single-point calibration with thermocouples in SignalExpress?

[JoshB]

I have a USB-6251 DAQ that I'm using with SignalExpress to measure some J-type thermocouples.  I'm looking to calibrate them, but it appears that I have to do a multi-point (>2 points) calibration.

Since the range that I care about is relatively close to 0C and I'm not too worried about a super-precise calibration, I'd just like to do a simple single-point calibration in an ice bath to remove the offset error.  Is this possible?  When I use the calibrate wizard in SignalExpress, it requires at least two points.

Furthermore, it appears that it won't extrapolate beyond those two points, so even if I just use an ice bath and a bath of water at room temperature (taking the calibration value from another digital thermometer that has been calibrated), it will clip the values to that range.  Very unhelpful.  Can I get around this?

Thanks,

Josh

PS  Sorry for cross-posting this in the LabView discussion board initially.  I didn't see that there was a SignalExpress board.

[Corby_B]

Hello JoshB,

Thanks for your post!

I was looking more into your question about only taking a single point calibration instead of a two point. Unfortunately you will have to take a two point calibration in Signal Express for this to work. It calibrates similar to how you would make a custom scale. It needs at least two different points to make this calibration so that there is a slope to calibrate to. So what you could do instead of calibrate is simply view the error in the calibration wizard on step 3 where it tells you the difference and then programmatically compensate for the error. There is a formula function in signal express that you can use to calculate this offset and program the difference.  You mention that it does not need to be super-precise so perhaps a software compensation will work for your application. If you have LabVIEW you can also do some calibration using VI's. see the following:

Thermocouple Calibration with System Calibration VI's
http://zone.ni.com/devzone/cda/epd/p/id/3157

Please post back if you have any other questions.

Cheers!

Corby_B
http://www.ni.com/support