Can I make a simple voltage recording when SCB-68 is configured for Cold Junction Compensation?

[User_1979]

Hi everyone,

I am using a 6221 PCI card and SCB-68 connection module. I have set the SCB-68 module switches so that the 5 thermocouples I have connected between AI1 and AI5 are using the Cold Junction Compensation of AI0. Everything works fine.

Could someone tell me if the differential inputs left AI6 and AI7 can be used for recording another kind of sensor (nothing to do with a thermocouple) ? I suppose I just need to set those 2 inputs to a simple voltage recording function? The previous switches settings enable to do this simple recording ?

Thanks,

User

[BruceAmmons · Accepted solution]

You can read whatever signals you want on the remaining channels.  Be careful, though.  If you scan at a high rate, the thermocouple inputs will not have time to settle.  Changing gains and ranges can mess you up, also.  One time I had to scan a shorted channel (either a jumper or an internal channel) to clear the inputs before switching to the thermocouples.  Adding "blank" channels to your scan list can do wonders.  You might want to read the manual to find out the scan order of the channels - I remember old E series cards scanned in reverse order sometimes.

Bruce

[User_1979]

Hi Bruce,

Thanks for your answer and your advice. So I will use my free channels for other sensors. 

Concerning your other remarks , I have planned setting the DAQ assitant at 100 samples and 1KHz for the thermocuples. Making an average of the 100 samples for each channel gives a good result from what I have seen in my last test. After this, with another DAQ assistant I am making some other kind of recording at another speed. I know this is not optimized using DAQ Assistant but loss of time and simultanity isn't a problem for me in this project.

However if I had used only one DAQ Assistant for my thermocouples and for the other sensors, a part from the rate vs thermocouples problem, not having the same ranges could have been a problem?

I also don't understand the channel order you mentioned. Still using a DAQ Assistant in what way would this effetc the measures?

[BruceAmmons]

Your plan sounds pretty good.  Just scanning thermocouples makes your readings pretty good.  It is when you combine scanning thermocouples and other channels that there are potential problems.  You might see the first couple of thermocouples reading several degrees higher than expected due to lack of settling time.  I experienced this at high scan rates (probably 10 kHz) with a lot of channels.  Since you seperated your channels, you should be fine.

Bruce

[User_1979]

Ok fine. Thanks again for your explanation and your time!

Regards,

User