How to Design Smart Gas and Water Utility Meters for the Utmost in Power Efficiency

Designing a smart water or gas meter can present a vexing low-power challenge for embedded control systems requiring RF connectivity. These metering applications are inherently battery powered, and the battery life for these systems is expected to exceed 20 years. This requirement is dictated by the utility provider since a single service call from a technician often exceeds the entire cost of the smart meter. This battery chemistry is preferable because of its very low self-discharge behavior and ability to last for up to 20 years in metering applications.

Most smart meter providers have determined that they can differentiate their products by extending their communication range. In their system network topology, a fixed number of meters would communicate usage and billing information to a single repeater mounted on a utility pole through a sub-GHz proprietary network. The repeater aggregates and transmits the collected information back to the utility provider over a cellular network modem or other backhaul channel.

There are a number of ways to improve the TX link budget. The most obvious solution is to increase the output power of the transmitter using a power amplifier (PA). This is also the most costly approach in terms of battery life. Another strategy is to enhance the protocol to minimize the number of dropped messages and subsequent retransmissions.

Let's consider three design requirements for one particular smart meter redesign:

                • Allocate 40 percent more power budget to TX functions to increase range

                • Maintain existing LiSOCl2 battery size (A) and capacity (3650 mA-hr)

                • Maintain existing battery service life of 20 years

The strategy is clear: Increase the power within the TX budget while not increasing its total power budget. The reductions would have to be found in other functional areas, namely the RX, active and sleep mode budgets.

Designing a smart water or gas meter can present a vexing low-power challenge for embedded control systems requiring RF connectivity. These metering applications are inherently battery powered, and the battery life for these systems is expected to exceed 20 years. This requirement is dictated by the utility provider since a single service call from a technician often exceeds the entire cost of the smart meter. Because of this long-life design requirement, nearly all gas and water meters use a battery chemistry of lithium thionyl chloride (LiSOCl2).

Most smart meter providers have determined that they can differentiate their products by extending their communication range. In their system network topology, a fixed number of meters would communicate usage and billing information to a single repeater mounted on a utility pole through a sub-GHz proprietary network. The repeater aggregates and transmits the collected information back to the utility provider over a cellular network modem or other backhaul channel.

There are a number of ways to improve the TX link budget. The most obvious solution is to increase the output power of the transmitter using a power amplifier (PA). This is also the most costly approach in terms of battery life. Another strategy is to enhance the protocol to minimize the number of dropped messages and subsequent retransmissions. Although a much lower power approach than simply adding a larger PA, this technique can still increase the new TX power budget by as much as 40 percent over the current power budgets.

Let's consider three design requirements for one particular smart meter redesign:

                • Allocate 40 percent more power budget to TX functions to increase range

                • Maintain existing LiSOCl2 battery size (A) and capacity (3650 mA-hr)

                • Maintain existing battery service life of 20 years

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