The Pressure-steam Sterilizer Temperature Control System Design

It has been over 20 years since the single-chip entered China, and it has been applied in the different practical projects because of it's characteristic, such as small bulk, multifunction, flexible extension, convenient use and so on. This thesis will introduce the application of single-chip AT89C52 in the temperature control system of pressure-steam sterilizer.The pressure steam sterilizer is composed of four parts, machine part, measurement part, control part and display unit part. The reasonable mechanism design may maximate the available space, saves material and transfigures the contour. The test system is using kinds of sensors to measure the informations need to be measured, for example the steam sterilizer requests to have the pressure and temperature targets, this need use the pressure transmitter and the temperature sensor. The different place of Sensors in sterilizer will obtain different results, for instance the temperature sensor near the gate, the demonstration temperature maybe low. The control part may use the microcomputer, the monolithic integrated circuit, PLC or the programmable logical component control. The control system is the pressure steam sterilizer hard core, if compares the pressure steam sterilizer with human, the machine part is the body and the control system is the heart.This task is studies the pressure steam sterilizer control system, promotes the technology in the original foundation, enables the sterilizer to achieve the disinfection antiseptic temperature in a short time and keeps the temperature in the stipulation time. The pressure steam sterilizer control system should have the following function:(1) displays its working condition;(2) has a good Human-Computer Interaction interface;(3) setups the antiseptic parameter willfully;(4) records the antiseptic process information automatically;(5) prints the antiseptic information and the curve have been recorded momentarily;(6) stops runnning and gives an alarm automatically when it breaks down or error in cause of movement process. This system's control principle is using the temperature sensor to convert the pressure steam sterilizer temperature signal into electrical signal, because generally these electrical signals are quite weak, needs to be magnified by the signal recuperation electric circuit and then deliver to the monolithic integrated circuit main chip by the mold/number transformation—that's the actual temperature of the pressure steam sterilizer can be measured. like this can determine the pressure steam sterilizer the actual temperature. Compare the acutal temperature with the beforehand ones, the monolithic integrated circuit outputs a control quantity by the fuzzy control method, which controls the bidirectional silicon-controlled rectifier's breakover angle after the digital-analog transformation, to realize controling the heating capacity, achieves the disinfection antiseptic effect.This control system consists of four parts:input unit(which samples theirput signal), output unit(which controls the temperature), keyboard unit(by which the operator can set the parameters and control the sterilizer)and display unit(which displays the temperature and time). Hardware circuit design, software design, anti-disturbance measurement etc, and A/D conversion and D/A conversion use 8 bits ADC0809 and 8 bits Dac0832 respectively, but scm extension interface circuit chooses 8255. The thesis aimed at the whole frame of the control system, working principle and hardware circuit to make an enucleated detailedly.The control system converts the actual temperature value accessed by temperature sensor into analog signal by ADC0809 converter, then transmits these analog signal to single-chip AT89C52, compares the analog signal with the setting value, calculates the error, adopts fuzzy-control arithmetic to revise the error, educing the corresponding quantity based on fuzzy-control arithmetic to control the switching-on time of controllable silicon driver (namely to modulate the switching-on angle of controllable silicon), modulates the heating power, accordingly realizes the control of the temperature.The final realization of the system objective is completed by the software, this primary task of the system software design is combining the hardware architecture to complete the system expectated function, including software architecture design and programming. In a performance fine monolithic integrated circuit application system, the reasonable software architecture is a foundation. The entire work can be decomposed into several independent operations, according to these operation's mutual connection and the time relationship, designs a reasonable software architecture. The duty of the software architecture design is definiting the program structure and dividing the functional module. The master routine general structure is carring on all kinds of initialization, and then waiting for the sampling period signal interrupt request. Each functional module can be divided into fixed time, data acquisition, digital filtering, control algorithm, demonstration and so on. Further draws the detail flowchart to each module after defining the duty and the mutual connection of each module. According to the definite flow chart, compiles the master routine and various modules procedure separately. Using the ready-made subroutine afap. when programming the master program and the other module program to reduce the workload. Generally, the programming language uses the assembly language, the assembly language execution speed runs fast and takes few internal memory, suitable to use in the real-time control system.The temperature intelligent control system based on single-chip AT89C52 can accomplish data sampling, data processing and data conversion automaticaly, can carry out fuzzy-control, and also can control sterilizer and display with operate the terminal unit, such as keyboard. When the actual temperature reaches the setted temperature, the setted time starts to decrease, once the time decreases to zero, the sterilization is over. In order to heighten the accuracy of the temperature control, fuzzy-control arithmetic is adopted in this thesis. The method of the system software design based on fuzzy-control theory is expatiated detailedly. Compared with traditional PID modulation,fuzzy-control arithmetic has obvious improvements in many facts, such as stability, accuracy, facility and so on.