CHAPTER 5
INDICATING INSTRUMENTS
Constantly used throughout this text is the
this chapter, you should be able to describe the
word monitor. As used in this text, monitor means
types of temperature and pressure measuring
to observe, record, or detect an operation or
instruments, liquid level indicators, electrical
condition using instruments. As a GSE3/GSM3,
indicating instruments, and miscellaneous sensors
your most important job aboard ship is to
used in the control and monitoring of GTEs and
monitor. As a watch stander, you observe and
auxiliary and support equipment.
detect malfunctions in the operating equipment
and take the necessary action to prevent damage
to the equipment. For accuracy, the best method
TEMPERATURE MEASURING
of observing and detecting a malfunction in equip-
INSTRUMENTS
ment is through use of indicating instruments,
such as temperature and pressure gauges. These
Temperature is the degree of hotness or
gauges range from direct acting, such as ordinary
coldness of a substance measured on a definite
thermometers, to electrically activated resistance
scale. Temperature is measured when a measuring
detectors. The main function of all indicating
system, such as a thermometer, is brought into
instruments is to give information on the
contact with the system to be measured. You often
operating condition of the equipment. When you
need to know the expansion of a liquid, the
are operating equipment, these instruments give
pressure of a gas, emf, electrical resistance, or
you the ability to compare normal operating
some other mechanical, electrical, or optical
conditions or preset limits to the actual operating
property that has a definite and known relation-
conditions. This comparison permits you to detect
ship to temperature. Thus we infer the tempera-
an abnormal condition before it causes major
ture of the measured system by the measurement
damage to the equipment. An example of this is
of some property of the system. The temperature
a main reduction gear (MRG) bearing failure. As
measuring instruments that we discuss are of three
a watch stander, by taking your hourly readings
types: mechanical, electrical, and mechanical-
from the bearing thermometer, you would notice
electrical. The mechanical-electrical temperature
a rise in temperature from hour to hour; you
instruments are switches.
would be able to inform your supervisor of a
suspected problem. If a sudden failure occurs,
MECHANICAL TEMPERATURE
such as loss of lube oil to the bearing, the sudden
MEASURING DEVICES
rise in temperature would activate a remote alarm
when it reached a preset point. The alarm would
Since temperature is one of the basic
alert personnel in the engine room and the EOOW
engineering variables, temperature measurement
station. This would allow the watch to institute
is essential to the proper operation of a shipboard
casualty control procedures to minimize the
engineering plant. You will frequently be called
damage. We used this example to emphasize to
upon to measure the temperature of steam, water,
you the importance of indicating instruments to
fuel, lubricating oil, and other vital fluids; in
shipboard operation.
many cases you will have to enter the results of
In this chapter we describe the various types
this measurement in engineering records and logs.
of indicating instruments that you, as a
Devices used for measuring temperature may
GSE3/GSM3, will come in contact with while
be classified in various ways. In this section we
operating and maintaining gas turbine propulsion
will discuss only the expansion thermometer types.
systems. These include temperature, pressure,
Expansion thermometers operate on the principle
level, and remote indicators. Upon completion of
that the expansion of solids, liquids, and gases
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