Watlow ANASOFT - Manual (Page 72)

62 ANASOFT User’s Guide
Appendix A: PID
Output Digital Filter
The output filter digitally filters the PID control output signal. It has a
range of 0-255 levels, which gives a time constant of 0-127.5 seconds.
Use the output filter if you need to filter out erratic output swings due to
extremely sensitive input signals, like a turbine flow signal or an open
air thermocouple in a dry air gas oven.
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.