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In this case, the sound pressure produced by the Sound Level Calibrator is 94 dB SPL =
1 Pa.
Note:
When step 5 is carried out, the change in voltage indicated on the meter will be
very small (within 0,2 dB). This is because of the very low attenuation due to the pream-
plifier.
Using BFO section of 2010 or an external generator
1.
Connect the generator output to the EXT. INSERT VOLTAGE socket on the rear
panel of the 201 0.
2.
Fit the microphone to the 2627 preamplifier and connect the 2627 to the PREAMP.
input of the 201 0.
3.
Apply the sound source to the microphone: If the Pistonphone Type 4220 is used,
this involves fitting the Pistonphone onto the microphone and moving the switch to
the
"Measure"
position. Note the voltage V indicated on the meter of the 2010.
4.
Switch the sound source off, but leave the sound source mounted on the micro-
phone to ensure that the microphone is terminated in the same acoustical imped-
ance.
Adjust the frequency of the generator to be the same as that of the sound source.
Depress the push button INSERT VOLT. CAL. "Ext." and adjust the output of the
generator until the voltage V indicated is the same as before.
5.
Then the calibration voltage from the generator is equivalent to the open circuit vol-
tage Eo of the microphone. This calibration voltage, Ec, can be measured by taking a
lead from the output of th.e generator to the DIRECT input of the 2010. The calibra-
tion voltage then can be read directly on the meter scale by depressing the "Direct"
INPUT and CAL. OFF push buttons.
The output from the generator should be terminated in the EXT. INSERT VOLTAGE
socket on the rear panel of the instrument while the calibrating voltage is being read
from the meter.
Again:
Open Circuit Voltage Sensitivity= Ec
I
Sound Pressure
Note:
a)
If the Type 4220 Pistonphone is used, it produces a sound pressure level of approx.
1 24 dB = 31,6 Pa. The generator frequency should be adjusted to 250Hz.
b)
If the Sound Level Calibrator is used, it produces a sound pressure level of approx.
94 dB = 1 Pa. The generator frequency should be adjusted to 1 kHz.
3.3. VOLTAGE MEASUREMENTS
3.3.1. Input Voltages up to 300 V RMS
1
.
Calibrate the 2010 as described in section 3.2.1.
31
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