Hardware connection
Signal input:
First, connect the control signal to the input port of the PLC control cabinet. If you need to manually control the start and stop of the fan, you can connect a push button switch. For example, connect the start button and the stop button to the digital input point of the PLC respectively, and generally use a DC 24V power supply to power the button circuit.
When the fan needs to be automatically controlled according to environmental parameters (such as temperature, pressure, etc.), the corresponding sensor should be connected. For example, the signal of the temperature sensor (such as PT100 thermal resistor) is converted into a standard analog signal (such as 4-20mA or 0-10V) through a transmitter and then connected to the analog input port of the PLC.
Signal output:
The PLC control cabinet is connected to the control circuit of the fan through the output port. For three-phase AC fans, a relay output type PLC is usually used to control the AC contactor. Connect the output point of the PLC to the coil of the intermediate relay, and the normally open contact of the intermediate relay is connected in series in the coil circuit of the AC contactor. The main contacts of the AC contactor are connected to the three-phase power supply line of the fan motor, thereby realizing the control of the fan motor.
Software programming
Start-stop control programming:
In the PLC programming software, write a logic program for the input points corresponding to the start and stop buttons. For example, using the ladder diagram language, when the start button is pressed (the corresponding input point becomes high level), set an output point to a high level, which controls the intermediate relay and the AC contactor to start the fan; when the stop button is pressed, reset the output point to a low level and the fan stops. This function can be achieved using the set (SET) and reset (RST) instructions.
Automatic control programming (taking temperature control as an example):
First, read the analog signal from the temperature sensor and convert it into the actual temperature value through the analog processing function block of the PLC. Assuming that the start and stop of the fan are to be controlled according to the temperature, when the temperature is higher than the set value (such as 30℃), the PLC program determines that the fan needs to be started to cool down. Compare the actual temperature value with the set temperature value through comparison instructions (such as CMP). When the actual temperature value is greater than the set temperature value, the output point is set and the fan starts; when the temperature drops to a certain range below the set value (such as 28℃), the output point is reset and the fan stops.
Parameter setting and debugging
Parameter setting:
For analog input and output modules, you need to set parameters such as signal type (such as current signal or voltage signal), range, etc. For example, for analog input modules connected to 4-20mA temperature signals, you need to set the temperature range corresponding to the range, such as 4mA for 0℃ and 20mA for 100℃.
Debugging:
First perform manual control debugging, press the start and stop buttons, and check whether the fan can start and stop normally. Then perform automatic control debugging, simulate environmental parameter changes (such as using a signal generator to change the analog input signal), and observe whether the fan can automatically start and stop according to the set logic. At the same time, it is necessary to check whether the fan’s operating status feedback signal (such as the overload signal of the thermal relay fed back to the PLC input point) can be correctly received by the PLC and processed accordingly, such as stopping the fan in time when the fan is overloaded.
