Operating Cycle of the PLC Processor

Question 1

What is the processor scan?

Answer 1

Reading the inputs, solving the program and writing to the outputs

Question 2

What is required to capture high-speed switching events using a pLC with a longer scan time?

Answer 2

Special programming instructions with interrupts or high-speed counter inputs

Question 3

If the PLC has a scan time of 9ms and is required to monitor a signal that ___________, the CPU will never notice the signal has changed state.

a. changes state once in 12ms
b. changes state very slowly
c. changes state once in 20ms
d. changes state twice in 5ms

Answer 3

d. changes state twice in 5ms

Question 4

Scan time is the time required ____________

Answer 4

To execute one cycle of the processor scan

Question 5

If the state of the inputs changes during the program scan, when does that change take effect?

Answer 5

During the start of the next program scan

Question 6

What are three items on which the scan time of the processor depends?

Answer 6

• Speed of the CPU
• Length of the program
• Total number of I/O to service
• Type of programming instructions

Question 7

During what portion of the operating cycle of a PLC does the processor read the input status and write to the outputs?

Answer 7

I/O Update