Red Lion P16 - Manual (Page 21)

21
ON/OFF CONTROL
The controller operates in On/Off Control when the Proportional Band is set
to 0.0%. In this control mode, the process will constantly oscillate around the
setpoint value. The On/Off Control Hysteresis (balanced around the setpoint)
can be used to eliminate output chatter. Output O1 Control Action can be set to
reverse for heating (output on when below the setpoint) or direct for cooling
(output on when above the setpoint) applications.
ON/OFF CONTROL -
REVERSE OR DIRECT ACTING FIGURES
Note: CHYS in the On/Off Control Figures refers to the On/Off Control Hysteresis
(  ) in parameter Module 2.
For heat and cool systems, O1 Control Action is set to reverse (heat) and the
Alarm 2 Action is set to cooling (O2). The Proportional Band is set to 0.0 and
the Relative Gain in Cooling to 0.0. The Deadband in Cooling sets the amount
of operational deadband or overlap between the outputs. The setpoint and the
On/Off Control Hysteresis applies to both O1 and O2 outputs. The hysteresis is
balanced in relationship to the setpoint and deadband value.
C
ontrol
m
ode
e
xplAnAtionS
ON Output 2 (O2) : ON
SP
OFF
INPUT
HEAT/COOL DEADBAND (db2) = 0
SP + 1/2 CHYS
SP - 1/2 CHYS
OFF OFF Output 1 (O1) : ON
CHYS
SP
SP + 1/2 (db-2) - 1/2 CHYS
SP + 1/2 (db-2) + 1/2 CHYS
SP - 1/2 (db-2) + 1/2 CHYS
SP - 1/2 (db-2) - 1/2 CHYS
HEAT/COOL DEADBAND (db-2) < 0
db-2
CHYS
CHYS
O2 ON
O1 OFF
O2 OFF
O1 ON Output 1 (O1) :
Output 2 (O2) :
db-2
Output 1 (O1) :
Output 2 (O2) :
SP - 1/2 (db-2) + 1/2 CHYS
SP - 1/2 (db-2) - 1/2 CHYS
O1 OFF
SP
O1 ON
O2 OFF
O1 OFF
O2 ON
CHYS
O2 OFF
HEAT/COOL DEADBAND (db-2) > 0
SP + 1/2 (db-2) - 1/2 CHYS
SP + 1/2 (db-2) + 1/2 CHYS
CHYS
O1 ON
O2 ON
INPUT
INPUT
SP + 1/2 (db-2)
SP - 1/2 (db-2)
SP + 1/2 (db-2)
SP - 1/2 (db-2)
ON/OFF CONTROL - HEAT/COOL OUTPUT FIGURES
PID CONTROL
In PID Control, the controller processes the input and then calculates a
control output power value by use of a modified Proportional Band, Integral
Time, and Derivative Time control algorithm. The system is controlled with the
new output power value to keep the process at the setpoint. The Control Action
for PID Control can be set to reverse for heating (output on when below the
setpoint) or direct for cooling (output on when above the setpoint) applications.
For heat and cool systems, the heat (O1) and cool (O2) outputs are both used.
The PID parameters can be established by using Auto-Tune, or they can be
Manually tuned to the process.
SP
TIME
P & I
P & I & D
P only P & D
INPUT
TYPICAL PID RESPONSE CURVE
OFF Output 1 (O1) :
SP
OFF
INPUT
DIRECT ACTING
SP - 1/2 CHYS
SP + 1/2 CHYS
ON
OFF Output 1 (O1) :
SP
OFF
INPUT
REVERSE ACTING
SP - 1/2 CHYS
SP + 1/2 CHYS
ON