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Design and Theory

Different ways the actuator can electronically provide feedback to where the actuator is in its stroke include:
  • potentiometer
  • Encoder
  • CAN bus output

Potentiometer

A potentiometer is an analog feedback device that provides a difference in resistance. As the actuator extends, the resistance changes. The resistance, or voltage drop, over the resistance can be measured to determine position.

Example potentiometer

Encoder

An encoder provides a pulse output as the actuator moves. The pulse output is usually for use by a control system such as a PLC. The control system can use the output to determine relative position. Being a relative position device, there is a need to “home” the system on initial setup and any time the control system loses track of the pulses (power outage etc.).

The image below shows an example encoder.  On the left is an example of the sensor used inside a Thomson actuator. On the right is an example of the trigger wheel used to trigger the sensor.

An encoder example

CAN bus

CAN bus provides data about the actuator digitally using CAN bus.   Position feedback and operational parameters are transmitted on the CAN bus.  This can simplify wiring.

CAN bus controlled system

In a CAN bus controlled system:
  1. Power is distributed to each device.  (red lines)
  2. Control system communications directly with actuators.  Position feedback and operational parameters transmitted on the CAN bus. (blue lines)

Traditional system

In a traditional system:
  1. Power is distributed to each device (red lines)
  2. Control system communicates with each control box separately. (control box orange,  communication lines yellow)
  3. Feedback from actuator requires additional wiring for each feedback device.  i.e. potentiometer or limit switches (Green lines)

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