Thermocouple problem with 6024E DAQ

[Computerman74]

Hey guys maybe you can help me out here. I set up a virtual channel for the
thermocouple and it works super
when I test it under the virtual channel setting, it's surprisingly stable
within .5 degrees which is more than expectable for what I am doing. Here is
the troubling part.
No mater what VI I use or I make The temp jumps around 3 to 5 degrees and is
erratic. I don't understand why it's so stable when I use the virtual channel
test interface.
Part of me thinks labview does this on purpose so you have to buy a signal
conditioner. ;o) I love labview, and they just love to sell stuff and I don't
blame them, but if the virtual channel test interface can read a stable temp
all day long then I would think there must be a way to stop
this without
conditioning. Any thoughts? BTW Thie same thing happens on two different PC's.
Thanks for the help guys.

[LesHammer]

How fast does it jump around?
Can you graph samples at, say 300 readings/second?
Does it look like 50/60 Hz line noise?

Les

[RIO-Todd]

Greetings,

Are you reading from the virtual channel in LabVIEW? You didn't mention this and so I'm wandering whether you are reading from the virtual channel in LabVIEW or if you are reading the voltage in LabVIEW and converting that to a temperature within LabVIEW.

If you're not reading from the virtual channel in LabVIEW, then I would suggest to try. You can simply open up a generic continuous analog input example in LabVIEW and rather than reading from a channel number in LabVIEW, read from the virtual channel name.

If you're reading from the virtual channel already in LabVIEW, then this does seem a little odd. What sampling rate are you using in LabVIEW? Or are you just reading one point at a time?

Let me know.

Regards,

Todd D.
NI Applicati
ons Engineer

[Computerman74]

>
>Are you reading from the virtual channel in LabVIEW? You didn't
>mention this and so I'm wandering whether you are reading from the
>virtual channel in LabVIEW or if you are reading the voltage in
>LabVIEW and converting that to a temperature within LabVIEW.
>
>If you're not reading from the virtual channel in LabVIEW, then I
>would suggest to try. You can simply open up a generic continuous
>analog input example in LabVIEW and rather than reading from a channel
>number in LabVIEW, read from the virtual channel name.
>
>If you're reading from the virtual channel already in LabVIEW, then
>this does seem a little odd. What sampling rate are you using in
>LabVIEW? Or are you just reading one point at a time?
>
>Let me know.
>
>Regards,
>
>Todd D.
>
NI Applications Engineer
>
>
>
>
>
>

Problem solved Thanks. Yes I was reading from the virtual channel. If I had
paid better attention I would have noticed that the Test panel in the virtual
channel setup says average value. The solution is to take an average. Here is
the Fix. Put the Sample Channel VI in a forloop. Out side the loop use add
array then connect to Divide symbol. Create a constant in the for loop N of
200. The divide constant must match this number. The higer the number the more
noise it removes. Basicly what you have here is a software signal conditioner
to a point. It works very well.
If you want to see the effects build a VI using random number Zero to one. Wire
a Control knob to the divide and forloop N.
Note that the zero to 1 stays with in a range of .4 to .6. Basicly it takes an
average.