Proportional Control - Honeywell CVL4022ASVAV1 Engineering Manual

Else if (V x 100% + M) > 100% Then 100%
Else (V x 100% + M)
V = Ep + Ei + Ed

PROPORTIONAL CONTROL

Proportional control is the function that determines the output
setting required to meet the load conditions. See Fig. 34 and
35.
Fig. 34. Proportional direct acting (cooling)
Fig. 35. Proportional reverse acting (heating)
In a direct acting control loop the output increases as the input
sensor value rises above the setpoint. In a reverse acting
control loop the output increases as the input falls below the
setpoint. Direct and reverse acting are selected based on
application requirements associated with the consideration
that the setpoint is the no load value of a measured variable
because it has 0 percent output when the energy input is
closed or off. The physical outputs are configured to match the
controlled devices (for example, normally open, normally
closed, energized on, energized off). See the following
application examples.
Direct Acting
Cooling
Dehumidification
Mixed Air
Static Pressure
Chilled Water Pump
Condenser Water Pump
The proportional calculation determines the proportional error
(Ep). Ep is the deviation from the setpoint of the sensed
medium (input sensor) divided by the throttling range in the
units of the input sensor. The setpoint is the value of the input
sensor that satisfies the control loop. When the input sensor
value is at the setpoint, there is no proportional error and the
output is 0 percent. The throttling range is the amount of
change in the sensed medium that is required to drive the
output from 0 to 100 percent. In proportional control the input
value must deviate from the setpoint to initiate a change in the
output.
The throttling range must be narrow enough to provide good
control without becoming unstable. The throttling range is
determined by a number of factors such as the control
application, the response time to the equipment being
controlled and the control algorithm in use. The narrower
(smaller) the throttling range, the more precise the control
operation. The wider (larger) the throttling range, the more
stable the control action. The objective is to set the throttling
range to achieve the optimum balance between precision and
stability.
29
Reverse Acting \
Heating
Humidification
Hot Water Pump
Lighting
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