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Basic PLC Ladder Programming Examples 23

Basic PLC Ladder Programming Training Examples for Beginners.  Hi friends, here we are starting unique a series of Free Training on PLC Ladder Programming & tutorials. These PLC Ladder Programs are important to learn basics of Ladder programs.

Example 7: Sequential control

If we serially connect the normally closed contact of Y2 in example 5 to the circuit of Y1 as an AND condition for Y1 (as the diagram in the left hand side), the circuit can not only make Y1 as the condition for Y2, but also allow the stop of Y1 after Y2 is enabled. Therefore, we can make Y1 and Y2 execute exactly the sequential control


Example 8: Oscillating circuit


The ladder diagram above is a very simple one. When the program starts to scan the normally closed contact Y1, Y1 will be closed because coil Y1 is Off. When the program then scan to coil Y1 and make it On, the output will be 1. When the program scans to the normally closed contact Y1 again in the next scan cycle, because coil Y1 is On, Y1 will be open and make coil Y1 Off and output 0. The repeated scans will result in coil Y1 outputs oscillating pulses by the cycle



Example 9: Flashing circuit


The ladder diagram is an oscillating circuit which makes the indicator flash or enables the buzzer alarms. It uses two timer to control the On/Off time of coil Y1. n1 and n2 refer to the set values in T1 and T2 and T is the cycle of the clock



Example 10: Trigger circuit



The rising-edge differential instruction of X0 makes coil M0 generate a single pulse of ΔT (one scan cycle). Coil Y1 will be On during this scan period. In the next scan period, coil M0 will be Off and the normally closed contact M0 and Y1 will all be closed, making coil Y1 continue to be On until another rising-edge arrives in input X0, making coil M0 On for another scan period and Y1 Off. Such kind of circuit relies on an input to make two actions execute interchangeably. Also from the timing diagram on the last page, we can see that input X0 are square pulse signals of the cycle T and coil Y1 output are square pulse signals of the cycle 2T.
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