3. Description
The calibrator
is
based
on a 1000
Hz
stabilized oscillator
which
drives a
piezoelectric bender. This bender
is
coupled
to
a membrane which produces
a sound pressure in
the
coupler volume. As the system
is
adjusted
to
reso-
Fig.
3.
1.
Operation
of
4230.
nate
at
1000
Hz and
is
driven at this frequency, the equivalent volume
is
very high.
In
order
to
avoid influence on the stiffness
of
the volume behind
the diaphragm
caused
by
change in static pressure, a Helmholz-resonator
construction
is
made. (Fig.3.2)
A
built-in
temperature compensation ensures accurate calibration over the
whole temperature range
of
the calibrator.(Fig.3.3)
A hold
circuit
is
included
to
facilitate operation. This
circuit
holds the signal
8
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