ITMC PLC Operations 3

Question 1

A PLC analog input module reads a 4-20 mA signal. A reading of 4 mA typically represents:

Accepted Answer

0% (minimum) of the process range

Answer

In a 4-20 mA loop, 4 mA represents the zero/minimum process value and 20 mA represents full scale.

Question 2

Which PLC memory type retains its data when power is removed WITHOUT a battery backup?

Accepted Answer

ROM or Flash EEPROM (non-volatile memory)

Answer

ROM and Flash EEPROM are non-volatile memory types that retain data without power or battery backup.

Question 3

In a PLC network using Modbus RTU, the device that initiates all communication transactions is called the:

Accepted Answer

Master

Answer

In Modbus RTU, the master device initiates all requests; slave devices only respond when polled by the master.

Question 4

What is the purpose of a 'watchdog timer' built into a PLC's CPU?

Accepted Answer

To reset the CPU if the scan cycle takes longer than a preset maximum time

Answer

The watchdog timer detects program hangs by resetting or faulting the CPU if a scan cycle exceeds the allowed maximum time.

Question 5

During PLC troubleshooting, forcing an output ON while in RUN mode will:

Accepted Answer

Energize that output regardless of the rung logic condition

Answer

Forcing overrides the program logic and holds the output at the forced state until the force is removed.

(ITMC) Industrial Technology Maintenance Certification Practice Test