Rohde & Schwarz UPD, Примечание к применению

Страница: 24 / 41

1GA16_1L.DOC ROHDE & SCHWARZ 23
5.2.4 Selecting the Sound Pressure Unit
With the aid of the UNITS softkey (F9, level 3) the unit of the sound pressure displayed as a measured
value or curve can be selected. This selection also determines the reference value and the reference
mode (lin. in V/Vr or log. in dBr). The following units may be selected:
linear reference:
•
µBar (F6): reference = sensgain-20dB;
•
Pascal (F7): reference = sensgain;
logarithmic reference:
•
dBspl (F8): reference = sensgain-94dB;
0 dBspl (sound pressure level) is defined as 0.0002 µBar (= 20 µPascal);
20
*
lg (0.00002) dB = -93.98 dB
•
SENSITIV (F9) reference = stored loudspeaker sensitivity
(see 5.2.5, Sensitivity Measurement and Radiation Angle)
•
dBr (F10) reference in dBV (may be entered);
•
REF SPK (F11) reference is the frequency response of a "golden unit".
Thus the GO/NOGO mode is implicitly switched on and the file name and tolerance values are
entered.
The sensitivity is that of the standard microphone in dBV/Pa and gain that of the measuring amplifier (see
section 5.2.3, Entry of Microphone Parameters).
Entry in dBr (F10) is useful, for instance, when the sensitivity of the sound pressure meter is specified as
⇒
1 V
^
0 dBV at 94 dBspl ==> reference = -94 dBV
or if a specific voltage generated by the microphone should be stored as a 0-dB line.
Note : In the case of sensitivity measurements the units
µ
Bar and Pascal cannot be entered. If they are
already set (via a response measurement), they are automatically changed to dBspl.
5.2.5 Sensitivity Measurement and Radiation Angle
The sensitivity measurement is a sound pressure measurement at a fixed frequency (measurement mode
SNS SNGL) or in a defined frequency band (measurement mode SNS RAND).
After selecting the measurement mode, the measurement frequency or the frequency band can be
entered in addition to the entries mentioned above (see sections 5.2.2 to 5.2.4) and to the selection of the
generator voltage. (SNS FREQ or SNS RNG). The entered frequency also serves a reference frequency
for the 0-dB line in the measurement of the transfer function. If no entries are made at all, the entries of
the last sound pressure measurement will be used.
Normally, sensitivity is specified in dBspl at 1 W and 1 m. For this reason the power amplifier should first
be set to 1 W (see section 5.2.2, Setting the Output Power) and the unit dBspl be selected (see section
5.2.4, Selecting the Sound Pressure Unit).
Pressing the START softkeys triggers a continuous level measurement (without graphics display of
measured values). Results are displayed in V/Vr or dBr and should be interpreted with the unit selected
under section 5.2.4 (Selection of Sound Pressure Unit).