Study On Online Detection System Of Moisture Content Of Manufactured Sand Based On Capacitance Sensor

The sand material which is convenient to obtain and low in price is an important building material in the preparation of concrete,and the moisture content of sand is an important indicator that affects the quality of concrete.At present,there are various methods for the moisture content of sand,like traditional drying methods,resistance method,inductance method and neutron detection method,etc.,but most of these methods are offline measurement,which takes a long time and the sampling is not accurate.A high-precision variable dielectric constant capacitance sensor will be developed for the detection of the moisture content of machine-made sand,the use of non-contact online measurement could effectively avoids the disadvantages of low repeatability,large hysteresis error,and poor linearity caused by uneven distribution of water content.Due to its sensitive dynamic response,the capacitive sensor can effectively capture the capacitance change of pF level in a short time,which is very suitable for the measurement of water content with high precision.In the practical application of capacitive sensors,the thickness of the electrode plate will generate a small amount of arc-shaped electric field lines on the side of the capacitor electrode plate,causing the edge effect of the capacitor.This paper will use the edge effect to design a capacitance measurement device for mechanical sand moisture content.This capacitive sensor is flat and can be mounted on large conveyors for non-contact and wear-free online measurement.Through theoretical analysis and experimental verification,a flat capacitive probe with a certain angle based on capacitor edge effects was developed to improve the measurement accuracy of the capacitance sensor by optimizing the shape and mechanical structure of the capacitor plate.Without affecting the movement pattern of the machined sand,the moisture content of the machined sand is monitored online.Through the high-precision integrated chip CAV444 and its supporting detection circuit,the serial port is used to communicate with the PC terminal and the human-computer interaction interface onthe PC terminal is designed to complete data processing and output of moisture content using the communication between serial port and PC terminal.Through the investigation of the use scene,it can be known that the water content of the machine-made sand in construction is generally lower than 5%,so the measurement range of the developed water content capacitive sensor is 0% ~ 5%.Experimental measurements show that the measurement range of the water content capacitive sensor is 0% ~ 5%,the output voltage is 0 ~ 5V,the hysteresis error is less than 2%,the repeatability error is less than 1.2%,and the measurement error is less than 6.2%.Therefore,the on-line detection system of the sediment content capacitance sensor has strong anti-interference ability,and can perform high-precision online measurement within the available measurement range.