Abstract Analyzed the principle of plasma sterilization, and accordingly gives the process of hydrogen peroxide low-temperature plasma sterilization and the workflow diagram of the device; put forward the requirements of the system design, and accordingly structured the system composition block diagram; according to the analysis of the sealing door movement process, put forward the programmable logic device to control the movement of its state diagram; micro-controller is the main controller of the entire system, through the micro-controller The program flow chart of the control system working is also given.
Keywords Hydrogen Peroxide; Plasma Sterilization Equipment; Microcontroller; Programmable Controller; Flowchart
The Design of the Plasma Sterilization Equipment and Its Process Control Using H2O2 in low Temperature
LEI Jian-long
Department of Electronics of Wuhan Institute of Shipbuilding Technology 430050
Abstract The principle of plasma sterilization is analyzed in the context of the plasma sterilization process. principle of plasma sterilization is analyzed, according which the process of the plasma sterilization using H2O2 in low temperature and its flow chart The system's design demands is put out, by which the structure frame is build up. The station diagram of movement of the gates controlled by PLD is put out by PLD. The station diagram of movement of the gates controlled by PLD is put out by analyzing the process of their moving. The MCU acts as the main controller of the whole system. The action flow chart of the MCU controlling the process of the system is also give out.
Key words H2O2; Plasma sterilization equipment; MCU; PLD; Flow chart
1 introduction
Sterilization is one of the most important basic work in hospitals, with the needs of medical work and the development of medical equipment products, the medical profession has put forward higher requirements and expectations of sterilization work, therefore, the business community is also working hard to research and develop new sterilization equipment suitable for today's needs. New sterilization equipment must have high efficiency, low temperature, low humidity, non-toxicity of certain characteristics, national scientific and technological personnel are committed to more perfect medical sterilization equipment research [1,2].
Hydrogen peroxide plasma sterilization is characterized by low-temperature, non-toxic, no residue after the completion of sterilization, can be used immediately. Because it has: ① does not use toxic substances, people and the environment are very safe; ② sterilization time is short, and can not have to be ventilated, the sterilized material can be used immediately after removal; ③ sterilization temperature is only 45 ℃, humidity is only 10% RH, is the real low temperature, low humidity; ④ only need a power supply, all the sterilization procedures automated, simple operation; ⑤ sterilization time is short, in the case of reducing the stock of the same instruments, can cope with more surgical needs. The sterilization time is short, in the case of reducing the inventory of instruments, the same can cope with more surgical needs, to achieve the goal of reducing costs, improve efficiency and increase revenue [3].
2 plasma sterilization principle
Plasma is a solid, liquid and gaseous state other than a new state system, people usually called the fourth state. It is a highly ionized gas cloud, plasma is produced by certain gases or gaseous substances under the action of a strong electromagnetic field, the formation of gas corona discharge, gas ionization, such as the use of hydrogen peroxide as the generation of ion clouds of the active body. Hydrogen peroxide is first in its initial state, and when an electric field of a certain strength is added to it, electrons are stripped from certain atoms, resulting in accelerated particle motion. When the stripped electrons recombine with the atoms, or when electrons in the activated atoms are transferred from a high-energy state to a low-energy state, a glow is produced. In the plasma cloud molecules collide and hydrogen peroxide is converted to hydrogen peroxide radicals and hydroxyl radicals, water and oxygen. The atomic oxygen, free radicals and other reactive substances, easy to react with proteins and nucleic acids in the bacterial body, disturbing the survival function of microorganisms. And in the process of plasma generation, due to the glow discharge, can release a large number of ultraviolet rays, can also play a disinfection role.
The sterilization mechanism mainly includes the following three aspects[4]:
□ The role of reactive groups:
A large number of reactive oxygen ions contained in the plasma, high-energy free radicals and other components, it is very easy to oxidize and denature with the proteins and nucleic acids in the bacteria, molds and germs, viruses, and make all kinds of microorganisms die.
□ High-speed particle breakdown:
After the sterilization experiment, through the electron microscope to observe the image of bacterial organisms and viral particles after the plasma effect, all presenting a thousand holes, which is due to the high kinetic energy of the electrons and ions generated by the breakdown of the etching effect.
□ The role of ultraviolet light:
In the process of the formation of H2O2 plasma excitation, accompanied by part of the ultraviolet light generated, this high-energy ultraviolet photons (3.3 ~ 3.6eV) by microorganisms or viruses in the absorption of proteins, resulting in the molecular denaturation and inactivation.
3 hydrogen peroxide plasma sterilization system process
Hydrogen peroxide plasma sterilization system sterilization process for the double-cycle sterilization, divided into four phases [5]: the preparation period, the first sterilization period, the second sterilization period, as well as the final ventilation period.
(1) vacuum period is the first stage of the sterilization process (1 torr that is, 1Torr (torr) = lmmHg = 1.33322 × lOZPa), the cavity pressure after evacuation down to 700 milliTorr, enter the plasma stage, which is controlled at 500 milliTorr, the short cycle of 10 minutes, the long and short cycle of 15 minutes, the water evaporates and is drawn out by vacuum pumps Outside the cavity, which helps to drive out the residual moisture on the surface or inside the article. 15 minutes after the ventilation valve is opened, the filtered air enters the cavity, when the pressure reaches atmospheric pressure, the vacuum pump works again to reduce the pressure inside the cavity to 0.4 torr. Then enter the second stage, that is, the first sterilization period.
