Thermocouple Readings from CRIO

[hkhiroya]

Hi,

I am fairly new to working with Compact RIO and I am having problems with thermocouples that I have connected. My setup has two thermocouple modules, the NI 9213 and NI 9211.

I have connected a Type K thermocouple (one each) to both of the units. I have used the FPGA Target vi to read from the Thermocouple channels together with the CJC and Autozero values of both the modules. I also have CRIO vi that references the FPGA vi and then uses the values and feeds them to the "Convert Voltage to Temperature.vi". I have attached screenshots of both the vi's.

The problem is the output I am receiving is -2 or 1 degree. When I touch the thermocouple the value increses to around 5 or 8 degrees.  The room temperature is around 24 degrees.

Can someone please help with where I am going wrong.

regards

Harshil.

[jkurtw]

Hi Harshil,

Which cRIO controller and back plane are you using? As long as you don't have a 9002 or 9004, then you can get away without programming the FPGA with CompactRIO Scan Mode, which will calibrate and scale your temperature channels for you.

If you have a chassis that only has a 1M gate FPGA, you can still use scan mode for your TC modules, see this KB:

http://digital.ni.com/public.nsf/allkb/122E971F52FD081A86257500007A046C?OpenDocument 

Using CompactRIO Scan Mode with LabVIEW: 

http://zone.ni.com/devzone/cda/tut/p/id/7338 

Kurt 

[hkhiroya]

Hi,

Thanks for the reply.

I have the cRIO-9073 chassis. 

Do I still have to use the scan mode? 

regards

Harshil.

[Ruhmann]

What version of LabVIEW are you using?  What is the name of the VI that you are using to linearize the data and convert it to Celsius on the crio controller?  There are two versions.  One that takes calibrated data and one that takes raw, integer data.  Make sure you are using the calibrated data version.  Looking at the examples for the modules should help.

[hkhiroya]

Hi,

I am using LabView 8.6. The VI I am using is called "Convert Thermocouple Reading" which is under numeric -> scaling.

Does the above VI take calibrated or raw data?

regards

Harshil 

[Ruhmann · Accepted solution]

Yeah, that's the wrong VI to use with CompactRIO.  I'm not 100% sure why that won't work, but I do know that the scaling VI you're using was designed to be used with NI-DAQ, not CompactRIO.  Please open up the examples for your modules to see the correct way to scale CompactRIO thermocouple data.  I hope those scaling methods will work for you.  You should find the examples here:

C:\Program Files\National Instruments\LabVIEW 8.6\examples\CompactRIO\Module Specific\

That's about the best advice I can give you, unfortunately.  If you need more detailed help, maybe someone else on the forum knows more than I do about scaling cRIO thermocouple data into degrees celsius.

[felipetortato]

Hi, Can you help me?

I have to read the thermocouples from a cRIO and I want to know if I have to use FPGA or Scan mode or if I can get it running Labview on PC. Can you answer me?

Thanks.