DAQ assistant scaled output limits

[Clueless114]

I tried to use the DAQ assistant function to acquire voltages and use the y=mx+b function to put my output in real units (psi) and it truncated anything above about 1500psi on the output. Full scale was 100,000 psi so needless to say most of my data was truncated. This seems like a pretty restrictive limition on scaled output values am I doing something wrong? My m value was 14286 and y=0.

Perry

[ryan_d]

Hi Perry,

It looks like you’ve set up your scale correctly. One thing that I can suggest is that you check your input voltage to make sure that value is expected. If you’re unable to exceed 1500 psi it might be because your signal never goes much above 100 mV. If your scaling still looks correct, please post back with information about your DAQ card, any drivers that your using, and anything else you think might be pertinent.

[Clueless114]

It is a USB-6259 with the mass terminal option with a breakout box. The input is set to +-10V and it does the same thing if I hook one of the 5V lines to the input channel. When I am not scaling the data everything is fine. I am also using the write to file assistant so that could be truncating something as well. I am using Labview 7.1 with Nidaqmx.

Perry

[ryan_d]

Hi Perry,

I’d like to narrow down what part of your application is causing this problem.  From what I can deduce from your posts, I believe the problem is either with how you are setting up the scale or with how you write to a measurement file.  Are you reading the data from the file or from a graphical display in LabVIEW to determine that your values are being truncated?

When you say, “When I am not scaling the data everything is fine” do you mean that you’re able to get valid voltage readings in LabVIEW or from a voltmeter? What range of voltages are you reading? Have you tried creating a new scale to see if you can get some valid readings?

When you say, “write to file assistant” do you mean the Write LabVIEW Measurement File Express VI? There aren’t any parameters to limit data precision. Could it possibly be the Write to Spreadsheet File.vi? This VI has a formatting string which could cause your data to be changed. The format specifier syntax can be found in the LabVIEW Help under Grouping Data Using Strings, Arrays, and Clusters » Strings » Format Specifier Syntax.

Let me know if this helps! 

Message Edited by ryan_d on 10-01-2007 06:16 PM