BRUEL & KJAER 2663, Technical Documentation Manual

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Chapter 2 — Operation
Accelerometer Input Connection
Preamplifiers Types 2663 and 2663 B
User Manual
BE 1068 – 12
9
2.3.2 Differential Connection
This section deals with the connection of Type 2663 or Type 2663 B to differential
types of accelerometer which have both poles of their piezoelectric element isolated
from their housing. The floating differential input of the preamplifier eliminates trans-
ducer ground loop problems. Also, noise pickup, common to both poles of the input,
cancels, giving a high degree of immunity from radiation pickup.
Plugs and Cables
Connections are made using a two-pole TNC plug, Type JP 0209, for 180
o
C (356
o
F)
operation. Both are available on separate order and can be fitted with the single- or
double- screened, two-core, low-noise cable specified in
section 4.1.2 . The inner con-
ductors of the cables have separate screens or are twisted wire-pairs so as to main-
tain the capacitive balance between both poles of the accelerometer output and
preamplifier input. Cable Type AO 0250, which has a connector fitted at both ends, is
also available.
Fig.2.4 Connection of differential accelerometer to Type 2663 (or Type 2663 B) using single-
screened, two-core, low-noise accelerometer cable
Single-screened Cable Connections
With single-screened cable, the two inner conductors are used to connect both poles
of the accelerometer output to the preamplifier input as shown in
Fig.2.4 . To prevent
the formation of a ground loop, the cable screen should be connected to the outer
shield of the accelerometer output only, or the preamplifier input only, but not both.
Similarly, if single-screened cable, having a separate screen for each inner conductor,
is used, then both screens should be connected to either one but not both shields.
Generally, connection of the cable screen to the shield of the accelerometer output is
preferred as this increases the mechanical strength of the accelerometer output
connection.
Double-screened Cable Connections
By using double-screened cable, much greater immunity from radiation pickup can
be obtained. This is especially important when working in industrial locations close
to heavy duty, electrical machines. A double-screened connection is shown in
Fig.2.5
and is similar to those used for single-screened cable, except that the outer screen is
connected to the shield of the accelerometer output and the inner screen to the
shield of the preamplifier input.
Input
Vibration Test Specimen
Preamplifier
2663
Differential
Accelerometer
grounded by
vibration test
specimen
E
D
B
C
A
F
890750e