Hi One as yet unaddressed question:
When you see “something odd” on your power monitor. What is the likely source? For stuff past a few hundred hertz, my bet is that the source is more likely to be “local” than “remote”. There are things like lightning hits that will put a nice spike on the line from a distance. This or that motor in this or that appliance is a much more likely source of a fast transient. Flip on this or that switching power supply …. who knows what the power line looks like. You can indeed pick up a cell phone as it is carried past this or that gizmo (maybe a computer speaker ….). Limited input bandwidth ( = filters) often equates to protection. It also may help reduct the “clutter” in the measurement. Bob > On Jan 22, 2022, at 2:56 PM, Robert LaJeunesse <lajeune...@mail.com> wrote: > > One thing that has helped me build survivable designs is utilizing high > impedance inputs, which means adding a buffer before an ADC pin if need be. > Most IC inputs clamp to the supply, and can withstand a milliamp or two of > current with out damage. ADCs typically want a low impedance source, so a > buffer powered from the ADC's supplies guarantees no overvoltage that can > cause excess current. A high resistance in series with the buffer input > limits its current under transient conditions, providing the needed safety > factor for noise spikes. Split that resistance up and add a low-leakage > silicon diode (e.g. BAV199) to the supply and now the input is seriously > protected with supply on, or off. > > One problem with TVS diodes on signal inputs is that they limit to an > absolute voltage, not one relative to the supply of the device to be > protected. The degree of protection varies whether the device is powered or > not. You must design for the unpowered situation, else things go poof when > power isn't sequenced right. That will happen sooner or later. > > Bob L. > > p.s. A note about capacitive coupling: Yes, well proven reliable for carrier > current systems BUT... with a sub-octave signal bandwidth far, far removed > from the power fundamental. This application is multi-octave and includes the > power supply fundamental. Big difference in application. > >> Sent: Saturday, January 22, 2022 at 2:15 PM >> From: "willl will" <w...@willwhang.com> >> To: "Discussion of precise time and frequency measurement" >> <time-nuts@lists.febo.com> >> Subject: [time-nuts] Re: Another reason to monitor line frequency :) - My AC >> measurement project & question >> >> On 1/21/22 7:00 PM, Robert LaJeunesse wrote: >>> Stick with the transformer. The use of a capacitive divider is predicated >> on the line waveform always being a sine wave. Dream on! All it takes is >> one good spike down the line, maybe only 20-30V amplitude, and your >> capacitive divider passes it right on to that ADC that has a much lower >> (3.3V?) limit. Guess what goes poof? >>> >>> Bob L. >> >> I am concerned about this even with the transformer, so I've added Ti's TVS >> chips & hookup the transformer after my UPS surge protection plug in the >> previous project. >> Definitely need to step up the protection level using an NTC resistor or >> something like that to handle mains voltage directly..... Or offload the >> concern to a surge protection plug. >> >> Will > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an > email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
