Introduction to the innovative principle of ZHJH-C series intelligent safety super workbench monitoring HEPA filter failure alarm

Tang Xinnan Shenshui Xingyan Guanghao, Shanghai Zhicheng Analytical Instrument Manufacturing Co., Ltd. Shanghai

The ultra-clean workbench is one of the main laboratories in the fields of life sciences, biochemistry, medical and health, agricultural research, food production, environmental monitoring, etc., and can provide local clean air purification equipment. The working principle is that indoor air enters the static pressure tank through the pre-filter, and then passes through a high-efficiency air filter (hereinafter referred to as HEPA filter) to remove various dust particles or aerosols, and finally forms a highly clean one-way in the operation area. Air flow and a positive pressure airflow environment that avoids the intrusion of external airflow.

I. A neglected worrying biotechnology hazard

With the development of modern biotechnology, biosafety issues have attracted the attention of the vast number of scientific and technological workers in the biosphere. The ultra-clean workbench is one of the most widely used basic equipments for biotechnology research, but its biosafety and effectiveness are seriously challenged by the effectiveness of its key components, HEPA filters. At present, in the ultra-clean workbench, which is widely used in China, due to the lack of effective monitoring of the critical component HEPA filter life in the product design process, it is difficult for the experimenter to intuitively judge the effectiveness of the HEPA filter. Serious consequences such as inaccurate experimental data, contamination of experimental samples, or repeated trials of experimental projects. At present, in the research and application fields of a large number of biological laboratories, universities, research institutes and bio-pharmaceutical enterprises in China, it is more common, and there are different degrees of problems of over-time service and ineffective use of HEPA filters. The safety and effectiveness of the net workbench is quite prominent, but on the other hand, the issue of the effectiveness of this worrying biotechnology has become a hidden danger that many people have overlooked.

Second, this is a design flaw that is not fully recognized.

At present, the ultra-clean workbench seen in the domestic market, its electrical control is basically similar to the control principle of the electric fan, which consists of a fan, a multi-tap transformer, plus a multi-speed speed switch. Control system. When the ultra-clean workbench is running, there is only a prompt for the wind speed position on the control panel, and there is no prompt for the operating state of the HEPA filter. Although some manufacturers are aware of the importance of prompting the experimenter to the HEPA filter operating state online, certain measures have been taken in product design. If a pressure probe is installed in the static pressure tank of the ultra-clean workbench, the pressure change in the static pressure tank is measured, and then the red-green section of the pointer pressure gauge or the digital pressure gauge is used in the display. The pressure change in the static pressure tank is shown above, the initial pressure is equal to the initial resistance of the HEPA filter, and the increase in pressure is equivalent to the increase in the resistance of the HEPA filter. Based on the designed pressure limit value, the remaining service life of the HEPA filter is judged and the relevant warning is issued to the experimenter.

But experiments have shown that this method is not authentic. Because the change of wind speed, air volume, pressure and resistance in the ultra-clean workbench is an interactive system that interacts and interacts with each other. For example, changing the wind speed gear changes the air volume, the wind speed will also change, and the pressure will follow. Therefore, the pressure change displayed by the device does not actually reflect the change in the resistance of the HEPA filter. Further, the judgment on the operating state of the HEPA filter is also inaccurate and not worthwhile. In order to make up for the defects that the equipment cannot judge on the operating state of the HEPA filter, many experimental personnel in China have taken measures to frequently replace the HEPA filter to improve the effectiveness of the purification function of the ultra-clean workbench. However, such a costly and laborious operation is difficult to maintain, and it is difficult to grasp when to replace the HEPA filter. Therefore, the equipment is still in use when the HEPA filter has failed but the experimenter cannot detect it. This is the real situation of the current use of ultra-clean workbench in biological laboratories in China.

