The sterilizer is an important device for protecting human health. In developed markets, both household and commercial sterilizers are widely used.
1. Sterilizer Control Analysis
This sterilizer performs sterilization for five categories: packaged items, instruments, latex, liquids, and others. The process is similar across categories, with differences handled by software.
There are four analog inputs: outer chamber temperature TW, outer chamber pressure PW, inner chamber temperature TL, and inner chamber pressure PL. There are 16 control outputs: outer chamber steam inlet valve IW, outer chamber steam exhaust valve OW, inner chamber steam inlet valve IL, inner chamber steam exhaust valve OL, vacuum valve ZK, drying air valve GZ, oil pump relay YB, vacuum pump relay ZB, electromagnetic hydraulic valves (high-pressure valve GF, rack valve CF, latch valve MF), and status indicators (power indicator PowerL, main power indicator PowerZ, fault indicator ERR, buzzer alarm AL).
The sterilizer consists of a high-pressure vessel with a jacket and sealed door, equipped with a vacuum pump, vacuum valve, steam valves, control components, and temperature and pressure sensors.
2. Control System Hardware Architecture
The actual chamber temperature and pressure are measured by semiconductor integrated temperature sensors AD590JH and integrated pressure sensor MPX5500D. The two temperature signals and two pressure signals are fed via P0.0~P0.3 into the 80C196CKB chip. The 80C196CKB includes an 8-channel 10-bit A/D converter, suitable for multi-channel data acquisition systems. A single A/D conversion requires 88 state cycles (22 μs with a 12 MHz crystal). This simplifies the hardware while meeting process requirements, which is beneficial for circuit reliability.
Digital inputs in the 80C196CKB undergo digital filtering and scaling, then are displayed on the LCD and compared with setpoints to produce the deviation E and deviation change rate EC for subsequent control. Parallel output interface chip 8255A is used to implement nearly 20 switch control outputs. Temperature control is achieved by adjusting the steam valve opening; the control signal is converted by a D/A and, after power amplification, drives the steam valve. The operator sets sterilization temperature, time, and vacuum pulse count via a keypad to satisfy various disinfection requirements.
The system uses a DS12887 parallel clock module.
The human-machine interface includes a keypad, display, and microprinter interface. The keypad is implemented as a software-scanned matrix; the program handles key decoding, debouncing, and confirmation. An 8255A provides the hardware interface for the keypad and printer. The display is an LCD module with a built-in T6963C controller, connected directly to the CPU, and is used to dynamically show temperature, pressure, time, and operation prompts. The printer records process parameters. The software implements the user interface using distributed rather than centralized modules.
All components run from a single +5 V supply. Because data acquisition signals can be susceptible to interference in practice, optocoupler isolation circuits are used at signal I/O points, and shielding and resistor measures are applied to ensure system stability.
3. Software Design
The system has many functions. To facilitate design and maintenance, a top-down, stepwise refinement structured modular design method is used. Functional routines are implemented as separate subroutine modules. The main program comprises initialization, sterilization mode selection and display, parameter comparison, and actuator output control. The core is the comparison of temperature and pressure parameters and the corresponding output control. Dynamic time display is handled by the Timer 1 overflow interrupt service routine. Acquisition and dynamic display of the four channels of temperature and pressure are performed by the A/D conversion complete interrupt service routine. Because the display routine is relatively large, running it inside interrupt handlers keeps the background program concise and improves software reliability.
The basic operation is: after initialization, start A/D conversions to acquire temperature and pressure signals. After processing, these data are compared with user-set operating parameters, and the system drives actuators to keep parameters within required process limits.
All system software is written in assembly language, providing high execution efficiency and reliable operation.
4. Conclusion
This is an embedded control system centered on the 80C196KB microcontroller. It provides comprehensive functions with a relatively simple design. Field use shows stable operation and reliable sterilization control. Compared with PLC-based sterilizer control systems with equivalent functionality, this design has lower hardware cost and a more user-friendly interface, making it suitable for wider adoption.
