Automation of Constant Head Orifice Off-Take Structure
Ghazali, Hapida (2005) Automation of Constant Head Orifice Off-Take Structure. Masters thesis, Universiti Putra Malaysia.
The efficiency of irrigation for paddy cultivation depends very much on water supply and demand to be provided during the growing season. Due to complexity in operating water intake structure, the Constant Head Orifice (CHO) was developed to overcome the problems which required intensive labour. A CHO off-take structure is an important structure in the irrigation scheme to facilitate measurement and provide constant irrigation water supply. Presently, all CHO off-take structures in Malaysia are manually operated. Target discharges are seldom met due to upstream water level fluctuations, and the operators are unable to cope with the opening and closing of the many orifice gates and the turnout gates. CHO’s are not automated due to the large number of gates involved in an irrigation scheme and there are many water level sensors required for the automation system. Automation is potentially one piece of the puzzle in trying to modernize and improve overall irrigation project performance. A CHO automation system was developed in this study in order to make improvement on the operational system of existing CHO structures by automating the gate operation through interfacing with Supervisory Control and Data Acquisition (SCADA) system. A double barrel CHO structure at Block M2 at secondary canal TB (Taliair B) in the Sg. Muda Irrigation Scheme, Seberang Perai Utara, Penang was chosen for the installation and testing of the automation system. The developed CHO automation system included mechanization of the intake and off-take gates, Programmable Logic Control (PLC), water level sensors, communication media and master control server. The system allowed the operator to automatically route scheduled changes in demand through their canal system utilizing water levels at the main canal and at the CHO stilling chamber, and time delay calculation. The “Kinetic Automation” controller unit can automatically maintain constant differential head at 100 mm. The master controller used the standard personal computer and customized SCADA package. Each gate is operated with Rotork IQ35F16A actuators which are controlled by the “Kinetic Automation” controller unit at site. Control is based on water level from MJK ultrasonic sensors and gate position sensor which was incorporated in the Rotork IQ35F16A actuator. Public Switch Telephone Network (PSTN) was used as a media of communication between the master controller and “Kinetic Automation” controller unit and MODBUS communication protocol. The study found that, there is a linear relationship between discharge and the gate opening. At a constant differential head, the discharge increased with increase in orifice and turnout gates opening. It was observed that there is a general increase in orifice gate opening for manual measurement compared to the automatic control. T-test comparison shows that the mean orifice gate openings for automatic control and manual measurement are not significantly different from one another. There was an overall increase in average discharge values between automation supply and manual gauging. Generally, the manual gauging discharges were higher than automation discharges for most flow settings. T-test comparison indicates that the average difference in discharge values from the automated supply and manual gauging is not significantly different from zero. In another words, the discharges from the two methods are not different from one another. The time required to open the gate by the automated CHO system increases with increase in orifice gate opening. A similar trend is observed for the manually-operated CHO. For any particular orifice gate opening, the time requirement for the automated CHO is always less than that required by the manually-operated CHO by as much as 1/11 to 1/5 of the time. There are huge benefits from the automation of the CHO; fast response in water supply, computerized control of water supply, easy and efficient operation, and well regulated irrigation water supplied remotely, easy maintenance and web enabled. The success of the project has eliminated the human problem and simplifies operational procedures. The CHO can be economically operated, with ease of discharge measurement and minimized cost of maintenance. Besides, DID needs to popularize the importance of Information Communication Technology (ICT) and automation of CHO in irrigation to its own staff as well as the general public. However this will require commitment from all those involved among all levels of government and private sectors
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