Watlow Series 988 - Manual (Page 120)

8.6 WATLOW Series 988 User’s Manual General Software Features, Chapter 8
General Software
Dead Band
Requirements
The dead band feature is standard on any Series 988 controller with two
control outputs. The dead band prompts will appear if the control outputs
are configured for heat/cool or cool/heat.
Overview
The dead band prompts, [db`A] and [db`b], located in the PID menus,
determine the amount of interaction between heat (reverse acting) and cool
(direct acting) control outputs. The dead band directly offsets the target set
point of the cool control output.
With a positive dead band, both control outputs will never be ON at the
same time. With the process in a positive dead band, the output value is
determined by adding the percent heat output to the percent cool output
and only applying the result to the correct output — cooling action if the
sum is negative and heating action if it is positive.
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WARNING:
If the dead band is
set to a negative
value, the heat
and cool outputs
can both be ON at
the same time.