Analog Input 1 and Simple test setup question

[edw]

Using MSeries 6250 with CB-68LP cable. Trying to run a simple test to see the DAQ work - I want to connect a simple 1.5 volt battery to Analog Input 1 (which I believe is port 33 on the CB-68LP - not sure) - and setup a simple acquisition VI and display the Amplitude verses Time. And connect and disconnect the battery to see the display change hopefully from 1.5 volts to zero etc. each time I connect and remove the battery source. Trouble is I see a Sine Wave (not sure why) - even with the battery out of the loop (not connected at all).  Any ideas on what I am doing wrong, This should be very simple right? Also I am tring to use the "Single Ended" input not "Diffeential".

thanks!

[TimoS]

that occurs because of the internal capacity of the board;
did you use an external pull down resistor?



Link: Ground Loops and Returns

[edw]

Hey thanks very much for responding. No - forgot the pull down. Just connected the positive lead of 1.5 volt battery directly to port 33. Still a bit puzzling why I get a Sine Wave?

Is port 33 the right port of Analog Input 1?

Been a while since I worked on the hardware side of things. Guess that's obvious! Re-learning though..

[Laura F.]

You are correct, pin 33 corresponds to AI 1 on your 6250.  To measure a voltage from a battery in RSE (Referenced Single Ended) mode you should also connect the negative terminal of your battery to AI ground (pins 32 or 67, among others).  It is easiest to test your hardware using test panels in Measurement and Automation Explorer (MAX).  Expand the devices and interfaces folder and then the NI-DAQmx devices folder and you should see an entry for the 6250.  Right click on this and choose test panels.  You will need to choose the correct channel and input configuration.  Once you do this you should be able to correctly measure the voltage of the battery.  After you verify this, I would work on making the VI that you described. 

Please let me know if this doesn't help,

Laura

[edw]

Thanks Laura.

Still a bit confused. What I would like to do is use all 16 Analog Input channels to eventually measure Sound (with microphones). So I believe I need to use a Single Ended but "how do I physically connect the inputs"?

Another thing I am trying to fingure out is how to use the "sound pressure" inputs.

I select the DAQ Assitant - then select "Analog Input" - then I attempt to select "SOUND PRESSURE" but I can't see any "supported devices" however I can see them under many of the other choices. I'm trying to utilize some of the built in SOUND VIs etc. To use the sound tools do I need to input "SOUND PRESSURE" data values?

[Laura F.]

Hello edw,

You would need hardware that supports sound pressure measurements in order to see devices when you choose that option in the DAQ Assistant.  I would urge you to take a look at this article about doing sound pressure measurements and recommended hardware.  If your microphones output a voltage that you would like to measure, you can setup your DAQ Assistant to do a voltage measurement instead.  To do a voltage measurement in RSE mode on AI 1 connect the positive lead of your source to pin 33 on the CB-68 and connect the negative lead to pin 67 which is AI ground.  You will want to make sure that whatever voltage source you connect is a floating source when you use the RSE configuration, meaning that it has no route to ground other than through the connection to your CB-68.  Were you ever able to do a voltage measurement of the battery using the test panels?  If you assign your CB-68 as an accessory in MAX (right click on the board choose properties>>accessory) you will be able to see a connection diagram of how to connect your wires when you make a task in MAX which proves to be helpful. 

Thanks,

Laura

[edw]

Laura - you're the best! thanks very much for responding. The pressure equipment/boards are super expensive. We are just trying to do some relatively simple audio measurements with relatively inexpensive gear - namely the 6250 etc.. I am new to using LabVIEW - and add to that crunched for time - so responses from people like yourself are great. I have not had all that much time to learn it thus far but we had thought it was a bit more intuitive to get up and running. I was hoping to find some VIs available that do what we need right out of the box - Read the microphone voltage, display the audio signal and write .wav files - doesn't everyone need this ( 🙂 ) - I did find a routine but it was built for traditional not DAQmx. I might need to get some expert support to get us moving faster on this.

thanks again!

[Laura F.]

Hi edw,

I have not come across any example that does what you are looking for using DAQmx.  You may be able to acquire your data in binary using the unscaled option from the DAQmx read VI and then use the write wav file VI.  This is really the only way I see it may be possible without actually having a DSA board.

Thanks,

Laura