LabView 7.1, FieldPoint FP-AI-100, VI shows different values than NI-MAX

[suamikim]

Hi,

In my VI i'm reading values from an analog FieldPoint-Module (AI-100). Now i've just figured out, that the values of 3 of the 5 read channels do not correspond to the values Measurement and automation explorer shows.

Because i wasn't sure, if there is a problem in my whole program, i just wrote a small test-VI, which showed the same results. The following screenshot shows the VI of the small program and i think it demonstrates the problem i'm facing:



The values for "Lufttemperatur" and "Luftfeuchtigkeit" should be all right (even though there is a little deviance at the "Luftfeuchtigkeit").
The values für "Zylinder-", "Versorungs-" and "Absolutluftdruck" do all not match (deviance between about 0.2 and 0.5 bar).

I hope, someone can help with this weired problem!

Thanks, mik

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edit:
After a little testing i figured out, that the shown values in my VI and in MAX only correspond to 100 %, when i switch off the scaling in MAX (Scale -> Disable).
Does anybody know this problem? To me it really looks like a bug, but i'm open to let me teach better!

[Andre_Saller]

Hello,

I have a guess:

the difference between the channels that work and that don´t is in the scalling. The ones that work fine use integer values for the scaling, those who don´t have floating point values in their scaling. It must have something to do with the decimal point.

I made some calculations that could prove this:

For example the channel "Versorgungsdruck": You can calculate the raw data backwards from the value shown in MAX:

x=(y+6.25)/1562.5=(6.900034+6.25)/1562.5=0,00841602176

Now we asume that because of an error, in LabVIEW the values behind the decimal point are ignored by LabVIEW, and we calculate the Y-Value again:

y=(1262*x)-6=(1562*0,00841602176)-6=7,14582598912

Here you go! Exactly what you see in LabVIEW.

So the value is calculated by LabVIEW in a different way then in MAX, because of LabVIEW ignoring all values BEHIND the decimal point, which can only mean that the decimal point settings don´t match.

You are using "Use localized decimalpoint" in LabVIEW (Can be seen on the frontpanel, as the decimal point is a comma instead of a dot). Try switching this option off (Menu: Tools->Options->Front Panel->Use localized decimal point)

remember that you have to restart LabVIEW, so that the cange takes effect.

Hope this helps!

André

Message Edited by Andre_Saller on 07-25-2007 03:06 AM

Message Edited by Andre_Saller on 07-25-2007 03:07 AM