BRUEL & KJAER NEXUS 2690 User manual

BI 5042−12
Technical
Documentation
The NEXUS™Range of
Conditioning Amplifiers
Types 2690, 2691, 2692 and 2693
Service Manual

Revision September 2004
BI 5042−12
Brüel & Kjær The NEXUS Range of Conditioning Amplifiers
Service Manual
The NEXUS™ Range of
Conditioning Amplifiers
Types 2690, 2691, 2692 and 2693
Service Manual
Valid from serial number 02340582

ii Brüel & KjærThe NEXUS Range of Conditioning Amplifiers
Service Manual
Safety Considerations
This apparatus has been designed and tested in accordance with IEC Publication 1010, Safety
Requirements for Electronic Equipment for Measurement, Control and Laboratory Use (see
specifications), and has been supplied in safe condition. This Manual contains information and
warnings which must be followed by the user to ensure safe operation and to retain the
apparatus in safe condition. Special note should be made of the following:
Safety Symbols
See the associated warning statements given in the User Manual
Chassis Terminal
Hazardous Voltage
Explosion Hazard
The apparatus 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 interface.
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.
Copyright © 1998, 2002 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.

The NEXUS Range of Conditioning Amplifiers
Service Manual
BI 5042 -12 iii
Contents
1. General Information....................................................................................................... 1
1.1 Edition Number ................................................................................................................ 2
1.2 Safety ................................................................................................................................ 2
1.3 Instrument Versions ......................................................................................................... 2
1.4 Service Policy..................................................................................................................... 3
Exchange Scheme ........................................................................................................ 3
Field Replaceable Parts................................................................................................ 4
Repair of PCBs.............................................................................................................. 5
Repair of Mechanical Parts ......................................................................................... 5
Repair Procedure ......................................................................................................... 5
1.5 Calibration and Testing.................................................................................................... 6
1.6 Special Tools and Equipment........................................................................................... 6
1.7 Front Panel........................................................................................................................ 7
1.8 Back Panel......................................................................................................................... 8
1.9 EMC Immunity ................................................................................................................ 10
2. Service Note.......................................................................................................................... 11
2.1 General............................................................................................................................ 12
3. Checking Procedure....................................................................................................... 13
3.1 Introduction.................................................................................................................... 14
Results Not Achieved................................................................................................. 14
Special Tools and Equipment.................................................................................... 14
Preparation ................................................................................................................ 14
3.2 Self-test Procedure ......................................................................................................... 14
3.3 Manual Checking Procedure.......................................................................................... 14
3.4 Checking Charge Channels ZX2692 .............................................................................. 15
Checking Calibrated Output..................................................................................... 15
Checking Low-pass Filters* ....................................................................................... 17
Checking High-pass Filters* ...................................................................................... 18
Optional Filters .......................................................................................................... 19
Inherent Noise* ......................................................................................................... 19
Checking Test Signals ................................................................................................ 20
Overload..................................................................................................................... 21
3.5 Checking Microphone Channels ZX 2690 and Sound Intensity Channels ZX 2691 ..... 22
Checking Calibrated Output*................................................................................... 22
Checking Low-pass Filters* ....................................................................................... 24
Checking High-pass and A-weighting Filters* ......................................................... 25

