In times of power electronics, power measurement is not only a multiplication of current and voltage, but primarily an analysis of interfering high-frequency and broadband signals. Sinusoidal qualities, as once electric current and voltage, are displaced by pulse packages; power ratings do not have only 50 or 60 Hz any longer. Beside the calculation of power for the fundamental oscillation and all signals, questions of harmonics, symmetries, flicker and start-up processes arise. Switching frequencies of drive mechanisms having several kHz require sampling rates of several hundred kHz and analogical bandwidths of input amplifiers. The demand of preciseness is far below 0.1 % and this should preferably be the case in the entire frequency spectrum and amplification range. |
DEWETRON power measurement
Have you ever thought about the complex mechanism of statements like P = U * I * cosPhi? Have you ever thought about the meaning of the current being a sinus? Do you even know the velocity of voltage? Does it even have a velocity (= frequency)?
Or is it wiser to say that voltage has many velocities (frequencies)? Isn't it more adequate to say that current does not only have one sinus, but a number of sinusoidal oscillations (haromincs)? Isn't it also adequate to say that power is the sum of all products of current, voltage and phase angle?
And this brings us right up to the discussion: What is happening to all these products? Parts with the same frequency can reach effects (active power) or only help to build up a magnetic field (reactive power). Some are necessary for the powering of electrical motors (fundamental oscillations) and some products result from the multiplication of components with different frequencies (distortion power).
Additionally, the question arises how high-frequent the analysis of the components of the electrical system has to be. If we talk about pulse-width modulated drives, we have sampling rates in the range of above 10 and 100 kHz.
Questions over questions ...
But fortunatly you do not have to worry about how to measure these things. We have already done that for you and products of the DEWE-xxx-PM series do not only have power measurement but also modules for harmonics analysis, symmetrical components and flicker. Long-term recordings as well as quick sampling rates for the examination of e.g. start-up procedures are possible.