I am trying to read thermocouples via SCXI chassis and SCXI 1100 mux. Using
the included thermocouple example with CW 2.0 I noticed that the resulting
temperatures are about 8 degrees too low.
Futher investigation shows that the example does not include binary offset
scaling (via CALGND channel), thus can not possibly be accurate for low
voltage signals like thermocoples. Labview 5.0 had a "scaling constant
tuner.vi" to account for this, but how is this done in CW???
I attempted to read binary values in from CALGND then add them to the raw
binary data from the thermocouple channels, then scale the data to volts
with the CWAIChannel.Scalemultiplier and CWAIChannel.ScaleOffset functions,
but this provided wildy innaccurat
e results.
Where/how do I add CALGND in this scaling function?
Interesting note: there is a function in the NIDAQ test panel (measurement
& automation neighborhood) that allows you to test an individual channel
directly. This too is innacurate for thermocouples until you click the
"advanced" tab then choose "Enable 0 mode Once at start". Once this is
chosen, the measurement becomes accurate. I assume that this provides a
function call to the CALGND channel. Thus NIDAQ supports it, Labview
supports it, but Component Works does not?
-michael annucci
Senior programmer/analyst
University of Florida
mike@energy.ufl.edu