Design Of High Sensitivity Sky Screen Control Circuit

The sky screen is a photoelectric test instrument for external ballistic flight parameters used in the field.In the conventional shooting range test,a single sky screen can be used as a synchronous triggering device for other external ballistic testing instruments,and two sky screen targets can be used with a chronometer to test the flight speed of the projectile.Detection sensitivity is an important indicator reflecting the detection performance of sky screen targets.In external ballistic tests,it is found that the detection sensitivity of sky screen targets is affected by factors such as the brightness of the sky and noise,which will affect the detection performance and stability of sky screen targets.Therefore,it is necessary to study a control method whose sensitivity can be adjusted with the sky brightness to realize the sky brightness adaptive function,so that the sky screen can work stably without causing false triggering.It solves the problems of inability to work stably and low sensitivity due to the influence of external noise and illuminance.This article analyzes the working principle of the sky screen control circuit,combined with the factors that affect the sensitivity,neither changes the lens parameters nor changes the slit width,and redesigns the control circuit and the corresponding control algorithm.My research is as follows:1)The factors affecting the sensitivity of the sky screen are analyzed from two aspects:external factors and internal factors.The external factors include:the shape of the target flying object,the external noise,and the brightness of the sky background;the internal factors include:the characteristics of the vacuum photocell,the parameters of the optical lens,the influence of the width and length of the slit aperture,and the threshold voltage of the comparator.Through theoretical analysis of the sky screen sensitivity model,combined with the influence of external factors and internal factors,it is determined that the threshold value is changed by adjusting the magnification factor γ of the circuit,taking into account the shooting height of the projectile,the length of the projectile,the brightness of the sky and the noise changes.The voltage Ut thus changes the control scheme of the sensitivity of the sky screen target,and a control scheme in which the sensitivity of the sky screen can change with the brightness of the sky when the sky screen is working is proposed.2)Aiming at the functions that the control circuit needs to realize,in the circuit design process,the parameters in the sensitivity model are corresponding to the control variables in the circuit design,and the single-chip control circuit,noise acquisition circuit,sky brightness measurement circuit,and programmable filter circuit are designed.Programmable amplifier circuit,comparator circuit,drive circuit and PCB design and control panel design of the entire circuit;the control algorithm part introduces the influence of projectile factors,sky brightness factors and noise factors on the sky screen circuit control circuit,and gives gain control algorithm.Through the combination of control circuit and algorithm,a control method whose sensitivity can be adjusted with the brightness of the sky is proposed.Without changing the existing lens and slit width,the sensitivity of the sky screen is improved,the stability is enhanced and the phenomenon of false triggering is realized.3)After tests and verification,these control circuits work properly as expected.The double diameter of the sky screens is higher,sensitivity is automatically adapt to different sky brightness,the amplitude fluctuation of the output signal is lower,and the problem that the sky screen is incorrectly triggered has been solved.