# Design and Test of Real-Time Detection System for Cleaning Loss of Rapeseed Harvester
## 2 Materials and Methods
### Signal Processing Circuit Design
#### 2.3.1 Amplifier Circuit  
Because rapeseed kernels are small, the weight is very light, and the weight of the carob shells and short stems in the impurities is smaller than that of other crops. The signal amplitude generated by the rapeseed cleaning material is small on the inductive plate, and it is difficult to process and analyze the signal. Therefore, an in-phase proportional amplifier circuit was designed to amplify the signals of rapeseed kernels and impurities, which was conducive to the subsequent processing and analysis of the signals. An in-phase proportional amplifier circuit is an amplifier circuit in which the output signal is in the same phase as the input signal and the voltage or current value is proportional to a certain value. The advantage of the amplifier circuit is that the input signal can be amplified by a high amount, which is beneficial to the analysis of small rapeseed signals. The design diagram of the amplifier circuit is shown in Figure 4. The original signal is fed into the circuit through the P3 interface, the capacitor C11 filters out the DC component of the input voltage u\({}_{\text{i1}}\) and the resistor R3 transmits the signal to GND as a reference plane. The operational amplifier LMH6702 MF and R5, R6 and R4 constitute the first-stage in-phase amplifier circuit. (The manufacturer of LMH6702 MF is Texas Instruments, and the Nanjing branch address is Unit 08-10, 8F, Building A, Shimaochengin International Square, NO.52 Andemen Street, Yuhuatai District, Nanjing 210012, Jiangsu Province, P. R. China). The magnification factor of the first-stage amplifier circuit is 9, and the specific calculation formula is shown in (1):  
\[\text{A}_{1}=\left(1+\frac{\text{R}6}{\text{R}5}\right)\text{u}_{\text{i1}} \tag{1}\]  
In Figure 4, the L5 and L6 electronic components are magnetic beads. Magnetic beads have high resistivity and inductance, which are equivalent to resistance and inductance in series, and the circuit symbol of magnetic beads is the same as that of inductance. L5 and L6 and C12, C13, C15 and C16 are used to filter out the power clutter to ensure that the chips U5 and U9 (the operational amplifier LMH6702 MF) work more stably. The principle is that L5 and L6 are connected to the circuit in series only to ensure that the direct current passes through, blocking the AC clutter, and the capacitors (C12, C13, C15, C16) are in parallel with the power supply and the ground, which can allow the alternating current to pass; that is, the residual AC clutter flows to the ground through the capacitor. Capacitor C11 was designed to filter out the DC component. However, in practice, due to the low probability of perfect consistency between the physical components produced by the manufacturer and the idealized device and the limitation of the component production process, the idealized device cannot be achieved, thus resulting in a very weak DC component in the amplifier LMH6702 MF to be amplified. Therefore, C14 was designed to filter and correct the signal after the first stage of amplification, which is used to filter the DC component of the output signal after u\({}_{\text{i1}}\) amplification. C17 was designed to filter and correct the signal after the second stage of amplification, which is used to filter the DC component of the output signal after u\({}_{\text{i2}}\) amplification. The amplified signal is filtered step by step by series capacitors in the amplifier circuit, and the actual error is reduced as much as possible by filtering, and the DC component is finally filtered out. When the device chip is affected by temperature, the output signal through the first-stage amplifier circuit will form a drift (superimposed irregular signal, this irregular signal energy is very weak, caused by the performance of the device itself). To solve this problem, the resistor R7 is designed to reduce the energy of this irregular signal until it is negligible.