BRUEL & KJAER 2663 Guide

Technical
Documentation
Preamplifiers
Types 2663 and 2663-B
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ËBE-1068---3Î
English BE1068–12

BE 1068 – 12
Preamplifiers
Types 2663 and 2663 B
User Manual

Revision April 2003
BE 1068 – 12
Brüel & Kjær Preamplifiers Types 2663 and 2663 B
User Manual
Preamplifiers
Types 2663 and 2663 B

Brüel & KjærPreamplifiers Types 2663 and 2663 B
User Manual
Safety Considerations
This apparatus has been designed and tested in accordance with IEC 61010 – 1 and EN 61010 – 1
Safety Requirements for Electrical Equipment for Measurement, Control and Laborato-
ry Use
(see specifications). This Manual contains information and warnings which must be
followed to ensure safe operation and to retain the apparatus in safe condition. Special note
should be made of the following:
Safety Symbols
The apparatus will be marked with this symbol when it is important that you refer to the
associated warning statements given in the Manual.
Protective Earth Terminal Hazardous Voltage
Explosion Hazard
The equipment is not designed to be used in potentially explosive environments. It should not
be operated in the presence of flammable liquids or gases.
Warnings
• Switch off all power to equipment before connecting or disconnecting their digital inter-
face. Failure to do so could damage the equipment.
• Whenever it is likely that the correct function or operating safety of the apparatus has
been impaired, it must be made inoperative and be secured against unintended operation.
• Any adjustment, maintenance and repair of the open apparatus under voltage must be
avoided as far as possible and, if unavoidable, must be carried out only by trained service
personnel.
Trademarks
TEFLON is a registered trademark of E.I. du Pont de Nemours and Company.
Copyright © 1990 – 2003, Brüel & Kjær Sound & Vibration Measurement A/S
All rights reserved. No part of this publication may be reproduced or distributed in any form
or by any means without prior consent in writing from Brüel & Kjær Sound & Vibration Meas-
urement A/S, Nærum, Denmark.

Contents
1. Introduction ........................................................................................................................... 1
1.1 About this Manual ........................................................................................................... 2
1.2 Preamplifiers Types 2663 and 2663 B.............................................................................. 2
Uses and Features........................................................................................................ 2
Description................................................................................................................... 3
2. Operation................................................................................................................................. 5
2.1 Environment ..................................................................................................................... 6
2.2 Mounting.......................................................................................................................... 6
2.3 Accelerometer Input Connection .................................................................................... 7
Single-ended Connections .......................................................................................... 7
Differential Connection .............................................................................................. 9
2.4 Output and Supply Connections ................................................................................... 10
Output Signal – Pins A and B .................................................................................... 11
Overload Detector – Pin D ........................................................................................ 11
Signal Ground Connection – Pin C............................................................................ 11
Power Supply – Pins C, E and F ................................................................................. 11
2.5 Circuit Adjustment for Acceleration Measurement ..................................................... 12
Low frequency Cut-off Adjustment.......................................................................... 14
High frequency Cut-off Adjustment......................................................................... 14
Output Bias Adjustment............................................................................................ 15
Sensitivity (Gain) Adjustment ................................................................................... 15
Grounded/Floating .................................................................................................... 16
2.6 Circuit Adjustment for Velocity Measurement............................................................. 16
Changing the Low-pass Filter ................................................................................... 18
Changing the High-pass Filter .................................................................................. 19
Velocity Sensitivity..................................................................................................... 20
3. Operating Characteristics......................................................................................... 21
3.1 Lower Limiting Frequency ............................................................................................. 22
3.2 Upper Limiting Frequency ............................................................................................. 23
3.3 Sensitivity........................................................................................................................ 25
3.4 Phase Response............................................................................................................... 26
3.5 Output Noise and Dynamic Range ................................................................................ 27
4. Accessories............................................................................................................................. 29
4.1 Cables and Plugs............................................................................................................. 30
Single-ended Input.................................................................................................... 30
Differential input ...................................................................................................... 31

