Position Sensors, Speed Sensors and Potentiometers

Potentiometer Terms and Definitions

Potentiometers  are: “Potential – Meters” that monitor the “potential” across a resistor

Potentiometers  are used in two key areas;
1- Position sensing; providing the feedback of actual position of device into a control system  
2- Control device  providing the ‘demand’ signal for a control system .
Example:  a passenger car interior ventilation system would have a control device on the instrument panel (knob) where one controls the vents position.  A second position sensor would be located on the actual vent to provide true position of the vent into a closed loop motion control system.

Potentiometers as position sensors- converting motion (rotary or liner movement) into an electrical output
PCR  Printed Circuit Resistor
PCB -Printed Circuit Board (typically FR4)
Voltage Divider – the Ratiometric property of all potentiometers divides the applied (input) voltage
Conductive Plastic / CP /  Resistive ink / ink – a blend of carbon with epoxy to create a hard wearable material that has conductive properties.  

Collector Track- a conductive trace used to ‘collect’ the signal off of the resistor track.
Contact –a conductive ‘link’ that moves across the resistor track and collector track.  Typically a precision stamping fabricated  in precious metal.  The contact  connects the resistor track to the collector, creating the signals  

Contacting technology – a reference to the feature that the contact  is touching the conductive plastic surface and moves across this conductive surface.  Contacting technologies are considered mature in comparison to…
Non Contacting technology where the sensing element does not contact the target while generating an output, typically Hall effect, Optical or Magneto Resistive
Contacting technologies are very low cost requiring only a PCB with conductive ink, a rotor / slider and a contact.

Potentiometers are “absolute” vs.  Incremental sensors
Absolute position sensors know their true position all the time, even with power interruptions.  When power comes back on, they ‘wake’ with know position
Incremental position devices (typically encoders) that ‘increment’ from one known position to the next, basically counting pulses to determine position to one full rotation.  Incremental sensors lose their true position at power off.