Smart Metering Frequency Products

In essence the standard smart metering system or smart grid is composed of one or more smart meters which have the ability to communicate with an in-home hub and a neighbourhood hub, which in turn communicates with a receiver being monitored by a utility company.

Smart meters are composed of three major blocks of circuits which may be integrated into a SoC or incorporated into the device as separate modules. The purposes of these modules are:

• Measurement
• Communication
• User interaction

All smart meters, regardless of the utility they are measuring, require accurate time-keeping in order to allow accurate data analysis and billing. Most importantly time synchronization also ensures reliable transmission of data to the neighbourhood hub and utility receiver in the wide area network as discussed below.

Not only is it important for smart meters to achieve accurate time synchronization, but they must also do so using only a tiny amount of power. Most gas and water meters will be required to maintain power for extended periods of time, reliant solely on battery power. This means every nanoamp of extra power consumption counts and it’s important to specify the lowest energy-consuming peripheral products possible for pairing with communication and measurement chipsets or smart meter SoCs.

In practice the requirements of smart meters mean additional specifications standards are required for frequency components: An operating temperature range of -25 to +55°C with a storage temperature range of -30 to +60°C is common within the industry, with ±10ppm stability over the operating temperature range being preferred to ensure radio frequency accuracy.

Ageing is also paramount: ±10ppm over 20 years is the widely accepted figure for ageing of frequency components within the smart metering industry.

Many types of communication protocol are common within smart metering systems including short range wireless standards for home or building networks, such as ZigBee and BLE (Bluetooth low energy). Neighbourhood area networks also make use of 2.4GHz ZigBee and BLE but also commonly use sub 1GHz communications. Finally WAN (wide area networks) may use GSM and 3G or Ethernet and fibre.

SMETS standard stipulates the use of ZigBee in some types of smart meter systems (see below) but for others engineers are free to find a novel solution.

These short-range networks within a smart meter system allow communication between the smart meter, in-home display (or "home-hub") and smart appliances within the building or home.

This type of communication between the meter, appliances and the home or building hub means the user can see a full picture of their energy usage, including a breakdown of that usage by appliance, great for monitoring peak time activity and energy budget expenditure. Some smart appliances and hub communications also allow for on/off signalling so an appliance can be controlled directly from the home hub.

For both Gas and Electric Smart Metering Equipment (GSME or ESME) the SMETS standard stipulates:

Both electric and gas metering equipment must also be "certified by the ZigBee Alliance as compliant"

The In-Home Display device used within the HAN must also meet both of these functionality requirements.

There are also auxiliary devices which may be included in the HAN section of a smart metering system, including prepayment interface devices and connected auxiliary load control switches.

In addition to the above requirements all smart meters must be registered and conform to DLMS (Device Language Message Specification) standards. DLMS have a conformance checking tool which you can find here.

In order to transmit data to a utility company the smart meter will then transfer data through a secure data network outside of the home, usually known as the wide area network.

WANs may consist of data transmission directly to the utility receiver, or depending on the density of meters and level of network coverage within an area, data may first be aggregated at a neighbourhood hub or data aggregation point (DAP) using ZigBee communication. This data is then parcelled into secure data packets and transferred using the WAN communication protocol.

Wide area network communication does not require the fast data rate necessary within HANs but must instead ensure the signal can be carried greater distances than those within the HAN. Protocols common to this level of network include Cellular GSM, LoRa, 3G technology and even Ethernet and fibre.

Lower data transfer rates are typically employed and available channels can be significantly narrower, requiring the use of smaller bandwidths.

Golledge recommend the following 32.768kHz crystals for use within smart metering projects. In particular:

• CM7V-T1A is available with a 6pF option help achieve low current consumption
• The most popular capacitance option for the GSX-317, 12.5pF, is perfect for pairing with the majority of industry chips

You can access more information on each of these 32.768kHz crystals below:

For boards that call for a 12.0MHz crystal timing solution, the GSX49-4 provides the lowest cost solution, whereas the GSX-331 features superb aging (±1ppm in the first year for many options) and has a small 3225 form-factor package to allow for more board space during the design stage.

Some of the communication protocols used within smart meters call for 24.0MHz and 26.0MHz frequency products. For meeting these frequency requirements we recommend the GSX-331 (with max. aging of ±1ppm first year for most options) and the GSX-333 (with max. aging of ±2ppm in the first year for most options)

Finally for projects which require 30.0MHz or 32.0MHz options we would recommend the GSX49-4 for projects where cost is paramount, and the GSX-331 for projects where aging is paramount. Don't forget our expert team will be happy to help answer any queries you have on using crsytals within your metering project. You can contact a team member here.

Both of our smart-recommended TCXOs feature aging of ±1ppm as maximum within the first year as standard, and both feature superb temperature stability options. The GTXO-93T usually represents the lowest cost option, whereas the GTXO-253 minimizes board space with a tiny 2520 form-factor package.

In particular TA0223A is perfect of filtering the 2.4GHz ZigBee band, ideal for use with meters utilizing this type of technology. Speak to our team today for more filtering options or for more details.

For metering applications which are required to withstand temperature fluctuations, the RV-8803-C7 RTC with temperature compensation and current consumption of only 240nA is a good option. Alternatively if power consumption is the determining factor in a design, the RV-1805-C3 consumes just 17nA in standby mode and is a popular option for meters which cannot easily access a power supply.