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Page Title:
Section IV. SIMULATING TANK UNIT PROBE CAPACITANCE |
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 TM 55-4920-325-14&P
When all tank unit probe resistance mea-
For example:
surements have been made, set Power ON/OFF
switch (2) to OFF.
MEGOHMMETER display=
0.5
k. Disconnect test set from aircraft and re-
connect aircraft wiring.
M e g h o h m m e t e r RANGE
SELECTOR switch setting=
X100
Actual resistance=
50
megohms
S e c t i o n IV. SIMULATING TANK UNIT PROBE CAPACITANCE
2-9. Scope.
NOTE
This section contains information and in-
Tank unit compensation capacitance
structions for simulating the capacitance of tank
can be simulated from 25 to 250 pF.
unit probes used on aircraft using liquid fuel gag-
g. To simulate tank unit compensation ca-
ing systems.
pacitance, proceed as follows:
NOTE
(1) Set FUNCTION SELECTOR switch
In order to avoid erroneous indications
(25) to TEST IND COMP SET.
when testing aircraft liquid fuel gages
(2) Set Capacitance RANGE SELECTOR
without compensating capacitors, the
switch (7) to lowest multiplier which will permit an
p r o t e c t i v e cover on the TEST IND
accurate reading on CAPACITANCE INDICATOR
COMP connector (21, figure 2-1) must
(6).
be installed on the connector. This pro-
tective cover has a pin which grounds
(3) Loosen COMP 25-250 MMF control
the compensator capacitor terminal and
lock (23).
eliminates stray capacitance.
(4) Adjust COMP 25-250 MMF control
2-10. Operating Procedure.
(22) and Capacitance RANGE SELECTOR switch
(7) until compensation capacitance determined in
WARNING
step f above, is indicated by CAPACITANCE lN-
Do not operate ungrounded test set.
DICATOR (6).
Proceed as follows to simulate the capacitance of
(5) Tighten COMP 25-250 MMF control
a tank unit probe:
lock (23).
a. Check that the grounding lead has been
h. To simulate tank unit probe capacitance,
properly connected (see 2-4b).
proceed as follows;
b. Check that power cable has been con-
(1) Set FUNCTION SELECTOR switch
nected to 115 volts, 400 Hz, single phase power
(25) to TEST IND-PROBE.
source (see 2-4c through e).
(2) Subtract largest 1000 pF multiple
c. Connect test set to aircraft liquid quantity
possible from value of probe capacitance to be
fuel gage system as shown in figure 2-3.
simulated as determined in step f above, without
obtaining a negative value,
to ON and allow test set to warm up for at least
For example:
five minutes.
Should the simulated probe capacitance be
e. Set CAP-RES CHECK switch (13) to CAP.
3355 pF, then
f. Determine the value of probe and com-
3955 pF=Simulated probe capacitance
pensation capacitances to be simulated. Refer to
-3000 pF=Largest 1000 pF multiple
applicable aircraft technical manual
955 pF=Remainder
2-13
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