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Service Manual Brüel & Kjær
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Contents
Optional Filters .......................................................................................................... 26
Inherent Noise* ......................................................................................................... 27
Checking Test Signals ................................................................................................ 27
Overload .................................................................................................................... 29
3.6 Checking DeltaTron Channels ZX 2693 ......................................................................... 31
Checking Calibrated Output..................................................................................... 31
Checking Low-pass Filters* ....................................................................................... 32
Checking High-pass Filters ........................................................................................ 33
Optional Filters .......................................................................................................... 34
Inherent Noise* ......................................................................................................... 35
Checking DeltaTron Supply Current......................................................................... 35
Checking Test Signals ................................................................................................ 36
Overload .................................................................................................................... 36
3.7 Checking Optional Single and Double Integration Filters ZE 0788 ............................. 38
3.8 Checking Optional A-, B-, C- and D-Weighting Filters ZE 0794 ................................... 39
4. Theory of Operation..................................................................................................... 41
4.1 Introduction.................................................................................................................... 42
4.2 Functional Description ................................................................................................... 42
Input Channel Modules............................................................................................. 42
4.3 Block Diagrams............................................................................................................... 42
5. Electrical Diagrams......................................................................................................... 45
5.1 FRP Policy ........................................................................................................................ 46
6. Mechanical Assembly................................................................................................... 47
6.1 Dismantling the Display Unit ....................................................................................... 48
6.2 Dismantling the Motherboard (ZE 0785) ...................................................................... 49
6.3 Dismantling a Channel................................................................................................... 50
6.4 Dismantling the Main Processor Board......................................................................... 51
6.5 Dismantling the Rear Circuit Board (ZE 0786)............................................................... 51
7. Servicing the NEXUS using ATAC ...................................................................... 53
7.1 Introduction.................................................................................................................... 54
7.2 Main Menu ..................................................................................................................... 54
7.3 Service 269X Menu......................................................................................................... 55
Connecting the NEXUS.............................................................................................. 56
Correction Factors...................................................................................................... 57
Adjust Polarization Voltage...................................................................................... 58
Adjust Frequency Response ...................................................................................... 59
7.4 Set Configuration........................................................................................................... 60

The NEXUS Range of Conditioning Amplifiers
Service Manual
BI 5042 -12 1
Chapter 1
General Information

Chapter 1 — General Information
Edition Number
The NEXUS Range of Conditioning Amplifiers
Service Manual Brüel & Kjær
2
1.1 Edition Number
If any major changes are made to the instrument and/or Service Manual, a new edi-
tion of the Service Manual will be released. Any new edition can be recognised by
the Literature Number (BI 5042-xx) given at the bottom of odd numbered pages,
where xx is the edition number.
The serial number from which each edition is valid is printed in the frontispiece of
this Service Manual.
Information concerning minor changes will be released in the form of a Service Note
which is dealt with in Chapter 2.
1.2 Safety
The equipment and modules in NEXUS™ amplifiers have been designed and tested in
accordance with IEC Publication 1010, Safety Requirements for Electronic Equipment
for Measurement, Control and Laboratory use, and has been supplied in safe condi-
tion.
Any work done on the instrument when open must be done by a qualified person
who is aware of the hazards involved, particularly ESD protection.
Note: The word WARNING denotes a hazard. It calls attention to a procedure,
practice, or like, which, if not correctly performed or adhered to, could result in
personal injury.
1.3 Instrument Versions
Hardware Version
The hardware serial number is printed on a label on the rear panel of the instrument.
Software Version
The type of NEXUS unit is shown on the instrument’s display when it is turned on,
for example “Type 2690, 2691, 2692 or 2693”.
Basically all types use the same NEXUS program. The program consists of boot and
application software, each with a software version, revision and history number. The
boot and application version numbers are displayed when the Self Test menu is
selected.
The version number indicates the main software version. Main versions only change
if the NEXUS amplifier is updated with completely new versions of the boot and
application software.

Chapter 1 — General Information
Service Policy
The NEXUS Range of Conditioning Amplifiers
Service Manual
BI 5042 -12 3
The revision number is changed for small updates of the program, e.g., error correc-
tions, minor new functions and special customer versions.
The history number is generally for internal releases, however, it is also used to
indicate minor changes to the program.
1.4 Service Policy
1.4.1 Exchange Scheme
The NEXUS range of amplifiers are part of the FRP (Field Replaceable Part) scheme.
The module exchange scheme is based on the reuse of parts. It thus enables
Brüel & Kjær to offer a price reduction on FRPs. To assure economical reuse, it is
important that no attempt is made to repair an FRP locally. This is for calibration
reasons. If components are replaced during repair of a NEXUS unit, a recalibration is
required and can only be performed on an ATAC system to ensure the accuracy of
the instrument. All FRPs are calibrated when delivered from Brüel& Kjær. If a repair
attempt is made and the part subsequently needs to be exchanged, the price of an
exchange FRP is 100% the price of a new one. The service technician must therefore
check whether a faulty part is covered by a module exchange arrangement before
starting fault finding and repair.
FRPs and spare parts are stock items in Nærum. Maximum handling time in Nærum
is one to three working days when spare parts are ordered via an FRP Order Form.
Add to this the transportation time.
Please contact Service Centre Nærum for the latest Service Policy.

