SSZTCT0 april   2023 DRV5013-Q1 , DRV5033-Q1


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    2.     Popular Sensing Methods for Incremental Encoders

Systems that have moving mechanical components often have a need to measure something rotating.


In a car, the speed of the wheels is used for the speedometer, traction control, anti-lock brakes, and cruise control. The engine’s RPM is monitored to control the transmission and stay under the redline.  Power windows are often controlled by a small motor with closed-loop rotational sensing. And let’s not forget, when your favorite song comes on, the radio system needs to sense the volume knob as you turn it.

Outside of cars, rotational sensing has many other applications, being used on motor shafts, fans, gears, turbines, and computer mouse wheels. This picture shows an example of using it to measure fluid flow rate:


The name for this type of sensor is rotary encoder. There are two main categories: absolute encoders (which resolve the exact position, in degrees) and incremental encoders (which detect relative change).  An easy example of an absolute encoder is a potentiometer.

Within the realm of incremental encoders, the two main types are “speed-only” and “speed and direction”. With the first type, the sensor simply pulses when any rotation occurs, and clockwise versus counter-clockwise are treated the same.  The second type adds direction information, and it’s accomplished by adding a second sensor; then the controller in the system considers the order of transitions between the two sensors to know which direction is being turned.