Q1. The PLC was invented by.
a) Bill Gates b) Dick Morley c) Bill Landis d) Tod Cunningham
Q2. The first company to build PLCs was .
a) General Motors b) Allen Bradley c) Square D d) Modicon
Q3. Classify the following as automatic control, manual control, discrete control or continuous control.
a) A sensor is used to turn on and off the lights of a room.
b) A temperature sensor is used to adjust the room temperature and maintain it at a set point.
c) A user starts the bottle filling machine, places the bottle on the conveyor belt to fill it with the
required liquid.
d) The luggage system at the airport.
e) A factory that makes red pens and has no human employees.
Q4. The part that monitors the inputs and makes decisions in a PLC is the CPU.
a. True b. False c. None of the above
Q5. One of the following is an input device
a. Motor b. Light c. Valve d. Sensor
Q6. Which one of the following is not a PLC manufacturer
a. Siemens b. Mitsubishi c. Microsoft d. ABB
Q7. Solenoids, lamps, motors are connected to:
a. Analog output b. Digital output c. Analog input d. Digital input
Q8. In a PLC āIā is used for output and āQā is used for input
a. True b. False c. None of the above
Q9. PLC stands for programmable logo controller
a. True b. False c. None of the above
Q10. To increase the number of inputs and outputs of the PLC, one can use expansion modules.
a. True b. False c. None of the above
Q11. An example of discrete (digital) control is:
a. Varying the volume of a music system
b. Turning a lamp ON or OFF
c. Varying the brightness of a lamp
d. Controlling the speed of a fan
Q12. A solenoid is an example of an output device.
a. True b. False c. None of the above
Q13. Which of the following statements is not correct?
a) The PLC rung output [-( )-] is a discrete output instruction or bit in memory.
b) Each rung of the ladder logic represents a logical statement executed in software ā inputs on the
right
and outputs on the left.
c) Input and output instructions in ladder logic do not directly represent the switches and actuators.
d) PLC input instructions are logical symbols associated with voltage at the input module terminals.
Q14. Which of the following statements is correct?
a) Ladder logic is a PLC graphical programming technique introduced in the last 10 years.
b) A ladder logic program is hard to analyze because it is totally different when compared with the
equivalent relay logic solution.
c) The number of ladder logic virtual relays and input and output instructions is limited only by memory
size.
d) The number of contacts for a mechanical relay is limited to number of coils on the relay.
Q15. Which of the following statements is NOT correct?
a) The status of each input can be checked from one location and outputs can be forced on and off.
b) All symbols in the RLL represent actual components and contacts present in the control system.
c) PLCs are not as reliable as electromechanical relays in RLL.
d) Input (-| |-) and output (- ( ) -) instruction symbols in the ladder logic represent only data values
stored in PLC memory.
Q16. Which of the following statements is NOT correct?
a) If a problem in a PLC module occurs, the module can be changed in a matter of minutes without any
changes in wiring.
b) Outputs can be paralleled on the same rung.
c) The physical wires between the input and output field devices and the PLC input and output
modules are the only signal wires required in the PLC system.
d) The cost and size of PLCs have increased significantly in the last 10 years.
Q17. Which of the following statements about a single pole double throw relay is NOT true?
a) It is called an SPDT type of relay.
b) It has one common contact.
c) It has two positions (NC and NO).
d) It has a center off position.
Q18. Which of the following statements about a single pole double throw relay is true?
a) Insulators are used in the armature to isolate the electrical switching contacts from the rest of the
relay components.
b) The NC contact and the pole are in contact when the relay is off.
c) It has just one coil.
d) All of the above.
Q19. Which of the following statements about RLL is NOT true?
a) NO contact symbol has two parallel lines to indicate an open contact.
b) RLL stands for Relay Ladder Logic.
c) NC contact symbol has the same two parallel lines with a line across them to indicate closed
contacts.
d) The right power rail is positive or the high side of the source, and the left power rail is the power
return or ground.
Q20. The _____ is moved toward the relay electromagnet when the relay is on.
a) Armature b) Coil c) NO contact d) NC contact
Q21. When a relay is NOT energized:
a) There is an electrical path through the NO contacts
b) There is an electrical path through the NC contacts
c) Neither the NO or the NC contacts have an electrical path
d) Both the NO and the NC contacts have an electrical path
Q22. Which of the following RLL applications is not normally performed in early automation systems?
a) On/off control of field devices
b) Logical control of discrete devices
c) On/off control of motor starters
d) Proportional control of field devices
Q23. Current flows into the _____
a) Input terminal of a sinking DC input module
b) Input terminal of a sinking output field device
c) Output terminal of a sinking input field device
d) All of the above
Q24. In a current sinking DC input module _____
a) The current flows out of the input field device
b) Requires that a AC sources be used with mechanical switches
c) The current flows out of the input module
d) Currents can flow in either direction at the input module
Q25. AC output field devices can interface to _____