Smart Metering Technology Promotes Energy Efficiency for a Greener World
Figure 1 shows an example of a traditional electromechanical meter—first developed in the late 19th century—that has a spinning disc and a mechanical counter display. This type of meter operates by counting the revolutions of a metal disc that rotates at a speed proportional to the power drawn through the main fuse box. Nearby coils spin the disc by inducing eddy currents and a force proportional to the instantaneous current and voltage. A permanent magnet exerts a damping force on the disc, stopping its spin after power has been removed.
Figure 1. Electromechanical energy meter.
The first step in meter evolution was the replacement of electromechanical meters with solid-state electronic meters. Electronic meters measure energy using highly integrated components, such as the ADE516x,1 ADE556x,2 ADE716x,3 ADE756x,4 and ADE77xx5 families of energy-measurement ICs.6 These devices digitize the instantaneous voltage and current via a high-resolution sigma-delta ADC. Computing the product of the voltage and current gives the instantaneous power in watts. Integration over time gives energy used, which is usually measured in kilowatt hours (kWh). The energy data is displayed on a liquid-crystal display (LCD), as shown in Figure 2.
Electronic meters offer several benefits. In addition to measuring instantaneous power, they can measure other parameters such as power factor and reactive power. Data can be measured and stored at specific intervals, allowing the utility to offer price plans based on time-of-day of usage. This allows savvy consumers to save money by running major appliances, such as washers and dryers, during lower-cost, off-peak periods; and utility companies can avoid building new power plants because less capacity is required during peak periods. Electronic meters are not influenced by external magnets or orientation of the meter itself, so they are more tamper-proof than electromechanical meters. Electronic meters are also highly reliable.
Analog Devices has been a key player in the transition from electromechanical meters to electronic ones, shipping more than 225 million energy measurement ICs to date. According to IMS Research, 75% of all energy meters shipped in 2007 were electronic rather than electromechanical.7
Figure 2. Solid-state electronic energy meter.
Meter Opens Up New Possibilities
Figure 3. Drive-by meter reader.
AMR to AMI
RF technology uses low-power, low-cost radios to wirelessly transmit the meter information, whereas PLC uses the power line itself. Analog Devices has developed solutions for both of these technologies, with the ADF7xxx family of short-range transceivers8 addressing the ISM band RF segment and the SALEM® family based on the popular Blackfin® processor9 addressing the PLC segment. Each of these technologies has its pros and cons. For water and gas meters in particular, RF technology is becoming the dominant choice due to the safety concerns of having power mains near water or gas. Water meters also have the added complication of often being buried underground. With electricity meters, a combination of both approaches is looking most likely, with North America favoring RF and Europe favoring power line. In the U.S., a small number of houses are typically tied to a single transformer, making PLC less economical. In some implementations, utility companies are deploying AMI using a blend, with power line used to communicate from the data collector to the electricity meter and RF used between the electricity meter and other in-home meters or devices. An interesting Google Maps page highlighting worldwide AMR/AMI deployments10 and field-trials shows up-to-date information.
RF Piece of an AMR/AMI-Enabled Utility Meter
Good radio sensitivity is also required because this translates into longer signal transmission ranges. Remember that the meter can be located in a basement or, even worse, underground—yet it needs to communicate with a radio on a pole some blocks away or with a utility van on the street. The lower the sensitivity, the closer the receiving radio needs to be to decode the messages correctly. For a mobile drive-by system, this simply means the van must drive closer to your house, but fixed network infrastructure must use smaller cells and a corresponding larger number of data collectors. High sensitivity will thus minimize network infrastructure costs.
Low power consumption is critical in battery-powered gas and water meters. Meter vendors often try to reduce power consumption in an energy meter because this allows them to port the same design to a water or gas meter. Also, in order to operate in the unlicensed portion of the spectrum, the communication protocol used by the meter and reader must comply with the radio emissions regulations in the country of operation. Several unlicensed bands exist worldwide, the most common ones being at 900 MHz, 2.4 GHz, and 5.8 GHz.
A majority of meter manufacturers have chosen radios in the 900 MHz bands for the links between meters, and between meter and data collector. Radios at these frequencies offer better communication range for a given power budget than competing 2.4-GHz technologies and, thus, allow much wider cell coverage for a given base station or data collector. From the utility’s perspective, however, a drawback of using this frequency band has been the lack of available standards. The sub-GHz bands are clearly the best technology choice for battery-powered gas and water meters, inspiring increasing demand for standardization to allow interoperability between different manufacturers’ systems. Wireless M-Bus, which has grown out of the wired M-Bus users group, is one example of a standard for communication between meters, and between meter and data collector. M-Bus11 is now part of the EN European Normative standard detailed in EN 13757. The Wireless M-Bus protocol is detailed in the EN 13757-4 variant. Other standardization efforts at 900 MHz are also underway.
The ADF702012 and the soon-to-be-released ADF7023 transceivers are examples of 900-MHz radios that are designed with metering in mind. Both devices are also suitable for systems that must comply with the Wireless M-Bus standard. A block diagram of the ADF7020 is shown in Figure 4.
Figure 4. Functional block diagram of the ADF7020.
The ADF7020 fully integrated, low-power radio transceiver operates in the license-free ISM bands at 433 MHz in China, 868 MHz in Europe, and 915 MHz in North America. It integrates the full transmit and receive RF sections as well as analog and digital basebands. Implementing a radio card for an AMR-enabled utility meter13 typically requires the ADF7020, an antenna, a small number of external passives, and a simple microcontroller to run the communication protocol, as shown in Figure 5. The ADF7020 significantly eases the burden of the external microcontroller by integrating an ultralow-power, 8-bit RISC core to run some of the lower-level communication functions. This can eliminate the need for a separate communications-specific microcontroller in many cases. Meter manufacturers are also choosing the ADF702x family over competitive parts because their radios offer best-in-class sensitivity and blocking performance, resulting in better range between meter and data collector. The ADF7020 offers blocking performance in excess of 70 dB, meaning that the wanted signal can be detected and decoded correctly even when an unwanted out-of-band signal is up to 70 dB higher than the wanted signal. Adjacent-channel rejection is approximately 40 dB, and sensitivity can be as low as –120 dBm depending on the data-rate. This is more than 20 dB lower than the best performing ZigBee® solutions.14
Figure 5. AMR-enabled utility meter.
Most industry participants recognize that a fully working home area network linked with the advanced meter infrastructure is a number of years away, yet the benefits of such a system mean that many companies are actively involved in developing solutions for home area networks today. A graphical depiction of the home area network is given in Figure 6.
Figure 6. Home area network.
AMI and the smart grid are seen as key potential technologies to improve energy efficiency, ultimately helping in the goal to reduce carbon emissions. Analog Devices is committed to providing innovative and energy efficient devices to enable this market and to doing its part in improving energy efficiency and promoting energy conservation in the years ahead.
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