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UniMAT PLC Application in HVAC industry
This project is a control system for the radar workshop of a military factory. The system is divided into three subsystems: water system, air conditioning system and acid-base exhaust system. Because of the importance of the project workshop, the dust-free room in the design is planned for the 10000-class construction design. The control accuracy of the dust-free room is 0.5 + and 5%. Pressure to keep the room +12Pa
The automatic control of HVAC system plays a very important role in ensuring the rational operation of the air conditioning system itself, reducing manpower and realizing safe operation, and it also plays a great role in promoting the development of HVAC system and technology. In the past few years, the automatic control of HVAC mainly relies on DDC control, but technicians gradually find that DDC can not achieve the desired goals for some projects with high control accuracy. PLC, which is widely used in industrial control, has gradually replaced DDC control in HVAC industry. In some large and complex projects, it is found that PLC has absolute advantages over DDC in both practicality and economy. UniMAT PLC with its powerful CPU control and unique module configuration optimization has gradually become the industry's preferred trend。
This project is a control system for the radar workshop of a military factory. The system is divided into three subsystems: water system, air conditioning system and acid-base exhaust system. Because of the importance of the project workshop, the dust-free room in the design is planned for the 10000-class construction design. The control accuracy of the dust-free room is 0.5 + and 5%. Pressure to keep the room +12Pa。The control points of the project are as follows:
The control system is divided into two control areas, water system and exhaust for a control area, dust-free room MAU and DC and FFU control system for a control area. Because some first-line brands of single temperature band transmitter sensors are more expensive, considering the economy, we use a single temperature sensor for resistance, other sensors for voltage type.
In the control scheme of the water system and exhaust system, the temperature is 4, and the other sensors are 10. AO output is 11, there are 11 PID control loop, in the configuration of 200 series of PLC maximum expansion function for seven modules. The best economic consideration is as follows,
Comparing with the same type of PLC of Siemens brand, we can find that UniMAT PLC has obvious advantages in both the function of CPU and the optimized configuration of modules.
In this control requirement, the clean room is designed as MAU fresh air system and indoor DC (dry coil) system,
4.Water control requirements
1). In the cooling water system, according to the temperature of the cooling water, the number of cooling towers started and the opening of the cooling bypass valve are controlled. To ensure the normal operation of the refrigerator.
2). The opening of the pressure difference bypass valve is controlled according to the pressure difference in the chilled water system.
3). Acid and alkali exhaust control the frequency of acid and alkali exhaust according to the pressure difference of the air duct.
4). Control of medium temperature water system and PCW heat exchange control the opening of heat exchange valve according to the temperature of water supply. In this system, the control of water temperature is very demanding. When the water temperature control deviation is large, condensation will occur on the surface of the water pipe, which may lead to the failure of the indoor machine. Thereby affecting the pass rate of products.
5). control the opening of steam valve according to the outlet temperature of hot water, so as to ensure the stability of hot water temperature.
5.Wind system control requirements
1. Control the opening of the fresh air valve according to the pressure inside the room.
2.MAU controls the opening of the preheating valve according to preheating to prevent the cold cracking of the cold dish pipe in winter.
3.Control the cold water and hot water and humidification of MAU according to the dew point.
4.according to the indoor temperature control corresponding to the opening of the DC valve.
5.FFU is divided into 10 groups, each group of 6, when one group of failure can easily find fault equipment. FFU starts in the order of 1-10 delayed start, turn off the other, prohibit 10 groups of simultaneous start, in order to avoid excessive starting current caused by the protection of equipment.
1. Process control: After field debugging, engineers find that the programming method is exactly the same as Siemens, and the field staff do not need to learn new programming methods, thus saving the time of field debugging, and the final control effect, especially PID, is very stable, to achieve the original design of the plan.
2. Cost performance ratio: 2 sets of control systems, such as the use of Siemens domestic PLC can not meet the requirements of points, if the use of Siemens imported module, the corresponding sensors need to use transmitters, in the cost of a great increase. After the adoption of the best PLC optimization scheme, the total cost is at least 50% less than that of SIEMENS.
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