Miller Magazine Issue: 132 December 2020

69 ARTICLE MILLER / december 2020 An essential, often overlooked, difference in the digi- tal microwave technology is the linearity and stability of the output. Resistive, capacitive, and analogue microwa- ve sensors have a nonlinear output making them very difficult to calibrate as they require numerous points to design the curve. Nonlinearity also implies low accuracy at the wet and dry end of the scale (Figure 1). Sensors with a digital measurement technique have a linear output, the sensor reading, and water content are directly and proportionally related. This method allows systems to achieve optimal calibration with a few points. In theory with a linear system, it is possible to achieve calibration with only two points. After these considerations, it is possible to define the ideal requirements of the moisture sensor: • In line with multiple readings per second, provi- ding quick feedback for the control to adjust on every batch. • Robust, made with high-quality materials to withs- tand tough industry conditions. • Linear output, stable over time, accurate in every condition and easy to calibrate. • Store multiple calibrations to be used with diffe- rent materials. • Ability to measure into the flow of the material. • Unaffected by dust or colours. • Unaffected by salt and minerals content. • Self-contained and easy to integrate into a pre-existing system. • Low maintenance and cost-effective. • Able to monitor from any device for full connecti- vity and remote analysis. • High-temperature resistance may also be required. • Some applications could also require ATEX or IE- CEx certificate. Thanks to the expert research and development team at Hydronix, all the above characteristics can be found in the microwave sensors with unique digital microwave technology made for the grain industry.