magnets are in the same relative positions.
Fuel pressure indicators may be located in the
However, if the transmitter magnet moves to a
cockpit by means of synchro systems. This type
new position, the voltages in the three sections of
of system is the same for both fuel and oil pressure
the transmitter are no longer the same. They now
indications. However, the oil system transmitter
is not interchangeable with the fuel system
differ from the voltages in the corresponding
transmitter.
sections of the indicator. Because of this
imbalance, current flows between the two units.
Look at figure 6-60. This synchro system
This circulating current sets up additional
is used to show fuel pressure. A change in
fuel pressure introduced into the synchro
magnetic lines of force in each stator, which
transmitter causes an electrical signal to go
establishes a magnetic force between the stator
and the magnet of each unit. Since the indicator
through the interconnecting wiring to the
magnet is free to turn, it moves to a position corre-
synchro receiver. This signal moves the receiver
rotor and the indicator pointer a distance
sponding to the position of the transmitter magnet.
The indicator magnet connects to the indicator
proportional to the amount of pressure exerted
by the fuel.
pointer by a shaft to provide a visual indication.
The electrical leads between the transmitter and
the indicator may be any reasonable length
NOTE: You can see in figure 6-60 that the
without noticeable effect on the indication.
transmitter has a vent to the atmosphere. This
allows the transmitter to accurately measure
FUEL PRESSURE SYSTEM
the differential between pump pressure and
atmospheric pressure.
The fuel pressure gauge provides a check
OIL TEMPERATURE SYSTEM
on the operation of the fuel pump and fuel
pressure relief valve. The pilot must check
the gauges often to ensure that the fuel pres-
Two types of oil temperature gauges are
sure is correct. With the fuel pressure correct,
available for use in the engine gauge unit. One
the engines have a full range of power at
unit consists of an electrical resistance type of oil
all altitudes. The fuel pressure gauge operates
thermometer, supplied with electrical current by
on the same principle as the oil pressure
the aircraft dc power system. The other unit, the
gauge.
capillary oil thermometer, is a vapor pressure
Figure 6-60.-Fuel pressure synchro system.
