Reference design for accurate water/heat flow monitoring

October 07, 2014 // By Graham Prophet
Maxim Integrated's complete, easy-to-use flow meter system achieves 10x better accuracy and ultra-low-power performance, lasting up to 20 years on a single battery.

Utilities can now improve water- and heat-metering accuracy by an order of magnitude, while operating for up to 20 years on a single A-size battery with the MAXREFDES70# ultrasonic flow meter reference design.

Traditional mechanical flow meters measure water and heat usage with spinning wheels that easily get out of calibration due to wear from friction and contaminants. This causes inaccurate meter readings and repeated, expensive on-site maintenance costs. Not only do these inaccurate readings reduce revenue, they also prevent leak detection, potentially wasting millions of gallons of clean water a year. The MAXREFDES70# ultrasonic flow meter is the modern alternative. This solid-state meter is 10x more accurate than mechanical meters, and 4x more accurate than competitive ultrasonic solutions. This accurate measurement is done without the use of heavy batteries, and the flow meter uses a single “A”-size battery that can last up to 20 years. Measuring as little as 0.5 litres of water per minute with better than 1% accuracy, its fast ultrasonic pulses can be customised to the pulse frequencies required by flow conditions. It can detect even minor leaks that the mechanical meters will never find. It maximises uptime and provides the most accurate data possible.

At the heart of the MAXREFDES70# reference design is the MAX35101, a complete time-to-digital converter with analogue front-end (AFE) that measures the difference of upstream and downstream ultrasonic pulses. Supporting flow measurement at low rates (< 30 l/hr), the MAX35101 offers the highest time-to-digital conversion accuracy (20 ps) on the market today.

It offers improved low-flow accuracy: time-to-digital accuracy of 20ps (4x better than competitive ultrasonic designs) with early edge detect and multihit capability. Easy to implement, the design includes free schematics, layout files, and firmware that are available for immediate use and customisation; an evaluation (EV) kit with the MAXREFDES70# board, transducers, and USB interface is available with evaluation software. A single “A” battery of 4Ahr capacity provides up to