Beckhoff EL3413-0000, Documentation

Page: 21 / 200

Product overview
EL34x3 21 Version: 4.4
2.3 Basic function principles
2.3.1 Measuring principle
The EL34x3 terminals operate with 1 analog/digital converter for measuring the current and voltage variables
of all three phases.
The measurement and processing of the three phases take place successively (45 µs offset) in exactly the
same way. The signal processing for one phase is described below. This description applies correspondingly
for all three phases.
Fig. 13: Voltage u and current i curves
2.3.2 RMS value calculation
The rms value for voltage and current is calculated over a measuring interval, in this case the period T. The
following equations are used:
u
(t)
: instantaneous voltage value
i
(t)
: instantaneous current value
n: number of measured values
Measuring interval
The choice of the right measuring interval is important for the quality of the measurement. The default setting
for the measuring interval is 10 periods (10 x 20 ms). 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).