Subject: [eman] Terminology: power

From: Juergen Quittek <[email-masked]>
Date: Tue, 26 Jul 2011 19:26:25 -0400

Hi John,

In draft-parello-eman-definitions-00 you define power as:

>      Power 
> 
>        Power is a rate of energy conversion.  As the unit of time 
>        approaches zero a power measurement is called an instantaneous 
>        power reading.  Typically when implementing Power monitoring in 
>        hardware, a measuring device may have to compute an average 
>        value per some unit of time to express a reading to approximate 
>        an instantaneous power measurement.  
>        Example: 
>        Reference: 
>        Derived from [ISO50001] 

This contradicts the definition of instantaneous power in the IEEE dictionary of standards terms where active power is "The time average of the instantaneous power over one period of the wave." This implies that the instantaneous power changes from zero to a maximum and back two times of a period, i.e. 100 or 120 times a second for common AC power. Typical meter implementations measure power over at least half a period. The result of their approximation is not called instantaneous power. It is the power over a (short) interval of time.

Again, I propose taking text from the IEE dictionary or a similar source.

    Juergen