How do I select the appropriate damper actuator control signal — on/off, floating, or modulating?

On/off (2-position) actuators are simplest and used for isolation dampers, garage exhaust fans, and smoke dampers where only open/close functionality is needed — typically 24V or 120V powered with an end-switch for position feedback. Floating (3-point) actuators accept open/close pulse signals from a controller with a runtime of 90–150 seconds and are used when the controller lacks an analog output but needs modulating control; the controller must track the inferred position through pulse timing. Modulating actuators accept a 0–10V or 4–20mA analog signal and provide true proportional positioning with feedback, required for economizers, VAV boxes, and precise temperature control applications. Per ASHRAE Guideline 36, modulating actuators on large AHU dampers should also support bus communication (BACnet MS/TP or Modbus RTU) to report actual position, runtime, and diagnostic data to the BMS for automated fault detection.