3 ms·
A standard household ammeter watches the electrons sashay back and forth in the wires and totals that up. e.g. you get billed for both current you use and curre
by jws 16y ago
A standard household ammeter watches the electrons sashay back and forth in the wires and totals that up. e.g. you get billed for both current you use and current you produce (since they never imagined that when they built the meter).
A "net-metering" ammeter determines if the electrons are cycling back and forth because you pushed them, or because the power company compelled them and tallies them appropriately.
Does anyone know how they determine "why" the current moved? At a first crack, I'd check the voltages very carefully on either side of the ammeter and decide which was bigger, but this is going to be complicated since there will likely be different answers across the complete cycle.
- mindslight 16y agoAll power meters work by measuring both voltage and current and multiplying. Even without local generation, power periodically (60/50Hz) flows back into the grid (except when the load is purely resistive aka power factor of 1). http://en.wikipedia.org/wiki/Power_factor http://en.wikipedia.org/wiki/Power_factor The mechanisms in old meters were just designed with the assumption that the net flow was always into the house (perhaps in response to the various tricks people would use to artificially slow their meters). A modern digital meter doesn't have to do anything special to measure the direction for net metering.
- pmjordan 16y agoTo elaborate on this: assume the sine waves of voltage difference and current are fully in phase when the house is net-consuming. Multiplying the voltage and current functions and integrating over time gives you the total energy consumption. When the house is net-producing due to solar panels, the current will be 180° out of phase with voltage, i.e. "negative" AC current. Multiplying and integrating yields negative energy consumption. Note that current is directional, so "negative" current isn't anything special - if you reverse the meter, the sign will be inverted.