Red Lion TCU - Manual (Page 74)

ON/OFF CONTROL
The controller operates in the ON/OFF
control mode by setting the proportional band =
0.0%. The ON/OFF control hysteresis band
(CHYS) parameter eliminates output chatter
around setpoint. For heat/cool systems, the
cooling output can also be used in the ON/OFF
control by setting the relative gain = 0.0
(GAN2). Additionally, the heat/cool parameter
(db-2) determines the amount of operational
deadband or overlap between the two outputs.
Th e phase of the contro l action can be
r e v e r s e d b y t h e o u t p u t c o n t r o l a c t i o n
p a r a me t e r . O N / O F F c o n t r o l i s u s u a l l y
characterized by temperature oscillations about
the setpoint value. Large hysteresis values
make the oscillations larger. ON/OFF control
s h o u l d o n l y b e u s e d w h e r e t h e c o n s t a n t
oscillations are acceptable.
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Figure 36, OP1 On/Off Action Figure 37, OP2 On/Off Action