Technology

Measurement of AC variables with the EL3783

Normal three-phase mains supply

The normal 3-phase low-voltage grids in Central Europe are characterized by the following interrelationship: rated voltage is usually the effective voltage U_RMS, e.g. 230 V_RMS, as a star voltage between one of the three live conductors (L1, L2 or L3) and neutral N.

Technology 1: — Voltages in three-phase mains supply of Central Europe

With a pure sinusoidal oscillation (unloaded grid) a maximum peak voltage (max. amplitude) of approx. ±325V_peak to N is calculated from the then valid crest factor from Technology 2: in the star voltage.

A phase-to-phase voltage of Technology 3: (RMS) can be measured between the live conductors.

RMS value specifications

	RMS value (_rms) specifications All AC value specifications in this documentation such as RMS specifications (_rms) refer to a 50/60 Hz 3-phase mains network with a sinusoidal waveform.

The EL3783 EtherCAT Terminal is a power monitoring terminal for state monitoring of a 3-phase AC voltage system. The following properties are characteristic of the EL3783:

3 channels measure -737...+737 V through analog-to-digital converters in 16-bit resolution as amplitude value
3 channels measure -9.2...+9.2 A through analog-to-digital converters in 16-bit resolution as amplitude value
all 6 analog input channels are measured simultaneously
the EL3783 is an oversampling terminal and can therefore record not just 1, but up to 100 samples per channel in each PLC/EtherCAT cycle. These are sent as a data packet to the controller via the cyclic process data.
The minimum sampling time is 50 µs, corresponding to 20,000 samples/second.
The voltage and current curve can have any form; the EL3783 is thus suitable only for AC measurements
the EL3783 can be synchronized with other EtherCAT device over Distributed Clocks, but can also be operated without Distributed Clocks with oversampling
no pre-evaluations or calculations of the amplitude values take place in the EL3783

Hence, the EL3783 is suitable for very different applications, for example

3-phase monitoring: the voltage and current to N are measured for a 3-phase load
3-load monitoring: the voltage and current to N can be measured for 3 loads even if connected to the same phase
each channel can measure as desired, provided the measured is referred to N
Measurement of non-sinusoidal amplitude curves, including rectangular

Evaluations and calculations of the raw data sent to the controller, such as active power (P), cumulative power consumption (W) or power factor (cos φ) must take place in the controller. The controller has sufficient computing power for true RMS or performance calculation and complex custom algorithms based on the measured voltages and currents.

	Design of voltage measuring range Low-voltage power supply systems are defined, for example, in IEC 60038. Since 2003 the specification here is 230/400 V_RMS ±10%, corresponding to ±357 V_peak. So that substantial spikes can also be measured, the EL3783 supports a measuring range of 520 V_RMS AC, corresponding to ±737 V_peak.