09-21-2014 12:22 AM
Hi,
I am trying to use myDAQ to realize both temperature measurement and digital output.
By reading this page I have learned that how I can create a task for temperature measurement using thermocouple with a certain NI device.
http://www.ni.com/white-paper/14338/en/
What I found to be really interesting is that when I create a task for myDAQ temperature measurement using a thermocouple when my NI myDAQ is connected with my PC, two AI ports ai0 and ai1 both appears in the create task window!!
I never found any information from NI myDAQ manual that "AI0 and AI1" can be connected directly with a thermocouple to measure temperature without using additional conditioning system. But this window suggests that myDAQ can be used in this way, is it?
I am still trying to do it this way, and I'll post some results here again.
I would be really appreciate if anyone could confirm or disprove my guess. Thank you.
PS:
Attached is the
09-21-2014 12:24 AM
Attached is the screenshots for "create new task" in NI MAX
10-09-2014 11:50 AM
I would guess the myDAQ uses comparable hardware to the USB-6008 and USB-6009. If this is true, you might want to take a look at this:
http://digital.ni.com/public.nsf/allkb/8166630BD6965EEA86256FDD0052E89C
You generally want to look at hardware that is geared towards this particular measurement.
10-09-2014 03:39 PM
Thank you for your reply.
I actually have a 9213 to do thermocouple measurments. I just want to know, if thermocouples can be connected directly to NI myDAQ it will be pretty convinient for me to make prototypes.
10-12-2014 08:23 PM
myDAQ spec sheet: http://sukjaro.eu/ELFT-NI-palyazat/myDAQ_Manual.pdf Look at page 36. You'll see the ADC is a 16-bit ADC. You'll also see there are only two input ranges for AI on the myDAQ: +/- 10V and +/- 2V. This means the +/- 2V range would offer the highest resolution for you.
4V/(2^16) = or 61uV That's larger than the voltage response of a thermocouple. If you look at the absolute accuracy, you're looking at +/- 4.9mV for the +/- 2V range of the myDAQ. 4.9mV is 4900uV. If the accuracy is only useful within 4900uV and you need a voltage response 56uV or less, you're using a tool that isn't well fit for the job.
Can they be connected directly? Sure. But, I definitely wouldn't suggest it. 4900 is 87.5 times 56. That's a pretty big jump and could lead to some inaccurate readings.