# Can a rotary incremental encoder, count more steps due to interferences

I have an incremental encoder having differential signals A-NotA, B-NotB I-NotI, that apparently randomly seems to count more impulses. It is possible to have more impulses due to electrical interferences ( IMO not because of the differential outputs ) or can this happen? The encoder is a Baumer BHK 16.05A.1024-I2-5 and a datasheet can be found here http://www.pdfdoc.ru/process-control/sensors-and-transducers/rotary-encoders/baumer/bdk-min-shaft-encoder-1024ppr-ttl-o-p-bdk-16-05a-1024-5-4-499-7598

The wiring is done by 5m cable with shield connected to ground at a single point ( near the encoder ) and we are not using twisted pairs.

• Data sheet link? – Andy aka Feb 9 '15 at 9:39
• @Andyaka I added more information in the question – Felice Pollano Feb 9 '15 at 10:38
• I can't get the link to work – Andy aka Feb 9 '15 at 11:13
• @Andyaka strange, it worked on my side. Anyway I replaced with another link. – Felice Pollano Feb 9 '15 at 11:25
• No, you can't. Just becsuse it has a brand name on it doesn't mean that part wasn't designed at 4:30 on a Friday and never touched again because it seemed to work. Reviews should catch things like that, but history is full of leakage. Perhaps you could experiment and try to find ways to cause false counts. – Chris Stratton Feb 9 '15 at 16:07

It is normal for a rotary encoder to go through the following sequence:

- A low     and B low
* A low     and B jittery
- A low     and B high
* A jittery and B high
- A high    and B high
* A high    and B jittery
- A high    and B low
* A jittery and B low


From a decoding perspective, one may either use the states marked with dashes or with asterisks. If one uses the states marked with dashes, then when the encoder is near a switching threshold, it may appear to jitter back and forth between two positions. If the decoder is designed correctly the overall rotation should be correct, since repeated jitters will cancel out, but a +/- 1 unit jitter may be annoying. If one uses the states marked with asterisks, apparent jitter will be eliminated (once an input changes, all future changes on that input will be ignored until the other input changes) but backlash will be increased by a tick.

If the decoding logic isn't implemented properly, it's possible for the jitter to cause unwanted counts in such a fashion that they don't cancel, but the solution in that case is to fix the decoding logic.