Average peak current

[antique]

Hi Folks

Need to see if I can get a little advice.

I have a setup and trying to measure current on 4 units using a shunt resistor. I am using a NI-9205 module and a 0.1 ohm shunt resistor. If I test the units steady state, the setup works fine. If the units are pulsing the data is displayed quickly and not able to get a good reading. I need to be able to log the data while the pulse is high. In the picture below is something like what I need to measure, and log and I will need to be able to do it with 4 units at one time. Would anyone have a suggestion on how I could do that?

Any help or advise would be appreciated.

[Bob_Schor]

Do you understand your NI-9205?  Do you understand what it means to "sample" data?  If you sample at the modest frequency of 1 kHz, you will have a good representation of your signal and can figure out how you want to process it to get the answer(s) you need.  I recommend that you spend a few hours with the excellent tutorials on DAQmx (and avoid using the Dreaded DAQ Assistant!).

Bob Schor

[antique]

Thank you for the reply. I am sampling at 1kHz we have about a 275mS on time and just know I am missing something. I have read the tutorials and taken the LabView training in the past as well as read the data sheets for all the devices I am using. Just need a little hint as to what I am forgetting to do. Could be a getting old thing I guess. I can see the correct current when the unit is on but do not want to log the off times. 

If anyone has a good suggestion it would be appreciated. 

Thank you 

[MHawk]

The NI-9205, while very capable, is not a simultaneous sampling module. There is one ADC which is multiplexed into the various inputs for measurements.  Make sure you have your system setup to scan through the channels fast enough to get the data you need.

If you're scanning 4 inputs at 1 kHz, it is possible it is setup to look at 250 samples / channel @ 1 kHz, then sequence through the channels.  That would cause the system to miss several events.

Posting some code might help the troubleshooting effort too.