Signal Conditioning

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Cut within specific range

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Hi,

 

I use MCdaq201 to acquire signal from a photodiode. What I see in oscilloscope, is a beautiful sine wave!,  exactly what I was expecting. Then, I connect  it to the PC via MCdaq-USB201, I see a signal which is  like it has been cut within a specific range. I've attached the screenshot of the output of labview program and tracerDAQ. Does anyone know what could be the reason?

 

Thanks 

Petar

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Message 1 of 7
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This has nothing to do with NI signal conditioning hardware. I suggest you post to the measurement computing web site for help with their hardware and software.
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Ok, I will. thanks for your reply.

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Just some quick hints...

 

Your DAQ may have a BIAS current, that can do funny things with photo diodes ... 

The input impedance of your DAQ and the scope migth be different.....

 

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


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Thanks for your reply, but I also connected an external resistor to the photodiode, but,,,,the output is the same :(...without any change

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See the DAQ input as a current source, a resistor and a capacitor 😉 (maybe even an inductivity is hidden somewhere... Who knows....)
Try a preamp... And most of the differences should be gone... However, the result will be the output of the preamp, could be the one desired...
Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


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Solution
Accepted by topic author Petar2015

Thanks so much for all your helpful advices, YES! We used a pre-amp between the photodiode and the DAQ device, and acquired the desired signal!

And, I'm really HAPPY! 🙂

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