Watlow Series 988 Enhanced - Manual (Page 8)

8 WATLOW Series 988 Enhanced Software Features
Sample Application
An application using differential control is to maintain glass temperature
of a freezer display case above dew point at a differential to the ambient
air temperature. A thermocouple at input 2 senses the outside air temper-
ature and adjusts the internal set point to maintain the glass temperature
10 degrees higher. Substituting values we have: glass temperature =
ambient + 10°.
In this application the system uses two type J thermocouples: one to
sense glass temperature (input 1) and one to sense the ambient air tem-
perature (input 2).
To configure the controller, first enable input 2 (set to ). To
enable the differential control algorithm set the control prompt in
the Global Menu to differential . Press the DISPLAY key. The lower
display will read 0, indicating no differential between input 1 and input 2.
Adjust the set point to 10. The internal set point for input 1 is now equal
to the input 2 value plus 10, which will maintain the boiler water temper-
ature 10 degrees higher than the outside air temperature.
Figure 9.8 - Freezer
display case with
differential control.