Output Connector ..................................................................................................... 32
4.2 Measuring and Recording Instrumentation ................................................................. 33
5. Specifications....................................................................................................................... 35
5.1 Specifications.................................................................................................................. 36
6. Service and Repair .......................................................................................................... 37
6.1 Service ............................................................................................................................. 38
6.2 Repair .............................................................................................................................. 38
A. Appendix – Ground Loop Noise ......................................................................... 39
A.1 Ground Loop Phenomena.............................................................................................. 40
Index ........................................................................................................................................... 41

Preamplifiers Types 2663 and 2663 B
User Manual
BE 1068 – 12 1
Chapter 1
Introduction

Chapter 1 — Introduction
About this Manual
Preamplifiers Types 2663 and 2663 B
User Manual
Brüel & Kjær
2
1.1 About this Manual
This user manual is an overall guide to Types 2663 and 2663 B preamplifier hardware,
including hardware descriptions, operating instructions and characteristics, specifica-
tions, as well as service and repair. It is advisable to read this manual before operat-
ing the preamplifier to ensure proper usage and measurement.
1.2 Preamplifiers Types 2663 and 2663 B
Fig.1.1 Preamplifier Type 2663
1.2.1 Uses and Features
The following applies to both Type 2663 and Type 2663 B.
Uses:
●Vibration measurement on aircraft
●Measurement of vibration in severe environments
●Vibration monitoring on industrial machinery
●General vibration measurement
Features:
●Complies with MIL – STD 810 D
●Sensitivity adjustable from 1 to 100 mV/pC
●Differential and single-ended inputs
●Adjustable high- and low-pass filters

Chapter 1 — Introduction
Preamplifiers Types 2663 and 2663 B
Preamplifiers Types 2663 and 2663 B
User Manual
BE 1068 – 12 3
●Adjustable output bias
●Overload detection
●Rugged construction
●Power supply: single or dual polarity
1.2.2 Description
Preamplifiers Types 2663 and 2663 B are charge amplifiers designed for use with pie-
zoelectric transducers in airborne applications. Type 2663 has a preadjusted frequen-
cy range of 0.5 Hz (–3 dB) to 33 kHz (–3 dB) whereas Type 2663 B has a frequency
range of 0.5 Hz (–3 dB) to 100 Hz (–6 dB).
Gain and frequency range can be adjusted by exchanging appropriate resistors in the
preamplifier circuit to meet user requirements. For operation with different types of
transducers, the preamplifiers have three built-in choices of input configuration. It
can be used with both single-ended grounded and single-ended floating transducers
as well as differential types. The rugged case of the preamplifier is constructed from
milled aluminium. The removable side cover is fitted with a rubber seal which pro-
tects the electronics from dirt, oil, humidity and other environmental contamination.
The preamplifier can be powered from either a single-ended or dual-polarity supply.
The input connector is a 2-pin TNC socket. The output connector is a 6-pin bayonet
socket containing both AC and DC signal output pins and two pins for the power
supply. It also contains the overload detector pin, which is pulled high during over-
load, and the signal ground pin. The input amplifier is a differential charge amplifier
and the frequency range of the preamplifiers is determined by the low-pass and high-
pass filter pair.
Fig.1.2 Simplified circuit diagram for Preamplifier Type 2663. For Type 2663 B, the high-pass filter is
replaced with a low-pass filter giving overall a 4 th order low-pass filter –6 dB at 100 Hz
Low-Pass
Filter
(Adjust-
able)
High-Pass
Filter
(Adjust
-able)
Gain
(Adjust-
able)
Output
Stage
Overload
Detector
Chassis
Ground
Grounded
Floating
Voltage
Regulator
Input
Amplifier
882255/2
AC out
Signal
Ground
DC
out
Bias
Adjustable

