(4)
Read ohmmeter. Resistance reading should not be less than 50,000 ohms. If value below limit is recorded, presence of carbon or excessive moisture may be indicated. Carbon yields fairly steady reading. Moisture tents to produce readings which waiver or drift after 5 to 30 seconds. Presence of moisture may be corrected by baking affected part of EGT system at 200° - 250°F (93° - 121°C) for 1 hour and checking again.
NOTE: False drift may be due to variations in applied voltage. To check for false drift, place prods in contact with each other for 10 seconds. Readings must not wander from full-scale deflection.
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77-21-01 Page 604 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. May 20/82
EXHAUST GAS TEMPERATURE THERMOCOUPLE BALANCING RESISTOR - ADJUSTMENT/TEST
1. Exhaust Gas Temperature Thermocouple Balancing Resistor - Adjustment
A. General
(1)
The exhaust gas temperature circuit resistance is adjusted by moving constantan lead terminals from post to post on the coarse and vernier adjustments. The resistance increment between two coarse adjustment terminals is 0.15 ohm and between two vernier adjustment terminals is 0.05 ohm. External circuit resistance, excluding the indicator, should be 15.00 ohms nominal (measured at 20士50C). Total circuit resistance, including the indicator should be 48 ohms (there is no resistance check of this).
(2)
To decrease the circuit resistance beyond coarse and vernier adjustment range, the resistor spool wire is shortened. To increase the circuit resistance beyond the coarse and vernier adjustment range, the spare, or a new, resistance spool is adjusted.
B. Equipment
(1) Wheatstone Bridge capable of measuring resistance to士 0.01 ohms at 15 ohms.
C. Prepare for Adjustment
(1)
Disconnect plug to exhaust gas temperature indicator on pilot's instrument panel for engine being tested. Connect Wheatstone Bridge between sockets 1 and 2 of indicator plug.
(2)
Remove side panel directly under right No. 3 window. Remove resistor cover from R202 (Eng 1) or R203 (Eng 2).
NOTE: If the resistance of the circuit can be adjusted to the values shown in Fig. 501 using the coarse (.15 ohms per post) and vernier (.05 ohms per post) adjustment perform step D.(l). If the circuit resistance can not be corrected by using the coarse and vernier adjustment, perform step D.(2) to increase or step D.(3) to decrease the resistance to the value shown in Fig. 501.
SYSTEMS RESISTANCE (OHMS) AMBIENT TEMPERATURE
15.00士0.05 20 士50C 68 士90F
14.97士0.05 10 士50C 50 士90F
14.94士0.05 0 士50C 32 士90F
500
Aug 15/77 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 77-21-11 Page 501
D. Adjust balance resistor.
(1)
Reposition airplane leads from one coarse and/or vernier adjustment terminal to another until circuit resistance in figure 501 is obtained.
(2)
Adjust resistor spool to increase circuit resistance.
(a)
Connect one airplane lead to coarse adjustment terminal A3 and other airplane lead to vernier adjustment terminal B2.
(b)
Disconnect resistance spool wire ends from terminals B3 and A5 with a soldering iron. (See figure 502.)
(c)
Replace used spool if replacement is available; if not, use spare spool for adjustment.
(d)
Carefully scrape insulation from end of resistance wire emerging from center of new or spare spool and solder wire to terminal A5.
(e)
Unwind several turns of resistance wire and clip end to terminal B3 with an alligator type clip.
(f)
Check circuit resistance with Wheatstone Bridge. Resistance should be greater than that shown in figure 501.
(g)
On the basis of approximately 0.7 ohms per foot (.058 ohms per inch) of wire, unclip wire from terminal B3 and unwind approximate amount needed to give correct resistance.
(h)
Clip wire to terminal B3 and check resistance.
(i)
Check resistance at points along wire until resistance value shown in figure 501 is obtained.
(j)
Cut wire at this point and carefully scrape insulation from end of wire.
(k)
Wind excess wire back on spool and once around center post, leaving sufficient length of wire to reach terminal B3 for soldering.
(l)
Solder end of wire to terminal B3.
(m)
Recheck circuit resistance. If slight adjustment is necessary, reposition lead terminals on coarse and fine terminal posts to obtain the proper resistance reading per figure 501.
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