Rohde & Schwarz UPD, Примечание к применению

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1GA16_1L.DOC ROHDE & SCHWARZ 31
5.4.2 Polarity Check by Comparison to Reference Phase Measurement
This procedure is based on the fact that incorrect polarity of a system causes a phase shift of 180°. For
the check a correctly poled reference system is set up at an exactly defined distance from the standard
microphone and the phase between generator signal and output of the standard microphone (or
microphone amplifier) is measured. This measured phase is stored as a reference value and an upper
and lower limit value of
±
45
∆
° is defined.
With a reference value below 45°, phase measurement mode -180 to +180° is selected, in all other cases
mode 0 to 360°. The DUT is then set up at the same distance and the phase is measured (at the same
frequency). If the measured value is outside the selected tolerance, the loudspeaker is incorrectly poled.
The inaccuracy of the distance between loudspeaker and standard microphone must not exceed 1/8 of a
wavelength (45/360). For this reason this method cannot be used at high frequencies. For the upper limit
frequency flim the following equation applies:
f
v
l
m
s l
m s
l
lim
. . /
= ⋅ = ⋅ =
45
360
300
0125 4125
•
v being the sound velocity in m/s, and
•
l the maximum deviation of loudspeaker - microphone distance in m.
FIG 15 Polarity check by phase comparison with a reference loudspeaker of correct polarity
(a phase difference of approx. 0
°
means that the polarity is correct, the absolute phase has no
significance)
This measurement can be selected under PHASE (F8, level 1) as SINGLE mode (F6, level 2).