Add _boardTempSensor_vs_aignd to existing task

[Taki1999]

Is there a way for me to create a virtual channel for Devx/_boardTempSensor_vs_aignd?  If I try to do this in MAX, I only get the option of using channels ai0-15.  I can create the virtual channel in LV using Create Virtual Channel but when I try to add additional channels to the task using DAQmx Create Task, I get an error for the task not existing in MAX.

The device is a PXI 6250 and I'm trying to read the onboard temperature sensor along with some other analog in voltages.  Data collection of the analog in voltages should be continuous so stopping and starting the task isn't really an option.

Any help would be greatly appreciated.

[Corby_B]

Hello Taki1999

Thanks for your post!

I see that you need to create a virtual channel for the CJC or board Temp Sensor on your 6250. Usually the creation of the Global Virtual Channel is done in Measurement and Automation Explorer (MAX). You can do this by right clicking on the data neighborhood in MAX and selecting create new. This will give you an option to create a global virtual channel. Let me know if this clears up your questions and errors!

Cheers!

Corby_B

http://www.ni.com/support 

[Taki1999]

Thanks for the response Corby.

However, my problem is still not solved.  I am not allowed to select Devx/_boardTempSensor_vs_aignd from the Create Global Virtual Channel dialog in MAX.   It appears that I'm only allowed to create a virtual channel for the EXTERNAL physical channels.  _boardTempSensor_vs_aignd is an INTERNAL channel.

I can access the internal channels from the Test Panel in MAX but I cannot create a virtual channel from it.

Any other ideas of how to create a task for an analog in acquisition using both INTERNAL and EXTERNAL channels at the same time?

[Corby_B]

Hello Taki1999,

I now notice that you are using a 6250 M series board. Un-fortunately That board does not have an on board temperature sensor. So the only options to you are constant or Channel (external). Even if you were able to select Internal you can only use one or the other. If you did want to use a separate CJC channel for each channel you could do something similar to the picture attached. If you would like to use a board that has an on board CJC you could use one of our products like this.  Have a good day and let me know if this clears up your questions/concerns!

Cheers!

Corby_B

http://www.ni.com/support 

[Taki1999 · Accepted solution]

I'm pretty sure that the 6250 M series DOES have an on board temperature sensor.  It is accessible on the calibration data tab in MAX under Current Temperature.  It's also accessible as a Calibration Property Node in DAQmx.  I can also read the channel directly by wiring in Devx/_boardTempSensor_vs_aignd to the DAQmx Create Virtual Channel VI.

 If I'm understanding correctly, it's impossible to mix internal and external channels in a task.  This is a bit disappointing.  I think I've found a software workaround but it's less than ideal in that it periodically interrupts my continuous measurement.

Thanks for your assistance.

[Mcdan]

Taki1999,

It is possible for M-Series devices to have both internal and external channels in the same task (this is not true of all NI devices).  DAQmx Create Virtual Channel.vi takes a comma separated list of channels.  For instance you could use Dev1/ai0,Dev1/_boardTempSensor_vs_aignd.  You can also use more than one instance of DAQmx Create Virtual Channel.vi to add channels to the same task (ie.. wire task output of the first instance into the task input to the second instance).  This is useful if you want to add channels with different settings to the same task (ie... you want one channel with a range of +/-10 V and on with a range of +/- 1 V).

Hope this helps,

Dan

[Taki1999]

Thanks McDan!

I think everything is working as expected now.

[Corby_B]

Hello Taki1999,

WOW, I was totally in the wrong here and thanks Dan for the post and clarifications. I was thinking more about an on board CJC temp sensor channel then the internal board sensor. Please see the picture below on how to access the on board temperature sensor using the 6250 in DAQmx. Have a great day everyone. 

Cheers!

Corby_B

http://www.ni.com/support 

[mdelsol]

Hi, I want to read same channel from PXI-6221 board. No problem reading the channel. My question is which is the scale factor to get the temperature in degrees?If I use DAQmx Create Virtual Channel using the instance AI Temp Built-In Sensor seams that works but can any one confirm me that the driver is performing automatically the correct conversion for this channel? Thanks in advance,Marc.

[Doug_L._Bear]

According to this KnowledgeBase the temperature can be returned in Degrees C.  I would imagine that if you are acquiring the ai_temp vs gnd it would return a voltage reading which would then need to be converted to degrees.