SACA Programmable Logic Controllers 4

Question 1

Which PLC addressing mode uses a fixed memory location that does not change during program execution?

Accepted Answer

Direct addressing

Answer

Direct addressing specifies an exact, fixed memory location in the PLC program that remains constant during execution.

Question 2

In a PLC ladder diagram, what does a normally closed (NC) contact represent in terms of the physical input signal?

Accepted Answer

The contact passes current when the input coil is de-energized

Answer

A normally closed contact in ladder logic passes current (is true) when its associated coil or input is de-energized or off.

Question 3

What is the primary purpose of a PLC's watchdog timer?

Accepted Answer

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

Answer

The watchdog timer monitors the PLC scan cycle duration and triggers a fault or system reset if the cycle time exceeds a preset maximum, preventing runaway programs.

Question 4

Which IEC 61131-3 programming language uses graphical blocks connected by signal lines to represent program logic?

Accepted Answer

Function Block Diagram (FBD)

Answer

Function Block Diagram (FBD) uses interconnected graphical function blocks and signal lines to represent control logic.

Question 5

A PLC analog input module receives a 4–20 mA signal from a pressure transmitter. What does a 4 mA signal typically represent?

Accepted Answer

0% of the process range (minimum span)

Answer

In a 4–20 mA loop, 4 mA corresponds to 0% (minimum) of the process variable range, and 20 mA corresponds to 100%.

SACA - Smart Automation Certification Alliance Practice Test

SACA - Smart Automation Certification Alliance Practice Test

SACA Programmable Logic Controllers 4