The sensor used for indicating a tank level is
Setting Pressure Switches
commonly called a tank level indicator (TLI). This
sensor will tell you the exact amount of liquid in
To set a pressure switch, you first have to set
a tank. In the following paragraphs we will
a known pressure in the operational range of the
describe the operation of each of these sensors and
switch. Normally, you do this by using a test setup
their applications. Refer to the manufacturers'
like that shown in figure 5-22. In an emergency,
technical manuals for more information on the
you can use the pressure of the system in which
procedures used to adjust each type of device.
the switch is installed. But you should reset the
switch as soon as possible using a calibrator.
Many types of pressure calibrators are used in the
TANK LEVEL INDICATORS
fleet. Refer to the manufacturer's technical
manual for the correct operating instructions for
Many tank levels on gas turbine ships are
your unit.
monitored to provide the exact liquid level in
them. Fuel tanks, for example, are monitored to
The adjustments on the pressure switches are
the same as the adjustments on the temperature
ensure they do not overflow. They are also
switches that we described earlier in this chapter.
monitored to let the engineer officer know the
amount of fuel aboard the ship. The sensors
used to monitor these levels are TLIs. Each of the
level-monitored tanks contains a level transmitter.
LIQUID LEVEL INDICATORS
A typical transmitter section contains a voltage
In a gas turbine propulsion plant, you will
divider resistor network extending the length of
have to monitor systems and tanks for liquid level.
the section. Magnetic reed switches are tapped at
l-inch intervals along the resistor network. The
Sometimes you are only required to know if a level
exceeds or goes below a certain preset parameter.
reed switches are sequentially connected through
Other circumstances require that you know the
series resistors to a common conductor. This net-
work is enclosed in a stem that is mounted ver-
exact level. If only a predetermined limit is
needed, you can use a float switch. This will make
tically in the tank. A float containing bar magnets
contact when the set point is reached and will
rides up and down the stem as the level changes.
sound an alarm. If you need to know a specific
In many tanks, you have to use more than one
level, then you must use a variable sensing device.
transmitter section to measure the full range. The
Figure 5-22.--Typical setup fur calibrating a pressure device.
5-17
