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1. INTRODUCTION
The Accelerometer Calibrator and Preamplifier Type 4292 is designed as
a small compact unit for vibration measurements. It forms the link between
the accelerometer and the Measuring Amplifier or Analyzer.
The preamplifier has a field effect transistor input stage which gives it an
extremely high input impedance (up to 2 Gr2), whereby a low lower limit-
ing frequency can be obtained for the combination of accelerometer
capacitance and preamplifier input impedance. To permit easy reading of
vibration levels when accelerometers which do not have simple sensitivity
figures are employed for measurements, the gain of the preamplifier may be
adjusted from
0
to
20
dB. For measurements of vibration acceleration an
output can be taken directly from the preamplifier, whilst for measurements
of velocity and displacement the 4292 includes 3 single and 6 double inte-
gration networks. The networks have different low frequency cut off limits
and can be selected using the INTEG RATION SWITCH, so that the best
possible signal-to-noise ratio is obtained for the required measurement fre-
quency range.
The calibrator consists of a small built-in vibration table which is fitted
with a
10-
32 NF hole for· mounting accelerometers. The table vibrates at a
frequency of 79.6 Hz
(w
=
500
radian/sec as specified by the DIN Standard
45.666) and produces an acceleration level of 1 g peak which may be
adjusted using an AMPLITUDE control. To facilitate checks of accelerome-
ter sensitivities and calibration of complete vibration measurement systems
the table contains a hermetically sealed chamber in which a small bronze
ball rests. The ball wi II just commence to vibrate when the acceleration level
of the table reaches 1 g peak. This condition may be heard and at the same
time seen on an oscilloscope which may be connected to the output of the
indicating·
instrument used for measurements.
Power for the 4292 may be provided using the B & K Microphone Power
Supply Type
2801,
or by any of the Measuring Amplifiers or Analyzers in
the B & K range.
3
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