USB-TC01 specification request for clarification

[Blokk]

Dear People,

We would like to clarify some accuracy data on temperature measurements carried out by using the USB-TC01 + J-type thermocouple.

We are just not sure how to use the given spec data to predict the available accuracy (and resolution) in the following scenario:

the sensor box is placed together with the J-type wire in a lab room, and the room temperature can vary between 20 and 25 Celsius degree. What is the reachable accuracy and resolution in this case (since the cold junction comp. circuit is "also in the room")?

By the way, we need to measure temperature in our experiment with at least 0.05 Celsius accuracy and the same resolution.

If USB-TC01 is not able to fulfil our needs, can you recommend us a different NI product(s)?

Thanks very much!

[PeterFoerster]

Hi,

you can look up the specs for the TC 01 here:

http://www.ni.com/pdf/manuals/372997a.pdf

With this data and the data of your Thermocouple you can calculate the accuracy.

Best regards,

[AnalogKid2DigitalMan · Accepted solution]

Standard thermocouple are typically accurate to only a couple degrees, what are the specs of your proposed J type?

EDIT: I would suggest using a Platinum RTD with a 4 wire connection as the sensor topology.

-AK2DM

[Blokk]

the thermocouple is also from NI (you can buy it together with the USB-TC01 "box").

But I think the "bottleneck" in resolution/accuracy is the cold junction compensation electronics, not the thermocouple?

I understand that, mostly people do not need high accuracy, but when we need, it could be nice from NI to offer an out-of-the_box  cheap/compact solution. Like a thermistor bridge built together with a precision voltage reference

I guess this such a thermistor bridge approach can definitely reach much better accuracy and resolution. But NI offer only very expensive hardware for such an assembly (PXIs, etc...).

I have found this for RTD platinum:

http://www.ni.com/pdf/products/us/3daqsc350-351.pdf

The accuracy is regarding the pdf spec file:

+- 0.3 + 0.005*T, so at room temp, the accuracy is about +-0.4 Celsius. Not enough. But for this, you need additional hardware to measure 3 or 4 wire resistivity.

Hmmm, maybe I am mixing again accuracy and resolution? 🙂 We could live with this accuracy, since in our case, the absolute value is not that important. The resolution what is really important.

I guess with an accurate resistivity measurement, we could reach even 1E-4 Celsius resolution? (if i remember well for a paper read some time ago...)