The most important chemical measurement for water quality is pH, but current pH sensors suffer from reference drift and high maintenance costs. This drift over time in the reference electrode leads to increasingly unreliable measurements. Therefore, most current ion selective electrode sensors cannot be used for monitoring over long periods of time without the need for frequent, labour intensive calibrations. Hence, they cannot be used to provide accurate measurements when deployed autonomously in smart sensor networks. The EU-funded pHenom project addressed this challenge by developing a next-generation pH sensor that incorporates a reference calibration technology. “We know we cannot stop the drift as it is intrinsic to the sensor, but we have achieved a novel way to track it, thereby allowing the sensor to self-calibrate,” states Steven Gahlings from the SME ANB Sensors and pHenom coordinator.
Drift problem solved
ANB’s patented ‘iRef’ technology provides a pH sensor that is manual calibration free and does not suffer from reference electrode drift during its entire deployment. It works by placing a second electrode into the reference chamber, alongside the reference electrode. This reference tracking electrode periodically measures any drift in the reference electrode and then automatically compensates for this in the pH measurement. “In this way, iRef eliminates reference drift and thus the need for manual calibration,” Gahlings explains. Researchers developed an iRef prototype capable of being integrated into commercial glass electrodes, which have been the go-to way for measuring pH since the 1920s. Testing showed that the iRef response is accurate enough to calibrate the glass electrode and can operate independently of even the most extreme changes to the reference chamber environment, including the ingress of contaminants.
A smart result
Calibration is autonomous with iRef, which means manual calibration is no longer needed, and the pH sensors can be easily deployed across the water resource network. According to Nathan Lawrence, the inventor of pHenom and CEO of ANB Sensors, “pHenom is a pH sensor that you simply turn on, throw into the water and take pH measurements.” The iRef technology allows conventional commercial glass electrodes to be converted into smart pH sensors. These can be installed in lakes and rivers, water supply infrastructure, reservoirs, pipelines and wastewater treatment plants and can be networked together for better management of Europe’s water supply and environmental monitoring. They can also monitor the marine environment and even the pH of cows’ stomachs. The pHenom project delivers the first smart, manual calibration-free pH sensor suitable for networking and compatible with the IoT. This allows companies and government-funded agencies to use their scarce monitoring management resources much more efficiently, thereby saving time and money. Gahlings concludes: “The best thing about pHenom is that everybody we have spoken to, from glass electrode pH sensor manufacturers to end users, have been excited about the revolutionary iRef technology and how it solves a 100-year-old problem to provide a pH sensor fit for the 21st Century.”
pHenom, pH sensor, calibration, water, reference electrode, iRef technology, glass electrodes, electrode drift, ion-selective electrode, smart sensor