Development of a medical sterilizer control system based on single chip microcomputer

introduction

Sterilizer is an important equipment for protecting human life and health. Both household and commercial sterilizers are very popular in developed countries.

Whether the sterilization of the sterilizer is qualified depends largely on whether the control system is reliable. Aiming at the practical problems of unstable sterilizer control system and unfriendly human-machine interface in a medical equipment factory, the author uses 80C196KB single-chip microcomputer to design a sterilization control system for the factory, eliminating the defects of the original system and adding some functions accordingly. Compared with 51 series single-chip microcomputers, 96 series have richer on-chip resources and it is relatively easy to design the system.

1. Sterilizer control analysis

The sterilizer is mainly used for sterilizing packages, instruments, latex, liquids and other items. The processes are generally the same, and the differences can be controlled by the program. From its working principle (Figure 1), it can be seen that various actions are controlled according to whether the temperature and pressure of the inner and outer pots reach the specified values.

There are 4 analog inputs: outer pot temperature TW, outer pot pressure PW, inner pot temperature TL, inner pot pressure PL; there are 16 control outputs: outer pot steam inlet valve switch IW, outer pot exhaust valve switch OW, inner pot steam inlet valve switch IL, inner pot exhaust valve switch OL, vacuum valve switch ZK, dry air valve switch GZ, oil pump relay on/off YB, vacuum pump relay on/off ZB, solenoid hydraulic valve (high pressure valve GF, rack valve CF, latch valve MF), signal indication (power indication PowerL, total power indication PowerZ, fault indication ERR, buzzer alarm ALarm).

Figure 1

As can be seen from the above figure, the main body of the sterilizer is a high-pressure container with a jacket and a sealed door, equipped with control devices such as a vacuum pump, vacuum valve, steam valve, and temperature and pressure sensors. The working process is shown in Figure 2.

Figure 2

2. Control system hardware structure

The hardware structure of the control system is shown in Figure 3:

Figure 3 Hardware circuit diagram

The hardware circuit of the control system is mainly composed of data acquisition, control quantity output, clock module, and human-machine interface hardware.

The actual temperature and pressure values ​​of the sterilization chamber are measured by the semiconductor integrated temperature sensor AD590JH and the integrated pressure sensor MPX5500D. The collected 2-way temperature signal and 2-way pressure signal are sent to the 80C196CKB chip from P0.0 to P0.3. In the 80C196CKB, there is an 8-channel 10-bit A/D converter, which is suitable for multi-channel data acquisition systems. One A/D conversion requires 88 state cycles (22μs when using a 12MHz crystal oscillator). Its advantage is that it greatly simplifies the hardware circuit while meeting the process requirements, which is beneficial to the reliability of the circuit.

After digital filtering and scaling, the digital quantity in 80C196CKB is displayed on LCD and compared with the setting to obtain the deviation E and the deviation change rate EC, which provide a basis for subsequent control. The parallel output interface circuit 8255A is used to realize the output control of nearly 20 switch control quantities. Temperature control is achieved by adjusting the opening of the steam valve. The control quantity is converted into analog output by D/A, and the opening of the steam valve is controlled after power amplification. The user sets the sterilization temperature, time and pulse vacuum times through the keyboard to meet various disinfection requirements.

Use DS12887 parallel clock module.

The human-machine interface mainly includes keyboard, display and micro-printer interface circuit. The keyboard adopts the form of soft keyboard, which is processed by the program to realize the recognition, de-jitter and confirmation of key codes; the hardware interface between keyboard and printer is realized through an 8255A. The display adopts an LCD display module with built-in T6963C controller (directly connected to the CPU) to dynamically display temperature, pressure, time and operation prompts. The printer is used to print relevant operating process parameters. The software implementation of the user interface is realized by decentralized rather than centralized software modules (see the next section).

All devices in this system are powered by a single +5V power supply. In actual applications, signals are easily interfered with during data collection. Therefore, optocoupler isolation circuits are used at the signal input and output contacts, and shielding resistors and other measures are taken to ensure the stability of the system.

3. Software Design

This system has many functions. In order to facilitate design and maintenance, a top-down and gradually refined structured module design method is adopted. All subroutines with independent functions are set as subroutine modules, and related functions are implemented by corresponding functional subroutines. The main program consists of initialization, sterilization category selection and related display, parameter comparison, actuator output control, etc. Its core is the comparison of temperature and pressure parameters and the corresponding output control; the dynamic display of time is executed by the timer 1 overflow interrupt handler; the temperature and pressure data acquisition and processing and dynamic display of the 4 channels are completed by the A/D conversion end interrupt handler. Since the display program is relatively large, it is run in the interrupt handler to make the background program concise, which is conducive to the reliability of software operation. The program flow is shown in Figure 4.

Figure 4

The basic process of program operation is: after initialization, A/D conversion is started to collect temperature and pressure signals. After processing, these data are compared with the operating parameters set by the user, and then different actions of the system actuator are determined to ensure that the operating parameters are controlled within the range required by the process.

The software of this control system all uses assembly language, which has high execution efficiency and reliable operation. Due to space limitations, they will not be introduced one by one.

in conclusion

This is a practical embedded control system with 80C196KB as the core, which has complete functions and relatively simple design. Practical application shows that the whole system runs smoothly and the sterilization control is reliable. Compared with the sterilization control system based on PLC with the same function, it has low cost, friendly human-machine interface, easier operation and good promotion value.