Question5 (100 Marks) 5) 5.1 PLC (Programmable Logic Control) is a small and pow

Question

Question5 (100 Marks) 5) 5.1 PLC (Programmable Logic Control) is a small and powerful computer which is designed for industrial controlling. PLCs' are commonly used to control a process or a machine wired to input (sensors) and output (actuators) devices. Describe the Scan [10 Marks] 5.2 On Delay Timers (TON), Off Delay Timers (TOF) and Retentive On Delay Timers Cycle of a PLC. (TONR) are commonly used timers/ timer blocks in ladder logic programming. Network 1 10.0 T33 IN TOF Network 2 133 00.0 Figure 5.1 Figure 5.1 shows an OFF delay timer which is activated by an external input (I0.0) The timer has given the pre-set value of 1s. Output (0.0) is enabled once the timer condition is true. Complete the timing diagram in Figure 5.2 by adding the timing graph of the output (Q0.0) signal. [20 Marks]

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Since there are multiple questions attached, and each question would require thorough explanation, I would answer only the first one:

5.1 A PLC operates much like a modern microcontroller, by continually " going through " the programs in its memory and executing the instructions. This " going through ", or sequential execution of the instructions, is nothing but the scanning by the PLC. It basically consists of three steps: 1) Input Scan 2) Program Execution and 3) Output Scan

1) Input Scan: In this stage, the PLC scans for all inputs, by reading the values off the input cards. These values may be a '0' or a '1'. These values are then stored in a table, and used for subsequent execution of program logic.

2) Program Execution: The PLC then executes the instruction it is assigned to carry out, using the logic values stored in the table in Step 1. It exceutes instructions one cycle at a time.

3) Output Scan: The PLC now changes the status of the outputs depending on the output of the logic execution carried out in Step 2.

It is to be noted that the PLC will always check for faults after every scan cycle. This process is repeated over and over again, in a loop.

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