Measure Vac signal with Vdc IO FP-AI-100

Sir,
We are trying to use hall-effect current sensor to measure motor currents. High accuracy is not required. So we are thinking of using FI-AI-100 to do this. But output of the hall-effect current sensor is about 0-5 Vac/60Hz. I wonder whether or not we can use FI-AI-100 here and what we may read back.
Anyone has any experience ? Thanks in advance.

Sir
Although the FP-AI-100 can handle the voltage you are going to be reading, it is not meant to be reading AC voltage. You would be able to accurately see the 60 Hz frequency of your signal, due to the ability to sample faster than twice your frequency, but you would not be sampling fast enough to accurately depict all of your peaks.

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Attachments:
Sensor_Configuration_Test.vi ‏60 KB

Good afternoon MiamiVipul,
Thanks for contacting National Instruments with your issue, we'll try and get you up and running as quickly and efficiently as possible.
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Attachments:
Simulator1.vi ‏114 KB

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How to send a ttl signal with a good exactitude less than 10ms?

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Better estimation of phase difference between two signals with variable frequency!

Hello LabView Gurus,
Being a power engineer and having just a little knowledge of signal processing and labview, I have been pulling my hair out for the last couple of days to get a better estimation of phase difference between two signals.
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You can observe that the estimation error increases after you push the button.
All I need to do is to reduce this estimation error and make it as close to the actual phase difference as possible. Any help would be greatly appreciated.
I am using LabView 2009 for this task.
The application is for electric machines and the stability/performance of machines under different faults.
Thank you for reading this far!
Regards,
Awais
Attachments:
v603.png ‏320 KB
v603.vi ‏186 KB

Jeff Bohrer wrote:
Basic math gives me a bit of pause on this approach. You are sampling at 50 times the frequency of interest so you get 50 samples per cycle. your phase resolution is 1/50th cycle or 7.2 degrees +/- noise. You will need to samlpe faster to reduce phase resolution or average multiple readings (at a time cost that is signifigant)
Jeff- (Hardly Working)
I am sampling at 100 times the sine wave's frequency and 200 times the square wave's frequency. Increasing the sampling rate completely solves my problem. But since I am acquiring several other inputs, I cannot afford a sampling rate higher than 5kHz.
F. Schubert wrote:
I'm not a signal processing expert, but here my basic understanding.
If you simulate sampling with 5kHz and a frequency of 50 Hz (and both are 'sync' by design), you always get an exact 5 periods. Any variation of your signals frequency gives you a propability to get 4 or 6 'trigger' events. That's an up or down of 20%!
The one measure to reduce such problems is using 'window functions'. They don't fit your current approach (counting instead of a DSP algorithm), so this needs to be reworked as well.
My approach would be to use the concept of a Locki-In amplifier. You need to phaseshift your ref-signal by 90°. Then multiply your measurement signal with the ref signal and the phase shifted ref signal. The obtained values for x/y coordinates of a complex number. Calculate the theta of the complex number (with the LV prim). Feed this in a low pass filter.
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I suggest you to check on wikipedia for some of the keywords I mentioned. Go also for the external links which lead to great tutorials and AppNotes on the signal processing basics.
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Felix
www.aescusoft.de
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An interesting view. the sine wave can indeed be looked as a second harmonic of the square wave. I will implement your idea and get back to you as soon as I get some results. But since I have very limited knowledge of signal processing, it might take me a while to get my hear around the solution you mentioned.

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Labview lovers.

Hi!
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Have a nice day!
graziano

Measure Vac signal with Vdc IO FP-AI-100

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