Figure 2-2. Temperature System Accuracy Check Setup.

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