Chapter 1 — Introduction
Preamplifiers Types 2663 and 2663 B
Preamplifiers Types 2663 and 2663 B
User Manual
Brüel & Kjær
4
The high frequency cut-off is determined by a 2-pole Butterworth low-pass filter pre-
adjusted to 33 kHz (–3 dB) for Type 2663; 100 Hz (–6 dB) for Type 2663 B. The cut-off
frequency may be adjusted between 250 Hz and 33 kHz, and with reduced specifica-
tions to 200 kHz. The low frequency cut-off is determined by a 4-pole Butterworth
high-pass filter and is pre-adjusted to 0.5 Hz (–3 dB). Two poles of the filter are ad-
justable to give a cut-off frequency from 0.5 Hz to 1 kHz. For frequencies greater than
3 Hz, the sensitivity is adjustable between l mV/pC and 100 mV/pC.
All the adjustments discussed above are made by replacing the appropriate resistors
with ones of the desired value and resoldering. Standard metal film resistors are used
and, to provide ease of access, these resistors and the grounded/Floating connection
are mounted on standoffs. The remainder of the preamplifier circuit is protected by a
shield. The basic formulae necessary to calculate the required values are printed on
this shield and within this instruction manual (see Chapter 2), which also gives a
comprehensive guide to the use of the resistors in specific circuits.

Preamplifiers Types 2663 and 2663 B
User Manual
BE 1068 – 12 5
Chapter 2
Operation

Chapter 2 — Operation
Environment
Preamplifiers Types 2663 and 2663 B
User Manual
Brüel & Kjær
6
2.1 Environment
The preamplifiers have a wide operating temperature range extending from –55oC to
+100oC (–67oF to +212oF). It can withstand shock levels up to 100 g (6.5 ms) and
meets the vibration requirements of MIL-STD 810 D, method 514.3, category 6, and is
therefore suitable for vibration measurements on helicopters, all kinds of aircraft,
and in most industrial environments. The preamplifier’s sealing prevents the influx of
dirt and oil and withstands up to 100% humidity, meeting the standards of both the
IEC 58.2.3, and MIL – STD 810D method 514.3 category 6.
2.2 Mounting
The small size of the preamplifiers enables them to be used in relatively confined
spaces where the use of other types of amplifier is restricted. They also have an
advantage in that they can be mounted close to accelerometers, thus eliminating the
need for long input cables which are prone to mechanically induced triboelectric
noise*.
The preamplifiers have a 4 mm (~0.15 in.) diameter hole at each corner of their hous-
ing for mounting purposes. They also contain an M 3 Metric Insert for grounding.
Fig.2.1 Mounting of Preamplifier Types 2663 and 2663 B
Ensure the preamplifiers are firmly fastened, where possible, on a vibration-free sur-
face, and that connection cables are properly anchored. The preamplifiers can with-
stand shock levels up to 100 g (6.5 ms) and meet the vibration requirements of MIL –
STD 810 D, method 514.3, category 6. Both preamplifiers’ (individual) mass is
167 grams. They should not be fastened to the vibration test-specimen on which the
accelerometer is mounted, as loading will alter the specimen’s vibration response.
*Triboelectric noise is a spurious electrical output produced by capacitance and dielectric changes in cables
when subject to mechanical excitation

Chapter 2 — Operation
Accelerometer Input Connection
Preamplifiers Types 2663 and 2663 B
User Manual
BE 1068 – 12 7
2.3 Accelerometer Input Connection
The input connector of Preamplifiers Types 2663 and 2663 B is a two-pole TNC sock-
et, which can be used with three input configurations:
●Single-ended floating
●Single-ended grounded
●Differential
Hum and other forms of noise due to ground loops and radiation pickup in a
vibration-measurement system can introduce considerable measurement errors. To
prevent this, it is essential that the accelerometer and preamplifier, together with
other instruments in the measurement system, are correctly grounded and screened.
The type of input configuration also has a considerable effect on the noise immunity
of the system. The three input configurations are covered in section 2.3.1 and section
2.3.2.
2.3.1 Single-ended Connections
Single-ended connections should be used when the preamplifiers are employed with
accelerometers which have one pole of their piezoelectric element connected to their
housing. It is suitable for most general vibration work. It is not suitable for work in
environments where a high level of electromagnetic radiation exists, as radiation
pickup can introduce noise. In such a case, the connection of a differential acceler-
ometer, as described in section 2.3.2, is preferred.
Plugs and Cables
Connection of a single-ended accelerometer to the preamplifiers should be made us-
ing one of the single-screened, low-noise accelerometer cables specified in section
4.1. These are fitted with microplugs which can be connected to the TNC input of the
preamplifiers using Adaptor Type JJ 0207. This connects the accelerometer housing
via the cable screens to the positive pole of the preamplifier input, thus completing
the measurement system signal-ground Iine.
Grounding
A problem often met in large vibration-measurement installations is the formation of
ground loops which introduce an error voltage that adds to the measured signal. To
avoid 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 instru-
mentation. Consequently, if the vibration test-specimen is grounded, then the trans-
ducer should be isolated from the specimen using an isolating stud and mica washer
when mounting (see Fig.2.2).
Warning: Disconnect the power supply before removing the preamplifier cover
and making any adjustments to the circuit.