There are many brands in the world that produce ultra-clean workbench, including LABCONCO in the US, FRUAN in Australia, BIOAIR in Italy, ESCO in Singapore, and SANYO in Japan. How do these international first-line brands ensure product operation? The integrity of the HEPA filter in the process has been considered, but the technical measures are not the same. If some high-performance wind speed sensors are added, the life of the HEPA filter is displayed on the indicator through the comparison of the lower limit of the wind speed. The user can predict the time to replace the HEPA filter through the warning light; some have special installations. The pressure gauge displays the pressure in the static pressure tank and monitors the operation of the HEPA filter at all times. In terms of maintaining a constant clean air flow, compensation measures have only been added from the voltage stability of the working line, but in the case of increased resistance of the HEPA filter, there is no clear solution for maintaining a constant airflow in the working area.

Third, the "constant wind speed" technology effectively solved this hidden danger

(1) The brewing of innovative ideas

In response to the above problems, ZHICHENG has established a research and development team composed of scientific research personnel. Technical innovation and technical research on the ultra-clean workbench. The team members proposed to develop a technical concept of an upgraded version of the ultra-clean workbench that can detect the HEPA filter in real time and when it is in an abnormal situation such as failure or damage, it can accurately and timely issue early warning and alarm signals. The project product is named "ZHJH-C intelligent safety ultra-clean workbench".

ZHICHENG's R&D team put forward an overall design plan based on how to solve the problem of effective use and safe use of the ultra-clean workbench. The design of the ultra-clean workbench should provide users with a humanized, safe and reliable operating environment. The operating parameters of the ultra-clean workbench can be seen at a glance, and the working state of the HEPA filter can realize online measurement, online monitoring and online alarm.

The experimental research of ZHICHENG company concluded that when the measured resistance of the HEPA filter reaches twice the initial resistance, it means that the HEPA filter has failed and needs to be replaced. The judgment is based on the fact that when the resistance of the HEPA filter increases, the pressure of the static pressure tank with the HEPA filter installed on the ultra-clean workbench increases synchronously, and the pressure difference to the atmospheric pressure also rises synchronously. If the measured differential pressure reaches twice the initial differential pressure, it also means that the resistance of the HEPA filter has reached twice the initial resistance. Therefore, the pressure difference can be equal to the measured resistance. The real-time detection of the HEPA filter resistance of the project product can be completed by measuring the pressure difference of the net pressure chamber. However, the experiment found that the change in pressure difference is related to the speed of wind and the amount of wind. In the case where the resistance of the HEPA filter is constant, the air volume is large and the pressure difference is also increased. Therefore, detecting the resistance of the HEPA filter requires a constant wind speed. However, in addition to the resistance, the wind speed is related to the power of the fan and the fluctuation of the power supply voltage. Therefore, it is necessary to study a new type of "constant wind speed" circuit that can stabilize the wind speed.

Through experiments, ZHICHENG researchers have established a specific technical solution, namely:

  1. Research and development of a new silicon resistive balanced differential differential pressure transmitter capable of measuring differential pressure to solve accurate measurement of differential pressure.
  2. Research and development of a new type of hot ball type thermal balance micro-wind speed transmitter that can measure the micro-wind speed to solve the accurate measurement of the micro-wind speed.
  3. Research and development of an electronic circuit capable of precise control of the micro-wind speed, so that the wind speed can be set as needed, and the wind speed adjustment system automatically controls the wind speed to a set wind speed value to form a stable air flow in the working area. Provides stable measurement conditions for the measurement of differential pressure.
  4. Research and explore the parameters of the HEPA filter failure warning point, failure alarm point and damage alarm point. After repeated experiments, ZHICHENG company researchers believe that:
    • When the HEPA filter resistance increases to 95% of the initial resistance value, the device issues a failure warning signal.
    • When the resistance of the HEPA filter increases to twice the initial resistance, the device issues a failure alarm signal.
    • When the resistance of the HEPA filter is reduced to 95% of the resistance during the last operation, it means that the HEPA filter has been damaged and the device sends a break alarm signal.