Chapter 1 — General Information
Service Policy
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Service Manual Brüel & Kjær
4
1.4.2 Field Replaceable Parts
Note: FRPs can only be obtained for NEXUS version 2.2 and later.
FRP Numbers
The FRP numbers are based on the normal part numbers with two extensions. The
general extension is FRF or FRR. The FRF (Field Replaceable (part) Forward) exten-
sion is used to indicate “new” parts from Brüel & Kjær and the FRR (Field Replaceable
(part) Return) extension indicates “defect” parts that are returned to Brüel & Kjær.
Initially full price is paid for an FRF. When Brüel & Kjær receives the FRR a credit note
for the difference will be issued. An additional single letter extension (A, B, C or D) is
used to identify input channels with an optional filter module and the type of filter
module, see Table 1.1.
Description Optional Filter Type FRP Forward No. FRP Return No.
Processor Channel
Module (ZD 0816) – ZD 0816–FRF ZD 0816–FRR
Microphone Channel
Module (ZX 2690)
No optional filter ZX 2690–FRF ZX 2690–FRR
ZE 0794 (A, B, C, D-filter) ZX 2690A–FRF ZX 2690A–FRR
Sound Intensity Channel
Module (ZX 2691, 2-chan-
nels) Note: Does not com-
ply with standards when
used with optional filters
No optional filter ZX 2691–FRF ZX 2691–FRR
ZE 0794 (A, B, C, D-filter) ZX 2691A–FRF ZX 2691A–FRR
Charge Channel Module
(ZX 2692)
No optional filter ZX 2692–FRF ZX 2692–FRR
ZE 0788 (Integration fil-
ter) ZX 2692B–FRF ZX 2692B–FRR
DeltaTron Channel Mod-
ule (ZX 2693)
No optional filter ZX 2693–FRF ZX 2693–FRR
ZE 0794 (A, B, C, D-filter) ZX 2693A–FRF ZX 2693A–FRR
ZE 0788 (Integration fil-
ter) ZX 2693B–FRF ZX 2693B–FRR
Table 1.1 FRP order numbers and return numbers. An extension (A, B, C, D) is used to
identify input channels fitted with an optional filter module

Chapter 1 — General Information
Service Policy
The NEXUS Range of Conditioning Amplifiers
Service Manual
BI 5042 -12 5
1.4.3 Repair of PCBs
Analogue Channel Boards
NEXUS is highly modular and all printed circuit boards are based on a multi-layer/
surface mounted technique which make repair mainly a question of identifying the
faulty module/PCB/channel and replace it with a “new” module/PCB/channel within
the FRP agreement.
Channels can be adjusted within ±0.001 dB from the theoretically “correct” value.
This adjustment can be performed on an ATAC system only.
Important: Do not interchange the PCBs that constitute a channel, between different
channels – they are calibrated as a single unit. If the PCBs are interchanged, the
instrument may lock up when it is switched on. If it is required to disassemble the
channels, the PCBs should be marked so that they can be assembled as they were
originally.
Analogue Channels With Optional Filter Modules
Input channels fitted with an optional filter module (analogue) must be calibrated
complete with the filter module. Table 1.1 includes separate FRP numbers for the
various combinations of input channels and optional filter modules.
Digital Boards
Identifying faulty digital boards is performed by use of the internal self-test proce-
dure. Refer to the self-test procedure in User Manual Vol. 1 and section 3.2 in this
Volume.
1.4.4 Repair of Mechanical Parts
Display/Front Panel
The display/front panel is considered to be a unit and is not part of the FRP arrange-
ment, since it is not practical to reuse any of the parts. If the display or front panel
cannot be easily repaired, they should be replaced with a new unit.
Mechanical Spare Parts
Mechanical spare parts can be ordered from Brüel& Kjær, see Chapter 6, Mechanical
Parts, for details of the parts available and their part numbers.
1.4.5 Repair Procedure
If a part in a NEXUS unit is found to be faulty, you have the following options:

