TM 55-4920-221-14
46. OVERHEAT INDICATOR.
38. THREE-PHASE AMMETER AND WATTMETER
When the overheat indicator (41, figure 6)
RANGE SELECTOR.
lights, it indicates overheating of the load resisters.
The three-phase ammeter and wattmeter range
47. DC AMMETER.
selector (57, figure 6) is used to increase the sensitivity
The dc ammeter (11, figure 6), used in
and range of the three-phase ammeter (5) and the
conjunction with the dc ammeter terminal selector (43),
three-phase wattmeter (39) in ranges of 1, 2, 5, 10, and
measures load currents for dc inputs, and field currents
20 kw. The selector must be placed on the 20 kw scale
for external exciters.
to energize meter circuit.
48. DC AMMETER.
39. HIGH-LOW FREQUENCY METER.
The dc ammeter (12, figure 6) is permanently
connected to the field circuit, and measures field current
measures frequency of both single- and three-phase
of ac generators.
inputs, ranging from 30 to 300, and 300 to 1000 Hz.
Select either 60 or 400 Hz by using the HIGH-LOW
49. DC VOLTMETER.
switch (7).
The dc voltmeter (13, figure 6) is used in
40. WATTMETER FUSE.
conjunction with dc voltmeter circuit selector (16) to
measure voltages as determined by the unit under test.
The wattmeter fuse (58, figure 6) protects the
voltage circuit of the three-phase wattmeter (39) on T1
50. VOLTMETER FUSE.
and T3 lines.
The voltmeter fuse (14, figure 6) is a short
41. HIGH-LOW SWITCH.
circuit protection for the dc voltmeter (13), when used on
the 3.5-volt scale.
The HIGH-LOW switch (7, figure 6) is used to
select the low (30 to 300 Hz) or high (300 to 1000 Hz)
51. PRESSURE GAGE.
range of the high-low frequency meter (6). With switch
The pressure gage (42, figure 6) measures
in LOW position, the frequency meter is removed from
pressures up to 20 inches of water. Units under test are
the circuit.
externally connected to the pressure gage tube (1).
42. AC VOLTMETER.
52. DC AMMETER TERMINAL SELECTOR.
The ac voltmeter (40, figure 6) measures
voltages for both single- and three-phase inputs, which
is used to phase either 50A -28V, 250A -28V or 500A -
are selected by the voltmeter phase selector (59).
28V terminals (35) or A+ terminal (54). Capacity of unit
43. FREQUENCY METER.
under test determines corresponding range scale (0-5 or
0-50) used by the dc ammeter (11).
frequency of single- and three-phase 400 Hz inputs with
53. VOLTAGE REGULATOR MOUNTING PAD.
the HIGH-LOW switch (7) in the position.
The voltage regulator pad (15, figure 6) is used
44. COOLING FAN INDICATOR.
for testing voltage regulators or, to control test generator
output during reverse-current cut-out test. Terminals
When the cooling fan indicator (9, figure 6)
are provided for voltage reading of carbon pile, main
lights, it indicates cooling fans in the load bank are
coil, and equalizer coil using external voltmeter
operating.
terminals (19).
45. FAN OFF-ON SWITCH.
The fan OFF-ON switch (10, figure 6) controls
power to the fan motors and to the meter-protecting
relay circuits.
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