The FWD is a small aluminum box
sometimes called a decade box. Figure 3-34 shows
containing an UV lamp source for viewing
an example of this box. These boxes, generally
oblong in shape, contain variable resistors. On top
the fluorescence resulting from the reaction
of the boxes you will see either four, five,
of free water in the fuel with a chemical-
or six rotary switches, depending on the type of
impregnated test pad. Incorporated into the box
are the FWD components necessary for view-
box used. Each switch will have the numbers
ing the fluorescence, including the UV light
0 through 9 on it. Below each switch you will
see a number known as the multiplier. Three
momentary switch, transformer, and test pad
holder slider.
terminals are on the right-hand side of the box
to connect it with the circuit(s). Some of the boxes
CONTAMINATED FUEL
may also have a decimal point, such as between
DETECTOR
switches (3) and (4) in figure 3-34.
The resistance boxes have different ohmic
The Contaminated Fuel Detector (CFD) (fig. 3-33) is a portable
value designations. Printed on the top of the box
instrument that determines the quantity of solid
you will find the upper limit. For example, a
contamination present in naval distillate and JP-5.
1-kilohm (KΩ ) box will range from 0.01 to 999.99
You are required to have one CFD on
ohms, a 1-megohm (M Ω) box will range from
board for each type of fuel to maintain your
1 to 999,999 ohms, and so forth.
operation fuel quality assurance and aviation
Each rotary switch on the box controls its own
certification.
variable resistor. These resistors are arranged so
The CFD consists of a fuel sample
that each resistor's value can be collectively added
container, a fuel-millepore filtration system (with
to each other. Using the figure and reading the
the filter), and a light transmission system to
switches from left to right, (1) is in the hundreds
determine the quantity of solid contamination on
place, (2) is tens, (3) is ones, (4) is tenths, and (5)
a millepore filter. It is reliable, accurate, and
is hundredths. To determine the value of a
rugged. This fuel detector is capable of providing
resistor, such as (2) in the figure, read the dial
a quick determination of the quantity of solid
setting, which is 3, and its multiplier, which is
contaminates in fuels.
RX10. This becomes 3R x 10 or 3 ohms x 10.
The contaminated fuel dectector is a self-
Therefore, the value of resistor (2) is 30 ohms at
contained unit. All components necessary for
this setting. Calculate all of the other resistors in
filtration and measurement of transmitted light
the same manner. Then add the values of each
are in one serviceable package. A drawer,
resistor together to get the total resistance of the
compartments, and holders are available for
box. What is the total resistance of the box in
storage of filters, sampling bottles, filter holder,
figure 3-34? If you figured it out correctly, it
power cable, and vital spare parts.
would be 730.19 ohms.
You will use these resistance boxes when
RESISTANCE BOXES
checking the calibrations of equipment, such as
At one time or another while performing
power turbine total inlet pressure (Pt 5.4) sensors
maintenance actions, you will use a resistance box,
and various transducers.
Figure 3-34.--Decade resistance box.
3-25
