The circulating fan control system mainly detects the temperature, vibration, temperature of the main motor core and other measuring points when the fan is running, and realizes the start and stop, regulation and protection of the fan through these measuring points. The flow rate of the fan is controlled by a given opening degree of the air door, and its speed is controlled by a given frequency. The system is mainly composed of INVT PLC, INVT HMI and other hardware. The PLC is installed on the top of the cabinet. It is the core part of the system. It has intelligent logic and provides accurate protection signals when necessary. The touch screen vividly displays the running status of the system and the value of the measuring points, and has a high human-computer interaction function.
The system has extremely high flexibility and reliability. The modular structure is easy to maintain, the graphical display is intuitive, and the operation is simple and convenient. It is an important guarantee for the safe operation of the fan.
2. Application design and implementationThis project uses INVT 16 point DI, 14 point DO, 2 point AI (demand 7 points AI), 1 point AO (demand 2 points AO), 4 points PT100 signal (demand 7 points PT100 signal) PLC, and HMI man-machine On the screen, make the following PLC wiring diagram according to the project requirements (Figure 1).
figure 1)
PLC program overviewThe main logic of the program: 1. Collect fan, motor bearing temperature, fan bearing vibration, air door opening feedback, speed frequency feedback 2. Local/remote control of the motor heater 3. Local/remote control of the circulating fan (start When the conditions are not met, it is forbidden to start the fan) 4. Air door opening on-site/remote control (freely set within the range of 0~100% according to the required flow) 5. Rotation speed on-site/remote control (according to the required speed at 0 Freely set within the range of ~50HZ) 6. When each temperature reaches the set alarm or shutdown value, the system will alarm or shut down.
figure 2)
Subroutine call (PT100 signal calculation, 4-20mA signal calculation)
Control object (motor heater), divided into local control and remote control
Circulating fan start conditions (the fan can be started only when the conditions are met)
Control target fan (start and stop signal output 2s pulse)
4-20mA operation subroutine
PT100 signal calculation (parts listed)
HMI screen overview
This screen monitors the setting of each measuring point parameter, alarm and shutdown value and range value of the system, and controls the start/stop of the heater and fan, the speed frequency, and the setting of the air door opening.
Note: When the conditions are not met, the start/stop button of the heater or fan will be displayed as "gray scale" and operation is prohibited.
System alarm and shutdown information will be displayed on this screen
The icon (left) is the actual measurement point value detected, the icon (upper right) is the status display area, and the icon (lower right) is the control area (4 buttons are displayed in "gray scale", indicating that it is not satisfied with the start/ Stop condition).
The figure below shows the layout of the components
The final circulating fan control system control cabinet
The INVT PLC and INVT HMI I experienced this time, although only a short-term contact, have made me understand and familiar with its basic applications.
Apart from its own programming port, INVT PLC also has a set of MODBUS communication ports, which can communicate with many upper computers to realize data exchange. INVT PLC has many types and comprehensive functions. Users can choose the appropriate CPU according to project requirements.
INVT's HMI design is closer to practical applications, and can transmit data with many PLCs. Many of its functions are only part of this, and there are more functions that users need to explore slowly. The products experienced this time have been working normally in the circulating fan control system for more than one month.
In general, INVT products are cost-effective, value-for-money, technical support is also in place, and have strong market competitiveness.
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