how to configure the dynamic range of an analog input

[igouzouasis]

Hello everybody.
I use the pci-6221 card and i want to record voltage values from 4 channels.
I found in the manual that the dynamic ranges are +-10, +-5, +-1, +-0,2V.
My question is: should i configure the dynamic range of an analog input at the specified default ranges or can i define arbitrarily the min and max value?
For example, the values i want to record are at the range 0,9-1,1V. And i want the maximum precision (all the available bits) on that range. can i do that?
thank you,
john

[Hani R]

Hi John,

The input ranges listed in the manual are the only selectable ranges available on the PCI-6221.  Defining an arbitrary range will not improve the resolution.  You can achieve a smaller input range by wiring a 1V reference to the negative terminal and performing a differential measurement on the signal.  For a signal that varies from 0.9V to 1.1V, you could then use the +/-0.2V range.  The KnowledgeBase article: KB 21DASU4U: Getting Full Analog Input Resolution of a Small Voltage Range Not Centered at 0 Volts describes this in more detail.  

[igouzouasis]

Thank you very much for your reply, Hani.