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Hand-held moisture meter based on LED technology


VTT has developed a prototype hand-held moisture meter based on near-infrared LED (NIR LED) technology for professional industry applications. The new sensor was recently tested in joint experiments with Valmet Automation. It measured moisture in a fast-moving paper web with the purpose of being utilised in troubleshooting applications in cardboard production lines.

NIR spectroscopy is a powerful tool for solving analytical applications and there are a variety of commercial sensors and instruments available for laboratory and on-line applications. Miniaturisation and cost reduction of optical spectrometers is expanding the scope of applications even further: hand-held, mobile and networked analytical sensors are useful in optimising production efficiency and quality for the complete business chain from purchasing or harvesting the raw materials to supply logistics, incoming inspections, process measurements, product delivery logistics, quality and authenticity in the retail and eventually for measurements serving end users. VTT has previously developed technology based on MOEMS FPI based spectrometer for high-volume applications. LED-based sensors cannot compete in price with MEMS technology in high volumes, but LEDs can offer cost-effective solutions and rugged construction for many small and medium-scale applications.

The LED-based sensor is a hand-held, non-contact gauge capable of measuring moisture and temperature within less than 1 second. Thanks to the low power consumption of LEDs, the system is fully battery operated and it can be controlled via Bluetooth by a mobile phone. The sensor operates at InGaAs region, where water has two distinct absorption bands: one at 1450 nm and the other at 1940 nm. However, the selection of NIR LEDs covers a wide range from the edge of visible light to over 4 microns, so the idea used in this moisture sensor can also be utilised for other analyses by changing the LED wavelengths and detector type.

VTT continues to work on this field by actively following advances in NIR LED technology and developing new applications.

Further reading:
Scientists developed a miniature gas sensor for mobile devices – Applications from monitoring air quality to healthcare & wellness