BRUEL & KJAER 2663, Техническая документация инструкция

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Appendix A — Ground Loop Noise
Ground Loop Phenomena
Preamplifiers Types 2663 and 2663 B
User Manual
Brüel & Kjær
42
A.1 Ground Loop Phenomena
A problem often met in large vibration measurement installations is the formation of
ground loops which introduce an error voltage that is added to the signal. This is
illustrated in
Fig.a.1 .
Fig.a.1 Illustration of ground loop phenomena and the use of grounded/floating connection on a
preamplifier
As shown in Fig.a.1 , a ground potential difference
Vg
exists between the structure
ground and the output ground. If Switch
S
is closed and the transducer is grounded
to the structure, then
Vg
(perhaps a few volts) will cause a current to flow through
the accelerometer cable and through the amplifier circuits, introducing an error volt-
age that adds to the signal.
To avoid the formation of ground loops, it is essential that the signal ground line is
grounded at only one point in the measurement system – preferably at the readout
or at the supply instrumentation. Consequently, if the vibration test specimen is
grounded, then the transducer should be isolated from the specimen by using an
isolating stud and mica washer when mounting (see
Fig.2.3 in section 2.3.1 ); alterna-
tively Switch S should be opened.
Input Amp.
Output Amp.
Output
Output Ground Structure
Input Ground
Vg
S
Transducer
Input
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