24.6 PRACTICE PROBLEMS
1. A switch will turn a counter on when engaged. This counter can be reset by a second switch. The value in the counter should be multiplied by 5, and then displayed as a binary output using (201-208)
2. Develop Ladder Logic for a car door/seat belt safety system. When the car door is open, or the seatbelt is not done up, the ignition power must not be applied. In addition the key must be able to switch ignition power.
3. TRUE / FALSE -- PLC outputs can be set with Bytes instead of bits.
(ans. true)
4. Create a ladder logic program that will start when input `A' is turned on and calculate the series below. The value of `n' will start at 1 and with each scan of the ladder logic `n' will increase until n=100. While the sequence is being incremented, any change in `A' will be ignored.
5. A thumbwheel input card acquires a four digit BCD count. A sensor detects parts dropping down a chute. When the count matches the BCD value the chute is closed, and a light is turned on until a reset button is pushed. A start button must be pushed to start the part feeding. Develop the ladder logic for this controller. Use a structured design technique such as a state diagram.
6. Design and write ladder logic for a simple traffic light controller that has a single fixed sequence of 16 seconds for both green lights and 4 second for both yellow lights. Use either stacks or sequencers.
7. A PLC is to be used to control a carillon (a bell tower). Each bell corresponds to a musical note and each has a pneumatic actuator that will ring it. The table below defines the tune to be programmed. Write a program that will run the tune once each time a start button is pushed. A stop button will stop the song.
8. The following program uses indirect addressing. Indicate what the new values in memory will be when button A is pushed after the first and second instructions.
9.