Chapter 2 — Operation
Accelerometer Input Connection
Preamplifiers Types 2663 and 2663 B
User Manual
Brüel & Kjær
8
For many measurement situations, isolating the transducer from the test specimen
may not be a convenient solution. Therefore, the preamplifiers contain a grounded/
floating connection which allows the separation of the input and output grounds.
Shown in Fig.2.3 is a picture of a preamplifier with the side-cover removed. For ease
of access, the grounded/floating connection is mounted on a stand connected to the
circuit. When you remove the jumper connection, the input is set to 'floating' and the
ground loop is broken.
Fig.2.2 Connection of single-ended accelerometer to Type 2663/2663 B using the Microplug-TNC
socket Adaptor Type JJ 0207 with single-screened, low-noise accelerometer cable
Fig.2.3 A section of Type 2663/2663 B’s circuit board is shown with the side-cover removed. The
Floating-Remove Jumper allows you to choose between a grounded or floating connection
For a Single-ended Floating configuration, remove the connection (jumper) between
the two pins on the stand. Note that the 'floating' facility should only be chosen
when the input ground and output ground are externally connected. If there is no
such connection, the 'grounded' configuration should be used.
For a Single-ended Grounded configuration, ensure that there is a good connection
between the two pins on the stand. Use a solder to make the connection.
Vibration Test Specimen
Preamplifier
2663
Single Ended
Accelerometer
plus
Isolating Stud
and Mica Washer
E
D
B
C
A
F
890748e
Input

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 180oC (356oF)
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

Chapter 2 — Operation
Output and Supply Connections
Preamplifiers Types 2663 and 2663 B
User Manual
Brüel & Kjær
10
Fig.2.5 Connection of differential accelerometer to Type 2663/2663 B using double-screened, two-
core, low-noise, accelerometer cable
Since the shield of the accelerometer output socket is part of the accelerometer
housing which is grounded by the vibration test-specimen, it is essential that the
outer-cable screen is not connected to the inner-cable screen or the outer shield of
the preamplifier input-socket.
Isolation
In some circumstances, particularly when using ready-made cables, it may not be
possible to avoid interconnecting the outer shield of the accelerometer output and
preamplifier input with the cable screen. A simple solution to this problem, which
may be employed when relatively short input cables are used, is to isolate the accel-
erometer from ground by using an isolating stud and mica washer for mounting. If
this is not possible, then disconnect the grounded/floating connection on the pream-
plifier circuit.
2.4 Output and Supply Connections
The output connector of the preamplifiers is a 6-pin bayonet socket. It contains two
pins for the power input to the preamplifier, as well as signal output, overload and
signal ground pins. The pin designations are shown in Fig.2.6. Included in the acces-
sories is a 6-pin, Cannon-plug connector (Brüel & Kjær Type JJ 0615 or JJ 0624) which
is described in section 4.1.
Fig.2.6 Type 2663/2663 B output socket (external view)
Input
Vibration Test Specimen
Preamplifier
2663
Differential
Accelerometer
grounded by
vibration test
specimen
E
D
B
C
A
F
890749e
890751e
V
V
Overload
DC out
AC out
Signal
Ground
A
F
E
B
C
D
-
+

