30 November 1998
Adjustable contact setpoint.
(5) The output control modes that can be used in combination are:
(a) Proportional mode, which varies the output proportionally to the error between the PV input
value and the controller setpoint.
(b) Integral mode, which modifies the output signal as a time related function of the error
between the PV input value and the controller setpoint.
(c) Derivative mode, which modifies the output signal as function of the rate of change of the
error between the PV input value and the controller setpoint.
(6) Each of these control modes has an assignable constant, which is adjusted in the process of
tuning the controller.
(7) The integral mode will have a feature that automatically stops the integration of the error signal
when the controller output signal reaches its minimum or maximum value. This feature is known as anti-
reset windup. If the process being controlled does not respond to the controller output for a period of time
(such as an overnight shutdown), continuing the integration of the error signal during that period would
result in the controller failing to respond to control the process immediately on startup. Without the anti-
reset windup feature, the controller would reverse the integration process on startup, but the reversal would
require a time period equal to the time period of the integration during shutdown.
(8) The controller will have the following selectable modulating control functions:
(a) Self tuning of control mode constants.
(b) Manual tuning of control mode constants.
(9) Self tuning allows the controller to select the optimal combination of proportional, integral, and
derivative control mode constants. The controller continues to use these selected constants until the self-
tuning control function is again selected. The Guide Specification requires that the self-tuning process be
operator initiated. Applications where self tuning is used are as follows:
(a) Mixed air temperature control.
(b) Heating coil temperature control for multizone hot deck and dual-duct hot duct
(c) Modulating valve and modulating damper preheat coil control.
(d) Cooling coil discharge temperature control for multizone cold-deck, dual-duct cold-duct,
and VAV system discharge temperature.
(e) Relative humidity control.
(f) Supply duct static pressure control.