USB-6210 Run two different Analog voltage ranges at once?

[BarkBark]

When selecting a voltage range for the analog inputs am I able to assign different channels different input ranges?  IE if half my signals are in the millivolt range and the rest are in volts can I set some channels to the +/-200mV range and the rest to the +/-5V?  

I feel like the answer is no but I was told of a competing device (LabJACK) with a multiplexed single ADC that could do it so I thought I'd check. 

[ybalam]

You should be just fine to do that. There's a good KB on this topic here!

[Kevin_Price · Accepted solution]

In addition to the general answer of "yes you can", there is a subtlety to watch out for when the voltage ranges differ so substantially.  If not careful, you can get a "ghosting" effect where some of the 3 V signal that was just multiplexed in hasn't yet bled off when you next try to convert a 9 mV signal.  You could get a 25 mv measurement.

Be sure to use the bias resistors and otherwise configure as recommended in the Field Wiring guide.  However, if your source signals are particularly unfriendly, you may need to take further measures.

An approach I like to take to investigate whether there's a problem is to group all the high voltage signals in the beginning of the channel list and the low voltage signals at the end.  V1,V2,V3, mV1,mV2,mV3.  That tends to isolate the potential problem to one specific point in the multiplexing -- the switch from V3 to mV1.  I then make a test-only channel list that repeats this first low-voltage signal multiple times.  V1,V2,V3, mV1,mV1,mV1,mV1,mV1.   Then I acquire a bunch of data and do some analysis on the distinct sample values for mV1 that were acquired on the same nominal sample but at a different point within the multiplexing sequence.  This helps me see *if* there's a problem and gives me a better idea how big it is.

-Kevin P