Application note; Welcoming Water Metering into the 21st Century

August 24, 2015 // By Graham Prophet
Maxim Integrated has posted an application note, by Kris Ardis, its Executive Director for Energy Products, that argues for an upgrade in water-metering technology – in support of its ultrasonic, time-of-flight-based MAX35101 device.

In its introduction the note contends, “... the Internet of Things (IoT) and smart utility grids have an opportunity to improve the world by deploying accurate, reliable water flow-measurement technology. Utilities need to understand and monitor how water is consumed so they can estimate water requirements, but their water meters today do not do a good job of helping us find waste. Given the increasingly scarcity of water resources, we all need to know where every drop of clean water is going. In short, we need a network of ubiquitous, smart water meters.”

Measuring water flow is actually hard. The most obvious way of measuring water flow is just how it has been done for decades–with a mechanical meter. A turbine inside a water meter rotates in proportion to the amount of water that passes, thereby detecting the flow of water. While this approach enables utilities to bill individual customers for their approximate usage, this method has flaws.” The app note goes on to observe that mechanical meters suffer from wear, contamination, mineral deposits, and that they are limited by mechanical inertia and friction to a not-very-low, lower limit of flow detection. (They have, in other words, a dynamic range problem.) “ Mechanical meters go out of calibration in as little as two years.

Maxim’s note continues by outlining solid-state solutions and focussing on its own offering (diagrams) based on time-to-digital converters working with ultrasonic pulses launched with and against the flow of the water. The 35101, the author asserts, “. ..solves all of the problems that have thus far prevented water meters from tracking wasted water or joining the 21st century in a connected IoT .”

Benefits include improved accuracy; “ Today's metering standards ask for accuracy at a low flow rate of ¼ gallon per minute [about 1 litre/min]. The MAX35101 can achieve 1% accuracy at 1/16 gallon per minute [~250 ml/min], which is the currently