When troubleshooting a pressure switch that cannot
monitor alarms. A typical pressure transducer is shown
in figure 6-3.
be adjusted, you will normally find that it needs to be
replaced. In most cases, the switching mechanism
Like the pressure switch, the operation of the
m a l f u n c t i o n s and the switch cannot be repaired.
pressure transducer is also simple. Pressure transducers
Sometimes the bellows or diaphragm malfunctions. In
sense absolute, gauge, or differential pressure. The
this case, also, you will have to replace the switch. When
transducer receives pressure through pressure ports. It
y o u must replace a pressure switch, refer to the
sends an electrical signal, proportional to the pressure
manufacturer's technical manual to make sure you have
i n p u t , through the electrical connector. Pressure
the proper replacement.
transducers are available in pressure ranges from 0 to 6
inches water differential to 0 to 10,000 pounds per
W h e n replacing a pressure switch, you must
remember that the switch is constantly energized even
square inch gauge (psig). Regardless of the pressure
if the equipment is not actually running. It is the closing
range of a specific transducer, the electrical output is
always the same. The electrical signal is conditioned by
and opening of the contacts that energizes the entire
signal conditioners before being displayed on an analog
electrical circuit. You must make sure that electrical
meter or digital display readout. The sensitive parts of
power to the pressure switch is secured before you begin
to replace the switch. Follow the basic troubleshooting
the transducer are enclosed in a metal box with a
t e c h n i q u e s and all applicable electrical safety
removable cover. The metal box provides pressure ports
precautions whenever you repair or replace pressure
and an electrical connection point. The range of the
switches.
transducer used depends upon its application.
Construction
PRESSURE TRANSDUCERS
Pressure transducers are square metal boxes that
A transducer is a device that receives energy from
c o n t a i n one or two pressure ports, an electrical
one system and retransmits it to another system. This
connector, and a circuit card. (See fig. 6-4.) A test jack
retransmitted energy is often in a different form than it
and two variable resistors are located on the circuit card.
was received. A pressure transducer receives energy in
One resistor is the span adjustment resistor and the other
the form of pressure and retransmits energy in the form
is the zero adjustment resistor. The transducer contains
of electrical current. A pressure transducer allows
no moving parts; therefore, it is very reliable. The
p r e s s u r e monitoring at remote locations on gas
turbine-powered ships. Pressure transducers provide the
pressure applied to the transducer is converted to an
electrical signal by the components on the circuit card
capability of sensing variable pressures and transmitting
t h e m in proportional electrical signals. Pressure
Maintenance
transducers are widely used in ship propulsion and
auxiliary machinery spaces. They are often used to
Maintenance performed on pressure transducers is
accomplished also by PMS. This maintenance includes
inspecting the transducer for damage, corrosion, and
proper operation.
Figure 6-3.--Pressure transducer assembly.
Figure 6-4.--Transducer construction.
6-3
