Design And Achievement Of Automatic Control System Of Air Cleaner In Clean Operating Room Of Hospital Based On PLC

In order to avoid contamination and infection caused during the operation, it must meet the requirements of national standard to the air cleanliness and pressure in the operating room. Besides, the air cleaner in the clean operating room must satisfy the requirements of the temperature and humidity in the operating environment. Air cleaner system consists of fresh air handling unit, cycle unit and air pipe. The fresh air handling unit is to provide fresh air for the operating room, fundamentally purify the air from outside and send it to the cycle unit after hydrothermal process. The air processed through the fresh air handling unit, and the air in the operating room is going to be filtered again in the cycle unit and send it back to the operating room after another hydrothermal process. Facilities such as surface cooler, electric heater and' electric moistening device are used in the air conditioner units to realize the hydrothermal process. The air is purified through three-level filter with low-efficiency, medium-efficiency and high-efficiency so as to meet the requirements of cleanliness. Ventilator is the power equipment which enables the air to move. The parameters monitored by controller are temperature, humidity and pressure differential in the Automatic Control System of Air Cleaner, and the devices which need to be controlled are air-heating and air-humidifying equipment, converter of ventilator and valves of all different kinds. The controller compares the parameter value with set value, and makes judgment, which motivates the control object to do the correspondent operation so that the control parameter could meet the requirements of the system.This paper succeeded in designing the Automatic Control System of Air Cleaner in the Da Shiqiao Central Hospital, and accomplished the stable operation of this system. SIMENS S7-200 series of PLC is the controller, corresponded with upper computer through PROFIBUS Fieldbus Technology. PLC is the bridge linking the upper computer, field sensor and actuator, which uploads the temperature, humidity and pressure differential collected by the sensor and transmitter from the lower-layer to the upper computer, and meanwhile transmits the controlling signals down to the field actuator. Redundancy structure of quantum hot standby is utilized in this design in order to improve the stability of the controlling system. Upper computer not only monitors the field as the operator's station, but also updates control program of the controller as the engineer's station. This paper, at the beginning, designed the general structure and controlling approach, and then introduced such general controlled variable and index as the analog and digital quantity monitored by controller. This paper focused on realization of the Automatic Control System of Air Cleaner, which included constituting the fresh air handling unit and cycle unit, and realization of real time monitoring at each function. Plus-minus pressure operating room used the separate cycle unit to realized air-conditioning, purifying and pressure difference controlling, which satisfied the particular requirements to the pressure by adjusting the air-valves. This system utilized PID control algorithm of PID controller to control temperature, humidity and pressure difference. The Automatic Control System designed in the system, at present, was already put into use, which operated well, attained all the criteria, and gained the recognition of users.