With the progress of science and technology and the development of economy, the application of clean technology is more and more extensive. At present, the requirements for clean rooms in the fields of electronics, pharmaceuticals, food, biological engineering, medical and other fields are also getting higher and higher, which integrates various aspects of technology, construction, decoration, water supply and drainage, air purification, HVAC and automatic control and measurement. This paper discusses the application of automatic instrument control and monitoring technology in clean room from the perspective of clean room.

Modern clean room technology divides clean room design and construction, clean room testing and inspection, and clean room operation into three categories, each of which includes automatic instrument control and monitoring technology. The purification project is a very systematic project, which includes the purification envelope structure and the purification air conditioning system.

Whether the entire system is reasonable and whether it can ultimately meet the indicators or parameters required by the air purification level and production process depends on the level of instrumentation detection and automation. For the whole air conditioning system, the air conditioning unit and the air duct are an important part of this system. Its role is to filter the air, heat or cool it, humidify or dehumidify it and send it to the required places. However, whether the air into the room meets the cleanliness requirements, and whether the temperature and humidity of the air meet the production requirements, it needs to be realized by the detection and control equipment.

1. Characteristics of Clean Room Air Conditioning System

High fan pressure head, large air volume · high temperature, humidity control precision · positive and negative micro differential pressure control precision · high efficiency requirements of the filtration system · variable air volume regulation requirements requires high stability and reliability.

According to the characteristics of clean room engineering, more reliable and stable performance is needed in control instruments and testing instruments, which can not only achieve the purpose of process production, but also save energy, reduce production costs, and protect the environment. Figure 1 is a schematic diagram of an air handling system that requires instrument control.

2 Control of Differential Pressure in Clean Room:

According to the process requirements, maintain a certain small differential pressure between the clean room and the surrounding space, which can be positive or negative pressure. Differential pressure can be controlled by air supply port, return air port or residual pressure valve.

Pressure difference control is a very important link in air conditioning system. Only by controlling the pressure difference in the purification area and ensuring reasonable air flow organization can the requirements of purification and process be achieved. For example, the clean workshop must maintain a certain positive pressure so that the outside unpurified air will not enter the purification area to ensure the cleanliness level; And through the different pressure difference control of each purification area, to achieve the role of purification zoning, in GMP requires that the pressure difference of different purification levels of areas should be controlled not less than +5Pa. In the biosafety clean room, the pressure difference control is the key means to ensure the safety protection barrier, and the "Technical Code for Biosafety laboratory Construction" requires that the negative pressure gradient of the laboratory must be controlled stably and reliably. Therefore, for purifying air conditioning systems, pressure difference control is very important.

According to the "Clean room Design Code" (hereinafter referred to as the "Code"), the indoor pressure of the clean room is higher than the external pressure, then it is a positive pressure clean room: on the contrary, it is called a negative pressure clean room. Positive pressure and negative pressure are relative, one clean room is a positive pressure clean room for the atmosphere, but it may be a negative pressure clean room for another room. The "Code" stipulates that the pressure difference between different grades of clean rooms, clean areas and unclean areas is not less than 5Pa, and the pressure difference between clean areas and outdoor is not less than 10Pa. Maintain at least 30Pa positive pressure difference between the clean room corridor and the unclean area. The basic principle of this pressure difference is that the supply air volume is greater than the return air volume, exhaust air volume, leakage air volume to achieve.

3 Clean Room Cleanliness Control:

The control of cleanliness is mainly achieved through the filter and a certain amount of air exchange in the room. The performance of the filter and long-term blockage will affect the cleanliness of the air. Therefore, it is necessary to detect the status of the filter, but also to master the operating status of the fan and the wind pressure of each air duct. Table 1 shows typical products for differential pressure monitoring and control:

4 Clean Room Air Volume Control

The air supply volume of the clean room is determined by the cleanliness level, but the air supply volume will inevitably change due to the influence of dust production, pressure difference and other factors, resulting in increased energy consumption of the equipment and increased operating costs. If the system adopts a frequency conversion device, and then sets detection and control devices on site according to the characteristics of the production process to adjust the exhaust air volume, and then changes the air supply volume successively. It can avoid the consumption of electric energy caused by the need to open the exhaust fan when the individual process is not produced. Due to the use of frequency conversion device, according to the required air supply value of the system, to change the fan speed, thus greatly reducing the power consumption. Figure 2 is a schematic diagram of air volume regulation.

5 Other Typical Products of Automatic Control Instruments

5.1 Temperature and Humidity Control Instrument:

Table 2 shows typical products of temperature and humidity detection and control instruments.

5.2 Wind Speed, Fan Control Instrument:

Table 3 shows typical products of wind speed measurement and fan control instruments

5.3 Control Instrument of Hot and Cold Water Circulation System:

Figure 3 is the principle diagram of hot and cold circulating water system

Table 4 shows typical products of control instruments for hot and cold water circulation systems

These can constitute the basic automatic control system of air conditioning in purification engineering. According to the requirements of the project, it can be composed of analog instrument automatic control system or computer control system.

5.4 Instruments and Meters That Need Maintenance and Overhaul During Construction Acceptance and Normal Production

5.4.1 Air Volume and Wind Speed Detection

The detection of air volume is the premise of other detection items, and also verifies the rationality of system design.

5.4.2 Static Pressure Difference Detection:

The static pressure difference between different levels of clean rooms or clean areas and unclean areas should be greater than 5Pa, and the clean room (area) and outdoor should be greater than 10Pa.

Some areas also require negative pressure according to specifications or process requirements.

5.4.3 Cleanliness Test

The sampling times for each clean room (area) should be ≥3 times, and different testing instruments should be selected according to the particle size range required by the cleanliness level.

5.4.4 Portable Temperature and Humidity Detection

The temperature and humidity were measured according to the "Clean Room Construction and Acceptance Code".

5.4.5 Illumination Detection

Test method according to "Clean Room Construction and Acceptance Code"

5.4.6 Noise Detection

Octave analyzer sound level meter. Background The test should be carried out at night when the air conditioning system is in full operation and all other equipment is shut down.

5.4.7 Detection of Microorganisms

At present, the detection methods of microorganisms are generally adopted by floating bacteria and settling bacteria. The basic process of determination is the process of catching-culture-counting.

The above is an overview of the application of clean room automation instruments.