I need to track the sine wave of a 240vac line. I want to isolate the ADC completely from the 240vac. I visualize a bridge and divider into an optical isolator with data and power on the other side to a remote micro and ADC. Does anyone have any recommendations for parts? I don’t want to reinvent the wheel, are there already devices available? Thanks.
Depending on what the precise objectives are, there’s a number of possible approaches. Optical isolation as suggested could suffice if the goal is to observe (near) zero-cross events, but will be troublesome if measurement of the actual line voltage is desired, due to the poorly-defined transfer characteristics of most optos.
Another approach might be to use a small transformer such as a FS12-090-C2 for isolation. With calibration one should be able to get reasonably accurate voltage measurements, though there will likely be some degree of phase shift due to the inductive properties of the transformer.
Another approach might be to connect the ADC to the line directly via a divider and isolate the data, rather than the measured quantity. This would probably yield better accuracy of measurement than either of the first two approaches. Assuming one doesn’t care to power the line side of things from the line itself, Analog Devices’ IsoPower line of digital isolators might be a useful tool, as they allow transmission of power across the isolation barrier in addition to data.
Of course if one wants to go down that rabbit hole, there’s also purpose-specific energy metering ICs that can measure voltage, current, power, reactive power, harmonic content, and (probably) the time since your neighbor’s cousin ate a grilled cheese sandwich. Options are available…
Thanks. Can you point me to energy metering IC’s mainly for my own education? I only need nearby event monitoring for now.
See the PMIC-Energy Metering product family for a bucket of options. The manufacturers’ sites probably do a bit better at highlighting differences among their own respective product portfolios, as this is a bit of an esoteric product type that doesn’t lend itself cleanly to normalized parametric representation.