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Measuring thermocouple temperature with PCI 7030/6040E DAQ card
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09-02-2002 10:52 AM
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Hello,
I am using the PCI 7030/6040E DAQ real-time card to acquire the temperature of two K-type thermocouple.
I have use MAX to configure two virtual input channels and set the CJC to 25 Deg. I have also connected a resistor of 50K bet the AIGND and the negative input channel(i.e channel 8 and 9).
However, when I run my VI, the temperature acquired from both the identical thermocouple is different by 4 to 5 deg. In certain time, the thermocouples also give incorrect reading. What could be the common problems.
When I test the virtual channels I configured in MAX, an error (error 10401) occurred, but, I am still able to run my VI with the virtual channels' name. And the virtual channels icon under
the Data Neighbourhood do not show crosses. Is this the cause of the inaccurary readings? How can such problems be solved?
I have modified the Thermocouple Measurement.VI downloaded form the website. In this VI, the AI Acquire Waveform.VI is being used. What should be the number of sample of input to be entered, inorder for the response of the temperature acquiring process to be real-time? I am currently using 10 samples for the number of samples input of the VI, and it take quite a while to see the changes of the temperature.
Why is it that, even there is no contact with the thermocouple, the temperature acquired each time is different?
I don't not used any SCXI or SCC devices, can i accuracy acquired temp without the help of these device. What is the main purpose of these devices?
Thanks
I am using the PCI 7030/6040E DAQ real-time card to acquire the temperature of two K-type thermocouple.
I have use MAX to configure two virtual input channels and set the CJC to 25 Deg. I have also connected a resistor of 50K bet the AIGND and the negative input channel(i.e channel 8 and 9).
However, when I run my VI, the temperature acquired from both the identical thermocouple is different by 4 to 5 deg. In certain time, the thermocouples also give incorrect reading. What could be the common problems.
When I test the virtual channels I configured in MAX, an error (error 10401) occurred, but, I am still able to run my VI with the virtual channels' name. And the virtual channels icon under
the Data Neighbourhood do not show crosses. Is this the cause of the inaccurary readings? How can such problems be solved?
I have modified the Thermocouple Measurement.VI downloaded form the website. In this VI, the AI Acquire Waveform.VI is being used. What should be the number of sample of input to be entered, inorder for the response of the temperature acquiring process to be real-time? I am currently using 10 samples for the number of samples input of the VI, and it take quite a while to see the changes of the temperature.
Why is it that, even there is no contact with the thermocouple, the temperature acquired each time is different?
I don't not used any SCXI or SCC devices, can i accuracy acquired temp without the help of these device. What is the main purpose of these devices?
Thanks
JeffBoettcher
Active Participant
09-03-2002 08:14 AM
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To resolve the problem of differing values between the channels, you might try a lower resistance resistor connecting channels 8 & 9 to AIGND, perhaps 1kOhm.
As for testing the virtual channels in MAX and getting the -10401 error, this is normal. Your Windows PC (and therefore MAX) cannot communicate with the DAQ board that is attached to a 7030 RT board. The only way you can communicate with it is to run LabVIEW code while targetted to the RT board, as you have mentioned *does* run without the -10401 error.
Another thing that might be causing your reading discrepencies is the range of the signal. The DAQ board you have is a RT-Series 12-bit DAQ board, designed for input ranges of -10V to 10V. It does have configurable input gains that will amplify the signa
l up to -50mV to 50mV and still be at full A->D range. In many cases, it is helpful to apply more gain than the DAQ board alone offers. Filtering is sometimes also useful. These are a few of the common functions of SCXI or SCC. Also important is that if your computer isn't right next to your measurement point, it is better to apply gain near the measurement and then send the signal back to the DAQ board, otherwise when your thermocouple leads pick up ambient noise, it is also amplified at the DAQ board. You might also check the shielding within each thermocouple.
One final note, the only part of this question that was *Real-Time* DAQ related was the -10401 error, which I believe I explained. You would get a larger audience and possibly more suggestions for solution if you posted in the general Data Acquisition group.
As for testing the virtual channels in MAX and getting the -10401 error, this is normal. Your Windows PC (and therefore MAX) cannot communicate with the DAQ board that is attached to a 7030 RT board. The only way you can communicate with it is to run LabVIEW code while targetted to the RT board, as you have mentioned *does* run without the -10401 error.
Another thing that might be causing your reading discrepencies is the range of the signal. The DAQ board you have is a RT-Series 12-bit DAQ board, designed for input ranges of -10V to 10V. It does have configurable input gains that will amplify the signa
l up to -50mV to 50mV and still be at full A->D range. In many cases, it is helpful to apply more gain than the DAQ board alone offers. Filtering is sometimes also useful. These are a few of the common functions of SCXI or SCC. Also important is that if your computer isn't right next to your measurement point, it is better to apply gain near the measurement and then send the signal back to the DAQ board, otherwise when your thermocouple leads pick up ambient noise, it is also amplified at the DAQ board. You might also check the shielding within each thermocouple.
One final note, the only part of this question that was *Real-Time* DAQ related was the -10401 error, which I believe I explained. You would get a larger audience and possibly more suggestions for solution if you posted in the general Data Acquisition group.
