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AD627 NonLinearity

Question asked by triley on Jul 18, 2012
Latest reply on Jul 19, 2012 by ScottH

I am having issue with a 4-20 ma measurement loop


The circuit is designed as follows, with the output connected to a 16-bit ATD (Burr Brown ADS8344). Not my selection, it is standard on the micronontroller board.


7-18-2012 11-57-30 AM.png


I am attempting to inject a signal with a 4-20 ma calibrator to verify operation, but am getting the following output:


7-18-2012 12-03-18 PM.png

The top graph is the AD627 response and the bottom is just a check of the calibrator into a 7.5 ohm load.


Any ideas about what could be causing this issue. Not the dramatic slope change after the 18 ma cal point. The left axis is the actual ATD counts on the microcontroller for the AD627.