Poly Phase Multifunction Energy Metering IC with Per Phase Information
The ADE7758 is a high accuracy, 3-phase electrical energy measurement IC with a serial interface and two pulse outputs. The ADE7758 incorporates second-order Σ-Δ ADCs, a digital integrator, reference circuitry, a temperature sensor, and all the signal processing required to perform active, reactive, and apparent energy measurement and rms calculations.
The ADE7758 is suitable to measure active, reactive, and apparent energy in various 3-phase configurations, such as WYE or DELTA services, with both three and four wires. The ADE7758 provides system calibration features for each phase, that is, rms offset correction, phase calibration, and power calibration. The APCF logic output gives active power information, and the VARCF logic output provides instantaneous reactive or apparent power information.
The ADE7758 has a waveform sample register that allows access to the ADC outputs. The part also incorporates a detection circuit for short duration low or high voltage variations. The voltage threshold levels and the duration (number of half-line cycles) of the variation are user programmable. A zero-crossing detection is synchronized with the zero-crossing point of the line voltage of any of the three phases. This information can be used to measure the period of any one of the three voltage inputs. The zero-crossing detection is used inside the chip for the line cycle energy accumulation mode. This mode permits faster and more accurate calibration by synchronizing the energy accumulation with an integer number of line cycles.
Data is read from the ADE7758 via the SPI serial interface. The interrupt request output (IRQ) is an open-drain, active low logic output. The IRQ output goes active low when one or more interrupt events have occurred in the ADE7758. A status register indicates the nature of the interrupt. The ADE7758 is available in a 24-lead SOIC package.
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This documentation describes the ADE7758 evaluation kit Hardware and Software functionality. The evaluation board (watt/VA/VAR-hour meter) is configured via the parallel port of a PC. The data interface between the evaluation board and the PC is fully isolated. Windows™ based software is provided with the evaluation board, which allows it to be quickly configured as an energy meter.
The ADE7754/ADE7758 evaluation board and this documentation, together with the ADE7758 data sheet, provide a complete evaluation platform for the ADE7758. The ADE7758 evaluation board can be configured by setting jumpers.
The evaluation board has been designed so that the ADE7758 can be evaluated in the end application, i.e., Energy Meter. Using the appropriate transducers on the current channels (e.g., CTs) the evaluation board can be connected to a test bench or high voltage (240 V rms) test circuit. On-board resistor divider networks provide the attenuation for the line voltages. This application note also describes how the current transducers should be connected for the best performance. The evaluation board requires two external 5 V power supplies (one is required for isolation purposes) and the appropriate current transducers.
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