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How can I know if 50Hz is a problem if I have rejection?

Question asked by KevinPhe on Feb 12, 2013
Latest reply on Feb 14, 2013 by KevinPhe

Hello Everyone (Anyone),

I have a sensor whose resistance which is extremely sensitive to power dissipation. To measure the resistance I use 4-wires and a low-frequency, mV to uV excitation. It sound like a good idea to use a hi-res ADC with sync filters to help pick out my signal. But (and the question follows) if I have mains hum on the lines it may very well be disturbing the resistor. If I have 50Hz rejection in my ADC I'll never see it's there. Is there any way I can know the quality of the signal? (Without getting into spectral analysis). Like (sort of) an output from the sync filter to say 'I'm filtering lots of stuff out' or ' I'm not doing much filtering at the moment - your signal is fairly clean'.


My resistor is typically 10k to 100k. I have to keep my excitation very small. The thing will see 1E-14 Watts. I have to use low frequencies because of stray capacitance. I have HF-filters on the lines. But my signal is necessarily tiny. Any suggestions?