Sensing Your Position

There are several types of position sensors, each of which provide feedback relating to their position. Two such methods of influencing a position is to use distance or rotation. Either way, a linear sensor can detect objects in a straight line, and a rotational sensor can detect any angular movements.

The Common Position Sensor – The Potentiometer

Potentiometers are available in a variety of sizes and designs, plus they are the commonest of all position sensors, as it is inexpensive and easy to install. The wiper contact is linked to a mechanical shift that can move angularly or linear. This causes opposition between the two end connections and the wiper/slider to give an electrical signal output, which provides a comparative relationship between the wiper positioned on the resistive track and its opposition.


Inductive Position Sensors

One particular type of position sensor that does not experience mechanical wear problems is the linear variable differential transformer (LVDT). This inductive type position sensor works on the exact same principles as the AC transformer used to measure movement. It accurately measures linear displacements. It consists of three coils wound on a hollow tube, one of which forms the primary coil and the additional coils form identical secondary’s, which connect electronically together, but are 180o out of phase on either side of the primary coil.

The object to be measured is connected to a soft iron ferromagnetic core (armature), which moves up and down or slides inside the tube. If the armature is placed exactly in the tube’s centre, the induced EMF’s in both secondary windings produce an output voltage of zero, as they are 180o out of phase and cancel one another out. When the core is pulled to either side of the null position, the induced voltage in either of the secondary’s will be greater than the other, and this will result in an output.

Rotary Encoder Optical Device Sensors

These position sensors resemble potentiometers, but they are non-contact optical devices used to convert mechanical movements into a digital signal. Optical encoders maintain the same basic principles. Light from an infrared light or LED course passes through a rotating high motion encoded disk containing the necessary code, which is either grey code, binary, or binary coded decimal (BCD). Photo detectors then scan the disk as it revolves, and an electronic circuit processes the data into a digital form, as the stream of binary output pulses fed to controllers and counters determines the angular position of the pole.

Position sensors vary from rotary encoders to the more basic potentiometers.

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