Solving key meter issues with a new energy measurement system on-chip

ADI’s ADE7169 energy metering IC solution addresses time-keeping, LCD, power management, and communication challenges in electronic energy meters.

As the market evolves to battery-operated energy meters with complex requirements, such as an LCD display, multiple-tariff billing, and remote meterreading, there is a need for more sophisticated system solutions. With more than 125 million energy metering integrated circuits (ICs) deployed in the field, Analog Devices is using its detailed knowledge of the market – acquired over the past eight years – to develop a new energy meter systemon- chip device with integrated peripherals that provides all the features needed to design and produce an accurate, reliable, and cost effective micro-processor based solution. (See Figure 1.)

ADE 7169 system diagram.JPG

The new ADE7169 features a high accuracy energy measurement processor using analog-to-digital converters with high precision voltage reference, power management with lowpower sleep modes and internal battery switching, low-current real time clock, level adjustable LCD driver, and an 8-bit singlecycle 8052 micro-controller core with embedded flash memory and RAM.

SYSTEM REQUIREMENTS

After growing slowly in the western world, the installation of energy meters with LCD displays is now accelerating to become a worldwide phenomenon. A typical system solution is detailed in Figure 2, but local energy providers call for a certain degree of flexibility in the design. This adaptability is partly supplied by the system’s microprocessor, which stores the program in flash memory, and also by providing a menu of solutions that address the following requirements for the meter:

  • Real-time clock (RTC)
  • Battery mode operation
  • LCD readability over temperature
  • Energy measurement capabilities
  • Communication media.
LCD energy meter system diagram.JPG

REAL-TIME CLOCK (RTC)

Keeping accurate time in an energy meter is critical when billing is associated with time of use. It is especially important when there is not constant communication between a meter and a reference clock. For these reasons, time-keeping accuracy has been added to the energy meter system requirements. The RTC needs to be accurate over temperature as well as over long periods of time. Also, because the shelf time of a meter can exceed one year, it is important to maintain very low power consumption for the RTC in battery mode.

The ADE7169 energy meter system-on-chip IC addresses these requirements by providing a low-current RTC – only 1µA – with temperature measurement in both normal and battery mode, thus enabling the compensation of the RTC over temperature, and maintaining its accuracy within 0.17 second/day or 2ppm. The RTC functionality is maintained at low supply voltages (2.4V), extending the operating life of the energy meter in battery mode. Digital compensation and short calibration time provide a reliable and easy-to-manufacture solution.

BATTERY-MODE OPERATION

ADE 7169 power management.JPG

A battery is necessary in an energy meter with an LCD to maintain features like the display, the RTC, and communication capabilities when there is a power outage. The current required to maintain these features is critical to designing a cost-effective solution. The ADE7169 uses a unique system architecture to minimise current consumption in battery mode, while maintaining critical features and performance.

For example, the temperature measurement is always active, ‘waking up’ the microprocessor only when the temperature has changed above a selectable threshold. The LCD display can be maintained in battery mode, requiring minimum biasing current. Finally, hardware events such as I/O, alarms or UART activity can wake the microprocessor up and start a new procedure.

These metering-specific features are combined with a unique internal battery switchover circuitry that applies the right power supply to the system, reducing components and removing potential problems for the meter system designer.

LCD READABILITY

LCD displays are made of polarised chemical materials that turn black upon sufficient excitation by an alternating voltage. The characteristics of these materials change with temperature. For example, the rms voltage level at which a black state is reached usually increases as the temperature decreases. This characteristic is well known, and is similar to the problem with cell (mobile) phones when they are operated in a cold environment.

The ADE7169 solves this LCD readability issue by having an LCD driving voltage that is digitally adjustable up to 5V, independent of the power supply. Associated with the internal temperature sensor, this feature provides all the circuitry necessary to maintain the LCD contrast over a wide range of temperature, without the need to change the LCD chemistry. In addition, this functionality is maintained in battery mode.

ENERGY MEASUREMENT

Building on Analog Devices’ experience in energy measurement, the ADE7169 provides the best analogto- digital converters, combined with the advanced signal processing required to make an accurate, robust, fully featured single-phase energy meter. Supporting IEC62053- 21 and ANSI C12.16 metering standard requirements with 4-quadrant energy measurement for watt, VAR and apparent power, the ADE7169 has built-in anti-tamper detection with two current inputs, and the possibility to connect shunt, CT and Rogowski coil current sensors. It also processes power quality measurements needed in high-end solutions. All these features make the ADE7169 and its variants suitable for most energy meter requirements, providing a combination of high performance and reliability.

COMMUNICATION

Different forms of communication are used in an LCD energy meter, ranging from infrared (IR) to RS485, power line communication (PLC), and RF. These communication media aim to manage the meter directly or remotely. Analog Devices provides a large portfolio of RF ICs and other communication solutions capable of serving each of these requirements. The ADE7169 is designed to interface with these solutions without compromising the reliability and accuracy of the energy measurement core, enabling meter manufacturers to implement solutions using their preferred vendor.

GSM and GPRS modules using Analog Devices’ RF chipsets are available from well-known vendors. For new designs, Analog Devices’ ISM RF transceivers (ADF7020 and ADF7021) for the US or European markets are now available. For PLC solutions, Analog Devices has also developed a turnkey design for a low speed, reliable PLC link designed to fit the noisy energy meter networking needs.

Finally, Analog Devices has developed unique isolation technology that can provide an isolated high-speed RS485 interface, with or without the need for an additional power supply. The ADM2490E or the associated ADM4850 with the new isoPower™ ADuM5241 enables an innovative implementation of isolated RS485 communication with the meter.

CONCLUSION

With the ADE7169, Analog Devices introduces a truly integrated energy meter system-on-chip, incorporating all the key peripherals necessary to implement a simple, reliable, cost-effective system. With the quality, reliability and performance of Analog Devices’ energy metering products, the ADE7169 solves the issues associated with a batteryoperated solution by integrating battery switching and power management features. Its innovative system architecture enables key functions, including temperature, time keeping, LCD display and UART, to be maintained in battery mode while consuming low power.

In addition, the ADE7169 uses Analog Devices’ expertise in mixed-signal technology to improve traditional microprocessor power supply monitoring, time-keeping and LCD display features with internal power-on resets, RTC accuracy to 2ppm, and up to 5V digitally adjustable LCD level independent of power supply.

The ADE7169 is the latest addition to Analog Devices’ well-established ADE™ energy metering system portfolio that includes 16 energy metering ICs and communication solutions that range from RF-ISM to GPRS, PLC, and isolated RS485. Its circuit innovations and broad portfolio combine to make Analog Devices the preferred vendor for many energy meter manufacturers, helping them to solve their most critical design issues.