BRUEL & KJAER 2203 - Vibration Amplitude Calculation

4. DESCRIPTION
In the technical description that follows reference is made to the block
diagram in Fig.4.1 .
Co
Mi
ndenser
crop hone
,.......
K:
~
Input
Stage
I
I
~ Attenuator
~ Amplifier
I
t
I
Reference
Oscillator
External
Filters
y y
~ Weighting
Networks
I
Amplifier
~-------------4
~ Attenuator
~ Amplifier
~ Attenuator 1-
I
I
I
R~~~er ~
Meter
Output
172206
Fig.4.1 . Block diagram of 2203
4.1. CONDENSER MICROPHONE
A condenser microphone is essentially a variable air dielectric capaci-
tor with a constant charge (0) impressed upon it by its polarization volt-
age. The total voltage (V) on the capacitor then is inversely proportional
to the capacitance (C).
V=
0
c
and a change in capacitance will result in a change in voltage since 0 is
constant.
In practice the capacitor is a thin metallic diaphragm mounted in close
proximity to but electrically insulated from a fixed back plate (Fig.4.2).
Sound pressure waves will displace the diaphragm, thus changing the
capacitance and the output voltage. The constant charge is provided
from a stabilized DC polarization voltage fed through a high resistance
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