Study And Design Of Portable Water Quality Sensor

Water quality detection technology based on optical method has the characteristics of high sensitivity,fast detection speed,non-contact and no pollution.The portable intelligent detection instruments have the advantages of small size,low power consumption,low cost,and simple operation.It is possible at any time and anywhere to meet water quality detection requirements and provide relevant water pollution data in the first time for environmental protection departments,as well as can minimize the damage to environment and surrounding people.Therefore,on the basis of comprehensive survey and market demands,a portable water quality sensor based on optical detection technology has been studied.The completed work are as follow:1?On the basis of reading the literature and researching the market fully,a stable and reliable Lambert—Beer law has been selected as the core instrument theory.Based on this theory,the output light intensity,measurement threshold,sensitivity and anti-interference performance of probe were designed and investigated:(1)Conical condenser water quality detection probe for enhancing signal intensity: in this dissertation,the realization of the converging conical probe output conditions were analyzed.When meeting the converging condition,the beam of the probe will focus on the output of the small side.Probe can enhance the performance under the conditions of low light and weak signal.Finally,an experiment was done to verify that the probe can effectively improve the utilization and out-beam intensity;(2)Threshold tunable and high sensitivity probe for different concentration environment: a simple structure which is similar to Fabry—Perot structure was designed.In order to improve the sensitivity and reduce the threshold of measurement system,through this structure,the angle of incident beam can be adjusted by the microcontroller to change the optical path length.With the increase of incident angle,probe sensitivity increases as well,for example,the sensitivity of 80° is 7.93272 1.46573(28)5.4121 times as high as that 0°(theoretical calculation value is 5.3262).And at the same time,it is 5 times longer than the conventional direct optical probe,which can significantly reduce the system measurement threshold;(3)Differential detection probe for eliminating measurement error: this probe is designed on the basis of threshold tunable probe and consists of the measurement channel and the reference channel configuration.The special structure is used to get differential signal to eliminate the measurement error caused by light source and optical path fluctuations,while can minimum the measurement threshold and increase the sensitivity.2?In order to complete the overall design of the sensor,appropriate electronic devices were selected to complete the system from the optical signal to electrical signal conversion.In this dissertation,the detailed signal processing module circuit was designed and the MULTISIM was used to simulate the results.Finally,we find that the simulation results are consistent with the theoretical design requirements.