Suggestions for multiple thermocouples sampling

[KSagarN]

Hello,

I am in need of a system which can 1) sample 32 thermocouples, and 2) control 32 Thermo-electric coolers (TECs, Peltiers).

Bit of research:  

1) I was looking at the cDAQ systems, and there was this 16-Channel Thermocouple Input Module. Maybe I can by 2 of these.

It says "High-speed mode for up to 1,200 S/s(aggregate)", which I am assuming sum of all input sampling rate? Does this mean (1200/16) S/s/ch -> 75 S/s/ch when I use all 16 channels? If someone can clarify, cause I am a bit confused.

2) For the output, I was looking at this 16-Channel Analog Output Module. Would this work for controlling the TECs?

3) Is there a difference between the chassis? I have not worked with a cDAQ system before, but would I be able to sample multiple AI and output over multiple AO simultaneously with the system I drafted above?  

I would be thankful for any clarification, or for any suggestions for a better system.

Thanks,

Sagar 

[Brandon_B]

Hello Saqar,

Thank you for using NI forums.  You are correct that the sampling rate is proportional to the number of samples taken.  This is due to the single ADC on the DAQ card which means that the channels are running in a multiplexed mode.  Thermocouples generally aren't sampled at a very fast rate to begin with so this shouldn't be much of a problem.  As far as the analog output module goes, I'm not too familiar with TEC's, but if you look at the specs for the 9264 the card is capable of outputting +/- 10V with a current drive of up to +/- 4mA per channel.  So if this is enough to drive the TEC (which I'm assuming it should be) then the 9264 should work.

You are in luck because we just released our new cDAQ 2 chassis.  Unlike the original cDAQ chassis (9172), which only had 1 analog input timing engine and 2 counters, the cDAQ-9174 and cDAQ-9178 have three analog input timing engines as well as 4 counters.  This meant that with the original chassis you could put all your AI channels in one task, but they would all have to operate at the same sampling rate with the same number of samples taken.  The new chassis allows you to split your AI channels into three different tasks, if necessary, so that you can operate at three different sampling rates.  You also have an AO, DI, and DO timing engine as well with the new chassis.  With the current application you have now, you are looking at using 4 modules already, and these are all analog modules.  The 9174 is a 4 slot chassis, which doesn't allow for any expansion if your application were to grow.  I would recommend going towards the 9178, which has 8 slots just in case you ever did decide that you wanted to add more modules.  I hope this helps and please let me know if you have any further questions.

Regards,

Message Edited by B.E.Z. on 10-07-2009 07:01 PM