DAQ Output Small Signal

[GiusTx]

Hi all, trying to generate a small output voltage signal (below 100uV) from one of the analog output voltage (AO, DAQ 6363) I found a very noise signal. It looks like the DAQ is working at the limit of its own capability. How can I make a clean small signal, both in generation than acquisition? 

Thank you for your help.

GTx

[JensG69]

Have a look at the device specs of a 6363: It says absolute accuracy for analog-out at the minimum range of +-5V is 935 µV. That's 10 times bigger than your desired value. I'd say, no wonder that you cannot generate a stable signal.

Regards, Jens

[Henrik_Volkers]

To measure small signal you use an amplifier.

To create small signals you use an an attenuator. 🙂

I used a voltage divider followed by a (low noise audio) buffer (with offset but I needed low freq. low voltage AC signals). Depending on the frequency range and accuracy needed the voltage divider can be as simple as two resistors or need some capacitive compensation. The buffer is needed if you need a low output impedance. If you just need a ~DC source (and measure the output anyway) you can try a 1000:1 resistor divider build from a 10k and a 10 Ohm resistor. Since the correct values would be a 9.99k and 10 you can try a bunch of 10k s 1% and select one that matches 😉 .

Caddock makes nice dividers and for a DC source a (active) zero offset OP would be needed.

And have a close look at termoelectric and galvanic elements in your setup! 

Clean(!) pure copper is a good starting point. (and don't touch the contacts, your fingerprint is always good for some µV 😉 )

Keithley is known for good low voltage equipment. Have a look at their Appnotes/Papers on low voltage measurements.

[GiusTx]

Ok, thank you for your reply!

that's clear! G.

[GiusTx]

Dear Henrik thank you for your reply...your suggestions look nice...I am going to try...