Chapter 1 — General Information
Calibration and Testing
The NEXUS Range of Conditioning Amplifiers
Service Manual Brüel & Kjær
6
1. Send the complete instrument to Brüel & Kjær headquarters in Nærum. A repair
time of up to 10 days + transport time must be allowed.
2. Locate the faulty part and replace it with an FRP and test the functionality of the
instrument. If other repairs are made (except for simple mechanical problems),
the instrument must be tested on an ATAC system to ensure that it is within its
specifications.
1.5 Calibration and Testing
Calibration, testing and adjustment must be performed on an ATAC system. A DANAK
accredited certificate can be made with this system.
The following type of calibration/test is offered:
●Accredited calibration – performed in Nærum and some Service Centres
●Traceable – performed in some Service Centres
●Initial Accredited (or traceable) Calibration – offered with a new product
●Manufacturers Certificate of Conformance (MCOC) – performed in Nærum only
(all new instruments are supplied with an MCOC)
●Adjustment – performed in Nærum and Service Centres with an ATAC system
Service contracts are not offered due to the low complexity of NEXUS. The typical
calibration turnaround time in Nærum is 10 working days – add to this the transpor-
tation time. A price-list for NEXUS calibration services is available. It can be submit-
ted upon request via SOS.
1.6 Special Tools and Equipment
To perform the complete checking procedure, troubleshooting, adjustment and up-
grade of a NEXUS amplifier, the following special tools and equipment must be availa-
ble:
●ATAC system (Only if calibration/testing is required)
●Type 1049/51 Sine/Noise Generator
●2636 Measuring Amplifier
●DMM A digital multimeter
●Oscilloscope A storage oscilloscope
●WB 1026 1 nF Adaptor with TNC to BNC connectors
●WL 1273 Microphone LEMO to 3 BNC connectors (or AO 0479)
●AO 0479 7-pin LEMO to BNC cable

Chapter 1 — General Information
Front Panel
The NEXUS Range of Conditioning Amplifiers
Service Manual
BI 5042 -12 7
●AO 0087 BNC to BNC cable
●AO 0127 BNC to Brüel & Kjær cable
1.7 Front Panel
Fig.1.1 Front panel of NEXUS Conditioning Amplifier
On/Off key. When switched off, nearly all circuits in the instrument,
including the interface and the charging circuit, are switched off.
Note: The battery will discharge if left in the instrument for a long
period (refer to Chapter 3 in Vol. 1).
The six soft-keys on the front panel allow you to select menus and
options and to specify parameter values. The function of the keys
depends on the selected menu. The current function will appear on
the display above each key.
See Chapter 3 in Vol. 1 for a detailed description of how these keys
are used.
The four red LEDs to the left of the display are instantaneous over-
load indicators for the associated channels. All types of overload
are indicated by these LEDs.

Chapter 1 — General Information
Back Panel
The NEXUS Range of Conditioning Amplifiers
Service Manual Brüel & Kjær
8
1.8 Back Panel
Fig.1.2 Back panel of NEXUS Conditioning Amplifier
RS–232 Host Serial interface socket for remote control and output of measure-
ment results (see Vol. 2). The RS–232 Host connector is a 9-pin D-
range female connector which is used for connection to a PC, a
remote control unit or the previous NEXUS unit in a “daisy-chain”
setup. NEXUS units with a total of up to 99 channels can be “daisy-
chained” (use AO 1440).
Warning: Switch off all equipment before connecting or dis-
connecting the digital interface. Failure to do so could damage the
equipment.
Warning: The socket screen is connected to chassis ground.
RS–232 Next Unit Serial interface socket for remote control (see Vol. 2). The RS–232
Next Unit connector is a 9-pin D-range male connector which is
used for connection to succeeding NEXUS units (up to 99 chan-
nels) in a “daisy-chain” setup. Another serially controlled instru-
ment (for example a DAT-recorder) can also be connected to this
socket. It is required that this instrument is connected as the last
unit in the serial chain.
Warning: Switch off all equipment before connecting or dis-
connecting the digital interface. Failure to do so could damage the
equipment.
Warning: The socket screen is connected to chassis ground.

