____ 30. In the hardwired relay control circuit shown, when the switch is closed, CR coil is:

a. / de-energized, the red light is off, and the green light is on.
b. / energized, and the red and green lights are both on.
c. / energized, the red light is off, and the green light is on.
d. / energized, the red light is on, and the green light is off.

____ 31. In the motor starter circuit shown, the main contacts M are:

a. / part of the power circuit.
b. / part of the control circuit.
c. / designed to handle the full load current of the motor.
d. / both a and c.

____ 32. The Boolean expression for the logic circuit drawn is:

a. / Y=A+B+C / c. / Y=AB+C
b. / Y = (A + B)C / d. / Y = ABC

____ 33. In conventional logic circuits, binary 1 represents:

a. / the presence of a signal. / c. / a high voltage level.
b. / the occurrence of some event. / d. / all of these.

____ 34. Which of the following number systems has a base of 16?

a. / Binary-coded decimal / c. / Gray code
b. / Octal / d. / Hexadecimal

____ 35. The central processing unit:

a. / serves only to supply power to the backplane.
b. / serves only to store the program in memory.
c. / looks at the outputs, makes the decisions based on the program, and sets the inputs.
d. / looks at the inputs, makes the decisions based on the program,
and sets the outputs.

____ 36. Which logic circuit represents the Boolean expression

a. / (d) / c. / (b)
b. / (a) / d. / (c)

____ 37. The scan time is the time required:

a. / to record the status of all output devices.
b. / to record the status of all input devices.
c. / for the information to pass from input to output.
d. / to execute one cycle of the total program.

____ 38. In order to energize the starter coil:

a. / the pressure switch, or the temperature switch, or the manual
pushbutton must be closed.
b. / the pressure switch, and the temperature switch, or the manual
pushbutton must be closed.
c. / the pressure switch, and the temperature switch, and the manual
pushbutton must be closed.
d. / all of the above.

____ 39. The symbol shown is that for a:

a. / light sensor. / c. / heat sensor.
b. / pressure sensor. / d. / proximity sensor.

____ 40. The decimal number 28 would be written in binary as:

a. / 01011. / c. / 10110.
b. / 00111. / d. / 11100.

____ 41. The main advantage of using the Gray code is:

a. / it can be easily converted to decimal numbers.
b. / large decimal numbers can be written using fewer digits.
c. / only one digit changes as the number increases.
d. / it uses the number 2 as its base.

____ 42. The Boolean equation for the logic symbol is:

a. / Y= A + B / c. / Y= A • B
b. / Y= AB / d. / either b or c.

____ 43. Block No. 4 of the PLC block diagram represents the:

a. / CPU. / c. / input module.
b. / programming device. / d. / memory.

____ 44. A(n) bit is used to detect errors that may occur while a word is moved.

a. / parity / c. / negative
b. / positive / d. / overflow

____ 45. If a PLC has a total scan time of 10 ms and has to monitor a signal that _____ then the controller may not detect this change.

a. / is constantly changing / c. / changes state twice in 5 ms
b. / is fast / d. / changes state once in 20 ms

____ 46. The basic rule for an OR gate is:

a. / if one or more inputs are 1, the output is 1.
b. / if one or more inputs are 1, output is 0.
c. / if one or more inputs are 0, the output is 1.
d. / both band c.

____ 47. 23.1. The diagram shown is a:

a. / input module wiring. / c. / output module wiring.
b. / ladder logic program. / d. / relay schematic.

____ 48. The Output Energize instruction:

a. / signals the PLC to energize or deenergize the output.
b. / is also known as the OTE instruction.
c. / looks and operates like a relay coil.
d. / all of these.

____ 49. The symbol in a ladder logic diagram

represents a:

a. / field input sensing device. / c. / v virtual relay coil.
b. / set of normally closed contacts. / d. / seal-in contact.

____ 50. Solenoid valves are available to control:

a. / oil flow. / c. / water flow.
b. / air flow. / d. / all of these