Section V. MEASURING EXTERNAL RESISTANCE

TM 55-4920-325-14&P

(3) Subtract largest 200 pF multiple pos-

( 1 0 ) Set PROBE MMF range selector

switch (200 pF step) (28) to largest 200 pF multi-

sible from remainder calculated in step (2), above,

ple, as calculated in step (3).

without obtaining a value less than 25' pF.

(11) Observe that capacitance value dis-

For example:

played by CAPACITANCE INDICATOR (6) multi-

The remainder in step (2), above, is 955 pF,

plied by setting of Capacitance RANGE SE-

then

L E C T O R switch (7) is value calculated as

remainder in step (2).

955 pF=Remainder step (2), above

-800 pF=Largest 200 pF multiple

(12) Set Capacitance RANGE SELECTOR

155 pF=Remainder

switch (7) to lowest multiplier which will permit an

(4) Set both PROBE MMF range selector

accurate reading on CAPACITANCE INDICATOR

(6) of value determined in step f.

switches (28) and (29) to OFF.

(13) Set PROBE MMF range selector

(5) Set Capacitance RANGE SELECTOR

switch (1000 pF step) (29) to largest 1000 pF mul-

switch (7) to lowest multiplier which will permit an

tiple, as calculated in step (2).

accurate reading on CAPACITANCE INDICATOR

(6) of remainder calculated in step (3), above.

(14) Observe that capacitance value dis-

played by CAPACITANCE INDICATOR (6) multi-

(6) Loosen PROBE 25-250 MMF control

plied by setting of Capacitance RANGE SE-

lock (26).

LECTOR switch (7) is value determined in step f.

(7) Adjust PROBE 25-250 MMF control

i. Set FUNCTION SELECTOR switch (25) to

(27) and Capacitance RANGE SELECTOR switch

TEST IND-TEST. Setting FUNCTION SELECTOR

(7) until capacitance calculated in step (3), above,

switch (25) to IND-TEST automatically applies

is indicated by CAPACITANCE INDICATOR (6).

simulated probe and compensation capacitances

(8) Tighten PROBE 25-250 MMF control

to aircraft liquid fuel gage indicator under test.

lock (26).

WARNING

(9) Set Capacitance RANGE SELECTOR

Make certain that when second test set

switch (7) to lowest multiplier which will permit an

is connected, ground lead has been

accurate reading on CAPACITANCE INDICATOR

properly connected as required in 2-4b.

(6) of remainder calculated in step (2).

Section V. MEASURING EXTERNAL RESISTANCE

2-11. Scope.

Connect aircraft wiring to be measured

across EXT RES terminals (18, figure 2-1) of test

This section contains information and in-

set.

structions for measuring aircraft wiring leakage

resistance.

cf. Set Power ON/OFF switch (2) to ON and

allow test set to warm up for at least five minutes.

2-12, Operating Procedure.

e. Set CAP-RES CHECK switch (13) to EXT

WARNING

RES.

Do not operate ungrounded test set.

f. Check that MEGOHMMETER indicator

Proceed as follows to measure aircraft wiring leakage

(14) is properly calibrated at ZERO and MID-

resistance,

SCALE points of indicator (see paragraph 2-8 f).

a. Check that the grounding strap has been

g. Set Megohmmeter RANGE SELECTOR

properly connected (see 2-4 b).

switch (17) to multiplier setting so that ME-

b. Check that power cable is connected to

GOHMMETER indicator (14) displays a reading

115 volts, 400 Hz, single-phase power source (see

closest to midscale. For example, a 50 megohm

2-4c through e).

resistance can be measured when the Me-

2-14