Multiple AMUX 64T Boards with AT-MIO-16F-5

[craig_neslen]

I'm working on a data acquisition system for up to 126 thermocouples using
multiple AMUX-64T boards daisy chained to one AT-MIO-16F-5 board. Right
now I'm just trying to get decent readings. When I read one or more
channels from one powered board, my TC readings look pretty good.
However, when I connect a second AMUX-64T board I maintain those good
readings if I only acquire data from one AMUX channel. If I try to scan
multiple channels on either powered AMUX board, the readings are no longer
accurate.

The address settings for both boards are correct and the MIO is set up for
differential readings. Also, NI-DAQ is reconfigured each time I
add/delete an AMUX. I have the TC's in a simple ice bath and am expecting
around -.95 mV. With only one powered AMUX board or scanning one channel
from 2 powered AMUX boards, I obtain readings close to this value.
Scanning multiple AMUX channels on 2 AMUX boards gives me readings around
-1.2 to -1.3 mV for each channel.

I've called technical help at National Instruments and haven't had any
luck yet. What am I missing?

Craig Neslen
nes...@plk.af.mil

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