ITMC PLC Operations 4

Question 1

A TOFF (Timer Off Delay) timer's output bit remains ON for the preset time after:

Accepted Answer

The rung condition transitions from TRUE to FALSE

Answer

A TOFF timer starts timing when its enable input goes FALSE, keeping the output ON until the preset delay expires.

Question 2

Which PLC I/O module type would you use to control a variable-speed drive (VFD) with a 0-10 VDC speed reference signal?

Accepted Answer

Analog output module

Answer

An analog output module produces a variable voltage or current signal (like 0-10 VDC) to command VFD speed.

Question 3

In ladder logic, what is the function of an Output Latch (OTL) instruction?

Accepted Answer

It sets a bit ON and holds it ON even after the rung goes FALSE

Answer

OTL (latch) sets a bit to 1 and it stays 1 regardless of rung logic until an OTU (unlatch) instruction resets it.

Question 4

When troubleshooting a PLC digital input that shows ON in software but the field device is known to be OFF, the FIRST check should be:

Accepted Answer

Verify wiring polarity and check for voltage leakage or a stuck contact

Answer

Wiring issues, leakage current, or stuck field contacts can falsely energize a digital input—verify these before hardware replacement.

Question 5

In PROFIBUS DP, the 'DP' stands for:

Accepted Answer

Decentralized Periphery

Answer

PROFIBUS DP (Decentralized Periphery) is designed for fast, cyclic communication between a master PLC and distributed field I/O devices.

(ITMC) Industrial Technology Maintenance Certification Practice Test