Development of a capacitive, non-invasive and coplanar-electrode transducer for measuring iron ore moisture

Currently, the mineral industry makes iron ore beneficiation processes in humid or natural moisture. Excessive moisture in iron ore can affect the beneficiation process, causing loss of productivity and transport issues, as well as reducing the efficiency of dewatering subprocesses and safety. The traditional technic for measuring iron ore moisture is the standard oven method, which is very accurate, but not very representative. Furthermore, it has a high time response: up to 24 hours for each mineral sample. Consequently, corrective and preventive actions to the process become inefficient. Alternative technics, as microwave method, performs online moisture measurements, but with low accuracy. Recently, we developed a high accuracy capacitive sensor for measuring ore moisture, but not online (bench device). This paper refers to the development of a capacitive, non-invasive, coplanar-electrode transducer for iron ore moisture measurement, designed for online applications. To achieve this, we constructed a signal conditioning system, based on an 8-bit microcontroller, and a driven shield for the sensor element. The system transmits the processed data via radio frequency to a computer. Also, it applies a statistical filter to the measurements, based on standard deviation and moving average, as a way for minimizing electromagnetic interference. The statical calibration results reached a coefficient of determination of 98.41%. The coplanar, non-invasive approach of the transducer offers the advantage of preserving the physical integrity of the sensor electrodes as well as a future online application.