by Rian Sullings, Manager Smart Metering and IoT - WaterGroup
Just like the smartphone revolution of the past decade, smart water meters are now incorporating more advanced sensors and technologies. These advancements bring about greater value and functionality from the new generation of meters and further support the business and uses cases for their deployments.
Digital water metering hardware can be placed into two distinct categories:
- Retro-fit Devices: an electronic device which is attached to an existing mechanical or digital meter to record water usage data. The retro-fit devices typically include wireless communication modules.
- Integrated Meters: a complete one part unit capable of measuring flow, on-board recording of water usage data, and wireless data transmission.
Both offer the ability to remotely collect water use data, yet each type is vastly different in appearance and method of operation. It is necessary to understand these differences when choosing a solution, especially for critical or larger scale deployments.
Accuracy and Reliability of Data
Perhaps the most significant difference is in how the flow of water is translated into digitised data. Retro-fit devices are most often connected to mechanical meters which contain pistons, stators, and turbines that are moved by flowing water. This movement is used to drive mechanical registers which indicate the meter reading. Retro-fit devices use sensors to detect the movement of mechanical parts and equate that to a volume of water being used. These sensors are typically mechanical switches or HAL effect sensors that detect the passing of a magnet fitted to an internal gear or a dial on the register, or use induction techniques to detect the movement of a particular dial. I've covered these types of interfaces in more detail here: Transforming Mechanical Meters into Smart Water Meters. These sensors output 'pulses' which are digital data points that are read by retro-fit metering devices.
The complexity of these mechanical systems means that there are multiple points of potential failure such as damaged sensor cables, stuttering of gears causing multiple pulses, electromagnetic interference, wear of moving parts, and so on. This can result in discrepancies between these three key aspects: 1) the actual volume of water used, 2) the value displayed on the physical register, and 3) the digital value stored in the retro-fit devices that is transmitted over the air.
Integrated meters on the other hand, generally use electronic measurement techniques such as ultrasonics to record the flow of water. This electronic measurement computation is logged in internal memory and gives the exact values that are displayed on the electronic register. This means that the digital data that is logged in memory is exactly what is shown on the register and is also exactly what is transmitted over the air to the meter data management server. This results in consistency of information displayed on the physical register and in digital data.
While the discrepancies between physical readings and digital readings with retro-fit devices is generally only a few percent, it only takes the slightest margin of error to raise concern of the trustworthiness of the technology, especially as digital metering is a relatively new concept for most households. The damage to trust and reputation can have deep long-term effects on public acceptance of digital metering roll-outs. It can also incur significant costs if inherently inaccurate data is used for billing purposes as many water users may question the legitimacy of their bills, which then incurs costs for utilities in manually validating readings, customer engagement, and dispute resolution.
Simplicity of Design
Integrated meters can use mechanical flow measurement techniques, however many use solid-state electronic techniques such as ultrasonics which are becoming increasingly popular. There are many advantages in using ultrasonics over mechanical meters for performance and accuracy, but in terms of integrated vs retro-fit digital metering, there are great advantages in terms of simplicity and elegance as a result of the design.
Solid-state metrology methods require electronic components such as processors, circuit boards, and batteries which must be securely enclosed. By integrating the components required for data logging and wireless communication inside the same enclosure as the metrology components, the outer casing design can be simpler and less complex which makes it less susceptible to external interference and damage. Integrated meters do not require awkwardly shaped add-on components which can be easily snapped off, nor do they require sensor cabling to be exposed externally to the meter making it susceptible to damage from animals, lawn mowers, vehicles, etc.
While some retro-fit devices address these issues by customising the enclosures to fit more closely to specific makes and models of water meters, they still suffer from issues arising from the disconnect between the mechanical meter and the data logging components. Many also continue to have protruding antennas which can be easily damaged.
Integrated digital meters now last as long as many mechanical meters, thanks in part to the rise of LPWAN wireless technologies such as NB-IoT, Sigfox and LoRaWAN. These low power wireless technologies make it possible to transmit detailed meter reading data on a single long-life battery pack for well over 10 years. Therefore, there is typically no need to replace radio components before the whole meter is due to be replaced. By integrating these technologies inside a water meter, the need for additional site visits and truck-roll throughout the life of the system are greatly reduced.
These new LPWAN technologies are intended specifically for uses cases where long battery life is essential. With water metering regarded as critical infrastructure, wireless network operators are obliged to maintain these networks as long as they are in use and with more utilities, government, and large commercial organisations adopting them for the long term, these networks are designed and scheduled to be supported long into the future. Future advancements will bring benefits to new devices but will not inhibit the ability of existing ones to operate and reliably deliver data.
Integrating Additional Sensors
In addition to integrating data logging, and wireless communications, integrated meters also offer the opportunity to include additional sensors inside the meter. While temperature can be used to indicate water quality and alert for frost issues, pressure sensors can also be used to indicate compliance with customer pressure requirements and detect leaks and bursts within the supply network.
Integrated meters are rapidly gaining popularity for smaller residential size meters but meters of all sizes can include integrated 'smart' components. Larger meters are more commonly adopting solid-state metrology such as ultrasonics and with these technologies becoming more power efficient; it is now possible for large solid-state meters to operate for their entire lifespan on batteries and also to include low power wireless communications.
Large meters tend to serve those who use large volumes of water. Where more water flows, the more that data can be used to solve problems and improve the sustainability of water supplies.