CHAPTER 2 OPERATING INSTRUCTIONS

TM 55-4920-401-13&P CHAPTER 2 OPERATING INSTRUCTIONS 2-1. Indicators, Controls, and Accessories. Tester indicators and controls are shown in figure 1- 40 and listed with their functions in table 1-12. Tester accessories are shown in figure 4-30 and listed with their functions in table 1-13. Table 1-14 lists those accessories common to most aircraft. 2-2. Instruction Plate. The lid of the instrument case contains an operating instruction plate that covers all tests performed with the tester. The fol- lowing paragraphs include all the tests as well as test setup diagrams. WARNING G r o u n d t h e t e s t e r w i t h t h e p i g t a il ground wire in the power inlet cable before using the tester. NOTE A flashing indicator indicated an out- of-range condition. Temperature indi- cator is designed to drift upscale to the out-of-range condition when input is open. CAUTION To prevent overheating of and possi- ble damage to the heater probes, de- termine that all probes being used will heat per paragraph 3-4b. 2-3. Aircraft Temperature System Check. Para- graphs a and b give procedures necessary to check the aircraft temperature system. Perform the pro- cedures in the order given. a. Thermocouple System Continuity (Heat Rise) Check. The continuity test checks continuity of aircraft thermocouple system by heating each en- gine thermocouple independently and checking for a temperature increase on aircraft temperature in- dicator. Refer to figure 2-1 and proceed as follows: (1) Turn FUNCTION SELECT, STD DAY, and MASTER POWER switches to OFF position. NOTE If continuity probe is not available perform continuity check with applicable heater probe. Junction box must be connected be- tween BH405 heater cable and heater probe, refer to Fig. 2-2. CAUTION To prevent overheating of and possible damage to heater probe if used in place of applicable continuity probe, insure probe has cooled to ambient temperature before performing temperature system accuracy check, para 2-3 b. (2) Connect BH405 heater cable between HEATER CABLE receptacle on tester and applicable continuity probe. (3) Place T/C INPUT switch in HEATER CABLE position and turn PROBE CONTROL potentiometer full counterclockwise. (4) Turn FUNCTION SELECT switch to HEATER PROBE, TEMPERATURE switch to HEATER PROBE TEMP SET, and MASTER POWER switch to ON position. Adjust PROBE CONTROL to test temperature (approximately 700° C). Place TEMPERATURE switch in OPERATE position. NOTE L o w e r t e s t t e m p e r a t u r e s r e q u i r e a l o n g e r s t a b i l i z a t i o n o f t i m e t h a n higher test temperatures. When probe c o n t r o l o v e r s h o o t s t h e t e s t t e m - p e r a t u r e , t h e P R O B E P O W E R l a mp t u r n s o f f t o i n d i c a t e t h a t p o w e r h as b e e n r e m o v e d f r o m t h e c o n t i n u i ty probe. Monitor the probe temperature b y t u r n i n g t h e T E M P E R A T U R E switch to OPERATE. (5) When temperature stabilizes at test tem- perature, PROBE POWER lamp flashes on and off rapidly. Apply continuity probe to each aircraft thermocouple junction. Aircraft indicator should indicate a temperature rise as each thermocouple is heated. A slight temperature rise on indicator is sufficient. The continuity check determines if all thermocouples are operating. All thermocouples must be operating before additional tests can be made. (6) In some instances, the aircraft indicator may not be sensitive enough to detect temperature rise. If this occurs, connect BH450 check cable to CHECK CABLE receptacle and to engine thermocouple harness. Use check cable adapter if required. Apply applicable con- tinuity probe or heater probe to each aircraft ther- mocouple junction. With T/C INPUT switch in CHECK Change 4 2-1