Controls; Pid Heat/Cool Control - gefran GFW ADV Configuration Manual

PID HEAT/COOL CONTROL

The controller can manage a heating output and a cooling output in a completely independent manner. Heating and
cooling parameters are described below. Parameters for PID (proportional band, integral and derivative time) control are
typically calculated by means of Autotuning and Selftuning functions.
Control actions
Proportional action:
action in which contribution to output is proportional to deviation at input (deviation = difference between controlled variable
and setpoint
Derivative action:
action in which contribution to output is proportional to rate of variation input deviation.
Integral action:
action in which contribution to output is proportional to integral of time of input deviation.
Proportional, derivative, and integral action
Increasing the proportional band reduces oscillation but increases deviation.
Reducing the proportional band reduces deviation but causes oscillation of the controlled variable (excessively low
proportional band values make the system unstable).
An increase in Derivative Action corresponds to an increase in Derivative Time, reduces deviation, and prevents
oscillation up to a critical Derivative Time value, beyond which deviation increases and there are prolonged oscillations.
An increase in Integral Action corresponds to a decrease in Integral Time, tends to annul deviation between the
controlled variable and the setpoint at rated operating speed.
If the Integral Time value is too long (weak Integral Action), there may be persistent deviation between the controlled variable
and the setpoint.
For more information on control actions, contact GEFRAN.
Heat/cool control with separate or superimposed band
Output with separate band
Control output with only proportional action in case of proportional
heating band separate from cooling band.
c_Pb
SP+cSP
SP
h_Pb
+100%
Control output
0%
-100%
PV = process variable
SP + cSP = cooling setpoint
c_Pb = cooling proportional band
Heat/cool control with relative gain
This control mode (enabled with parameter Ctr = 14) asks you to specify cooling type. The PID cooling parameters
are then calculated based on heating parameters in the ratio specified (ex: C.ME = 1 (oil), H_Pb = 10, H_dt =1, H_It = 4 im-
plies: C_Pb = 12.5, C_dt = 1 , C_It = 4)
Apply the following values when setting cycle times:
Air T Cool cycle = 10 sec.
Oil T Cool cycle = 4 sec.
Water T Cool cycle = 2 sec.
NB.: Cool parameters cannot be changed in this mode.
80963B_MSW_GFW_11-2012_ENG

CONTROLS

Output with superimposed band
Control output with only proportional action in case of proportional
heating band superimposed on cooling band.
PV
Time
SP
c_Pb
SP+cSP
h_Pb
+100%
Control output
0%
-100%
PV = process variable
SP = heating setpoint
h_Pb = heating proportional band
PV
Time
49