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ZFD400xT
Voltage input
Current input
2.6.2
Signal processor
Digitising
Calculation of active
power
© Landis+Gyr
Figure 4. Type of measurement ZFD400xT
The ZFD400xT with Aron circuit records the phase currents I1 or I3,
together with the corresponding voltage U12 or U32, with its two measuring
elements. It cannot therefore construct any actual single-phase values. In
addition, the phase angles between voltage and current always have an
additional 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
Figure 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
further 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
corresponds to the product of voltage component with the current
component parallel to the voltage). Thereby the harmonics up to 1 kHz are
measured correctly.
D000062026 en a – E650 Series 4 – ZMD400AT/CT, ZFD400AT/CT – User Manual
).
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Device description
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