VERDER CARBOLITE GERO HZS 12/900 Installation, Operation And Maintenance Instructions page 38

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.
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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