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Additionally, an hour meter must be provided to continuously register the
hours of engine operation.  The information is used for performing prescribed
maintenance and inspections.
Alarm and Shutdown Systems.  Audible and visual alarms are required in
the operator's cab to signal when the engine speed, coolant temperature, or
lubricant pressure enter the final 10 percent of their safe operating range, as
specified by the diesel engine manufacturer.  If the limit of any of these safe
operating ranges is violated, then the engine's controls must automatically shut
it down.
Auxiliary Diesel Engine-Generator Sets.  The auxiliary diesel engine-
generator sets are independent of the main sets.  Their function is to provide
limited power on the crane when the main set is not running.  Depending on the
crane electrical system design, they may be AC or DC units.  They are sized to
power the ancillary equipment and additional specific loads such as a hydraulic
power unit, an air compressor of main diesel engine starting system, or the
charging circuit of its own batteries.
These sets are standard commercial products.  They are mounted in the
same manner, and fueled from the same source, as the main diesel
engine-generator sets.  The exhaust should be completely separated from that of
the main set.  On floating cranes, the auxiliary diesel engine-generator set is
installed in the barge.
Instrumentation.  Instrumentation is normally limited to the engine speed
(RPM) tachometer, coolant temperature gauge, lubricating oil pressure gauge, and
hour meter all mounted on the diesel engine-generator set.  Alarms and shutdown
systems are usually omitted.
Motor-Generator Sets.  Motor generator sets are used for drives with
electro-mechanical adjustable voltage control of shunt-wound DC motors. Motors.  Depending upon the source of power available, the motor of the
motor-generator set could be either an AC squirrel cage motor or a DC shunt-wound
motor.  Both types of motors have the constant speed characteristic needed for
this application. Generators.  The generators used are separately excited shunt-wound type.
The output voltage of the generator is varied by changing its field strength.
Field relays shunt out or add in various segments of resistance in series with the
generator field; the less resistance there is in the field circuit, the higher the
output voltage is.  Alternatively, a manually operated rheostat could be used to
vary the resistance in series with the generator field.  Loop voltage, and
therefore drive motor speed, is changed proportionally to generator field
strength.  The resistors in the field circuit are selected to provide evenly
spaced speed points; in the fifth speed point, all resistance is removed from the
field circuit.  For a hoist motor, the resistance in series with the field is
different in each speed point for hoisting and lowering directions.  Polarity of
the generator output voltage is reversed by reversing field polarity.


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