BRUEL & KJAER 4294, User Manual

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Calibration Exciter Types 4294 and 4294-002 – User Manual 6
2.5 Transducer Sensitivity Check
For determination of the actual sensitivity of transducers, calibrated preamplifier and
indicating instrumentation are required. Although not intended for absolute sensitivity
measurement, the following procedure provides an approximate sensitivity check, sufficient
for determining whether a transducer functions correctly and has not been damaged during
previous use.
1) Attach the system transducer to the vibration table (finger-tight is sufficient) of the
calibrator using either a 10–32 UNF Stud YQ-2962 of Mounting Disc DB-2996. See
section 2.3.
2) Connect the transducer to the vibration measurement system using a suitable low-noise
cable, for example, that supplied with the transducer. If a voltage preamplifier is
employed, it is important that the particular cable supplied with the transducer is used,
otherwise the voltage sensitivity of the transducer will be affected.
3) In the case of a vibration meter, RMS indication of acceleration and an appropriate
measurement range should be selected. If a conditioning preamplifier featuring direct dial-
in of charge or voltage sensitivity is employed, the relevant sensitivity specified on the
transducer’s calibration chart should be entered before setting the range of the calibrated
indicating instrumentation.
4) Switch on the preamplifier, indicating instrument and calibrator in that order. The
transducer is now subjected to a sinusoidal acceleration of 10 ms
–2
RMS ±3% using
Type 4294 or 3.16 ms
–2
RMS ±3% using Type 4294-002.
5) A calibrated vibration meter will display the transducer output directly in terms of
acceleration, enabling the transducer sensitivity to be determined using:
where:
S
c
is the calculated transducer sensitivity in pC/ms
–2
or mV/ms
–2
, depending on whether the
vibration meter has a voltage or charge preamplifier
S
0
is the nominal transducer sensitivity for which the vibration meter is calibrated
A
i
is the meter acceleration indication in ms
–2
A
0
is the reference acceleration level: 10 ms
–2
for Type 4294 or 3.16 ms
–2
for
Type 4294-002
6) If a calibrated voltmeter together with a fixed sensitivity preamplifier is employed for
transducer calibration, the transducer sensitivity may be calculated using:
where:
S
c
is the calculated transducer sensitivity in pC/ms
–2
or mV/ms
–2
S
c
A
i
S
0
⋅
A
0
---------------
=
S
c
V
0
A
0
P
s
⋅
----------------
=