110802-2221 EDT

mohsin_2011:

You need to understand the difference between watts and watt-hours. Watts is a measure of power, the rate of doing work. Watt-hours (or KWH) is a measure work or energy. So power is the derivative of the instantaneous energy curve (its slope).

If you know the average power, px, of a load for a small time period, tx, where the power is not changing much during tx, then the energy used over that time period is approximately ex = px * tx. The smaller the tx periods are the closer the approximation is to the actual energy used during tx. Take contiguous samples like this over "whatever time period" you want and add them together. The result is the energy used over the "whatever time period".

The TED systems use an accurate 1 second time base I believe. Every 1 second a new average power value is provided for the past 1 second. If you add all these up for 3600 seconds, 1 hour, and divide the watt-seconds by 3600, then the result is watt-hours for the last 1 hour. If you added the values for 7200 seconds, and divided by 3600, then you would have the watt-hours used in a 2 hour period.

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