(II) Optimization of key technologies

One of the key technologies is used to clean the differential pressure measurement circuit of the Taiwan filter: a new type of silicon resistance force balanced differential pressure transmitter.
(Utilities model patent: a differential pressure measuring circuit for purifying a console 200520040408.8)

The actual working condition of the filter is determined by the differential pressure measurement of the clean bench filter. The existing differential pressure measuring device has poor measurement accuracy, poor repeatability, poor interchangeability, or cost due to the selection of the sensor itself and the design of the input circuit, the amplifying circuit, and the power supply in the differential pressure measuring circuit. Higher problems are difficult to promote in actual use.

The key technology provides a differential pressure measuring circuit for a clean bench filter to solve the above problems of the conventional differential pressure measuring device. The new silicon resistance-balanced differential pressure transmitter has the following technical features:

  1. The differential pressure measuring circuit comprises a power source, a pressure sensor and an amplifying circuit, wherein the pressure sensor is powered by a constant current power supply circuit, the output of the pressure sensor is connected to the input of the differential input amplifying circuit, and the output of the differential input amplifying circuit is connected to the input of the amplifying circuit. ;
  2. The pressure sensor is a silicon pressure sensor with a micro differential pressure sensor. Its output is a bridge circuit.

The second key technology is a new type of hot ball type thermal balance micro-wind speed transmitter for solving accurate measurement of micro-wind speed.
(Utilities model patent: a wind speed measurement control circuit for purifying the console 200520040409.2)

The usual wind speed measurement can be measured by the impeller or rotor frequency measurement method, but it is difficult to use on the ultra-clean workbench due to factors such as installation location and use environment, and the differential pressure measurement conversion method is adopted by the filter net, and the filter Accumulated use of its resistance will gradually increase and produce errors. Long-term real-time work can be achieved by using hot ball or hot wire method, but the products on the market generally have high price, poor linearity, poor consistency, complicated correction, etc., and it is difficult to use on the ultra-clean workbench.

This key technology provides a wind speed measurement circuit to solve the above problems of the conventional wind speed measurement method. The new hot ball type thermal balance micro-wind speed transmitter has the following technical features:

  1. The wind speed measuring circuit comprises a power source, a wind speed sensor and an amplifying circuit, wherein the wind speed sensor is powered by a constant current power supply circuit, the output of the wind speed sensor is connected to the differential amplifying circuit, and the output of the differential amplifying circuit is connected to the input of the amplifying circuit;
  2. The wind speed sensor used in the measuring circuit is a hot ball wind speed sensor, which uses a hot ball wind speed sensor produced by Beijing Detector Factory. In order to optimize the performance of the project's product breeze measurement, the project team members and the technicians of the Beijing Detector Factory jointly carried out technical research on the existing breeze measurement performance of the hot ball sensor. ;
  3. The novel hot ball type thermal balance micro wind speed transmitter comprises a power source, a wind speed sensor and an amplifying circuit, wherein the wind speed sensor is a hot ball type sensor, and the hot ball heating is powered by a constant current power source circuit;
  4. The output signal of the circuit is processed by software nonlinear curve fitting method to ensure the accuracy, consistency and stability of the measurement.

The third key technology to determine the specific parameters of the HEPA filter failure point, damage point and warning point
(There are no ready-made examples at home and abroad for reference)

After repeated trials and demonstrations by the project team and related issues with relevant users, ZHICHENG company researchers confirmed that when the resistance of HEPA filter increases to 95% of the initial resistance value, the equipment sends a warning signal for failure, which enables the user to have Replace the HEPA filter at the right time. In the simulated operating state, when the resistance of the HEPA filter increases to twice the initial resistance, when the device issues a failure alarm signal, the number of colonies in the detection purification zone has been greatly exceeded, indicating that the HEPA filter has been unable to meet the biological test for air purification. Claim. This experiment verified the practical effect of the HEPA filter failure alarm function in ensuring the safety and effectiveness of biological experiments.

