Beckhoff KL3403 Series Documentation page 15

Product overview
The default setting for the measuring interval is 50 ms, corresponding to 2.5 T in a 50 Hz mains system and
3 T in a 60 Hz mains system. Experience shows that this is a good compromise between measuring speed
and stability. Deviations from this value are only advisable in the event of particular measurement
requirements (e.g. high measuring speed, low signal frequencies or special current curves).
Power measurement
Active power measurement
The KL3403 measures the active power P according to the following equation
P: Active power
n: number of samples (64000 samples / s)
u : Instantaneous voltage value
(t)
i : instantaneous current value
(t)
Power s curve
(t)
Fig. 5: Power s curve
(t)
In the first step, the power s is calculated at each sampling instant:
(t)
The mean value over the measuring interval is calculated. Here too, the correct choice of the intervals is
important, as described in section RMS value measurement (the interval can only be changed
simultaneously for U, I and P).
The power frequency is twice that of the corresponding voltages and currents.
Apparent power measurement
In real networks, not all consumers are purely ohmic. Phase shifts occur between current and voltage. This
does not affect the methodology for determining the rms values of voltage and current as described above.
The situation for the active power is different: Here, the product of effective voltage and effective current is
the apparent power.
KL3403 Version: 3.1.0 15