14.6 PRACTICE PROBLEMS
(Note: Problem solutions are available at http://sites.google.com/site/automatedmanufacturingsystems/)
1. How are timer and counter memory similar?
2. What types of memory cannot be changed?
3. Develop Ladder Logic for a car door/seat belt safety system. When the car door is open, or the seatbelt is not done up, a buzzer will sound for 5 seconds if the key has been switched on. A cabin light will be switched on when the door is open and stay on for 10 seconds after it is closed, unless a key has started the ignition power.
4. Write ladder logic for the following problem description. When button
A is pressed a value of 1001 will be stored in
X. When button
B is pressed a value of -345 will be stored in
Y, when it is not pressed a value of 99 will be stored in
Y. When button
C is pressed
X and
Y will be added, and the result will be stored in
Z.
5. Using the status memory locations, write a program that will flash a light for the first 15 seconds after it has been turned on. The light should flash once a second.
6. How many words are required for timer and counter memory?
7. A machine is being designed for a foreign parts supplier. As part of the contractual agreement the logic will run until February 26, 2008. However, after that date the machine will enable a `contract_expired' value and no longer run. Write the ladder logic.
