configure voltage input range

[hslmwall]

I'm using a USB-6221 card with SignalExpress 3.0.

The spec. for the 6221 card specifies 4 analog input ranges of +/- 10V, 5, 1 & 0.2. 

My question, how is the input voltage range on the  card set to one of the specified ranges?

The nearest thing I can find in SignalExpress is the "DAQmx aquire" step, looking at the "configuration" tab of "step setup". There's a panel called "settings", there are Signal Input Max and Min boxes, but the context help states that this is the expected values for the channel after scaling.

I've also looked in MAX but I can't see any way for me to directly configure one of these ranges.

Can anyone explain how this works?

Mike

[AdnanZ · Accepted solution]

You are looking at the right thing. When you specify the min and max, the DAQmx driver will then automatically select the best range for that signal. Say for example, the board supports +/-.1, +/-1, +/-5, and +/- 10 volt ranges and it's a 12 bit board. If you enter max/min of +/- 2, then the board will be set to the +/-5 volt range. Your resolution is then 10 volts (total voltage swing) divided by 4096 (2**12).

If you were using LabVIEW, you can get the actual voltage range selected by using the DAQmx Channel properties AI.Rng.High and AI.Rng.Low. If you specify a min and max that is less than the actual signal amplitude and it is greater than the actual range used, then you will clip your input signal. DAQmx does not do an autoscale. Have a look at Page 4-2 in the M-Series Manual.