TM 55-4920-401-13&P
( a ) A i r c r a f t I n d i c a t o r C h e c k C i r -
D’Arsonval type indicator, the appropriate re-
cuits. The aircraft indicator check circuits (figs. 1-
sistance (R21-R25, fig. 1-18) is selected with the
18 and 1-19), located in the probe control section of
RESISTANCE & A/C INDICATOR CHECK switch.
the analyzer/trimmer, supply calibration check sig-
Since null-balance indicators do not draw current
nals to the TEMP indicator and to the aircraft indi-
when they are balanced, R19 in figure 1-19 assures
cater simultaneously. Switch poles are identified in
that the A/C IND ADJ has approximately the same
these figures and poles of the same switch are
range as it does in the circuit of fig. 1-18.
joined with broken lines. When checking a
Figure 1-18. Aircraft Indicator Check Circuit for D’Arsonval Indicators.
(b) Spread Circuit. Spread signals (fig. 1-
tion of S4, except ALL, one of the chromel leads is
16) are applied through the spread cable to the
connected to the SPREAD position of deck 7 of the
SPREAD CABLE receptacle on the probe control.
FUNCTION SELECT switch. In the ALL position,
Eight chromel signals are applied to eight poles of
all chromel leads are connected to the SPREAD pos-
the SPREAD switch on the probe control and func-
ition of deck 7. The alumel lead is common to all the
tion switch board. Each pole supplies its signal
alumel leads and is connected to the SPREAD posi-
through a different contact position corresponding
tion of deck 8 of the FUNCTION SELECT switch.
to one of eight engine thermocouples. In any posi-
1-17
