 2 (Refer to instrument operating instructions). Its
default setting is 2%. If overshoot of the load temperature occurs – often a
problem at low temperatures – then FF Trim can be reduced in order to limit the
amount of overshoot. However, if FF trim is reduced too much, the load may not
reach the desired temperature. If the load does not reach the desired temperature
or is slow in the final stages, FF Trim can be increased: a maximum of 10% is
suggested.
Feed Forward View
When attempting to control at very low temperatures it can become a problem to
achieve stable control because of excessive power being supplied during heating.
The available power can be limited using the power limit parameter OP.Hi, make a
note of the original settings before adjusting. For power settings please refer to the
fuse and power section at the back of the manual. If the parameter is normally set
to 100%, try initially setting it to 50% to improve stability. Avoid settings below 40%
where possible (though some furnaces require low settings for reasons
unconnected with cascade control).
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4.0 3508 Dual Loop Cascade
