Figure 11-22.Magnetic float switch.
of each of these sensors and their applications. Refer to
necessary. When multiple sections are used, they are
the manufacturers technical manuals for more
information on the procedures you should use to adjust
each type of device.
TANK LEVEL INDICATORS
Many tank levels are monitored to provide the exact
liquid level contained. For example, fuel tanks are
monitored to make sure they do not overflow. They are
also monitored to let the engineer officer know the
amount of fuel aboard ship. The sensors used to monitor
these levels are TLIs. Each of the level-monitored tanks
contains a level transmitter. A typical transmitter section
contains a voltage divider resistor network that extends
the length of the section. Magnetic reed switches are
tapped at 1-inch intervals along the resistor network.
The reed switches are sequentially connected through
series resistors to a common conductor. This network is
enclosed in a stem that is mounted vertically in the tank.
A float containing bar magnets rides up and down the
stem as the liquid level changes.
In many tanks, you may have to use more than one
transmitter section to measure the full range. The
physical arrangement of some tanks makes this
electrically connected as one continuous divider
Two types of floats are used. In noncompensated
tanks, the float is designed to float at the surface of the
fuel or JP-5. For seawater-compensated tanks, the float
is designed to stay at the seawater/fuel interface.
CONTACT LEVEL SENSORS
Many times, you do not have to know the exact level
of a tank until it reaches a preset level. When this type
of indication is needed, you can use a contact or float
switch. Two types of float level switches are used on gas
One type of float level switch is the lever-activated
switch, which is activated by a horizontal lever attached
to a float. The float on this switch is located inside the
tank. When the liquid level reaches a preset point, the
lever activates the switch.
The other type of level switch has a
mag-net-equipped float that slides on a vertical stem. The
stem contains a hermetically sealed, reed switch. The
float moves up and down the stem with the liquid level.