 |
|||
|
|
|||
| ||||||||||
|
|  MIL-I-24078 (SHIPS)
4.5 Rejection. - The results of each test shall be compared with specification requirements. Failure
to conform to this specification for any group A, B or C test shall be counted as a defect, and the equip-
ment shall not be offered for delivery.
4.6 Test procedures. -
4. 6.1 Operating test. - The operating test shall consist of a voice transmission test for each inter-
communication station with a complete operational test using a type LS-385/SIC or LS-386/SIC unit and
an LS-458/SIC unit.
4.6.2 Amplifier gain. - The sound source for the test shall be the test laboratory speech generator
(artificial voice) adjusted so as to deliver a sound pressure of 4 dynes per cm2 at a frequency of 1000 c. p.s.
under free field conditions at a point of axis and 18 inches in front of the ring on the speech generator. The
loudspeaker to be tested shall be mounted in its front panel and placed 18 inches in front of and on axis of,
and facing the ring on the speech generator. The loudspeaker shall be connected to a resistive load corre-
sponding in value to the normal amplifier input impedance. The voltage developed across the resistor shall
be measured to determine conformance with 3.26.9.
4.6.3 Sound output pressure test. - Three type LS-518/SIC or LS-519/SIC intercommunication stations
shall be connected together for normal operation. One of the stations shall be placed with its reproducer
at a point 18 inches in front of and on axis and facing the ring of the artificial voice. A 2sound source from
the artificial voice shall be adjusted so as to deliver a sound pressure of 4 dynes per cm at the warble
band frequencies specified in 3.26.14 under free field conditions at a point on axis and 18 inches in front
of the ring on the artificial voice. The station under test shall have the selector key for the two other sta-
tions depressed and the press-to-talk switch shall be operated. The sound output pressures at the two
other stations (with volume control in maximum position) shall be measured. Both stations being trans-
mitted to shall be acoustically insulated from each other.
4.6.4 Overall frequency response test using loudspeaker as a microphone. - Conditions of overall
frequency response test shall be as specified in 4.6.3 except that, in lieu of the warble frequencies specified
in 3.26.14, a constant sound pressure at a frequency which shall be varied continuously from 200 to 8000
c. p.s. shall be employed. The overall frequency response shall lie within the limits shown on figure 2.
4.6.5 Overall frequency response using a type IC/MPM-4 microphone. - Test conditions shall be as
specified in 4. 6.4 except that the sound source pressure shall be 100 dynes per cm2 and the distance from
the microphone to the artificial mouth shall be 1/4 inch.
4.6.6 Amplifier endurance test. - A resistive load of 1667 ohms shall be connected across the normal
output terminals of a station. A 1000-cycle sine wave signal of such value as to produce rated output at
rated output voltage shall be applied to the microphone input terminals. The station shall be energized and
the press-to-talk switch shall be depressed for a period of 7 seconds and then released for a period of 15
seconds. Immediately upon completion of 20,000 operations the station shall be connected for normal
operation. There shall be no noticeable change in the quality of speech transmitted, nor shall the output
decrease greater than -2 db from the output measured at the beginning of the test. Amplifier endurance
tests shall be conducted in the hands-free mode, at rated load, for a period of 24 hours.
4.6.7 Amplifier noise and microphonics. - With a 150-ohm resistor connected to the microphone
input terminals, and full power applied to the amplifier, the output voltage across a resistive load (of such
value as to draw rated output power at 70 volts) shall not exceed the following values when measured with
an unweighed full range voltmeter. The measurement shall be made under two conditions of test, once
while the component is held fixed and again while the component is under vibration in accordance with
3.26.12.
(a) Component stationary. - Maximum measured voltage shall be O. 22 volt r. m.s. (50 db below
rated output voltage of 70 volts).
(b) Component under vibration. - Maximum measured voltage shall be O. 31 volt r. m.s. (47 db
below rated output voltage of 70 volts).
13
|
|
Privacy Statement - Press Release - Copyright Information. - Contact Us |
Click
here for thousands of PDF manuals