Chapter 2 — Operation
Output and Supply Connections
Preamplifiers Types 2663 and 2663 B
User Manual
BE 1068 – 12 11
2.4.1 Output Signal – Pins A and B
Pins B and A provide the AC output signal and DC output signal respectively. The
maximum output signal voltage available at the preamplifier output socket is 7 V
peak-to-peak with a maximum output current of 5 mA. The output is short-circuit
protected and has an output impedance of 50 . This enables the use of relatively
long output connection cables without their shunt capacitance influencing the useful
frequency range available for measurement.
The output bias is preadjusted to 2.5 V and is adjustable from 0 to +5.5 V referred to
supply ground (+0.5 V to +5.5 V for single supply).
2.4.2 Overload Detector – Pin D
The overload detector signal is output through pin D. It contains five inputs from
different stages of the preamplifier circuit and is pulled high on overload.
This could, for example, be used to drive the event marker of a level recorder and
can be used in systems for remotely recording or monitoring vibration signals.
2.4.3 Signal Ground Connection – Pin C
The signal/ground signal is output via pin C. Since the 0 V line of the supply is part of
the measurement system signal ground line, it should only be grounded via the chas-
sis of the readout. If connected to the supply chassis, then the signal ground line
should be disconnected from the readout chassis to prevent the formation of a
ground loop. To keep radiation pickup to a minimum, the signal line of the readout
should be connected to its chassis and the supply chassis should be connected to
the earth of a mains supply.
2.4.4 Power Supply – Pins C, E and F
Power is provided to pins E and F by a dual-polarity DC supply with voltage between
±20V and ±32V (see Fig.2.7), or by a single-polarity DC supply, between pins C and E
with voltage between +20 V and +32 V (see Fig.2.8).

Chapter 2 — Operation
Output and Supply Connections
Preamplifiers Types 2663 and 2663 B
User Manual
Brüel & Kjær
12
Fig.2.7 Dual-polarity DC supply, signal-input and -output connections with Types 2663/2663 B
The use of a dual-polarity supply with voltage exceeding 20 V is generally preferred
as better suppression (<60 dB at 1 kHz) of mains-carried noise and common-mode
signals is obtained. With dual or single-polarity supplies providing less than ±20 V (or
+20 V), the built-in voltage stabiliser circuit of the preamplifier follows the line volt-
age of the supply.
Fig.2.8 Single-polarity DC supply, signal-input and -output connections with Types 2663/2663 B
+
-
+
-
E
D
C
B
A
F
Signal Ground
AC Output
DC Output
Preamplifier
2663
Chassis
Readout
±20V to ±32V
Dual Polarity
DC Supply
(max. 30mA)
Chassis only
to
mains Ground
Signal Ground
plus chassis
to
mains Ground
891981/1
+
-
+
-
E
D
C
B
A
F
Signal Ground
AC Output
DC Output
Preamplifier
2663
Chassis
Readout
±20V to ±32V
Dual Polarity
DC Supply
(max. 30mA)
Chassis only
to
mains Ground
Signal Ground
plus chassis
to
mains Ground
891982/1

Chapter 2 — Operation
Circuit Adjustment for Acceleration Measurement
Preamplifiers Types 2663 and 2663 B
User Manual
BE 1068 – 12 13
2.5 Circuit Adjustment for Acceleration Measurement
In order to produce the most stable unit possible, the preamplifier parameter values
are adjusted by changing the appropriate circuit resistors. Fig.2.9 shows the pream-
plifiers with the side-cover removed. It contains six resistors which are easily re-
placeable and the floating/grounded connection. These resistors are mounted on
stands from the main preamplifier circuit and the remainder of the circuit is protect-
ed by a shield. The basic formulae necessary for calculation of the resistor values
required for particular parameter values are printed on the shield. Standard, metal
film resistors should be used.
Fig.2.9 Type 2663/2663 B with side-cover removed
The following parameters are adjustable:
●Low frequency cut-off
●High frequency cut-off
●Output Bias
●Sensitivity
●Floating/Grounded
Both section 2.5.1 and section 2.5.2 deal with the procedures needed to change the
high and low frequency cut-offs. Changing the output bias of the preamplifier is ex-
plained in section 2.5.3, while selection of the gain is covered in section 2.5.4 and
grounded/floating connection is covered in section 2.5.5. If velocity measurement is
of interest, the preamplifier can be adjusted to operate as an integrator. This is dealt
with in section 2.6.
Note 1: Before beginning any measurement, screw the preamplifier cover back onto
the preamplifier housing so as to keep radiation pickup to a minimum.