# Expressions used with Rotary Encoders

Hi :)

While I am reading and collecting information about rotary encoders , I faced some troubles about the meaning of some expressions concerned with encoder ,which make me to be confused and stray, these expressions or words are :

-Count per revolution (rotation)

-Pulse per revolution

-Tick per revolution

-Transitions per revolutions

-Number of transitions

-Number of state changes

I thought the transition is same as state changes which means change from high to low or low to high , but what about the others what is the diffenece among them (count , tick ,pulse ,transition .... etc)? and what the relationship between transitions and pulse ? Could anyone clarify that , please

Well I can only partially help. The first thing to know is there are different types of rotary encoders. They do not all work the same way. The most common rotary encoder are sometimes called "gray code" encoders. They have 2 pins that are pulsed based on which direction you turn the encoder. If you turn it one way, the pin for that direction pulses for each step it is turned. If you turn it the opposite direction, the other pin pulses for each step in the turn in that direction. Your micro has to count the pulses from both pins and increment or decrement some variable accordingly. Steps per revolution refers to how many pulses you get in one complete 360 degree rotation of the encoder. So a 16 step encoder has 16 steps in one 360 degree rotation and a 48 step encoder has 48 steps (just to name 2 examples).

There are other types of encoders that actually output values by using different combinations of highs and lows across multiple pins. There are encoders that count in hexadecimal, octal, binary, etc. The datasheets for these usually have a table that shows you what value corresponds to each combination of pins. There are usually more pins on these kinds of encoders.

Hi,

-Count per revolution (rotation)

-Pulse per revolution

-Tick per revolution

Are all the same , that is, how many pulses you get in a full rotation, 360Deg, of the encoder.

-Transitions per revolutions

Is as you have said, the number of changes in level, so a pulse has two changes, low to high, then high to low. So you will have twice as many transitions as pulses per revolution. Transitions would be that same as state changes.

Most encoders have two outputs, A and B, when you turn the encoder say clockwise, pulse out of A lags the pulse out of B by 90deg of the pulse cycle. For anti-clockwise B lags A by 90deg of pulse cycle. Some have a C or Z output which outputs a pulse for each turn, this used if you need synchronization with some device.

Tom.... :)