TM 55-4920-401-13&P
Figure 2-2. Temperature System Accuracy Check Setup.
cables of unequal length will produce
erroneous readings. Never connect a
cold heater probe to the tester when it
is regulating other probes at an el-
evated temperature. To do so could
cause overheating of the hot probes.
(4) Place a heater probe over each engine
thermocouple. The heater probes must fit firmly
and be positioned properly on the thermocouples.
(5) Turn FUNCTION SELECT switch to
HEATER PROBE position, T/C INPUT switch to
HEATER CABLE position, TEMPERATURE
switch to HEATER PROBE TEMP SET position,
and MASTER POWER switch to ON position.
(6) Adjust PROBE CONTROL until TEMP in-
dicator reads approximately 600 ºC. Turn TEM-
PERATURE switch to OPERATE position to read
probe temperature.
NOTE
Check applicable technical manual
for exact test temperature and adjust
PROBE CONTROL accordingly. While
heater probes are heating, PROBE
P O W E R l a m p b u r n s c o n t i n u o u s l y.
Probe control will overshoot test tem-
perature and lamp will go out until
probe temperature falls below set tem-
perature. After test temperature has
been reached (PROBE POWER lamp
flashes), allow five minutes “soak”
time. The time necessary to heat and
stabilize probes depends upon line
voltage, ambient temperature, and air
currents. Some engines, after being
idle for some time, collect moisture on
the thermocouple terminals and extra
time must be allowed for this mois-
ture to evaporate. Normally a 10-
m i n u t e “ s o a k” time is sufficient.
However, if after 10 minutes, the sys-
tem is not within limits, an addi-
tional 20 minutes "soak" time should
be allowed. If the system is still not
within tolerance, out-of-tolerance dif-
ference is system error.
(7) If necessary, place cover over engine tail.
cone to obtain stabilized test temperature.
(8) The difference between the heater probe
temperature indicated on the tester and the aircraft
i n d i c a t o r r e a d i n g ( o r a i r c r a f t t h e r m o c o u p le
temperature as read on the tester when engine is
not installed in aircraft) is the error in the aircraft
system and should not exceed allowable engine
2-3
