VI Logger - displaying data

[Prachi Shrivastava]

Hi

I am using USB 9201/9221 VI logger (Lite)  for measuring voltages. Each channel meaures voltage wrt to the comm channel as per the connection diagram. Is there a way to measure and display the voltage acorss any two channels. .
Any help/suggestion in this context is appreciated.

Thanks
Prachi

[Brian F.]

Hello Prachi. 

As I read your post, I am assuming that you would like to measure the difference in two analog input channels.  For instance, if 3 V is measured on AI0 and 5V is measured on AI1, you would like to read 2V (5V-3V) in some manner.  If this is indeed correct, the 9201 is not capable of doing this via hardware.  Many of our cards support differential measurements which take measurements on 2 different AI channels and return the difference between the two voltages.  However, differential measurements are not supported on the 9201; only reference single ended measurements (RSE) are supported on this device

If you have LabVIEW, this difference measurement could be done in software and displayed on a front panel indicator fairly easily.

Brian F
Applications Engineer
National Instruments

[Prachi Shrivastava]

Hi Brian,

Thanks for the reply.
When you say that differential plot can be obtained by using the labview software, could you suggest  how could I go about it. I am new to this labview programming. I would really appreciate that.

Thanks
Prachi

[Brian F.]

Hello Prachi. 

In order to do this in LabVIEW, first we will have to learn about how to acquire 2 RSE voltages from our DAQ device.  There are great tutorials and examples on how to acquire analog input signals.  Examples can be found inside LabVIEW by navigating to Help>>Find Examples.  This will launch the NI example finder and allow you to search the examples.  Please select 'Browse According To': 'Directory Structure.'  Then, select DAQmx>> Analog In>>Measure Voltage.llb>> Acq&Graph Voltage-Ext Clk.vi.  This example will provide a good start for acquiring signals.  Also, a great tutorial on DAQmx in LabVIEW is available at:

Learn 10 Functions in NI-DAQmx and Handle 80 Percent of Your Data Acquisition Applications

http://zone.ni.com/devzone/cda/tut/p/id/2835

Searching www.ni.com for daqmx will yield many more results that will teach you about programming with this driver. 

After you have acquired both voltages successfully, you will simply need to use a subtract function to find the difference between the 2 voltages and then feed that output to a waveform chart indicator on the front panel.  For a basic introduction into LabVIEW, please refer to:

LabVIEW Introduction Course - Three Hours

http://zone.ni.com/devzone/cda/tut/p/id/5243

Good luck on your application.  This should provide a great start for you.  If you have any further questions, we will be happy to help. 

Brian F

Applications Engineer

National Instruments