How Does an Electrical Company Measure Energy Consumption?

[gkangelexa]

Electrical companies charge you based on how much energy you use ... So this means they first calculate the total Power based on the voltage they give each household and the current drawn... P = IV
but then they have to multiply the total power consumption times the time it is on in order to find the total energy consumption...
How can they know this data? How can they know how long a lightbulb or the television was on?

 

[Drakkith]

The device attached to your house or apartment is called an Electricity Meter. It is designed to measure how much power you use over time. Typically they measure this in Kilowatt Hours. One kilowatt of power use over one hour is one Kilowatt hour.
See here: http://en.wikipedia.org/wiki/Electricity_meter

 

[berkeman]

Electrical companies charge you based on how much energy you use ... So this means they first calculate the total Power based on the voltage they give each household and the current drawn... P = IV
but then they have to multiply the total power consumption times the time it is on in order to find the total energy consumption...
How can they know this data? How can they know how long a lightbulb or the television was on?

This is called "metrology", and is at the core of electric power meters.

Typical ICs that can be used for metrology are the Analog Devices ADE7768 and ADE7763.

http://www.analog.com/en/analog-to-...rgy-measurement/ade7763/products/product.html

The IC samples the current and voltage of a single-phase circuit at a high sample rate (much higher than the 50/60 cycle power frequency), and calculates the instantaneous power for each sample. Those are added up (the time between samples is known) to get the energy numbers.

 

[russ_watters]

Old style meters were just a spinning disk and a set of counters. Time was utterly irrelevant to the issue, except that they sort of tried to schedule the meter readings about a month apart.