Explain Briefly From What You Notice About The Digital.

1. Design and draw a ladder diagram circuit suitable for a PLC which will fulfil the following control requirement:

A momentary push switch is to be recognised, remembered and used to switch on an output for a period of 30 seconds. After 30 seconds this output is to be switched off and must be off for 0.5 seconds before a second output switches on.

The second output remains on until a second push switch is operated to turn it off. If the second push is operated at any time then the current output must turn off and the system await the press of the first push. The rungs of the ladder diagram must contain interlock contacts which prevent both outputs being on at the same time.

2. Redesign and improve the pelican crossing ladder diagram given of FIGURE 1 of lesson PLC - 6 - 2 by adding timer rungs and counter rungs between rungs 12 and 14 (or any similar workable scheme) together with the necessary contacts inserted in the amber and green man lights of rungs 7 and 10, etc. The chart below shows the required sequence of events. Note that a section of the chart is repeated a total of 16 times. The time intervals are given below.