Position Sensors Circuits Review

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Position Sensors Indicators Circuits Review

A Position Sensor is any instrumentation or device that is utilized to detect position measurement or an objects location. It can either be an absolute position sensor or a relative one (displacement sensor). Position sensors can be either linear or angular.

As described within Potentiometer Position Indicator and Linear Variable Differential Transformer ( LVDT ) or Linear Voltage Displacement Transducer, position sensor or detection devices provide a method to determine the position of a valve or control rod. The four types of position sensors discussed within Instrumentation are limit switches, reed switches, potentiometer position sensors, and LVDT's. Reed and limit switches act as ON/OFF indicators to provide open and closed indications and control functions. Reed switches can also be used to provide coarse, incremental position indication.

Potentiometer and LVDT position sensors provide accurate indication of valve and rod position throughout their travel. In some applications, LVDT's can be used to indicate open and closed positions when small secondary windings are used at either end of the valve stem stroke. The indicating and control circuitry provides for remote indication of position and/or various control functions. Position indications vary from simple indications such as a light to meter indications showing exact position.

Control functions are usually in the form of interlocks. Pump isolation valves are sometimes interlocked with the pump. In some applications, these interlocks act to prevent a pump from being started with the valves shut. The pump/valve interlocks can also be used to automatically turn off the pump if one of its isolation valves go shut or to open a discharge valve at some time interval after the pump starts.

Position sensor valves are sometimes interlocked with each other. In some systems, two valves may be interlocked to prevent multiple valves from being opened at the same time. This feature is used to prevent undesirable system flow-paths. Control system interlocks are normally used to prevent outward or inward motion of certain elements unless certain conditions are met.

The following are some position sensors operating technologies available today:

  • Inductive Non-Contact Position Sensors
  • String Potentiometer (aka String Pot)
  • Linear voltage displacement transducer (LVDT)
  • Potentiometer
  • Capacitive transducer
  • Eddy-current sensors
  • Hall effect sensor
  • Proximity sensor(optical)
  • Grating sensor
  • Rotary encoder (angular)
  • Seismic displacement pick-up
  • Piezoelectric transducer
  • Photo diode array
  • Mechanical limit switch
  • Optical position sensor

Typical Automotive Induction Position Sensor Circuit

Typical Reed Switch Type Position Sensor

Typical Potentiometer Type Position Sensor Circuit

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