many of the visitors asked me about the ladder logic i wrote on the sample project. actually it is only a small part of automation. A lot more can be done but that is the basic to move a pneumatic actuator which is largely used in industries such as automotive manufacturing.
ok i think it is best for us to go back to the example i gave in the sample project page. Please save the ladder logic from the link and we will go rung by rung for better understanding. it is important if we have the same view that the vertical line on the left hand side of the ladder logic represent 24V potential and the vertical line on the right hand side represents 0V potential.
At rung 0 (numbered there 0000), we can see that when we first press the start button (addressed at 0.00), it will ON the bit address 200.00. This bit 200.00 is an empty bit and can be used for sequencing purposes. You can also use other empty bit address as your sequencing bit. After 200.00 ON, it will latch itself so that it will remain in ON state. If any of the alarm (250.01 and 250.03) turns ON, the sequencing bit will turn OFF and the actuator will stop.
At rung 1, since the cycle will start when the cylinder has not come out yet, so the BWD reed switch (reed switch at the bottom) will initially turn ON (it is set as the origin). Input Bwd reed switch is addressed at 0.01 and when it is turned ON, second sequencing bit 200.01 will also turn ON and latch itself. The first error timer will turn ON to count the time taken for the actuator to reach forward reed switch. The time allowed as in this programming is only 10 seconds for the actuator to complete its first half cycle.
At rung 2, this rung will ON the output coil 250.00 that will later be connected to the solenoid valve in rung 9 and the actuator will keep going forward (since addressed 200.01 has been latched) until the forward reed switch is ON.
At rung 3, if the error timer forward T5 has exceeded the 10 second, it will turn ON the address 250.01 (alarm for first half cycle forward).
At rung 4, when the actuator has moved forward, it will move until it reaches the forward reed switch, then the forward reed switch (0.02) will turn ON. Sequence bit 200.01 that was latched before at rung 1 will allow the sequence bit 200.02 (ready to OFF SV) to turn ON and latch itself. Error timer backward will also turn ON until one cycle complete sequence bit (200.03) is turned ON.
At rung 5, the latched sequence bit 200.02 will also latched 250.02 to turn OFF the solenoid valve so the actuator will move backward.
At rung 6, if the error timer forward T5 has exceeded the 10 second, it will turn ON the address 250.03 (alarm for second half cycle backward).
At rung 7, the latched sequence bit 200.02 will allow sequence bit 200.03 to turn ON and latch itself when the actuator goes backward and turn ON the Bwd reed switch. Now the actuator has completed 1 cycle and if this is achieved, the turned ON sequence bit 200.03 will not allow the alarm at rung 6 to turn ON.
At rung 8, this rung will make the system runs in a cyclic manner. After 1 cycle is completed, the sequence bit 200.03 will turn ON and latch itself and therefore turning the reset cycle bit addressed at 200.04 to turn ON. When this bit is turned ON, it will turn OFF the second sequencing bit (200.01) at rung 1 and therefore turning OFF other sequencing bit (200.02 and 200.03) since they are also interrelated. When 200.03 is turned OFF, it will also turn the reset cycle bit 200.04 OFF. So the system will go back as normal and the second cycle will start as soon as the bwd reed switch is turned ON. This rung is very important because it causes to system to loop.
At rung 9, 250.00 will turn output bit 100.00 ON so that the solenoid valve will ON until 250.01 is turn ON.
At rung 10, when either one of the alarm 250.01 and 250.03 is turned ON, output bit 100.01 that is connected to the alarm light will turn ON and the light will be switched ON. This is a good example on how to call the same output multiple times in your programming.
PS: take note that in this example, the alarm will only ON momentary to stop the system. it is purposely not latched.
December 8th, 2008 | Tags: automation, automation direct, automatizacion, book on plc, free plc book, industrial plc, ladder diagram, ladder logic example, ladder logic tutorial, OMRON, omron plc programming, PLC, plc automation, plc books, PLC open, PLC programming, PLC software, programmable logic controller | Category: Uncategorized | Comments (1)
