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S4-Q80.) What is a PLC?

a.) An inexpensive controller that can replace many other expensive controllers.
PLCs usually are not inexpensive and when they are, they are very limited in functionality. They
would not be suitable to replace expensive controllers in most cases.
b.) *A controller used exclusively for I/O functions and is completely programmable.
Correct. The only function of a PLC is to perform I/O. It is completely programmable by the
end user.
c.) A preprogrammed device whose configuration can never be changed once shipped.
This would not be very useful. A PLCs usefulness is its ability to change I/O configurations and
programming.
d.) A device that has only very limited fixed I/O. PLCs can never have adaptive I/O.
Most PLCs are designed to have adaptive I/O to let the end user configure it for whatever application
is required.

S4-Q81.) Engine sending units are often Analog (varying voltage level) devices. How can they interface
with Digital (on/off) controllers?

a.) *Analog to Digital (A/D) internal conversion logic
Correct. High speed A/D conversion is possible with a host of converters to choose from.
Ladder, Flash, Successive Approximation, etc.
b.) That is determined by the engine manufacturer
It is determined by the controller selected, sometimes by the end user.
c.) Inductive to switched reluctance conversion
This has nothing to do with A/D conversion or controllers.
d.) By increasing the number of digital switches
This is an ambiguous response. Increasing the number of digital switches to the analog device or the
controller would have no effect.

S4-Q82.) How does an RTD measure temperature?

a.) By changing its semiconductor properties with heat
RTDs are not semiconductors.
b.) *By changing resistance with heat
Correct. Resistive Temperature Devices change their resistance with temperature. They are
usually used in conjunction with a Wheatstone Bridge.
c.) By changing its internal pressure with heat
RTDs do not use pressure.
d.) An RTD is a radio telemetry device and sends data to the controller
RTD is resistive and has nothing to do with telemetry.

S4-Q83.) What are the most common parameters monitored on the control panels of generators?

a.) PF, Watts, Amps
While important Power Factor is usually not monitored at the generator, but at the load such as a
factory load center. Watts can be calculated.
b.) PF, Watts, VAC
While important Power Factor is usually not monitored at the generator, but at the load such as a
factory load center. Watts can be calculated.
c.) *VAC, Amps, Hz
Correct. Volts, Amps, and Frequency are the primary concern.
d.) Watts, Amps, VAC
Watts can be calculated.

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