The information control transformation program has the advantages of economy, powerful function and convenient control.
The Xinjie FC Series PLC is a small programmable controller with powerful functions, compact structure and rich instruction set. It can be equipped with a variety of special modules, with good scalability, low price and powerful features, wide voltage range and Wind ows-based programming tools, making people more flexible and convenient to solve automation tasks.
The lower position machine in this example uses the domestic FC series PLC as the field controller, which consists of the host FC-32R-E plus the analog expansion module FC-8AD and the Pt100 temperature acquisition expansion module MD-16AD-PT.
The operating parameters of the unit are collected by sensors or sensor transmitters. The operating parameters collected by the author include refrigerant discharge pressure, exhaust temperature, suction pressure, suction temperature, compressor lubricating oil temperature, chilled water outlet temperature, chilled water return water temperature, cooling water outlet temperature, cooling water return water. Temperature, chilled water flow and cooling water flow. The temperature parameter is collected by Pt100 platinum thermal resistance temperature sensor. The lead wire is connected to the MD-16AD-PT expansion module to complete the digital conversion of the temperature resistance analog electrical signal PLC and saved to the corresponding register of the PLC host. The pressure parameter is collected by a diffusion silicon type strain gauge pressure sensor transmitter, which converts the pressure parameter into 0~5V analog quantity electric signal, inputs it to the FC-8AD analog quantity expansion module, performs A/D conversion, and finally saves. To the PLC host corresponding register. The target flow switch is used to sense the chilled water flow and the cooling water flow as conditions for the operation of the unit.
The touch screen used in this example is a CoolmayHM series HM-5A type touch screen. It is an open human interface product that provides a standard serial interface to connect to other devices. The supported communication methods are mainly serial communication, which supports communication with mainstream PLCs on the market today; the powerful 32-bit processor is used, the operation speed is faster, the power consumption is smaller, and the operation is more stable. The touch precision is accurate, durable and long in touch life; it has strong anti-interference ability and meets the electromagnetic compatibility requirements of industrial environment.
This example uses a new type of networking, which is to connect the PLC directly to the local area network with the RS232 to TCP/IP networking module. With this module, the controller, sensor transmitter connected to Ethernet becomes simple, convenient and economical. One end of the module is the RS232 connector connected to the PLC, and the other end is a crossover network cable connecting the Ethernet switch (or hub) or PC. It converts the data transmitted from the PLC to the TCP/IP communication protocol from the serial communication protocol. On the Ethernet; on the contrary, it is also possible to convert the data of the TCP/IP communication protocol transmitted on the Ethernet into the data of the serial communication protocol. Then, as long as the author configures the SSVSPM virtual serial port software on any client PC on the local Ethernet network, the data transmitted from the PLC can be connected and become the virtual serial port signal of the PC. The virtual serial port is set as an external device of the industrial control configuration software installed on the client PC, so that the data received from the local area Ethernet is stored in the real-time database of the configuration software. Conversely, the data of the configuration software can be reversed by the PC Ethernet networking module PLC, realistic two-way real-time communication.
A PC as a host computer and a server on the local area network must have a configuration engineering application developed by the network version configuration software. In this way, other clients on the local area network are authorized to input the IP address into the upper computer server in the IE browser, and the configuration project can be entered in the IE browser to realize multi-site network control.
2PLC control program development
After completing the configuration of the PLC input and output interface, the author first writes and organizes the PLC control strategy, and then develops the PLC control program. In order to make the program debugging intuitive and clear, to facilitate system debugging and modification and function expansion, the PLC control program adopts modular structure design. According to the working requirements of the chiller, the author divides the control program into the following subroutine modules:
(1) Data acquisition module: The parameters collected by the sensing (transmission) device are sequentially stored in the register of the beginning of W1792 (the first expansion module) and the beginning of W1824 (the second expansion module).
(2) Refrigeration unit safety protection and alarm module: including water flow protection, high and low pressure protection, oil temperature protection and compressor winding temperature protection. When these parameters exceed the safe value, the PLC urgently issues an order to shut down the compressor and all other equipment.
(3) Boot module: When the start button of the site is pressed or the remote start signal is received, the PLC first starts the cooling tower fan for 1 min, then turns on the cooling water pump for 3 min, then starts the chilled water pump for 3 min, and then uses the Y-start mode. Start the compressor. Since the compressor of the air conditioning system is a three-row six-cylinder reciprocating piston compressor with an unloading mechanism controlled by a solenoid valve, no-load starting can be achieved, reducing the starting current and impact on the grid.