According to the increase of HEPA filter resistance, the wind pressure increases, and the surface pressure of HEPA filter increases. The experiment of simulating the damage state of HEPA filter proves that the damage is most likely to occur at the midpoint of the HEPA filter, and the damage occurrence area is collected. The size data, after data processing, compares the resulting resistance changes, it can be concluded that when the HEPA filter resistance is reduced to 95% of the resistance at the last operation, the HEPA filter has been damaged and the test result is more realistic. ,reliable.

The fourth key technology, the realization of HEPA filter alarm technology

According to the project requirements, ZHICHENG company research and development has carried out research on the measurement and control of wind speed, air volume, resistance and pressure difference and other related parameters, and designed an advanced CPU micro-processing chip with sound and light alarm function and related automatic control circuit. . The project product presents the characteristics of intelligent control:

  • Realized the technological innovation of “constant wind speed” operation;
  • Programmable intelligent control system;
  • A dot matrix LCD screen with backlight for full Chinese or full English display;
  • Wind speed, air volume, differential pressure, timing and other multi-parameter display on the same screen, important at a glance;
  • When the HEPA filter is abnormal, it can realize sound, light and all Chinese (English) visual alarms;
  • With power-off recovery function, when the external power supply is powered off and the call is resumed, the device can automatically start and run according to the original setting procedure;
  • With parameter memory function, one setting can be stored permanently;
  • Wind speed stepless setting, automatic control;
  • Automatic timing cleaning, automatic UV lamp disinfection and clock display function;
  • Manual/automatic mode display makes it easy for users to choose according to their needs. (Manual mode without HEPA filter alarm function)
  • The touch buttons and the beautiful film panel form a very human-friendly human-machine dialogue interface.

Fourth, the innovator's harvest

After hard work and hard work, ZHICHENG scientific research personnel finally successfully developed the "ZHJH-C series intelligent safety ultra-clean workbench" in 2006. Since the issues involved in the technical concept are extremely useful at the level of use and the importance of biotechnology, they have been approved and funded by the Ministry of Science and Technology's SME Technology Innovation Fund. The project products were successfully converted and officially launched in 2007. ZHICHENG has thus become the only inventor of the “smart and intelligent ultra-clean workbench” that has accurate implementation of on-line measurement, online monitoring, online failure warning and alarm for the HEPA filter operating state of the core components of the ultra-clean workbench. Through the scientific and technological achievements retrieval of Shanghai Science and Technology Information Institute, its intelligent control design has reached the international advanced level, and has obtained the authorization of many invention patents and utility model patents of the State Intellectual Property Office.

In summary, "ZHJH-C intelligent safety ultra-clean workbench" condenses the collective wisdom of ZHICHENG researchers, and is a new ultra-clean workbench with independent intellectual property rights in China. The successful research and development of products has greatly improved the effectiveness and safety of the use of ultra-clean workbench in the life sciences and even the microelectronics industry. This has played a positive role in breaking foreign monopoly and revitalizing China's national industry. “ZHJH-C intelligent safety ultra-clean workbench” has obtained the core “constant wind speed” technology:

  • Support for the establishment of the SME Technology Innovation Fund of the Ministry of Science and Technology (Certificate No.: 05C26213100472)
  • Shanghai High-tech Achievement Transformation Project (Certificate No.)
  • Shanghai Patent New Product Title (Certificate No.: SHZX062025)
  • Shanghai key new product title (certificate number: 07XP05106)
  • National key new product project (Certificate No.: 2008GRC00019)
  • China Instrument and Meter Industry Gold Award - Invention Patent: "Detection Device and Detection Method for Filters in Biosafety Devices" (Patent No. X)
  • Utility model patent: "a differential pressure measuring circuit for purifying the operating table" patent number (200520040408.8)
  • Utility model patent: "A wind speed measurement control circuit for purifying the console" (Patent No. 200520040409.2)

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