Electrical actuator with means for preventing dither at a limit switch
AssigneeHoneywell Inc.
InventorMarvin D. Nelson
Life of this patent
Estimating the term…
Abstract
The tendency of a motor-driven actuator driving against a dynamic (non-frictional) load to return upon reaching the limit switch sufficiently to again close the limit switch and create a persistent oscillation at the limit position can be prevented by placing a positive temperature coefficient thermistor across the limit switch involved. Such loads typically arise in actuators having spring-driven return capability, and can also arise when positioning air dampers and other loads where the actuator force is opposed by a spring or gravity.
Claims5
In an actuator whose output element is driven by a motor having a pair of terminals for applying power to the motor for driving the motor in a first direction, a limit switch through which power for driving the motor in the first direction passes, and a feature on the output element for opening the limit switch when the output element drives in the first direction to a predetermined extreme position, an improvement for preventing dither of the output element under the influence of a dynamic load at the predetermined extreme position, comprising a positive temperature coefficient (PTC) circuit element connected across the limit switch.
Dependencies are inferred from the claim text.