(4) Temperature control and energy regulation module: The chiller is a product of Shanghai Carrier, and the compressor has an unloading mechanism. The author uses the chilled water effluent temperature as the adjusted parameter and uses stepped energy regulation. Since the unit has three unloading mechanisms, it can be designed into three energy levels: 33%, 66%, 100%. With the change of the chilled water effluent temperature, the PLC determines that the corresponding energy cylinder is put into operation. Compared with the two-position adjustment, the step energy adjustment method has higher adjustment precision, and the compressor can save energy and reduce consumption.
When the chilled water outlet pump reaches the lower limit of 6, the chiller is in a constant temperature standby state. At this time, the chilled water pump is kept in a cooling operation state. The cooling tower and the cooling water pump are stopped after 2 minutes of operation. The purpose is to completely dissipate the residual heat of the cooling water, which provides good conditions for the next start of the chiller, and saves energy compared to the cooling tower and the cooling water pump.
(1) Shutdown module
This refers to a normal shutdown. As for the downtime, it is combined with the (2) module. When the stop button is pressed or the stop command from the computer network is issued, the PLC first issues the command to shut down the compressor. After 1 minute, the chilled water pump is turned off, and after 2 minutes, the cooling water pump and the cooling tower fan are turned off.
The author has set that after the compressor is stopped, it must be turned on again after 3 minutes. This is because after the compressor is stopped, the high and low pressure of the refrigeration system has not been balanced. If it is turned on immediately, the starting torque of the compressor motor will be too large, the starting current will be too large, and there is a danger of burning the motor and causing the impact of the power grid.
(2) Cooling tower energy saving control module
Considering that the air conditioning season is long, it is necessary to operate the air conditioning unit when the temperature is low. For this purpose: when the cooling water inlet temperature is lower than 25, the cooling tower fan stops running; when the cooling water inlet water is higher than 30, the cooling tower fan resumes operation. The function of this setting is to ensure that the condensing pressure of the chiller is not so low and affect the refrigerant supply amount of the evaporator, and the energy consumption of the unit can be reduced.
3 touch screen configuration development
CoolmayHM series touch screen configuration software is CoolDRAW, CoolDRAW provides users with screen configuration, drive settings, alarms, recipes and other functions. The screen developed by the author using CoolDRAW touch screen configuration software includes: startup screen, parameter monitoring screen, alarm screen and so on. The startup screen is the first screen that appears on the screen when the touch screen is running. On this screen, the organic group device graphics and the compressor power-on touch key and the stop touch key are configured, and the chilled water outlet temperature and the cooling water inlet temperature are displayed. The main parameters. After the system is powered on, you can press the power on touch button and the stop touch button on the startup screen to open and stop the unit. Of course, the hardware on the door panel of the PLC is also equipped with a hardware open, stop button, as a redundant backup. On the parameter monitoring screen, all the parameters collected by the sensor (transmission) are displayed. On the alarm screen, it can display the currently occurring alarm information and the flashing of the warning light, and set an alarm sound when an alarm occurs. On each screen, there are switching buttons for switching to other screens, and both set dynamic alarm bars to display the current alarm information.
4 summary
After the hardware construction and software configuration development settings according to the above scheme, the air conditioning system runs successfully, and the PLC, touch screen and network monitoring and control meet the expected requirements. After the transformation, the working condition of the chiller is much better than that before the renovation. The chilled water effluent temperature fluctuation range is small, the load is automatically added and reduced according to the water temperature, reducing the waste of waste, effectively avoiding some useless power consumption, achieving energy saving and consumption reduction. effect. Operators can perform multi-site network operations and monitoring on the LAN client, improving the working environment. If the LAN is connected to the Internet, we can use the IE browser to access the configuration project on any client on the Internet, and monitor the chiller just like the host computer.
In this example, the PLC, touch screen, networking module and virtual serial port software, configuration software and other software and hardware devices are all made in China, with reliable quality, strong performance and low price, low transformation cost and good economy. The office PC can be used as the upper computer, which saves equipment and operates at the same time, and monitors multiple locations for flexible arrangement. The cost of building local Ethernet is now low, and the control of chillers can be incorporated into a building automation network or a property management network. Therefore, this example provides a good reference and valuable reference for the intelligent transformation of buildings in the old central air conditioning system.
Of course, the air conditioning system control of this example can further expand the function, and the temperature monitoring of the air-conditioned room can be realized by expanding on the existing basis, so that the function of the system is more perfect.
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