Wireless Communications For Smart Meters Enable Smarter Consumers

Nov. 28, 2011
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Fig 1. A smart meter may include one or more sensors interfaced to front-end electronics, an energy source with the associated power-management circuitry, a communication node, and a microcontroller for system management.

Fig 2. Smart Metering’s MultiReader system is based on the Analog Devices ADF702x family.

Fig 3. Three-input MultiReader-C Units can be connected to up to three pulse emitter devices and provide real-time water consumption, stored data based on a fixed calendar, and measurements processed applying specific algorithms.

Fig 4. The MultiReader-R battery-powered repeater typically is installed on a pole and is used to extend the range of the single meters. It communicates with meters, other repeaters, and concentrators.

Progress in technology is making possible the replacement of mechanical and electromechanical meters for energy, water, and gas with digital meters showing advanced functionalities. With these new tools in their hands, users are evolving from a purely passive role to a more active one, in which everyone can take control of their consumer habits and define their own strategy to save resources. The key word is “communication.” With the new technology, utilities and users can communicate, paving the way for new scenarios of smart usage of primary resources.

Smart Meters

There are several advantages to using smart meters. Utility companies can benefit from the automated data collection, avoiding human errors due to manual readings and, ultimately, reducing labor cost. Also, statistical data collection becomes easier, allowing optimal sizing and utilization of the distribution network. Diagnosis and instantaneous fault detection enable predictive maintenance, resulting in a more efficient and reliable distribution network. Utilities can also offer additional services such as real-time pricing, based on different time slots during the day. Some operations can be postponed in time, when the cost of the service is lower, so users can save money and utilities can effectively manage peak demands.

Once connected to the home network, smart meters can provide useful information about the consumer’s habits. It will be possible to know the energy consumption of a washer cycle, the water required to water the garden, or the daily gas consumption for heating. Several studies show that simple awareness can produce savings of 20% or more. Given the opportunity to save money by curbing resource use and given the technology to take action to reduce it, consumers will take the action, with savings up to 50%.

Smart meters will allow a reduction of the primary resources on the user side, as well as savings on the losses on the utility side, ultimately helping to reduce carbon emissions and making the Earth a greener place to live.

Smart Meter Structure

Depending on the application—energy, gas, or water metering—a smart meter may have one or more sensors interfaced to front-end electronics, an energy source with the associated power-management circuitry, a communication node, and a microcontroller for system management (Fig. 1).

Several technologies are available when implementing a networked metering system, though two are beginning to dominate the market: wireless short range (SRD) and power-line communications (PLC). PLC is especially suited for energy metering, since the power-line carrier is available for free. For water and gas meters, SRD is becoming the obvious choice due to the lack of a suitable power-line carrier. Also, gas and water meters are battery powered, making power consumption very critical.

To achieve the best tradeoff between power consumption and communication range, meter designers are choosing radios in the sub-GHz bands, like 915 MHz in North America, while in Europe the bands of interest are 868 MHz and 433 MHz, with a growing interest in the 169-MHz band. Most meter manufacturers are also considering the 2.4-GHz frequency band, which is free worldwide.

However, for a given power consumption, radios communicating at these frequencies have a shorter range than sub-GHz radios. Wider range is vital for gas and water meters, which can be placed in hostile environments for RF propagation, like basements and underground pits.

Multireader Systems

Advances in wireless short-range transmission are making possible the monitoring of water distribution networks. Water use typically is monitored using mathematical models and sporadic measurement at the input of the distribution network and user connections. Today, with suitable hardware, it is possible to perform synchronized, multiple measurements that allow proper management of the distribution network.

The meter allows automatic meter reading (AMR), which can be used for billing but also to detect losses in the network. With synchronized and frequent measures on inputs and outputs, utilities can perform a water budget on a monthly, weekly, or even daily basis. This way, it will be easier to detect losses in the network due to failures or illegal water usage. Utilities also can offer additional services to their customers, like loss detection in the user network by monitoring consumption during nighttime or off-peak hours.         

A battery-powered wireless network for water monitoring is a difficult requirement. The meters need to work for several years, 10 years, or even 15 years, with a limited source of energy, in a hostile environment. Electromagnetic interferences due to outband interferers such as radio and TV broadcasting, GSM basestations, or inband interferers like remote controls can reduce the receiver sensitivity and in some cases can block the receiver itself. Also, weather conditions or metallic objects like drain pipes or parked cars can compromise antenna performance and radio-wave propagation. High humidity levels and thermal cycling can induce mechanical stresses or affect battery performances too.

All these factors can affect the overall reliability of the system and impact maintenance costs that must be kept very low. Given these operating conditions, the device should be very sensitive and robust in the presence of interference. It also should require low power consumption. Smart Metering conducted a benchmark between available short-range devices and chose the Analog Devices ADF702x family of wireless transceivers, which was demonstrated to be the best on the market in meeting these demanding requirements.

Smart Metering has developed the MultiReader System, based on the ADF702x family, to meet the needs of the utilities for water monitoring (Fig. 2). It comprises the water meter MultiReader-C, the repeater MultiReader-R, and the concentrator MultiReader-G.

The MultiReader-C is a battery powered counter that can be connected to up to three pulse emitter devices (Fig. 3). The meter can provide real-time water consumption, stored data based on a fixed calendar, and measurements processed by applying specific algorithms. All these capabilities allow several services like synchronous measurements on different points, water consumption in a specified time interval, and reporting of other useful information like reflux, counter shutdown, and user losses.

The MultiReader-R is a battery-powered repeater typically installed on a pole (Fig. 4). Used to extend the range of the single meters, it communicates with meters, other repeaters, and concentrators. The MultiReader-G collects the data from meters and communicates with a central office via the GSM network.

Installation and maintenance of a reliable wireless network for water metering requires hardware, software, and system management capabilities, which Smart Metering has developed over time.

ISM-Band Transceiver Technology

Analog Devices SRD transceivers cover from 75 MHz up to 1 GHz. The most popular devices are the medium-band ADF7020, (100 to 200 kHz, up to 200 kbits/s), the narrow-band ADF7021 (9 to 25 kHz, up to 32 kbits/s), and their derivatives. Flexibility is one of the main characteristics of these devices. Several parameters can be programmed to achieve the best tradeoff between performance and power consumption.

The transceivers allow amplitude shift keying (ASK), frequency shift keying (FSK), on-off keying (OOK), Gaussian frequency shift keying (GFSK), and minimum shift keying (MSK) modulation schemes, programmable output power from –16 to +13 dBm, and many programming options for the low-noise amplifier (LNA) to trade off sensitivity, linearity, and current consumption. The differential LNA input stage, the power-amplifier (PA) ramp control, and the Gaussian and raised cosine data filtering all help the device work properly in a complex electromagnetic environment.

Of the same family, the ADF7023 embeds an 8-bit communication processor for the packet handling, radio control, and smart wake-mode functionality.  The communication processor eases the processing burden of the companion processor by integrating the lower layers of a typical communication protocol stack.

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