LabVIEW
DAQmx Scaling - Why the min/max inputs of the DAQmx Create Channel.vi change with scaling?
By design if we use the DAQmx scaling, we need to keep in mind, that the DAQmx Create Channel.vi 's max/min inputs do not describe the pre-scaled range (raw voltage input range for the ADC for example), but the scaled one! See a snippet as an example below. In this example, I have two different types of analog pressure transducers, with different min/max voltage output ranges. No problem here, I just take the higher scaled "max" value (and if the "min"s are different, I would take the smaller of them as min input) and use it for the DAQmx Create Channel.vi.
Ok, lets imagine, we need to measure very different analog signal sources, for example one is with a scaled range of 0-3000 mbar, and the other is 0-1 Watt (like a powermeter). Beside, both pre-scaled ranges are for example 0-5 Volts!
If I use the value "3000" as max input for the Create Ch.vi, I will lose resolution for the other physical AI channel, is this correct? Or the ADC will "scale back" the scaled range for both channels, and use 5 Volts for both cases during measurement? I am a bit confused as you see 🙂
Of course, we could just use arrays for these min/max values instead of a single value pair, and set different ranges for the Create Channel VI. But now we have a problem. The low cost DAQ devices do not support different ranges (because they have a single ADC as much as I know), so we will get runtime error in this case.
When I faced the above problems, I just skipped using the Scaling VI: I acquire simply the raw voltage values, and I do the scaling on my own...
So these things make me think: would not it be more logical/intuitive if the min/max inputs of the DAQmx Create Channel.vi are always in pre-scaled units?? (in my case Volts). Why it was decided to use scaled range(s)?
Nevermind.....I see it in the help file. That seems really odd to me for some reason. I learn something new everyday on this forum. 
