Q.: Are there other proposals - better ways - to measure low noise on a Fluke 732A ? How do we know that the measured values with the DMM7510 are not mainly dominated by its own noise floor as it seems that the noise contribution of the 732A should be much lower ... ()
Hello,
if you want to measure noise then you should ever define the kind of noise and the bandwidth.
so what kind of noise do you want to measure?
- wideband noise (uVeff) (e.g. 10Hz-100kHz)
example measurement setup with a AN83 (LT) amplifier (1000:1) and a digital scope (RMS) or AC RMS millivoltmeter.
- 1/f noise (uVpp) (e.g. 0.1 - 10 Hz)
example measurement setup with a LNA (10000:1) and a scope (2mV/div resulting in 0.2uV/Div)
- popcorn noise (uVpp)(usually below 1 Hz)
longer pulses could be measured with a >= 6.5 digit DMM (if below 1uV resolution can be obtained by HPIB/RS232)
shorter can be observed with a 1/f measurement setup
of course you should always determine noise floor of your setup (e.g. measuring 8 AA NiCd/NiMH cells at constant temperature).
with best regards
Andreas
Edit: be aware that AN83 contains a bug regarding frequency response.
To get a flat frequency range you have to change R9 = 5K19