Beckhoff EL34 Series Documentation page 28

Product overview
application, it may make sense to regularly synchronize the clock with an external clock. By default, the clock
is set once at system startup based on the local Windows system time, taking into account the set time zone,
usually UTC.
In addition, the interval can also be restarted manually via the "Reset Interval" output bit or directly from the
application, for example to obtain statistics on a process that varies over time.
Calculation of the neutral current
Since the EL34xx terminals have direct access to the instantaneous current values of all three phases, the
neutral current can be calculated or estimated, assuming that no current is lost to the system (in other words:
the differential current is zero). The calculated (i.e. not measured) current value is output in index "F601:13
Calculated Neutral Line Current [} 188]".
Since in the worst case all measurement errors add up, the maximum measurement error is correspondingly
higher.
The additional possibility of measuring a fourth current value in the EL3453 means that either the differential
current or the neutral current can be calculated. The other current can be measured directly using the fourth
current channel. Due to the usual conditions and the corresponding measurement tolerances, however, it
makes much more sense to measure the differential current with the aid of a summation current transformer
and have the neutral conductor current calculated. Further information on this can be found in the chapter
Application examples [} 259] under the section Power measurement including residual current measurement
[} 267].
Harmonic calculation
The EL34xx terminals perform an internal harmonic analysis for all current and voltage channels. For this
purpose, a fundamental wave in the frequency range from 45 to 65 Hz is determined at the beginning
(separately from the system frequency). The frequency value determined for the voltage harmonics can be
read, for example, from index 99 (plus channel offset) of the variable output values and the amplitude in volts
from index 98. The same applies to the current values - see "Variable output values".
The actual harmonic measured values are output as a percentage of the fundamental wave amplitude. It
should also be noted that the zero harmonic indicates the DC component of the signal.
28 Version: 1.5 EL34xx