electrical charge measurement with NI 4451 DSA

[jim_mech]

   

Hello there!

I am using NI 4451 with LV 6.1 and  Sound & Vibration 3.0.

What I want to achieve is to measure electrical charge.So, I am applying a known voltage 
signal across a known resistance and I measure the current that passes through the resistance.
Finally, I am integrating the current waveform in order to obtain the charge. I acquire 
the voltage signal in one of the AI channels and then integrating , using "SVT Integration.vi"
found in the Sound& Vibration 3 Toolset.

However I think that the results I am getting are not quite correct.The phase difference between
voltage and the computed charge is greater than T/2 and it's depending on the cut-off frequency
of the high-pass filter.

I wonder if the  "SVT Integration.vi" is oriented only towards acceleration integration. I would
like to ask if there is another way to integrate the voltage waveform. Attached find the vi I am
using for the integration.

Any comments/suggestions/corrections on this thoughts as wells as on the implementation procedure
are welcome!


Thanks in advance for your time!!




Kind regards,

Dimitris

[preston_johnson]

If possible, try turning off the AC coupling feature of your DSA device.  This will remove one high pass filter.  Also, if you are confident the measured current has no DC content in the waveform, you can either open the SV Integration VI and remove the high pass filter, or use the standard integration functions in LabVIEW that do not have a high pass filter built in. 

[jim_mech]

Preston thank you  for your prompt reply!

I will try what you mentioned but I  would like to ask you  sth concerning  the standard integration functions in LabVIEW that do not have a high pass filter built in. If I am not mistaken these functions do numerical integration, so the result is a number and not the integrated waveform.Is that right or should I check them again?

Thanxxxxx!

Dimitris

[Elizabeth_S]

Hi Dimitris,

Numeric Integration.vi  performs numeric integration on an input array and outputs a numeric value.

Integration.vi performs integration of a function (with a start and end value) and outputs the integrated curve. 

Regards,

Elizabeth S.

Applications Engineer

National Instruments