Watlow Series 988 - Manual (Page 121)

WATLOW Series 988 User’s Manual 8.7 General Software Features, Chapter 8
General Software
TL TL W W W WA A
PROCESS
L1 L2 L3 L4
DEV
% OUT DISPLAY
MODE
AUTO
MAN
SERIES 988
input 1 output 1
output 2
E nv ironme nt a l Cha mbe r
limit
heater
temperature
sensor
chiller
limit
sensor
Sample Application
An engineer for an environmental chamber manufacturer, who is design-
ing the heating and cooling system for a new chamber, wants to minimize
the energy costs of operating the chamber. She has chosen the Series 988
and will configure the heat and cool outputs with a positive dead band.
When the chamber temperature is near ambient the cooling and heating
systems had a tendency to buck one another, resulting in inefficient use of
energy. The engineer started with a dead band of five degrees, but in the
process of tuning the system for optimal control, the setting was reduced
to two degrees. This made the chamber more energy efficient and reduced
wear on the refrigeration system.
Figure 8.7b -
Environmental
chamber with dead
band.
Figure 8.7a -
Dead band graph.
77
°
cooling action
no action
heating action
75
°
set point
2
°
dead band
primary
set point
cool
set point
75 + 2 = 77 °
[`SP1] [`dbA] cool set point
( )