Study On The Measurement System For Fringing Electric Field Sensors

Fringing electric field (FEF) sensors which belong to novel capacitive sensorare widely used in non-destructive measurement of product characteristics inindustrial process control, including moisture, porosity, viscosity and density, withthe advantages of single-side access, adjustable signal strength and tomographycapability.This thesis analyzed the lumped parameter equivalent circuit of FEF sensorand introduced the floating voltage measurement mode and the short-circuit currentmode. Transfer functions and equivalent circuits of the two modes are given, andthe expressions of capacitance and conductance between electrodes are derived.Comparing the short-circuit current mode with the floating voltage mode in abilityof anti-stray capacitance and complexity of electric circuit, it is more suitable formeasurement.Based on LabVIEW platform, a measurement system is designed andexperiments have been done. The hardware included signal driving andconditioning circuit, with the functions of sweeping in wide frequency range andanti interference of stray capacitance. The software is comprised of drive signalgeneration, signal collection, frequency-sweep measurement, data calculation andresult display. The6mm wavelength sensor is designed for moisture measurement.Comparing the measurement of the system with the output of LCR-819, it showsthe system owns better performance than LCR-819.The FEF sensor measurement system is designed with TMS320F28335DSPfor multi-channel real-time measurement and control. The hardware included DDSfrequency-sweep driving circuit, anti interference signal measure circuit,simultaneous sample circuit with multiple high resolution ADCs, man-machineinterface and communication interface circuit. It builds the good platform for theindustry onsite measurement.