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Mechanical Components - Potentiometers, Encoders, LVDTs

Sensors: Linear / Angular Position

 


Linear / Angular Position

Potentiometers
Servo
Potentiometer
Potentiometers

Potentiometers utilize a variable resistor to convert an angle or displacement to a resistance/voltage. They operate by moving a contact along a resistor to produce a voltage proportional to the position.

 


Encoders

Encoders
Rotary Encoder
An encoder is a sensor of mechanical motion. It translates motion (such as position, velocity, and acceleration) into electrical signals.

Absolute encoders have a unique value for each mechanical position and thus the position is known "absolutely". With this type of encoder, the position information is never lost and is instantly available as a digital word on power-up.

 

 

Incremental encoders have output signals which repeat over the range of motion and thus each mechanical position is not uniquely defined. The current position sensed is only incremental from the last position sensed. Thus at power up, the position of an incremental encoder is not known since the output signals are not unique to any singular position. They are made up of 2 major parts, the disk and the sensor. The disk of an incremental encoder is patterned with a single track of lines near the outside edge of the disk. The disk count is defined as the number of dark/light linepairs that occur per revolution (CPR). As a rule, one or more tracks are added to generate a signal that occurs once per revolution (index signal), which can be used to indicate zero or home on the encoder.

Count and direction information can be obtained from both absolute and incremental encoders.

 


LVDT/RVDT

LVDT
LVDT
LVDT or Linear Variable Differential Transformer operates with two small transformers sharing the same magnetic core. As the core moves the output of one increases while the other decreases. The 'out of balance' current is a measure of the core position with the best linearity occurring at the mid way point when the transformers are almost in balance.

The LVDT is sensitive, reliable and repeatable.

The accepted mode of operation is to measure a perfect sample (a setting master) and to then measure the unknown sample. Thus the accuracy is derived from the setting master and the LVDT is used as a comparative tool. The master is measured once a day, or whenever the temperature changes to effectively calibrate out all other variables relating to support fixtures etc. Angular displacement or rotation using an RVDT - Rotational Variable Differential Transformer.

 

 




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