TB 11-6625-666-50
b. Visual and Mechanical Requirements.
position that the dial is vertical to the
(1) Windows.
The window should not be
ground plane, the meter should be rotated
loose, cracked, or scratched to the extent
360 by making 4 successive turns of 90
that visibility is impaired.
each. The pointer should not deflect more
(2) Zero corrector.
than 1 from zero for portable instruments,
(a) The action of the mechanical zero
2 for 4 1/2-inch and larger switchboard
corrector should provide a range of
instruments, nor more than 2 percent of he
adjustment above and below the zero
total scale length for 2 1/2- and 3 1/2-inch
point of not less than plus or minus 2
instruments.
percent of the total scale length.
(10) Friction. The zero corrector should be
(b) The zero corrector assembly should
turned until the pointer hits the stop below
have sufficient friction to prevent it
zero. The direction of turning should be
from shifting due to vibration or shock.
reversed until the pointer barely leaves the
(3) Cleaning.
stop. The pointer should not come to rest
(a) Parts of the assembled instrument
above zero with the zero corrector in this
should show no signs of rust,
position.
corrosion, or fungus growth.
(11) Sealed and ruggedized meters.
The
(b) The case should be removed and the
following
requirements
should
be
internal parts inspected for presence
applicable to repaired, sealed, ad
of lint, metallic particles, or other
ruggedized meters:
foreign matter which might impair
(a) After installing the movement in its
operation.
case, the unit should be thoroughly
(c) Meters having sealed cases should be
dehydrated at a temperature of
opened for inspection purposes only.
approximately 65 C. for not less than
(4) Terminals.
4 hours.
(a) The instrument should be complete
(b) The meters will be sealed after repair
with terminal nuts, lockwashers, and
at existing temperature and humidity
mounting hardware.
conditions immediately after the
(b) Terminal threads should not be
dehydrating cycle.
crossed, scarred, or damaged in any
c. Electrical Requirements.
way.
(1) Friction.
Following the calibration,
(c) Solder lug terminals should be
untapped readings should be taken on
cleaned of excess solder and eyes in
both ascending and descending scale to
terminals should be open,
observe and determine the change in
(5) Dials. The dial should not be discolored or
indication due to friction.
damaged to the extent readability is
(2) Position. Instruments should be tested in
impaired. All calibration markings should
the position in when they are normally
be legible.
used.
(6) Case and base.
The case and base
(3) Calibration points.
Instruments having
should not be bent, dented, or cracked.
either uniform or nonuniform scale
(7) Brush contact.
Instruments having a
calibration, except frequency meters and
brush contact bonding the metallic bezel
decibel meters, should be checked at
ring to other parts should be inspected to
three points; preferably, one point in the
insure proper contact of the brush with the
upper portion of the scale, one point in the
bezel ring.
center portion, and one point in the lower
(8) Appearance and finish.
The external
portion. Meters without an external zero
appearance of a repaired instrument
corrector should also be checked at zero.
should compare favorably with a new
(4) Accuracy. The calibrated accuracy should
instrument.
Touching up of finish is
be within the following percentage limits of
permitted.
the full-scale value:
(9) Balance. The pointer should be set to
(a) AC & DC switchboard instruments 4
zero. With the meter held in such a
1/2 inches and larger, 1 percent.
TAGO T41A
2
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