Capacitive Grain Moisture Sensor

Determining the moisture content of grain products is very important for the quality, yield and cost of the production line. For this purpose, in-line or off-line, destructive or non-destructive measurement methods are widely used. In this study, an in-line, non-destructive capacitive humidity sensor is designed using analog switching based synchronous demodulation technique. The sensor system is tested under laboratory conditions and then installed in a real flour production factory. The results are tested and compared with reference humidity measurement systems. As analog switching based synchronous demodulation technique used in this study is an effective, cheap, and robust technique for achieving high signal-to-noise ratio (SNR); and a proper front-end circuit also minimizes the effect of temperature change on the sensor output, and effective, low cost sensor system is achieved. The sensor, while measuring the same product for long periods, shows almost no output change during day and night. Moreover its output for different type and humidity products show very similar values compared to reference systems. Hence, the designed capacitive moisture measurement system is shown to be a good non-destructive in-line sensor alternative in terms of cost and performance.