SACA PLC Programming and Troubleshooting 4

Question 1

In a PLC ladder logic program, what is the function of a TON (Timer On-Delay) instruction?

Accepted Answer

It energizes the output after the rung has been continuously true for a preset time

Answer

A TON timer starts accumulating time when the rung goes true and energizes its done bit only after the accumulated time reaches the preset value.

Question 2

Which PLC addressing mode uses a memory location that can be changed during program execution to reference different data table elements?

Accepted Answer

Indirect addressing

Answer

Indirect addressing uses a pointer stored in memory to reference data table elements, allowing dynamic data access during runtime.

Question 3

A PLC output module is showing a fault LED. Which is the FIRST diagnostic step a technician should take?

Accepted Answer

Check the field device wiring and verify supply voltage at the module terminals

Answer

Verifying supply voltage and field wiring at the output module terminals rules out external causes before replacing internal components.

Question 4

In Structured Text (ST) programming, what does the following expression evaluate to if VarA = 10 and VarB = 5? Result := (VarA > VarB) AND (VarB <> 0);

Accepted Answer

TRUE

Answer

Both conditions are true (10 > 5 is TRUE, and 5 ≠ 0 is TRUE), so the AND operation returns TRUE.

Question 5

What is the purpose of a watchdog timer in a PLC system?

Accepted Answer

To detect if the scan cycle exceeds a maximum allowed time and fault the CPU

Answer

The watchdog timer faults the PLC CPU if the program scan does not complete within the configured maximum scan time, preventing runaway or stuck programs.

SACA - Smart Automation Certification Alliance Practice Test

SACA - Smart Automation Certification Alliance Practice Test

SACA PLC Programming and Troubleshooting 4