Measuring Ampifier Type 2525
User Manual Vol.1
Brüel & Kjær
5–4
Chapter 5 –The Measurement Set-up Menu
Gain
CHARGE FLOATING Charge input for use with “floating” configurations (see
section 3.1.5).
CHARGE SINGLE-ENDED* Charge input for “grounded” configurations (see section
3.1.5).
5.5 Gain
5.5.1 Introduction
Selecting any of the Gain menu options opens up gain sub-menus.
The input and output gain work together to adjust the sensitivity of the transducer
to the requirements of measurement equipment further along on the measurement
chain (tape recorders, analyzers and so forth). As a general rule of thumb, the input
gain should normally be set to the value required by the output instrumentation,
and output gain set to 0dB. If an overload occurs during measurement, the input
gain is reduced until the overload disappears, and the output gain adjusted until
the desired overall gain is achieved.
The fine gain is used in conjunction with the specified sensitivity of the transducer
to provide a value on output that is easy to work with.
Note: At 0dB, 1nC corresponds to 1V at the AC output.
5.5.2 Input Gain Select
The Input Gain Select menu allows you to select the amplification of the input
signal (transducer output) to the amplifier. The options are:
–20dB*
–10dB
0dB
10dB
20dB
30dB
40dB
50dB
60dB
5.5.3 Fine Gain Select
The fine gain select allows you to normalize “awkward” transducer sensitivities so
that the output sensitivity is a convenient “round” figure. For example an acceler-
ometer sensitivity of 1.7pC/ms
-2
can be normalized to a convenient output sensitivi-
ty (for example 1mV/ms
–2
). This greatly simplifies setting up, calibrating and
reading the measuring system.
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