View Full Version : re servo encoder

19-06-2010, 10:39 AM
Hi guys i have a encoder that has 3 channels A B N got it cheap of eBay
but my driver only uses A B would it work fine if i just left N not connected ??
dont know that much about encoders muddled through in the past
would just try it but i dont have my driver here at moment


19-06-2010, 12:45 PM
Its probably an Index... 1 count per 360 revolution... If your driver doesn't have it, it won't matter if you don't hook it up. I'm no expert btw... just an opinion.


19-06-2010, 12:52 PM
Just connect the A and B, As said, the N is most likley the index, and your driver doesn't need it.

23-06-2010, 07:29 PM
Bit late........ but if you are using a home switch you can "and" the N channel and the switch to get a very accurate and repeatable home position control.

23-06-2010, 11:23 PM
Bit late too! It's very likely the index pulse. Basicly it should give one pulse per rev and is used by some drives for a variety of things like homing, or as a marker pulse to trigger positon checks etc etc. If ungated, its out of phase with a and b (which are 180 degrees out any way) which means between the A and B rising edges (or falling edges) you get an extra rising or falling edge which all means that homing is at twice the resolution of the encoder. 2000 line encoder with quadrauture on a 4mm pitch screw is 0.0005mm a step = v v v small to begin with but if you do have to rehome a lot during a job and are backing off from a home switch (they get dirty and can change over time) for example could be a small growing error, but its really very very small and the tool deflection will be bigger, the following error much bigger in general. Index allows the machine to count revs and return to the same one, exactly. Sometimes there are an additional 4 wires which are the compliments but the drive clearly doesn't need them either!

24-06-2010, 07:57 AM
thanks guys that would be even better if i could use n channel for homing have to look in to this
cheers paper work makes no referance to what N does apart from it being a channel
it does mention channels A-B saying 90deg (distance from A to B is at least 0.45 us at 300khz) but thats it

24-06-2010, 08:30 AM
thanks guys
just confirmed on the manufactures web site that channel N can be used to set home position
also says i can use A B channels to measure speed not that i will use it