Noise signal on resistor with VI Voltmeter - usb6218

[Giakko]

Hi, I'm acquiring a Volt signal from a resistor with  usb6218. the resistor is connected to a IR photocell . If voltage is high, this mean that there's an obstacle . problem is that I have a noise on the signal and this gives me some problems. you can remove it?  I attach some pictures. Thanks for your help
 

[Giakko]

attachments :

[LiciaP]

Hi Giakko,

your connections are correct if you perform a differential acquisition.

Try to acquire the signal in Measurement & Automation Explorer to see if the problem is still there.

Verify with a scope your signal to see if it is noisy at origin.

Also try to short AI0 and AI8 and verify if 0V are correctly acquired or if the card has some problems.

I also suggest you to read this tutorial, which is really detailed, about the correct connections for different signal sources and possible techniques to reduce noise.

I hope it will help!

Bye!

Licia

[Henrik_Volkers]

How long are the cables?

What type of cable?

Shielding, grounding?

What banwidth do you need?

What's the resistor value?

Can you use a transimpedance amplifier to get a low impedance signal?

[Giakko]

Hi, I included a capacity (10microF) to the resistor (1,2Mohm) to cut high frequencies. Now the signal is clean. thanks for your help.

[Henrik_Volkers]

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Giakko wrote:
Hi, I included a capacity (10microF) to the resistor (1,2Mohm) to cut high frequencies. Now the signal is clean. thanks for your help.

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Just some notes:

Have you checked/thought of  the leakage current of that capacitor? 

A 100mV Signal is just 83nA  and eletrolytic caps can go easely in that direction.

Have you checked the input impedance of your DAQ? Just had a look.. OK 10G is fine 😉  However how about the BIAS current? 100pA x 1M2 = 0.12mV sounds fine ....

Have fun