02-14-2013 10:56 AM
My main goal is to acquire Temperature data from miliVots by using my the DAQmx for capturing the data and I suppose the thermo linear module to change the miliVolts to Temperature .If you look inside the Themo Linear module it says that it needs the voltage to be in microVolt (1000 miliVolt).
1b) Do I need to change my miliVolts to Volts and then put it inside the thermolinear module? Or do I need to change my miliVolts to microVolts and then to the module?Or I can just let them be miliVolts and LabView will do all the work for me using the thermolinear module
2b) Does the Cold Junction Voltage needs to be in miliVolts, microVolts or Volts?
Thank you
Alex
02-15-2013 01:55 PM
Alex,
In the future these questions are better suited for our Multifunction DAQ Forum.
First of all what the model numbers of the NI hardware you are using? I suspect you may be using an SCXI module and the following Knowledge Base article may be of use to you.
02-19-2013 09:58 AM
Dear Isaac,
I am really sorry for late response as I was not in the office.
I am using a DAQ card 6024E with labview 2012. For testing I have put a CB 68LP terminal block which I have grounded for having 0 V thus when running my labview vi to have the cold junction temperature of my thermocouple (25C=1mV -> 0.001 for type K thermocouples)
But when we will do the real testing normaly the volatage I get from my thermocouples (inside the gasifier) is in mV with an offset and a intensification for all the different channels ( I have 8 thermocouples each one has it's own offset and intensifications)
The questions is:
Do I have to change the mV I get from my thermocouples in Volts (/1000) and then pass it from the thermo linear module?
Should be the the CJV constant of the themo linear module be in Volts or mV?
Another solution to this problem will be to use the DAQAssistant but everytime when LabView finish the set-up of the module and does the building vi process I get the error
"LabVIEW Code Generation failed to execute. This may occur if the code gen engine is not properly installed, or if you are using a LabVIEW version under development"
I have updated my drivers and re-install LabView and I am still getting the same error
I will really appreciate your help on those matters
Kind Regards
Alex
02-20-2013 01:21 AM
Dear Isaac
Do you know also how it is possible to move the discussion in the Multifunction DAQ Forum. as you suggested?
Kind Regards
Alex
02-21-2013 12:00 PM
Having a thermocouple reading in mV is common. However, the Convert Thermocouple Reading.vi you are takling about expects a voltage from a CJC sensor (Integrated Circuit) between the thermocouple and the data acquisition device. The CB-68L terminal block does not perform any cold junction compensation as it is only a breakout screw terminal and has no additional circuitry built in. The varying offsets are likely a result of other signal conditioning needed. The previous link I provided discussed modules that perform this signal conditioning for thermocouples however I do not believe they are compatible with the NI-6024E. The SCB-68 has cold junction compensation however it would not be able to read 8 thermocouples. We sell devices specifically designed for thermouple reading with signal conditioning included that can be configured simply in a DAQmx Task.
However, if you wish to use the NI-6024E with the CB-68L, more than likley you would need to create circuitry to amplify the mV signal to Volts (gain 1000) and perform signal condtioning since you would be acquiring from the analog input channels. Below are additional links relevant to cold junction compensation.
As far as moving this discussion to the other forum, I am unable to do that. However, if you desire to create a new post there you can reference this discussion.