TM 55-4920-244-14
OPERATING INSTRUCTIONS
Section I. CONTROLS AND INSTRUMENTS
nometer (12) and in RANGE position when tak-
2-1. General.
ing temperature readings.
This section describes, locates, and fur-
f. Switch SW-2. Switch SW-2 (16) con-
nishes the operator sufficient information per-
nects either the heater cable (heater probe ther-
taining to the various controls and instruments
mocouples) or the check cable (engine thermo-
provided for the proper operation of the tester.
couples) into the potentiometer circuit.
WARNING
g. Switch SW-3. Switch SW-3 (19) is
used to place the proper aircraft circuit resistance
Careless operation or im-
in the bridge circuit when performing the resist-
proper setting of the con-
ance test or adjusting the resistance of the
trols will cause damage to
engine thermocouple harness.
the tester. For this reason,
h. Switch SW-4. Switch SW-4 (21) is
it is important that the
used to place the resistance matching the air-
operator know the function
craft egt indicator into the test circuit.
of every control and instru-
i. Potentiometer R-1. Potentiometer R-1
ment.
(22) is a variable resistor used to zero the gal-
Controls and instruments necessary for op-
vanometers (12) during the egt indicator check.
eration of the tester are located in the instru-
j. Switch SW-7. Switch SW-7 (23) is a
ment compartment (fig. 1-1) beneath the probe
three-position switch, marked OFF, MECH.
storage compartment.
ZERO, and RANGE. The OFF position shuts off
the power to the R.P.M. CHECK circuit, the
2-2. Operator's Controls (Figure 2-1).
MECH. ZERO position is used when mechanical-
a. Temperature Regulator Knob. The tem-
ly zeroing the galvanometers (25), and the
perature regulator knob (4) is used to adjust a
RANGE position is used when taking an RPM
reading.
brush-type variable voltage regulator. The volt
age regulator has a 20-ampere capacity and a
k. Mechanical Zero Knob. The mechani-
maximum voltage output of approximately 130
cal zero knob (24) is used to mechanically zero
percent of the input voltage.
the galvanometer (25) when switch SW-7 is in
b. Switch SW-8. Switch SW-8 (9) is a
MECH. ZERO position.
ratio selector switch used when making an insu-
l. RPM KNOB. The RPM knob (2) is
lation check.
used to adjust the percent scale of the R.P.M.
c. Temperature Selector Knob. The tem-
CHECK circuit to the percent RPM signal out-
perature selector knob (10) is used to zero the
put of the engine tachometer generator.
galvanometer (12) when heating heater probes.
m. Switch SW-1. Switch SW-1 (3) is a
d. Mechanical Zero Knob. The mechanical
five-pcsition switch used to select the proper cir-
zero knob (13) is used to mechanically zero the
cuit of the tester to make the T/C (thermo-
galvonometer (12), when switch SW-6 is in
couple), E.G.T. (egt indicator, INSUL. (insula-
MECH. ZERO position.
tion), or RES. (Resistance) checks, and OFF
(power still applied to heater probe circuit).
e. Switch SW-6. Switch SW-6 (14) is a
two position switch. It is placed in MECH.
n. Switch SW-5. Switch SW-5 is located
ZERO position when mechanically zeroing galva-
on the switch box (fig. 2-8). Switch SW-5 is a
