This first project is to convert a traditional On/Off motor control that use relay become PLC driven , in this project we use CPM2A plc, below is the image of traditional On/Off controller using relay:
This is how the controller work :
1. Mg is a contactor tree pole , servicing as electromekanik switch for the motor. Its normally open (NO) switch.
2. Contact of Mg pole driven by Mg coil.
3. Pb2 is a stop button, and its nomally closed (NC) push button switch.
4. Pb1 is the ON button.
5. And a contact control Mg work for latch Pb1 (start button)
6. Th= thermal relay for motor overload protection.
When PB1 On then coil Mg energize, control contact Mg will close and latch PB1, in the same time Mg main contact also close and motor ON,
If Pb2 pushed, coil Mg deenergized, Mg main contact opened and motor will off.
Next step : I/O assigment :
Pb1 =000.00 (Start)
Pb2=000.01 (Stop)
Out_motor=010.00; this address will drive the coil of motor contactor, Mg
For I/O assignment its dependent on PLC area memory, you can refer area memory information in CPM2 A manual book.
And the ladder diagram :
In mnemonic , this program written as:
Load 000.00
Or 010.00 (its internal contact, that driven by internal coil with address 010.00)
And Not 000.01
Out 010.00 (actifated internal relay 010.00, and so its contact)
Program Explanation :
When Pb1 is pushed, then coil 01000 is activated, because Pb2 is a NC (normally closed)
Subsequencelly Pb1 is latced by 010.00 (internal contact).
External terminal of 01000 activated Mg contactor, and motor will run.
Or 010.00 (its internal contact, that driven by internal coil with address 010.00)
And Not 000.01
Out 010.00 (actifated internal relay 010.00, and so its contact)
Program Explanation :
When Pb1 is pushed, then coil 01000 is activated, because Pb2 is a NC (normally closed)
Subsequencelly Pb1 is latced by 010.00 (internal contact).
External terminal of 01000 activated Mg contactor, and motor will run.
