Can the measurement limit be “auto adjusted”?

[老王]

As the document says, set input limit properly can improve the precision of measurement.but in measuremnts, the input limit always has to be setup(call the function “DAQmxCreateAIVoltageChan”) before starting test.
But the real signal to be measured is always varies in a certain range,for example,varies from 5mV to 5V. If you set the input limit to 5V,then digitalizing error when measuring 5V is much larger then measuring 5mV. If the input limit can be adjust the 10mV or 5mV in time ,the measurement precision can be largely improved.Is there any method or an algorithm?

[Salvador_Santolucito]

Hi,

I have answered this question in the other post for this:

http://forums.ni.com/ni/board/message?board.id=230&message.id=2238

-Sal

[Moschdschlotzer]

Hi Salvador,

i am also interested in adjusting the measuring range of my PXI 6123 card. I am doing acceleration measurement on a gear box. For example i measure the acceleration on speedstages from 1000 to 5000 rpm in steps of 100 rpm. The acceleration at 5000 rpm is much bigger than the acceleration at 1000 rpm.  I think it would be better to change the measuring range between each measurement (speed step) because of less quantisation error. I found a way to change the measuring range with a property node. (there it asks me for a maximum value and a minium value). But i am doing a 4 channel measurement with the same task and i didn't find a way to change the measuring range for every channel separately. Is it possible??? What do you think about changing the measuring range?

regards

Jens

[David S.]

Hi Jens -

You're almost there. In DAQmx you can set the ranges while adding a channel to the task, or through a property node later on.  Either way, just call the function/VI repeatedly, changing the physical channel each time you call it.

I'm not sure which API and driver you're using, but here's an example using LV 8.2.1 and DAQmx.  I tested it using a simulated device.