05-05-2014 03:54 PM
Hello All
I have a problem with what appears to be static electricity induced noise on thermocouples.
We are testing with a sand like medium flowing across a plexiglass window and measuring temperature in the flow. The interaction of the air/sand mixture flowing across the plexiglass creates a significant amount of static and our thermocouple readings are severly impacted. Is there a way to filter the signal so my data and signal analysis tools ignore obvious off-scale readings ?
The filtering i see seems to only apply to high freqency noise. I would like to trim the signals from the TCs to ignore any measurements above 700DegF and below 32Degf.
Thank you
Solved! Go to Solution.
05-06-2014 10:02 AM
Hi AeroEng,
It might be helpful to see what the current state of your acquisition VI is - just to get an idea of your overall architecture. I can think of a couple of alternatives.
Hopefully this helps!
05-06-2014 10:14 AM
Thanks Xavier
I was headed down the path of the coerce function but i wanted to make sure that there was not a simpler way to alleviate the issue.
I thought that in NI-MAX one could limit the range of the measured signal. It seems to work with other analog measurements that the range that is set in the task, sets the limits of the measured signal.
thanks
Peter
05-07-2014 02:45 PM
AeroEng,
You are completely correct - that is another alternative way. A higher voltage seen on the 6225's input will be clipped at its maximum value. However, you will need to know which voltage on your thermocouple leads is associated with your desired limits and select the appropriate input range accordingly. You also will only have a couple of options (from it's specifications page, the 6225 has ±10V, ±5V, ±1V and ±0.2V as possible ranges - any other selection for Max and Min will coerce to one of these values) so you might clip too much or not enough of your undesired signal.
As I said, there are various methods to achieve what you are looking for. Another one (which would give you more custom control over the behavior of your data) could be to use a custom scale that deals explicitly with values that are over a certain threshold (http://digital.ni.com/public.nsf/allkb/0464919A11C092E386256D800079C3BB).
Hope it helps!
05-07-2014 04:16 PM
Myself, I would try to dissipate the static charge. It can't be good for the equipment...