MIL-PRF-19004B
on the edge of each flange, and one vertical measurement on the top edge of
each flange. The maximum amplitude of vibration shall be the maximum single
reading and not an average. The operating frequency at which the maximum
amplitude occurs shall be measured. Exceeding vibration limits specified in
3.9.2 is cause for rejection.
4.7.4 Performance. Performance tests shall be conducted in accordance with
AMCA 210. Any of the alternate test stands and associated instrumentation may
be used. The total pressure or the volume or both not being within the
specified limits is cause for rejection.
4.7.4.1
Stall and recovery.
Tests shall be conducted in accordance with AMCA
210.
4.7.5 Airborne noise. Octave band sound power levels for a fan-motor unit
shall consist of the measurement of sound pressure levels and the computation
of sound power levels in accordance with procedures and instrumentation
requirements defined in AMCA 300-96, and amendments to those procedures as
identified herein. The fan-motor unit shall be operated at the design point
during airborne noise testing, see 3.17.1. Dual speed fans shall be operated
at high speed during noise tests. All sound measuring instrumentation shall
be laboratory calibrated within one year of the date of test, excluding the
reference sound source which shall comply with the laboratory calibration
requirements stated in AMCA 300-96. A random incidence response microphone
and a type I (precision) sound level meter conforming to the requirements of
AMCA 300-96 shall be used. The minimum distance between the extreme points of
the microphone swing as described in AMCA 300-96 shall be 27 ft., and the
speed of traverse of the microphone shall not exceed 2.4 ft./sec. Sound
pressure readings shall be a time-weighted average over an integral number
(one or more) of microphone swings. Sound pressure level readings shall be
averaged over a minimum period of observation of 30 sec. Resilient mounts
shall be loaded within the design load range for the type of mount selected.
The frequencies of the natural modes of vibration of the mounted fan in the
vertical direction shall not exceed 11 Hz or one-fourth of the lowest forcing
frequency of the fan, whichever is lower. When a duct section is attached to
a fan-motor unit to facilitate measurements, it shall have the same interior,
open cross sectional dimensions as that of the fan-motor unit to which it is
attached. There shall be no exposed sound absorbing material on the interior
or exterior surfaces of the attached ducts. No sound attenuating devices
shall be installed within attached ducts.
An orifice plate shall be
installed if necessary to obtain design pressure at a known operating point.
If an orifice plate is installed, it shall be a quiet type that does not
produce excessive flow-induced noise.
4.7.5.1 Total sound power. Test procedures and calculation procedures to
determine total sound power levels for a fan-motor unit shall be in accordance
with Appendix H of AMCA 300-96, installation type B: free inlet/ducted outlet,
and Figure 4 of AMCA 300-96. The fan-motor unit and attached discharge duct
with orifice plate shall be placed entirely within the reverberant test room.
4.7.5.2 Inlet sound power. Test procedures and calculation procedures to
determine inlet sound power levels for a fan-motor unit shall be in accordance
with Figure 2 of AMCA 300-96, installation type D: ducted inlet/ducted outlet.
No orifice plate shall be installed in the inlet duct. The fan-motor unit and
attached discharge duct with orifice plate shall be placed entirely within the
chamber, and sound pressure level measurements shall be made within the
reverberant test room. Acoustical treatments shall be placed within the
chamber to provide an acoustic seal at the penetration in the wall separating
the chamber from the reverberant room as necessary to ensure that no noise
contributions are transmitted from the chamber into the reverberant test room.
4.7.5.3 Outlet sound power. Test procedures and calculation procedures to
determine outlet sound power levels for a fan-motor unit shall be in
accordance with Figure 3 of AMCA 300-96, installation type B: free
inlet/ducted outlet. An orifice plate shall be installed within the discharge
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