What module will allow voltage output with CompactDAQ

[jgh@AET]

Hello,

Up to this point, my data acquisition experience is limited to NI CompactDAQ chassis with Signal Express using plug in modules (9219 and 9237) for strain and voltage input with Signal Express.  I now need to output a constant voltage (10V or so) to a potentiometer and then acquire the resulting voltage at 50 kS/s.  So, this eliminates the 9219 because the max sampling rate is only 100 S/s. 

NI has voltage output modules to fit the CompactDAQ.  So, will I need a voltage output module to send a voltage to the potentiometer and then another voltage input module to acquire the voltage drop from the potentiometer?  Maybe there is another way I can get a constant 10V DC voltage from the CompactDAQ chassis, or maybe my 9237 module?  Would "Custom Voltage with Excitation" work with a Voltage input Module?

With the voltage output modules, how do I output voltage with Signal Express, perhaps the "Generate Signals" step?  That doesn't seem to give me any hardware/modules resources to select from like the "Acquire Signals" step. 

Thanks a lot!

[Izzzzz]

Hello jgh@AET,

The NI-9263, NI-9264, and NI-9269 are cDAQ analog output modules capable of producing a constant 10V excitation. Please ensure that your potentiometer does not exceed the current rating of the analog output module. For example the NI-9263 is capable of driving up to 1mA. In Signal Express you will first have to create a function step where you decide what kind of signal you want to output( DC, or sinusoidal). Then, you will add the DAQmx Generate Signals>>Analog Output Step where you can configure the output of the cDAQ module. The DAQmx Generate Step will output the signal created by the user in the function step. If you decide to go this route you will need another Analog Input module in order to acquire the voltage drop from your potentiometer.

The NI-9237 is capable of both sourcing the 10V excitation to your potentiometer and reading the voltage drop from your potentiometer. Again please be weary of the current draw from your potentiometer which may affect the total power the NI-9237 can deliver discussed in this KnowledgeBase Article. You are correct in using an AI Custom Voltage with excitation if you are only concerned with the drop across the potentiometer. The NI-9237’s maximum sampling rate is 50KHz. If you need a faster sampling rate I would focus your application on an analog output module and input module.

Please let me know if you need clarification on the statements above.

Best Regards,

Izzy O.

Applications Engineer

National Instruments

ni.com/support

[jgh@AET]

Thanks Izzy.  I was not aware the 9237 could measure voltage directly.  So, I would configure it to output 10V excitation in the "Custom Voltage with Excitation" step, then what I would acquire would be the voltage drop?

[Izzzzz]

Hello jgh@AET

You are correct.

Best Regards,

Izzy O. 

Applications Engineer

National Instruments 

ni.com/support

[jgh@AET]

Thank you so much.  I really appreciate the help.  Just one more question though (hopefully).  I typically set up a "Save to ASCII/LVM" step to save data as text files which are easy to open in Excel.  When testing multiple destructively tested samples, this also allows me to quickly save data in one folder with individual test sample files which are named in the step setup.  When doing it this way, I need to click run to start acquiring data and then click stop to end. 

Is there a way to set up triggering or start/stop conditions within the "Save to ASCII/LVM" step so that data will be recorded when the voltage reaches a certain value?  It appears that the triggering within the "Save to ASCII/LVM" step does not give the start/stop condition settings that something like record/log allows.

Thanks again,

Justin