Actuator Mounting Alternatives; Positive Positioners; Multiple Actuators - Honeywell AUTOMATIC CONTROL Engineering Manual

DAMPER SELECTION AND SIZING
when either no control signal is applied or power to the actuator
is lost. The damper blades will open in a normally open
application. Selection is based on the desired damper position
when power or air is removed from the actuator.

ACTUATOR MOUNTING ALTERNATIVES

Actuators can be installed externally (outside a duct) or
internally (inside a duct). See Figures 20 and 21.
Fig. 20. Internally Mounted Electric Actuator.
Fig. 21. Externally Mounted Pneumatic Actuator.
ENGINEERING MANUAL OF AUTOMATIC CONTROL

POSITIVE POSITIONERS

Some actuators are equipped with position-sensing feedback
controls or circuits that are called positive-positioners. The
feedback system senses the actuator position, whether rotation
or stroke, and compares it to the position dictated by the control
signal (input). If some outside force (e.g., friction or torque on
damper blades) disturbs the actuator position, the feedback
mechanism causes the actuator to correct its position. It also
minimizes any effect of hysteresis inherent in the actuator. It is
not recommended to use more than one positive positioner per
bank of dampers (multiple sections connected together).

MULTIPLE ACTUATORS

Multiple actuators can drive sections of a multiple section
damper (Fig. 22) in unison. Multiple sections should be all
linked together both in vertical and horizontal stacks. When all
sections are linked together, actuators should all have the same
operating range, torque, and stroke to prevent damper blade
twist and binding.
M10420
Fig. 22. Control of a Multiple Section Damper.
M10435
Multiple actuators can also be used for unison operation of
two or more dampers in different locations. All actuators in
this arrangement must have the same input signal (e.g., voltage,
pressure, current), timing, and stroke to provide uniform
opening and closing.
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M10421