USB NI-DAQ Thermocouple Measurements

[rattofest]

Hi,

I'm a newbie to NI-DAQ, and I am trying to make thermocouple measurements while also monitoring a DC voltage. I currently have the NI USB-6251 Multifunction DAQ, and am planning on purchasing some NI field-cuttable thermocouples.

What additional hardware do I need? Also, what software solutions are there for cold-junction compensation and filtering? I am currently using LabVIEW 7.1; are there any VI's that help me with signal conditioning?

Thank you.

[McKala[DE]]

Hello rattofest,

In hardware there are a couple solutions.  Did you purchase the mass termination version of the USB-6251?  There are CJC sensors in the SCB-68 and there are signal conditioning modules such as the SCC-TC02 that you can plug into the SC-2345 carriers or the SCC-68.  If you have the mass termination version, you'll want a cable to connect to your connector block, a connector block with a built in CJC, like the SCB-68 or a carrier such as the SC-2345 or SCC-68 with SCC-TC02 modules. 

In software you can apply a constant CJC value, which is the temperate of the CJC to a DAQmx task.  The shipping example Acq Thermocouple Sample VI is probably a good starting place for you. 

Let us know if you have any further questions,
Micaela

[immi]

Hi,

Recetly I purchased USB 6251 and SC 2345 but later I have noticed that I can't use SC 2345 with USB 6251 (terminal block). This all happned becasue the product website did not mention clearly the difference beteween mass termination and connector block etc. Well, Is there still a way to use SC 2345 with USB 6251 with connector block by means of some cables connectors readily available at NI. Hope someone of you have some decent solution to this problem.:mansad:

immi

Message Edited by immi on 04-21-2007 03:29 AM

[Matt_A]

Hello immi,

Do you know how long ago you purchased these products? National Instruments offers a 30-day return/exchange policy, so if it was within that period you should be able to exchange your NI USB-6251 Screw Terminal for an NI USB-6251 Mass Termination. If you contact our Sales department and reference your order number, they should be able to tell you if your products are eligible for exchange.

[immi]

Hi Matt,

Thank you very much for the reply. I am afraid, Its now more than a month that this product was received by our company and I received it few days back from my company store house. I understand now, there is no other way except placing a new order...:mansad:

Anyway many thanks for your kind reply

immi

Message Edited by immi on 04-24-2007 12:14 AM

[Matt_A]

Hello immi,

It may also be worthwhile to contact your local National Instruments Field Sales Engineer to discuss your options with them. If you do not know who your local representative is, you can post your zip code to this forum and I can look it up for you.

[VBK]

hello friends

I am thinking of using NI  USB based data acquisition system(NI USB 6255 or 6259) for temperature measurement application.

Temperature sesors will be thermistors. is there any need for separate signal conditioning apparatus like amplifier, filter etc.? For USB based devices whether we can have inbuilt excitation supply the one which will be used to calculate change in resistance in terms of voltage.?

[Matt_A]

Hello VBK,

Based on the specifications you described I would recommend that you consider the NI USB-6255 M Series Mass Term U.S. (120V) with an SCC-68 I/O Connector with 4 SCC Module Slots and an SCC-RTD01 RTD Input module. 

If you have more configuration questions I would recommend that you contact us directly. Our representatives will be more than happy to help you configure your measurement system and give you pricing and availability information. This webpage will give provide you with more information about how to contact us.

[VBK]

Can you help me in clarifying the concept of accuracy/interchangeability specifications associated with a thermistors/RTD's

they are mentioned as Ro plus minus 0.06%. What is a meaning of that?

Even OMEGA make themistors have two such specifications  (0.1C & 0.2 C on both sides) alongwith various temperature range.

Vaibhav

Please see the link for more information

http://www.omega.com/Temperature/pdf/44000_THERMIS_ELEMENTS.pdf

[Matt_A]

Hello Vaibhav,

I do not see where R0 is listed in the document you linked, but it would seem to me that the accuracy/interchangeability is listed in both temperature and resistance. So, R0 is likely to be the resistance of the thermistor at room temperature. The document you provided states the following:

"The accuracy specification of ±0.1% or 0.2% means
that each thermistor’s resistance will fall within these
limits between 0 and 70°C (32 and 158°F).
Table 2 illustrates the interchangeability values for the
model numbers 44004 (±0.2°C) and 44033 (±0.1°C) at
a number of temperatures."



I also attached the document which shows these values. Is there anything specific that is confusing about these documents?

Message Edited by Matt A on 09-17-2007 07:59 PM