Data Acquisition and Linearization of Sensors: Greenhouse Case Study

Abstract

This work presents an overview of data acquisition, data logging and supervisory control of different parameters in a greenhouse. Raw measurement data from various parameters (surrounding temperature, pH of liquid, CO2 gas concentration) are acquired using DAQ and logged in a database for further analysis and supervisory control. For sensing the physical parameters, LM 35, pH probe, CO2 gas sensors are used. These sensors and DAQ needs uninterrupted power supply. For this purpose renewable energy is used to generate clean energy. Solar radiation can be used to generate electricity using PV (photo voltaic) cell and power conditioning circuit. This thesis is used to study the electrical characteristics of PV cell, which can be used to generate electricity from solar radiation for greenhouse purpose. Simulation studies have been carried out to know the electrical characteristics of PV cell for various irradiation levels. The sensors, which are mentioned above are mostly linear sensors. To use a nonlinear sensor suitably for data acquisition purpose, first of all the sensor linearization is done. In this work a thermistor is considered and its nonlinear characteristics are linearized using two methods (curve fitting method, Steinhart-Hart equation).