PLC Test - Free Test, Topics, Sample Questions and Answers
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What Is a PLC Test?

The PLC test is a tool to access one's knowledge and skills in the maintenance and repair of programmable logic controllers (PLC). The test usually covers the core aspects of PLCs, such as programming, I/O devices, etc. Another substantial part of the test is dedicated to the interpretation of ladder diagrams and troubleshooting.


Who Takes the PLC Test?

PLC tests are designed for applicants of various fields, including:

  • Computer Technicians
  • Commercial and Industrial Equipment Technicians
  • Electronics Engineering Technicians
  • Electrical and Electronics Repairers

In addition, PLC questions can appear on a variety of other tests, especially those dealing with maintenance, such as the Amazon Maintenance Technician Test or the MultiCrafTest.


Ramsay Corporation’s PLC Test

Although there are many PLC tests out there, the Ramsay PLC test is by far the most popular among employers.

Ramsay Corporation is the largest and most professional test provider for technical assessments, used by giants such as Amazon, Walmart, and JLL. 

The Ramsay PLC test contains 50 questions on 5 different topics, 10 questions each:

  • PLC and I/O Basics
  • Programming Basics
  • Ladder Logic 
  • Peripherals and Systems
  • Troubleshooting

The test is untimed, but you are expected to complete it within 1 hour.


PLC Test Sections and Sample Questions

Note: All sample questions you will see below are all based on the Ramsay PLC test. 

 

PLC and I/O Basics

This section comprises questions related to the introduction of PLC. It deals with topics such as the different uses and applications of PLCs, safety, I/O (input and output) devices.

PLC and I/O Basics Sample Question

Pick an appropriate sensor for the circuit shown below:

PLC Test - IO Sample Question

 

A. Temperature sensor
B. Solenoid
C. Humidity sensor
D. Limit switch
Correct Answer
Incorrect Answer

The schematic shown is the interface between the digital output sensor and a PLC with the help of the Digital I/O module. Any digital output sensor can be interfaced with the PLC in the schematic.

A digital sensor is a device that converts the sensed physical quantity into a logic level as 0 and 1. The PLC reads this logic through the digital I/O module and performs the required actions based on the sensors’ feedback.

A solenoid is an actuator, and therefore (B) cannot be true.

Temperature and Humidity sensors are analog output sensors and require an analog input module on the PLC. Thus, (A), and (C) cannot be correct either.

Limit switches are digital output sensors and require a digital I/O module to be interfaced with the PLC. Therefore, (D) is the correct answer. 

 

Ladder Logic

This section deals with the visual representation of PLC programming in ladder diagrams. Most questions will require you to interpret the diagram and answer a question based upon it.

Ladder Logic Sample Question

The PLC program shown below controls a burner (B) with three gas detectors surrounding it (s1, s2, and s3).

The burner will be lit _______.

PLC Test Ladder Logic Sample Question

 

A. if any one of the sensors detects gas.
B. if any two of the sensors detect gas.
C. only if all three sensors detect gas.
D. The answer depends on the specific sensors detecting gas.
Correct Answer
Incorrect Answer

The Burner (B) is dependent upon three ladders. Each ladder contains two sensors. There is an “OR” condition between each combination and an “AND” condition between two sensors on each ladder. “OR” condition means “if any of the logic is true” whereas “AND” condition means both logics must be true.

Consider ladder 1. If s1 and s2 are an AND condition then the logic will be true if both of the sensors detect gas.

The same goes for s3 and s1 on ladder 2.

However, all ladders are in OR condition with the others. Therefore, if any of the ladders is true, the burner will be lit.

So, in order to light the burner, any two of the sensors must detect gas (either s1 and s2, s3 and s1, or s2 and s3).

 

Programming Basics

The programing section deals with the internal programming of the PLC and the functionality of its different components.

Questions in this section are often more fundamental and theoretical and require you to show understanding of basic concepts, such as programming languages, number systems (binary, octal, hexadecimal), and components (CPU, RAM, etc.)

Programming Basics Sample Question

Logic functions use logic 0 and 1 which are electrical signals of: 

A. 0 V and 1 V
B. 0 V and VCC (power supply of logic function)
C. 0 v and 5 V
D. Logic signals are not electrical.
Correct Answer
Incorrect Answer

Logic functions are electrical/electronic devices used to perform special combinational logic with their input signals. These logic signals are electrical in nature and are represented as 1 and 0.

Logic 1 stands for the higher level of the voltage supply of the logic function, whereas logic 0 is the ground potential – which is always 0 V.

However, since logic functions can operate on a variety of power supplies, the voltage of logic 1 can vary, so B is the correct answer. 

 

Peripherals and Systems

The peripherals and systems section covers the devices attached to the system at the input or output source. Questions in this section may cover things like types of cables and ports, function blocks, and transmission rates (baud, bit).

Peripherals and Systems Sample Question

The standard connector used for serial communication is ___________. 

A. RJ45
B.DB9
C. RJ50
D. RJ11
Correct Answer
Incorrect Answer

The industry has standardized all kinds of connectors to help troubleshooters during the maintenance procedure.

In serial communication, DB-9 is the standard connector as shown below. Therefore, (B) is the correct answer.

RJ45 (A) is a standard connector for network cables.

RJ50 (C) and RJ11 (D) are not defined as standard connectors for serial communication.

PLC Test Peripherals Sample Question

 

Troubleshooting

In most cases, you will be required to take a PLC test as a part of the hiring process for technical positions. These jobs require a broad knowledge of troubleshooting, and this test section will be a major part of your score.

Usually, you will be presented with a scenario depicting a problem with a PLC or one of its components and will be requested to detail the actions to locate and/or solve the problem.

Troubleshooting Sample Question

The status indicator of the PLC output module is ON, but the interfaced device does not turn ON. The voltage at the output port is correct. What can be the problem?

A. CPU is not running properly
B. The fuse on the output line is blown
C. The interfaced device is faulty
D. All of the above
Correct Answer
Incorrect Answer

If the status indicator is ON, this implies that the logic is coming from the CPU and it is working properly. Thus, (A) cannot be the correct choice.

If the voltage at the output port is checked and is in the acceptable range, this implies (B) cannot be correct as well. The only possible solution is the interfaced device is faulty and must be replaced.

Therefore, (C) is the correct choice.


Summary

The PLC is a very common test in the electrical and electronics industry and requires a broad base of knowledge to successfully pass. PLC test sections are also common in maintenance, multicraft, and electricity tests.

Being familiar with the basic definitions and components of PLCs, mastery of ladder diagrams reading, and a sense for troubleshooting are all essential for passing with a high score.

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