scxi-1300/scxi-1303

[andrew_JKTA]

Hi,

I have a SCXI-1600 DAQ control module (USB) connected in my SCXI-1000 chassis. Next to the SCXI-1600 I also have:

1.SCXI-1102 module with a SCXI-1303 terminal block connected to it

2.SCXI-1581 module with a SCXI-1300 terminal block connected to it

The function of the SCXI-1303 is to minimise errors caused by thermogradients whereas the function of the SCXI-1300 is for cold junction compensation.

I am trying to take thermocouple readings but since there is only one thermocouple, how can I connect them to BOTH the SCXI-1300 for CJC AND the SCXI-1303 to minimise errors?

To put it simple, I would like my thermocouple reading to go through both modules for signal conditioning

Hopefully not too confusing and sorry if it is a really simple question. You can probably tell I'm a beginner to all this 😄

Thank you very very very much,

Andrew

Message Edited by andrew_JKTA on 09-13-2007 06:02 AM

[Russ@Davis]

I don't know whether to say you 'can't' or 'shouldn't!

The nature of thermocouples, you are introducing errors by connecting the TC to more than one device.

I would have to pull some manuals, but double check the SCXI-1102 module.  I believe one of the modules has the ability to indicate CJ.  You have to read that channel along with the channel the TC is connected and apply the correction programmatically.

I would also have to question the required accuracies that you need to apply both types of correction.  It sounds like you are trying to beat the inherit error of the the TC's

[AdamB]

Hi there,

Thanks for using the NI forums!

I would have to agree with Russ.  I think a better plan of action is to oversample the thermocouple and average over say 10 values.  This would be a much better approach to increasing accuracy.

All you are really doing by connecting to 2 different modules is introducing twice as much metal interface errors (usually overcome by a CJC).

What kind of accuracies are you expecting to get?

Thanks

AdamB

[andrew_JKTA]

Hi,

Thanks for the replies, I've just realised i don't need the scxi 1581 current excitation module because i am using thermocouples. So now all I have to do is connect the thermocouple to scxi 1303 and then to scxi 1102 and then let the scxi 1600 (which is next to the 1102 in the chassis) digitize the data?

Do I need to ground the thermocouple? It is the NI ready made E-Type Thermocouple Wire (Fibreglass).

Also, I found a lookup table for E-type thermocouples here:

http://www.dataforth.com/catalog/pdf/an107.pdf

Does this table also apply for the thermocouple I am using?

Thank you all so much !! 😄

Andrew

[AdamB]

Hi there,

You don't need to ground the signal it should work fine without it. 

The best thing to do in MAX is to set up the task as a Thermocouple task.  If you do this and set the thermocouple type as E type, then the driver will actually set up the appropriate lookup table so the information you see in the calling programming language will be the realworld temperature.  So no need for the lookup table.

I hope this answers your questions.

Feel free to post back if you have anymore.  I'm here all day

AdamB

[andrew_JKTA]

Thanks very much!

I have another question haha:

As I mentioned before, I have a SCXI-1600 USB DAQ module, a SCXI-1102 Module and a SCXI-1303 terminal block. Do I connect all of these to the chassis before turning on the power and connecting to the PC or do I install the DAQ module only before adding the other modules?

I read "DAQ Getting Started Guide" and "SCXI Quick Start Guide". The former seems to say install the DAQ first whereas the latter seems to say add all the modules and terminal blocks before powering on but it does however mention that I should only do this if my system already has a controller established. What does this mean and which installation order should I follow?

Thank you once again for your time.

Andrew

[JamesC]

Hi Andrew,

Those manuals were written before the SCXI-1600 was released, when you used to have to have a PXI or PCI DAQ device in your computer.

Now you can just add all your modules to the chassis, and then turn on your chassis and connect the USB cable to the PC and let Windows find the DAQ device (Add New Hardware). At this point you can do into MAX and add the SCXI-1000 chassis that you have.

Regards
JamesC
NIUK and Ireland