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  • KM34Z128 Single Phase Power Meter

  • Created: Dec 14, 2015

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A power meter is a device that monitors the energy consumption of another device or group of devices that requires electricity to operate. With the growing consumption of energy, a very reliable energy meter is really needed. In this reference design, the KM34Z128 single-phase power meter, which is based on the freescale’s kinetis-M series, addresses the need for an accurate and cost-effective energy metering. Inside this single phase power meter is the MKM34Z128CLL5 32-bit MCU designed to be a high accuracy analog front end and an LCD driver.

The KM34Z128 single-phase power meter is splitted into three parts: power supply, digital circuits and analog circuits. Its power supply is made up of an AC-DC switch mode power supply (SMPS), 3.3V linear regulator adjusted to 3.6V, and power management. The main supply for the power meter is the 50/60Hz mains regulated by the SMPS, which is capable of delivering a continuous current of up to 80mA at 4.125V. However, if there is a power interruption, the 3.6V Li-SOCI2 backup battery temporarily supplies the power meter. The microcontroller (MKM34Z128MCLL5), debug interface, LCD interface, LED interface, IR (IEC1107), isolated open-collector pulse output, isolated RS232, push-button, and tamper detection belongs to the digital circuits section. The digital part can be configured to support both basic and advanced features. In the advanced configuration, the 128 KB SPI flash, 4 KB SPI EEPROM, 3-axis digital accelerometer, and UMI and RF MC1323x-IPB interfaces are needed to support the advanced features. The last part of the power meter is the analog circuits which measure the phase current, phase voltage, and backup battery voltage.

The power meter measurements are displayed on the 4 x 22 segment LCD. The values shown on the LCD are date, time, line voltage, line current, signed active power, signed reactive power, apparent power, signed active energy, signed reactive energy, battery voltage, active energy pulse number, reactive energy pulse number, software revision-product serial number, and class according to EN50470-3. This power meter allows external load with a maximum current consumption of 80A. The KM34Z128 single-phase power meter is ideal in monitoring the energy consumption of home devices.