Watlow CLS - Manual (Page 110)

102 CLS User’s Guide
PID Tuning and Control
The output filter can also enhance PID control. Some processes are very
sensitive and require a high PB, so normal control methods are
ineffective. You can use a smaller PB- and get better control- if you use
the digital filter to reduce the high and low process output swings.
You can also use the filter to reduce output noise when a large
derivative is necessary, or to make badly tuned PID loops and poorly
designed processes behave properly.
Reverse and Direct Action
Reverse action is an output control action in which an increase in the
process variable causes a decrease in the output. Direct action is an
output control action in which an increase in the process variable causes
an increase in the output. Heating applications normally use reverse
action and cooling applications usually use direct action.