7. Assuming the hardwired circuit drawn in Figure 5-60 is to be implemented using a PLC program, identify a. All input field devices b. All output field devices c. All devices that could be programmed using internal relay instructions 8. What instruction would you select for each of the following discrete input field devices to accomplish the desired task? (State the reason for your answer.) a. Turn on a light when a conveyor motor is running in reverse. The input field device is a set of contacts on the conveyor start relay that close when the motor is running forward and open when it is running in reverse. b. When a pushbutton is pressed, it operates a solenoid. The input field device is a normally open pushbutton. c. Stop a motor from running when a pushbutton is pressed. The input field device is a normally closed pushbutton. d. When a limit switch is closed, it triggers an instruction ON. The input field device is a limit switch that stores a 1 in a data table bit when closed. 9. Write the ladder logic program needed to implement each of the following (assume inputs A, B, and C are all normally open toggle switches): a. When input A is closed, turn ON and hold ON outputs X and Y until A opens. b. When input A is closed and either input B or C is open, turn ON output Y; otherwise, it should be OFF. LS1 PB1 CR1 PL1 SS1 PS1 CR1 LS2 LS3 CR2 PB2 PB3 CR2 LS4 CR3 L1 Figure 5-60 Hardwired circuit for Problem 7. L2 CR1 SOL A CR2 SOL B SOL C CR3 PL2 c. When input A is closed or open, turn ON output Y. d. When input A is closed, turn ON output X and turn OFF output Y. Basics of PLC Programming Chapter 5 97
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