DAQ Assistant does not output scaled values

[John_Easton]

Hello all - 

Potentially stupid question, but here goes: I'm using the DAQ Assistant to read in 4 analog input voltages, continuous sampling acquiring 1 data point at 10 Hz, using LabView 12 on a machine with a simulated USB-6341 DAQ device (because my office is more comfortable than the lab!). I want to scale the first two signals from voltage to temperature and relative humidity, respectively. I used the "Create New . . . " from the "Custom Scaling" pull down in "Voltage Input Setup" tab for each of these channels, named and gave the slope and intercept for the respective linear scalings, and hit OK.

When I test the code - and again, I'm not on a machine with a "real" DAQ system, I'm using a simulated device, and it looks like NI MAX generates a long period sine wave with some noise on top for this purpose - I do not get the scaled results from my "signal", I get the raw voltage. (If you run my code, which I'll attach, Relative Humidity should range from 0 to 100 and temperature from -40 to 60, not 0 to 5, for example.) 

So, what's going on? Is there some flag or setting I missed? Will the scaling only work on "real" voltage data from a "real" DAQ instrument, instead of a simulated one (which is why I've mentioned it twice!)? Do I need to do something in NI MAX as well as Labview?

Thanks for any help you can give.

John Easton

[JKMM · Accepted solution]

Simulated devices will not respond to custom scaling.  They are just meant to allow you to configure your device without errors when you don't have the device on hand.

 "NI-DAQmx simulated devices create a noisy sine wave for all analog input channels. Configuration of other simulated data is not available at this time."  

http://www.ni.com/white-paper/3698/en

They generate a sine with an amplitude equal to half of your specified input range.  If you want to work with simulated data that would be more realistic to your application, you could write a VI to generate the data and have a case structure to handle both the "simulated" and "real" cases, so you could switch back and forth depending on whether you have access to the hardware.

I just verified all of this with a PCI-6254 I have installed, and a simulated PCI-6254.

[John_Easton]

Thanks for the help! I had a feeling that was what was going on.