Page 88 - Apprentice Manual_Neat

S4-Q84.) Why must an ammeter selector switch be the “make-before break” type?

a.) To prevent voltage spikes and power surges
Neither type would create voltage spikes.
b.) *To prevent arcing and current flow interruption
Correct. Break-before-make would allow the current to stop flowing for the brief time
the switch is in transition. This is due to the fact that ammeters are always wired in series with
the circuit. Furthermore, with full current flowing through the switch, there would be an arc
drawn when the switch was opened. If the current has another path, then no arc would occur.
c.) To prevent over-current situations
Neither type would prevent this.
d.) Ammeter selector switches are “break-before-make”
Not true (see answer b).

S4-Q85.) Are DC gauges ever found on engine control panels?

a.) No, AC is what is being generated and what needs to be monitored
Most signals monitored on an engine are DC.
b.) Yes, the DC used to create the generator field only
Most signals monitored on an engine are DC also.
c.) *Yes, engine functions such as oil pressure, water temperature, and DC voltmeter and or
ammeter
Correct. Most signals monitored on an engine are DC.
d.) No, any DC signals are converted to AC so that only one type of gauge must be purchased and
stocked
It would not be cost effective to convert every signal to AC.

S4-Q86.) Mod Bus is:

a.) *A universal communications protocol and system
Correct. Mod Bus was developed by Modicon for PLC to PLC communication. It has been
adapted to other controllers, automotive and various other applications.
b.) A modular electrical bus system used to change amounts and direction of current
Incorrect. This may exist, but has not been named Mod Bus
c.) A modernized data bus carrying various manufacturers protocols
In order for one controller to communicate with another (even from different manufacturers), only
one protocol is allowed.
d.) A commuter bus with a generator to supply power to the modern commuter carrying laptop PCs,
Portable DVD players, etc.
While this sounds plausible, there are none on record at the time of publication.

S4-Q87.) Which symptom best describes the failure of an over-speed sensor?

a.) Engine starts, but then will not progress past idle
If the sensor fails the controller would not know what idle was.
b.) Engine will not start
Over-speed sensors only prevent the engine from going over speed, not from starting.
c.) Engine starts and oscillates between idle and full RPM repeatedly
The failed sensor would not detect for either of these parameters.
d.) *Engine starts, proceeds to full RPM, but then shuts down immediately
Correct. A failed over-speed sensor would allow the engine to continue to full speed until the
failsafe shut the engine down.

EGSA Apprentice Certification Program Study Guide - Page 80