Research On Urban River PH Acquisition System And Sensor Based On IOT

With the development of economy,all kinds of industrial sewage and domestic sewage are discharged into the urban river,which leads to serious pollution and destruction.The acidity and alkalinity of water quality,that is,pH value,is an important indicator of water pollution,changes in composition and chemical changes in the water environment will change the pH value.Due to the uncertainty of urban river water pollution,it is necessary to monitor the pH value of each region in the river.Demand for this,this paper designs and builds a set of multi node real-time sampling system based on the technology of Internet of things.Each detection node connected with a p H sensor,collects data and transmits to the system base station through the Zigbee wireless module,and the base station stores the each node data with its position information and time information to the cloud database,for web or mobile terminal reading.The core of the whole system is the pH sensor.During the design and construction,the E-201-C type compound electrode type p H sensor of Shanghai instrument electric science instrument Limited by Share Ltd is selected for the sensor,and its linear calibration and temperature compensation are carried out.However,the electrode sensor is easy to aging,bulky,easy to damage,susceptible to temperature and other shortcomings,and then the new type of fiber-type pH sensor was studied.First,both ends of the core fiber and standard single-mode fiber phase welding,the formation of fine-core fiber interferometer.When the broad-spectrum light source is transmitted through the fine-fiber interferometer,the interference spectrum of the broad-spectrum light source is translated with the change of the refractive index of the external material.The central wavelength of the interference spectrum is linear with the refractive index of the external material,and the sensitivity is 142nm/R.I.U,but the impact of temperature is very low,only 18 pm/°C,make up the electrode sensor susceptible to temperature shortcomings.Then,the polyethyleneimine and sodium alginate sensitive film were coated on the surface of the core fiber interferometer by layer self-assembly technique.The experimental results show that the center wavelength of the interfering peak will shift in a different pH buffer,and linearly with the pH value.The linear regression coefficient kis-1.25105,the regression constant bis 1528.62106,to achieve pH sensing.The sensor has a good repeatability and faster response time,between about 110-120 s.Finally,it is found that the common heavy metal ions in the urban river,copper,zinc,cadmium and lead do not destroy the sensitive film,which can be used to detect the acidity of the urban river.