[Ether]

Originally Posted by ttnn58

we tried to use this encoder:
http://www.andymark.com/MA3-A10-250-...-p/am-2899.htm

That's an absolute position encoder:

Product Overview:
This kit contains one encoder and one encoder cable. The MA3 is a miniature rotary absolute shaft encoder that reports the shaft position

Select an encoder that's designed to measure speed.