07-25-2012 10:07 AM - edited 07-25-2012 10:08 AM
Be very careful with the differential measurements when trying to go up to 20V. Each input of the differential has to be in the range of -10V to +10V relative to GND or you will damage the device. See page 14 of the specification.
07-26-2012 12:03 PM
The 6008's not going to read +20V very well... its range is -10 to +10 relative to ground.
Use a voltage divider or 10x scope probe and multiply by that factor in software.
There's no "autorange" feature on the 600x boards either. You can set it to the highest range and figure out what scale you need to be at in software if you want that feature.