TM
55-6680-234-40
nitude and frequency to the rotor speed. Each
2. Purpose of the Dual Tachometer Indicator
motor assembly includes a stator and housing
The purpose of the dual tachometer indica-
within which a starter and rotor are mounted
tor is to provide, on one dial, readings in
on the same shaft with a magnet assembly.
RPM of the rotational speed of the turbojet
The magnet assembly extends into and rotates
engine shaft and of the speed of the rotor.
within a drag cup. The drag cup is mounted
The indicator is used with two pole tach gen-
on the same shaft with its associated pointer;
erators conforming to Specification MS28054-
this shaft operates against a hairspring that is
1.
wound up when the shaft is rotated in the
direction of increasing dial indications. Signals
3. Equipment Records
in the stator cause the rotor assembly to rotate
at a speed proportional to their magnitude
The Army equipment record system and
and frequency. The magnet assembly then in-
procedures established in TM 38-750 apply to
duces torque in the drag cup assembly propoir-
this equipment. The applicable forms as re-
tional to the speed of rotation of the magnet as-
quired by TM 38750 shall be used.
sembly. Turning against the hairspring, the
drag cup positions the pointer to correctly in-
4. Description
dicate the rotor or engine speed.
The dial of the indicator is divided into two
concentric scales; an outer scale, calibrated
5. Leading Particulars
from 0 to 7200 RPM, provides readings of
Table 1. Leading Particulars
the engine sped while the inner scale, cali-
brated from 0 to 360 RPM, indicates rotor
Required Power - - - - - - - - as supplied by mating
speed. Speeds are indicated by two concen-
- - - - - - - - - - - - - - - - tachometer generators,
- - - - - - - - - - - - - - - - - - - MS28054-1
trically mounted pointers. Each pointer is
Range - - - - - - - - - - - - - - - - - - - - - - - --
driven by a separate and independent internal
Engine Scale - - - - - - - - - - - - 0-7200 RPM
motor assembly. The large rear pointer, in-
Rotor Scale - - - - - - - - - - - 0-360 RPM
dicating engine speed, is mounted directly on
Dial Spread - - - - -- - - - - - - - - - - - - -- -
the shaft of the forward motor assembly. This
Engine Scale - - - - - - - - - - - 288 degrees
Rotor Scale - - - - - - - - - - - 293.5 degrees
motor is connected to and actuated by a ta-
Temperature Range - - - - - - -54 to +71 C
chometer generator that provides a signal pro-
- - - - - - - - - - - - - - (-64 to +159.8F)
portional in magnitude and frequency to the
Case Size - - - - - - - - - - - .3-inch dia.
engine speed. The short front pointer is
Engine Tachometer
mounted on an extension shaft that passes
Generator RPM. - - - - - - - - (0.6386) (indicated engine
through the hub of the rear pointer and ex-
RPM)
Rotor Tachometer
tends through the central shaft of the front
Generator RPM - - - - - - - - (0.65l6) (indicated engine
motor to be driven by the rear motor. The
RPM)
rear motor is actuated by a tachometer genera-
20.383 to 1.0
Engine to Rotor RPM
tor providing a signal proportional in mag-
Ratio.
3