(2) The first sterilization period is divided into injection stage, diffusion stage, plasma stage. First of all, the injection needle pierced the capsule containing a concentration of 59% hydrogen peroxide, as the cavity has been pumped into a high vacuum, hydrogen peroxide quickly vaporized and fully diffused, this process of hydrogen peroxide has a lethal effect on biological tissues. The capsules are located in cassettes, each containing ten capsules, which can complete five sterilization cycles. The position of the cassette and the injection is controlled and monitored by software, and the injection process lasts six minutes. Filtered air then enters the chamber (2 minutes for the short cycle and 10 minutes for the long cycle), allowing the hydrogen peroxide to diffuse into all corners of the chamber and onto the surfaces of the instruments to be sterilized. The vacuum pump again reduces the pressure in the chamber from 760 torr to 0.5 torr, entering the plasma phase, where the chamber is loaded with radio frequency for two minutes, a glow discharge occurs, hydrogen peroxide is derived from the plasma, which intervenes and destroys microbial production, and the plasma gas is converted into harmless water vapor and oxygen as soon as the radio frequency stops. Finally, the vacuum pump again reduces the pressure from 0.5 torr to 0.4 torr, entering the third stage, which is the second sterilization cycle.
(3) the second sterilization cycle and the first sterilization cycle is exactly the same, after the end of the plasma stage, into the fourth stage, ventilation stage.
(4) In the ventilation phase, the air inlet valve opens, filtered air enters the chamber, the pressure returns to atmospheric pressure, and the sterilization process ends. The entire sterilization process lasts 55 minutes with a long cycle of 72 minutes.
The workflow of the designed hydrogen peroxide low temperature plasma sterilization equipment is shown in Figure 1.
4 System design and architecture
According to the analysis of the working process of hydrogen peroxide low-temperature plasma sterilization equipment and the requirements of the actual working environment of the hospital, the following design requirements are put forward:
※ Dimensions: 752 (width) × 1675 (height) × 835 (depth) mm . The sterilization chamber consists of two sealed doors in front and back, and its movement is controlled by four motors, which control its up and down movement and tensioning respectively.
※ Weight: 430Kg
※ Total volume: 80 liters
※ Usable volume: 71 liters
※ Power supply: 210V-240V/50-60HZ16A single-phase 3KW
※ Operating environment: 5 ℃-40 ℃, 0 ℃-95% relative humidity
※ Operating environment: 5 ℃-40 ℃, 0 ℃-95% relative humidity
. 95% relative humidity
※ Sterilization temperature: 35 ℃
※ The whole process: 30-70 minutes
※ Hydrogen peroxide dosage: 7m L
※ Display and Printing: front and rear each a 5.6-inch LCD screen display, real-time display of the work process and operation. Tips. And there are alarm devices (vacuum pump overheating and sterilization end alarm), automatic storage and printing function.
※ start and process control mode: all operations through the touch screen a key to start and support the completion of the operation, at the same time, each step can also be completed manually through the touch screen.
※ Industrial cell phone module: can be through the general mobile communication network transmission of sterilization process information and data.
According to the technical requirements of the equipment, the design of the system composition block diagram shown in Figure 2.
4.1 System Composition Block Diagram
4.2 State Transfer Diagram of Door Motion and Tension Control
The motion of the two gates in the system is completed by the programmable logic device, and the state transfer of the door motion and tension control is realized by the programmable logic control device (PLD) (shown in Fig. 1), which can realize the high stability and real-time control. In the state control transfer diagram, divided into the initial, idle, door 1 up, door 1 tight, door 2 up, door 2 tight and hand dynamic seven states, of which the hand dynamic specially designed for manual control, hand dynamic when the user can be (control box panel) hand control point, you can also click to start, re-entering the automatic door movement and tightening control state. Its movement state transfer map shown in Figure 3.
4.3 Vacuum cycle water inlet, discharge sterilization process of the microprocessor timing flowchart
The sterilization room work process is realized through the microcontroller to microprocessor control of the vacuum cycle water inlet, discharge sterilization process, in the process of controlling the synchronization of printing and sending cell phone text messages; in the cycle of water inlet, discharge sterilization process of the vacuum control, i.e., in the process of the vacuum degree is greater than 0.5 When the vacuum is greater than 0.5 torr, the vacuum is pumped, and the vacuum is stopped when it is pumped to 0.4 torr. If a cycle is not carried out in the vacuum, then carry out a vacuum, or in a cycle of vacuum is not to 0.4 torr continue to pumping vacuum. Its working time sequence flow chart as shown in Figure 4.
The development of hydrogen peroxide low-temperature plasma sterilization equipment is now in the implementation stage, due to the use of the above-designed process control program, its control part of the work is stable and reliable, and low cost.
References
[1] Wei Jingrong, Li Bin. Progress in the use of medical sterilization equipment[J]. Medical and Health Equipment,2005, 26(9)
[2] Shen Yijun. Introduction to hospital sterilization equipment[J]. China Medical Equipment, 2005, 2(l0)
[3] Huang Jingxiong. Research on low temperature sterilization[J]. Chinese Journal of Hospital Infection, 2002(8):601-60
[4] Laroussi M, Richardson J P. Dobbs F C. Effects of non-equilibrium atmospheric pressure plasma on their cell morphology pathways of bacteria and on their cell morphology[J].Appl phys lett, 2002.8l(2):772-774
[5] Ni P. Working principle of hydrogen peroxide low-temperature plasma sterilization system and precautions for use[J]. Medical Equipment Information, 2005, 20(7)