TM 55-4920-401-13&P
position, and MASTER POWER switch to ON
position.
(2) observe reading on tester
TEMP indicator and adjust A/C IND ADJ control to
test temperature (usually 600 °C).
(3) The difference in the indication of the
tester TEMP indicator and the aircraft indicator is
the error of the aircraft indicator and should not
exceed allowable technical manual tolerance.
(4) If aircraft indicator exceeds technical
manual tolerance, repair or replace indicator.
(5) Turn FUNCTION SELECT and MASTER
POWER switches to OFF position before removing
cables from tester and aircraft.
d. Temperature Circuit Resistance Check
(D’Arsonval Indicator(s)). In the resistance
check, the resistance of the aircraft thermocouple
wire, thermocouples,
and resistance spool is
measured on the tester RESISTANCE CHECK
meter. Refer to figure 2-6 and proceed as follows:
C A U T I O N
A h i g h r e s i s t a n c e c o n d i t i o n is
d a n g e r o u s b e c a u s e t h e a i r c r a f t
temperature indicator will read low
and the engine will be o p e r a t i n g
above indicated temperature.
(1) Turn FUNCTION SELECT, STD DAY,
and MASTER POWER switches to OFF position.
(2) Connect BH485 instrument cable to
INSTRUMENT CABLE receptacle on tester and to
BH823 resistance check adapter.
(3) Disconnect aircraft thermocouple leads
from indicator(s).
(4) Connect one set of aircraft thermocouple
leads to resistance check adapter terminal block.
Make sure polarity is correct. If there are two
indicators, the other set of leads is left disconnected.
(5) Turn RESISTANCE & A/C INDICATOR
CHECK switch to proper resistance position. (See
proper aircraft maintenance manual for resistance
value).
(6) Turn
position and
position.
FUNCTION SELECT switch to RES
MASTER POWER switch to ON
(7) RESISTANCE CHECK meter on tester
should read within technical manual tolerance. If
not, adjust resistance spool in aircraft for proper
resistance. One increment on meter equals 0.05
ohm.
C A U T I O N
Check and clean all connections in the
t h e r m o c o u p l e s y s t e m b e f o r e
adjusting aircraft resistance spool.
D e f l e c t i o n o f m e t e r n e e d l e in
c l o c k w i s e d i r e c t i o n i n d i c a t e s
excessive resistance.
(8) If resistance is within tolerance, proceed
to check insulation resistance as described in
paragraph e.
(9) Turn FUNCTION SELECT and MASTER
POWER switches to OFF position before removing
cables from tester and aircraft.
e . I n s u l a t i o n R e s i s t a n c e C h e c k . I n t he
insulation resistance check, the resistance between
the thermocouple conductors and aircraft ground is
measured first, followed by a check of the resistance
between the conductors. Refer to figure 2-7 and
proceed as follows:
(1) Turn FUNCTION SELECT, STD DAY,
and MASTER POWER switches to OFF position.
(2) Connect BH485 instrument cable to
INSTRUMENT CABLE receptacle on tester and to
BH821 insulation check adapter, and disconnect
both leads at aircraft indicator.
(3) Turn FUNCTION SELECT switch to
INSUL position, INSULATION CHECK switch to
RX1000 position, an MASTER POWER switch to
ON position.
(4) Short alligator clips together. Meter
should read 0 ohms.
(5) Connect one lead of insulation check
adapter to a bare thermocouple lead in aircraft and
connect other lead to aircraft ground.
(6) INSULATION RESISTANCE meter should in-
dicate resistance specified for aircraft being checked.
(7) Disconnect engine thermocouple harness
from airframe thermocouple harness.
(8) Disconnect insulation check adapter from
aircraft ground and connect to other thermocouple
lead.
(9) I N S U L A T I O N R E S I S T A N C E m e t er
Change
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