measuring temperature using thermocouple and scb-68

[andrew_JKTA]

Hi,

I am trying to measure temperature in the range of 0 to 100 degrees celsius and I have decided to use a thermocouple. I also have an SCB-68 and a PCI-6024E DAQ board.

I have heard that for thermocouples, a lot of signal conditioning has to be used. For example, CJC (which is built in in the SCB-68). Am I right?

Also, I have heard the signal has to be amplified and filtered etc...

Is there a DAQ board which has these built in signal conditioning functions required for thermocouple measurements because I was thinking of buying a new board anyway and I don't want to buy SCXI equipment for signal conditioning.

Is this all the equipment I will need? (thermocouple, scb-68 and DAQ board)

Thanks very much in advance,

Andrew

[vijayks]

Signal conditioners vary with applications such as level of amplification, the sampling frequency etc. Hence, it is a wise thing to buy a signal conditioner suited for your application seperately than to have it integrated on board.
Not sure if i am allowed to say this .. but signal conditioners are available from other companies too. But i OCCASIONALY find the NI ones to be more cost effective and easier to integrate into our applications .... (depends on how much of time and effort you are willing to put in )

Secondly, since you got the thermocouple and daq board just try to measure the temperature and see how much of a resolution you get inspite of noise... Follow the basics.. ground all connections properly, use differential connections...
Noise will prevent you getting a very accurate measurement. If you are measuring zero to 100 and you need a resolution of 1 degree then, i think you can survive with this existing setup...
vijay

[andrew_JKTA]

Hi,

Thanks very much for your swift reply

I am planning on buying a new E-type thermocouple and was wondering whether I should choose the grounded type or the ungrounded type. Is the grounded type better because I don't have to worry about common-ground voltage?

Also does this mean I can connect my thermocouple straight to the SCB-68 (with CJC enabled) and then to the PCI-6024E without linearizing and amplifying the signal?

Thanks again,

Andrew

[vijayks]

Grounded type seems to be more accurate and more sensitive. Also, i would like to know the sensitivity of your thermocouple. I see that it is typically 9uV/C (I didn't realise that it is so small, when i was posting you the last time... hence was contemplating on using it directly ;-)). It's not going to possible to measure straightaway with SCB-68. Definitely requires amplification & Signal conditioning. Try NI SCC-TC01/TC02 and see if that would suit your purpose... Else get a third party thermocouple signal conditioner (or if you have somethings lying around in the labs) and just feed the output of it as a normal voltage input into your SCB-68. The signal conditioner needs a Cold junction compensation, hence signal conditioers exclusively built for this should be used.
Not too complicated i guess !

vijay

[andrew_JKTA]

Thanks vijay,

So all I have to do is connect the thermocouple to the SCC-TC01 and then to the SCB-68 and then to the PCI-6024E?

I've just realised that I need to measure the temperature at four different points simultaneously. Does this mean I need four thermocouples and four SCC-TC01s since the SCC-TC01 has only one channel?

I also noticed that the specifications of the PCI-4065 and PCI-4070 specifically states that one of their measurements types is "thermocouple". Do I need one of these boards or is my PCI-6024E (which can only voltage) sufficient?

Thank you so much,

Very grateful for your help, (and sorry for my stupid questions, I'm a complete beginner to all this) haha

Andrew

[vijayks]

Hey Andrew

Same as you , i am beginner too ! i have my own set of stupid questions which i have been trying to exhaust, but keeps building up! So, no regrets !

4 thermocouples (at 4 different points) would mean 4 different channels. I wonder if NI has multiple channel signal conditioners.
Now, thinking more on this.. you could save on buying more signal conditioners if you multiplex your data reaching the signal conditioning stage... One advice is to create a new post with this issue as the header, let's see what others got to say. you can also call the product advisors and talk to them on this...

Good luck

Vijay

Message Edited by vijayks on 07-28-2007 04:20 PM

[andrew_JKTA]

Hi Vijay,

I did some more searching and I found the SCXI-1112 which seems to contain all the signal conditioning I need and it has eight channels. Although I wasn't too keen on purchasing SCXI products, I might have to give in and buy this (along with four thermocouples). What do you think?

Thank you very much for all the help you have given,

Regards,

Andrew

Message Edited by andrew_JKTA on 07-30-2007 04:54 AM