Research On Signal Processing System Of Multi-channel PVDF Piezoelectric Thin Film Grain Loss Sensor Based On DSP

Grain loss sensor is one of the key technologies for optimizing the operating parameters of combine harvester,reducing harvest loss,realizing refinement and intelligent harvesting.Aiming at the harvest loss detection of combine harvester in favor of using multi-channel grain loss sensor to obtain grain loss amount information,a set signal processing system of multi-channel grain loss sensor utilizing PVDF films was studied in this research.The 12 channels grain loss sensor utilizing PVDF films were used as the research object,and the DSP was used as the core processor.The method of identifying physical particles colliding with the sensor from the sensor’s sensing signal was proposed.And the performance test of the signal processing system was completed in the laboratory.The main contents and conclusions of this research are summarized as follows:(1)The grain collision experiment was carried out based on the grain loss test bench,the output signal of grain loss sensor utilizing PVDF films under no-load condition,the response signal amplitude and convergence time parameter under the action of grain collision were analyzed.According to the functional requirements of the signal processing system of multi-channel grain loss sensor,the overall research scheme of the system was constructed.(2)The hardware platform required for signal link of signal processing system of multi-channel grain loss sensor utilizing PVDF films was analyzed.The hardware design of each function module was completed according to the hardware architecture of the system,including signal conditioning module,DSP core processor module based on TI company TMS320F28335,A/D conversion module,CAN communication interface circuit and power supply circuit.The selection of key components in signal conditioning module is realized by the method of circuit simulation analysis.And the circuit board of each function module was designed and manufactured.(3)Based on CCS 6.1.3 integrated development environment,the software functions of the system were developed,including synchronization sampling program for multi-channel data using A/D conversion module,arithmetic mean filtering algorithm,collision particle recognition and counting algorithm based on large number judgment and time window,the underlying driver of eCAN module on DSP chip and the communication service program based on CAN bus protocol.(4)Based on the hardware platform of signal processing system,the performance of signal conditioning module,A/D conversion module,digital filtering algorithm and CAN bus communication module were tested independently.And the test results verified that the design of each function module can meet the actual functional requirements of the signal processing system.(5)The main factors affecting the detection performance of signal processing system were analyzed.Using the two regression orthogonal rotation combination design method,the detection performance of the signal processing system is ideal for the for the identification of the collision particles under the boundary condition setting of the threshold voltage Y_T is 0.7 V,and the time window W is 5.5 ms.Under this boundary condition setting,the detection error range of the system to ABS pellets that collided with the single channel of the PVDF piezoelectric thin film sensor was-5.0%~6.0%,and the average absolute error is 3.8%.Under this boundary condition setting,the detection error range of the system to ABS pellets that collided with six channels of the PVDF piezoelectric thin film sensor was-3.3%~6.3%,and the average absolute error is 3.2%.