## ASSIGNMENT PROBLEMS

1. Draw the timer and counter done bits for the ladder logic below. Assume that the accumulators of all the timers and counters are reset to begin with.

2. Write a ladder logic program that will count the number of parts in a buffer. As parts arrive they activate input A. As parts leave they will activate input B. If the number of parts is less than 8 then a conveyor motor, output C, will be turned on.

3. Explain what would happen in the following program when A is on or off.

4. Write a simple program that will use one timer to flash a light. The light should be on for 1.0 seconds and off for 0.5 seconds. Do not include start or stop buttons.

5. We are developing a safety system (using a PLC-5) for a large industrial press. The press is activated by turning on the compressor power relay (R, connected to O:013/05). After R has been on for 30 seconds the press can be activated to move (P connected to O:013/06). The delay is needed for pressure to build up. After the press has been activated (with P) the system must be shut down (R and P off), and then the cycle may begin again. For safety, there is a sensor that detects when a worker is inside the press (S, connected to I:011/02), which must be off before the press can be activated. There is also a button that must be pushed 5 times (B, connected to I:011/01) before the press cycle can begin. If at any time the worker enters the press (and S becomes active) the press will be shut down (P and R turned off). Develop the ladder logic. State all assumptions, and show all work.

6. Write a program that only uses one timer. When an input A is turned on a light will be on for 10 seconds. After that it will be off for two seconds, and then again on for 5 seconds. After that the light will not turn on again until the input A is turned off.

7. A new printing station will add a logo to parts as they travel along an assembly line. When a part arrives a ‘part’ sensor will detect it. After this the ‘clamp’ output is turned on for 10 seconds to hold the part during the operation. For the first 2 seconds the part is being held a ‘spray’ output will be turned on to apply the thermoset ink. For the last 8 seconds a ‘heat’ output will be turned on to cure the ink. After this the part is released and allowed to continue along the line. Write the ladder logic for this process.

8. Write a ladder logic program. that will turn on an output Q five seconds after an input A is turned on. If input B is on the delay will be eight seconds. YOU MAY ONLY USE ONE TIMER.

9. Use the timing diagram below to design ladder logic. The sequence should start when input X turns on. X may only be on momentarily, but the sequence should execute anyway. Note that output A is normally on.

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