Carbolite Gero 3508 Installation, Operation And Maintenance Instructions page 30

4.0 3508 Dual Loop Cascade
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.
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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