VAV Controller Motors – Pulse vs Analog

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VAV controllers are tasked with moving a damper to control the volume of air leaving a VAV box. The electronic motor used in Computrols’ VAV-B and UNI-C controller can be either pulse or analog – let’s compare those options.

Pulse-type actuators feature two control inputs – applying 24VAC to one input drives the actuator clockwise while applying 24VAC to the other input drives the actuator counterclockwise. 

Analog-style actuators feature one control input – applying 2-10 VDC to that input modulates the actuator to a position that is proportional to the control input.

Both the UNI-C and VAV-B controllers include the pulse-style actuator by default, with the Analog-style actuator available as an upgrade option.  Some users prefer this upgrade for the below reasons:

  • Actuator position.  With a pulse-style actuator, you do not know the actual commanded position of the damper. While this position can be loosely calculated by tracking the pulses in each direction, this is a rough estimate at best and is subject to error. With the analog-style actuator, you always know the exact commanded position.

  • Control logic. With pulse-style control, you need logic to pulse the actuator in one direction or the other, which also requires the use of timer logic to avoid pulsing the motor for too long in one direction. With an analog motor, a simple PID loop can be utilized to control the position of the actuator.