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Description of Unit
ZFD400xT
Voltage input
Current input
1.5.2
Signal Processor
Digitizing
Calculation of active
power
D000030110 d – E650 Series 3 (ZMD400AT/CT, ZFD400AT/CT) – User Manual
Fig. 1.4
Type of measurement ZFD400xT
The ZFD400xT with Aron circuit records with its two measuring elements
the phase currents I1 or I3, together with the corresponding voltage U12 or
U32. It cannot therefore construct any actual single-phase values. In addi-
tion, the phase angles between voltage and current always have an addi-
tional angle of 30° and are therefore not representative.
High resistance voltage dividers reduce the voltages U1, U2 and U3 (58 to
240 V) applied to the meter to a proportionate amount of a few mV (U
further processing.
Internal current transformers reduce the input currents I1, I2 and I3 to the
meter (0 to 10 A) for further processing. The secondary currents of these
current transformers develop voltages proportional to the input currents
across resistors, also of a few mV (U
Fig. 1.5
Principle of signal processor
ZxD400AT active energy meters do not measure reactive energy.
The analogue signals Ux and Ix are digitised in Sigma-Delta converters
(analogue-digital converters with highest resolution) with a sample rate of
1.6 kHz and then filtered. A following calibration stage compensates for the
natural errors of the voltage divider or current transformer, so that no fur-
ther adjustment is necessary in the subsequent processing.
Calibrated digital instantaneous values of voltage (u) and current (i) for all
three phases are then available as intermediate values for the formation of
the required values in the signal processor.
The instantaneous value of active power p is produced by multiplying the
instantaneous values of voltage u and current i (the active component cor-
).
I
13/93
) for
U
© Landis+Gyr AG
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