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b. Event-driven control is a function allowing the UMCS to activate a control output in response to a
specific event or state of the monitored utility system. For example, UMCS control of a swimming pool
filtration system may provide for backwashing of the filter when the filter DP exceeds a specified limit.
Implementation of event-driven control requires that the UMCS monitor the parameters related to the
event (in the example, filter DP).
c. Two position control is a function allowing the UMCS to activate a two-state device to control
utility system parameters within specified limits. For example, UMCS control of a steam-to-hot water heat
exchanger may provide for opening the steam valve when the hot water temperature falls 2 degrees F
below the setpoint and closing the valve again when the hot water temperature reaches 2 degrees F
above the setpoint.
d. Floating point control is a function allowing the UMCS to change the position of a final control
element (such as a valve) by increments in response to deviation of a utility system parameter from its
setpoint. As long as the value of the utility system parameter is within a specified deadband around the
setpoint, the final control element maintains its current position. Floating point control is normally used
when changes in utility system load are gradual.
e. PID control (or proportional-plus-integral or proportional-only control) is a function of feedback
controllers allowing the UMCS to continuously modulate a final control element in response to deviations
of a utility system parameter from its setpoint. PID control is normally provided for utility system
parameters requiring close control or experiencing rapid load swings. Proportional (gain), integral (reset),
and derivative (rate) values must be selected for specific control applications and are not all applicable for
every control loop.
f. Sequences of operation are combinations of applications programs and these other basic control
functions to describe all operational requirements for specific utility systems. Sequences of operation will
address different operational modes such as system startup, normal occupied operation, unoccupied
operation, heating and cooling modes and failure modes. Typical sequences of operation for utility
systems commonly found on Government installations are provided in Chapters 8.