Water, gas, and electric utilities worldwide are rapidly deploying “smart metering” solutions to enhance operational efficiency and to better serve their customers. While the vast majority of utilities still use mechanical or analog metering technologies, “smart metering” solutions are being widely adopted throughout North America, with nearly half of all customers now being connected to some form of “smart metering” solution.
Automated meter reading (AMR) was the first wide-scale application of RF technology, recording, and communicating valuable customer-specific data that provides the foundation for automated metering infrastructure (AMI) solutions. Many of the technologies developed for AMR/AMI systems have been translated to other remote wireless applications, paving the way for the industrial Internet of Things (IoT).
Investments in AMR/AMI technology make sound economic sense for utilities, since these systems eliminate the time-consuming task of physically reading meters and shield field staff from potential customer confrontations if service needs to be shut-off or restored. AMR devices deliver accurate near real-time data that helps reduce delinquency rates, shorten payment cycles, simplify enforcement, streamline collections, aid troubleshooting, and reduce lost revenue caused by leaking pipes and theft of services.
The Endpoint is Key
The heart of any AMR/AMI solution is the endpoint, which can be designed either as a fully integrated absolute encoder register and RF transceiver or as a stand-alone encoder register working in concert with a separate RF transceiver. In water meter applications, the endpoint is often installed in an underground pit, where harsh environmental requirements demand that the endpoint be constructed from resilient materials, with the entire enclosure being UV-resistant, waterproof, fully encapsulated and hermetically sealed to protect the solid state electronics against moisture and humidity. The ideal endpoint should be equipped with a standard external antenna to ensure strong signal strength. In some instances, the endpoint can be attached to the building exterior of the dwelling, based on region and climate. The endpoint can also be connected directly to the existing water or gas meter as a retrofitted device.
AMR technology has been dramatically transformed from first generation rudimentary, one-way, short range RF systems, to more sophisticated devices that provide full two-way wireless connectivity between the endpoint and Fixed Network Transceivers (FNTs), strategically located throughout densely populated areas, with the entire network communicating via the TeslaNet Cloud Based Meter Data Management System. The proximity of the endpoint to the FNT varies, based on the signal transmission power, with 1 W transmission being ideal for achieving the widest possible transmission radius within the FCC unlicensed bands. Limiting both the length and the frequency of communication cycles increases battery life while reducing electromagnetic radiation emissions to levels 10,000 times less than comparable technologies, or roughly 5 percent of the EM radiation emitted by the average cell phone each month.
Advanced endpoints collect and transmit data using two-way communications, providing securely encrypted near real-time data to support a variety of functions, such as providing accurate measurements of energy consumption, warning of potential tampering or leaks, providing low battery status, indicating reverse flow, average flow rates, peak flow rates, etc. Enhanced product functionality demands energy from the battery, so a backward-looking design approach is needed to adapt product functionality to the performance characteristics of the battery.
LiSOCL2 Chemistry Delivers Long-Term Power
Electric utility meters draw small amounts of energy from the power grid to actuate the endpoint and thus do not typically require self-powered solutions. Water and gas meters, on the other hand, cannot be connected to AC power for safety reasons, so a self-contained power supply is required using long-life lithium batteries. The vast majority of remote wireless water and gas meters are powered by bobbin-type lithium thionyl chloride (LiSOCL2) batteries. LiSOCL2 chemistry is ideal for AMR/AMI devices and other remote wireless applications due to its high energy density, high capacity, wide temperature range, and exceptionally low self-discharge rate.
The main limitation of LiSOCL2 chemistry is high passivation characteristics, which limits energy output under high pulse discharge conditions. Remote wireless devices that require high pulses to support two-way communications need standard LiSOCL2 chemistry to be specially modified to generate and store high pulses.
This solution is preferable to the use of supercapacitors, which require more complex circuitry and a much larger space envelope, which is highly problematic for long-term deployments, including the need for balancing circuits when multiple supercapacitors are connected in series. Supercapcitors also feature a very high self-discharge rate of up to 60 percent per year.
Use Battery Only When Needed
It is possible to achieve 25-year battery life in AMR applications and 23-year battery life in AMI applications by precisely matching product functionality attributes to LiSOCL2 battery characteristics and by limiting power consumption wherever possible.
Designing a 25-year AMR device begins by thoroughly evaluating all available bobbin-type LiSOCL2 batteries. Since no two brands deliver the exact same performance, a main selection criteria must be to choose the cell that delivers the highest overall capacity along with the lowest annual self-discharge rate, which ranges from less than 1 percent per year to over 3 percent per year. Such a difference may not seem too substantial. However, once you consider the cumulative impact over a quarter century, even a small difference in the annual self-discharge rate can significantly impact long-term battery operating life. Using accelerated test methods with elevated temperatures to simulate long-term annual self-discharge rates may not necessarily reflect actual battery usage under real-life environmental conditions.
Energy conservation can be achieved through intelligent system architecture and design, including the skillful integration of low-power microprocessors and peripheral devices in combination with a low power communications protocol. To further limit power consumption, the endpoint must be designed to transmit only upon request, and then to limit power consumption during active interrogation and communication operations. These goals can be achieved by cycle management and communication timing.
The ideal solution employs a battery status indicator that accurately measures actual energy usage to provide up-to-date information regarding available battery capacity. When measured energy consumption reaches a point where approximately 85 percent of available battery capacity has been exhausted, a battery status icon on the LCD display can indicate a low battery status, and a warning message can be sent with every RF transmission. When 5 percent of calculated battery capacity remains, transceiver functionality should be shut off, giving the utility several billing cycles to retrieve current data reading and replace the endpoint. The replacement unit can be field programmed with data from the expiring endpoint to ensure full data integrity.
This design approach ensures that the self-powered AMR device will operate maintenance-free for decades, delivering maximum battery operating life and uncompromised product performance to achieve a lower total cost of ownership and a maximum return on investment: a relevant goal for all remote wireless devices.