Measurement of Water Depth in a Class A Pan Using Ultrasonic Transducer and Programmable Logic Control (PLC)

Abstract

The aim of this study is to compare water depths measured by manually and PLC from a Class A Pan in field conditions using ultrasonic transducer. The study was conducted in garden of Faculty of Agriculture, University of Kahramanmaras Sutcu Imam in the summer season of 2019. A steel meter was used to measure water depth manually in the evaporation pan. Using the ultrasonic transducer, PLC measured water depth from the evaporation pan between 140 and 223 mm water depth at 8:00 am. An ultrasonic transducer is attached one end of sliding buttress, at which was 50 cm above from its inner-bottom at the center of the evaporation pan. The ultrasonic transducer was set to be able to read water depth and calibrated using sliding buttress. A program was written in CODESYS-ST language to measure the water depth from a Class A Pan using PLC, which was connected the ultrasonic transducer and uploaded to PLC. With the program, digital water depths were converted to millimeter water depths. To be able to read the water depth more accurately, each depth value read by the PLC was determined by averaging 30 measurements made successively at 300 millisecond intervals. In this processes, moving average method was used. Water depth measured by PLC was saved on the SD (secure digital memory) card. In the manual water depth measurements, there were 26 observations. The water depths on the manual measurement dates were matched with the water depths measured by PLC. A regression analysis was performed between the water depths measured by the steel meter and PLC in the pan, and determination coefficient (R2) was result as 0.96. The Mean Absolute Percent Error (MAPE) of these two data sets was calculated as 2.3%. The level of agreement between the two data sets; if the MAPE is below 10%, it is considered “very good”. The results of this study revealed that the PLC could measure the water depth close to the measured manually water depth in the evaporation pan with an ultrasonic transducer.