Sterilizers are important equipment for protecting human life and health. Developed countries such as household sterilizers and commercial sterilizers are popular.
Whether the sterilization of the sterilizer is qualified depends largely on whether the control system is reliable. For the practical problems of unstable control system and unfriendly human-machine interface of a medical equipment factory, the author uses 80C196KB single-chip microcomputer to design sterilization control for the plant. The system eliminates the defects of the original system and adds some functions accordingly. Compared with the 51 series single-chip microcomputer, the 96 series has more on-chip resources and the design system is relatively easy.
1 sterilizer control analysisThe sterilizer mainly sterilizes five kinds of packages, instruments, latex, liquids and other types, and the processes are substantially the same, and the differences can be controlled by programs. According to the principle of operation (Fig. 1), it is known that various operation controls are performed depending on whether the temperature and pressure of the inner and outer pots reach a predetermined value.
A total of 4 analog input: external pot temperature TW, outer pot pressure PW, inner pot temperature TL, inner pot pressure PL; control output a total of 16: outer pot inlet valve switch IW, outer pot exhaust valve switch OW, Inlet steam inlet valve switch IL, inner pot exhaust valve switch OL, vacuum valve switch ZK, dry air valve switch GZ, oil pump relay on and off YB, vacuum pump relay on and off ZB, electromagnetic hydraulic valve (high pressure valve GF, rack valve CF, door latch valve MF), signal indication (power indication PowerL, total power indication PowerZ, fault indication ERR, buzzer alarm ALarm).
Figure 1 Working principle
It can be seen from the above figure that the main body of the sterilizer is a high-pressure container with a jacket and a sealing door, and is equipped with a vacuum pump, a vacuum valve, a steam valve and the like, and a temperature and pressure sensor. The working process is shown in FIG. 2 .
The hardware structure of the control system is shown in Figure 3 below:
Figure 3 control system hardware structure
The actual temperature and pressure value of the sterilization chamber are measured by the semiconductor integrated temperature sensor AD590JH and the integrated pressure sensor MPX5500D. The collected 2 temperature signals and 2 pressure signals are sent from the P0.0 to P0.3 to the 80C196CKB chip. In the 80C196CKB, there is an 8-channel 10-bit A/D converter for multi-channel data acquisition systems. An A/D conversion requires 88 state cycles (22 μs with a 12 MHz crystal). The advantage is that the hardware circuit is greatly simplified in the case of meeting the process requirements, which is beneficial to the reliability of the circuit.
The digital quantity in the 80C196CKB is digitally filtered and scaled. On the other hand, it is displayed on the LCD. On the other hand, compared with the setting, the deviation E and the deviation change rate EC are obtained, which provides the basis for subsequent control. The parallel output interface circuit 8255A is used to realize the output control of the near 20-way switch control amount. The temperature control is realized by adjusting the opening of the steam valve, and the control amount is converted into an analog output by D/A, and the opening of the steam valve is controlled after the power is amplified. The user sets the sterilization temperature, time and pulse vacuum times through the keyboard to meet various disinfection requirements.
Adopt DS12887 parallel clock module
The human machine interface mainly includes a keyboard, a display and a micro printer interface circuit. The keyboard adopts the form of a soft keyboard, which is processed by the program to realize the identification, debounce and confirmation of the key code; the hardware interface of the keyboard and the printer is realized by a 8255A. The display uses an LCD display module with a built-in T6963C controller (connected directly to the CPU) for dynamic display of temperature, pressure, time and operational prompts. The printer is used to print the relevant operating process parameters. The implementation of the user interface on the software is implemented by decentralized rather than centralized software modules.
All devices in this system are powered by a single +5V power supply. Due to the actual application, the signal is easily interfered during data acquisition. Therefore, an optocoupler isolation circuit is adopted at the signal input and output contacts, and shielding resistance is taken to ensure the stability of the system.
3 software designThis system has many functions. In order to facilitate design and maintenance, the sub-programs with independent functions are set as sub-program modules by using the hierarchical module design method which is gradually refined from top to bottom. The related functions are all corresponding function sub-programs. achieve. The main program consists of initialization, sterilization category selection and related display, parameter comparison, actuator output control, etc. The core is the comparison of temperature and pressure parameters and the corresponding output control; the dynamic display of time is interrupted by the timer 1 interrupt handler. Execution; temperature and pressure data acquisition processing and dynamic display of 4 channels are completed by the A/D conversion end interrupt processing program. Since the display program is relatively large, running in the interrupt handler makes the background program simple, which is beneficial to the reliability of the software operation. The program flow is shown in Figure 4.
Figure 4 program flow chart
The basic process of program running is: start A/D conversion after initialization to collect temperature and pressure signals. After processing, these data are compared with user-set operating parameters, and then determine the different actions of the system actuator to meet the operating parameters. Within the scope of the process requirements.
The software of this control system adopts assembly language, which has high execution efficiency and reliable operation. It is limited by space and will not be introduced one by one.
4 ConclusionThis is a practical embedded control system with 80C196KB as its core. It has complete functions and relatively simple design. The practical application shows that the whole system runs smoothly and the sterilization control is reliable. Compared with the PLC-based sterilization control system with the same function, it has low cost, friendly man-machine interface, easier operation and good promotion value.
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