Is there a very cheap way to measure several voltage differences of 0.1V to 10V (to ~1% accuracy at 10Hz, say), where each pair of measurement terminals may be tens of volts away from the ground of the circuit that needs the measurements?
As far as I can see, one either isolates each analogue signal before it reaches the ADC (using one isolating amplifier per channel - not cheap), or has one serial ADC per channel (not cheap -- I was hoping to multiplex a single ADC), each floated at the appropriate level, with optoisolation of the ADC output.
Are there any other strategies? Isolated DC/DC power supplies are themselves not enormously cheap (~£3/unit) so ideally I would want something that doesn't require a power supply floated at the level of each measurement input. Is this possible?