DIO 6533 Change Detection returning duplicate values

[dhoepner]

I am using a DIO 6533 with change detection to read gray code values from an absolute encoder.  However, I am frequently getting duplicate values returned in the results buffer.  Here is an example:

1    89 
129 89 
129 88 
1    88  
1    88        <-- Duplicate value.
1    72  
129 72 

We have examined the bus with a logic analyzer and see nothing unusual at the times when this is happening.  There is no obvious noise on the bus.

Additionally, we are seeing another pattern of values that is concerning. 

129 66 
129 67
1    67
1    65   
1    67  
1    65
129 65

There should be no repeat values, even seperated by one count.  Again, everything looks good on the logic analyzer.

[Jonathan_S1]

Hi,

Thanks for contacting us!

What rotation speed are you using on the encoder?  If you speed it up or slow it down does it make any difference?

Is it possible that your encoder is slipping or that there is a high amount of noise in the system?

Thanks!

Jon

[dhoepner]

Hi,

 I am primarily testing with gray code encoders where only one bit is changing at a time.  Changing the rotation speed of the encoder has no effect on the issue.  Typically, we are running at a speed where one of the bits is changing every 20ms.

There is no slippage.  We have looked at the data with a logic analyzer and everything seems to be working fine. 

Noise has been one of the things that we have been looking at.  However, all of the signals look very clean.