Incremental Encoder Pulse vs Count

As a robotics engineer, I frequently work with packaging applications. Often, this includes having robots follow parts on a moving conveyor. This is possible with the use of encoders. Once an object is identified by a camera or a sensor, a trigger signal is sent to an encoder which then starts measuring the distance the object travels along the conveyor. Armed with this information, robots can predict when the object will get into their work area and chase after it.

Typically, the number one criterium when selecting an encoder for your application is resolution (or number of pulses per revolution of encoder shaft).

Naturally, you would want to select the highest resolution within your budget. The more, the better right? But that is not necessarily the case, as it depends on how frequent the receiving device can take in encoder pulses. Hence you need to pay attention to the minimum and maximum limits for the number of encoder pulses or counts such device can accommodate. In turn, this affects the size of your encoder wheel as well (if your encoder is wheel-mounted, as opposed to drive shaft-mounted).

At one point, I thought that the terms pulse and count refer to the same thing, but they don't. The fact is

Number of Counts =  Number of Quadrature Pulses x 4

You may also want to know that

Number of Counts Per Meter (CPM) 
             = Number of Wheel Revolutions per meter x Encoder Resolution x 4
Number of Counts Per Second        
             = CPM x Conveyor speed (m/s)

For those who want to understand various types of encoders, incremental versus absolute encoders, magnetic versus optical encoders, and more, below is an easy read from encoder manufacturer Dynapar. Just click on the picture.