Chapter 1 — General Information
Back Panel
The NEXUS Range of Conditioning Amplifiers
Service Manual
BI 5042 -12 9
DC 10 – 33 V Coaxial DC-socket for connection to an external 10 to 33 V DC
source. Complies with ISO DP 7637/1, 12 V and DP 7637/2, 24 V. The
conditioning amplifier can be set to charge the battery from an
external 14 to 33 V DC source. If the external power source has lim-
ited capacity, for example a car battery, you can switch off the
charging circuit, or you can choose to charge the internal battery
with the NEXUS unit in power-down mode.
Warning: The DC-socket/cable ground is connected to chassis
ground.
Battery The intelligent QB 0048 metal-hydride battery is inserted from the
back panel. You can take out the battery during use without inter-
rupting the setup or a measurement, if the instrument is connected
to an external DC source.
Warning: When storing the battery for long periods of time,
remember to fully charge it before storage. If this is not done, you
may have difficulty making the battery accept charge when you
come to re-charge it at a later date.
Chassis ground, RS–232 interface ground and power ground.
Input Ch. 1 to 4 Up to four input sockets. Inputs can be single-ended or floating,
except for the Microphone input that operates in floating mode
(note that signal ground and chassis are connected through the
microphone). The type of connector(s) will depend on the configu-
ration of the associated input channel:
●Charge: TNC connector (TNC to 10–32 UNF adaptors pro-
vided)
●Microphone: 7-pin LEMO socket and Sound Intensity: 7-pin
LEMO socket (special adaptor required – refer to NEXUS
Order Form BA 0287), (two modules required for Sound In-
tensity)
●DeltaTron: BNT connector
Warning: If floating input is selected, care must be taken to
limit the signal ground current in order to prevent electrical haz-
ards. Maximum is 50 mA. The instrument will limit the voltage to
20 V, to prevent hazardous voltages.

Chapter 1 — General Information
EMC Immunity
The NEXUS Range of Conditioning Amplifiers
Service Manual Brüel & Kjær
10
1.9 EMC Immunity
NEXUS amplifiers do not require ferrite cable clamps to comply with EMC Emission
standards (EN 50081–1 and EN 50081–2).
The ferrite cable clamps are only required for compliance with EMC Immunity stand-
ards (EN 50082–1 and EN 50082–2). No problems should occur under normal use and
it is therefore only necessary to fit the clamps when the instrument is used in electri-
cally hostile environments such as powerful electrical fields.
For such cases the cables for the power supply, the RS–232 interface and all floating
inputs/outputs must be fitted with the appropriate ferrite cable clamps. Clamps
LK 0013 are used for BNC, RS–232 and accelerometer cables and the power supply
cable. The clamps must be fitted as close to the input/output sockets on the instru-
ment as possible. Cables for single-ended inputs/outputs and for the chassis ground
must not be fitted with ferrite cable clamps.
Output Ch. 1 to 4 Up to four BNC output sockets. You can select grounded or floating
mode. The output is protected against short-circuiting and voltage
overload, even when the instrument is switched off.
Warning: If floating output is selected, care must be taken to
limit the signal ground current in order to prevent electrical haz-
ards. Maximum is 50 mA. The instrument will limit the voltage to
20 V, to prevent hazardous voltages.

The NEXUS Range of Conditioning Amplifiers
Service Manual
BI 5042 -12 11
Chapter 2
Service Note

Chapter 2 — Service Note
General
The NEXUS Range of Conditioning Amplifiers
Service Manual Brüel & Kjær
12
2.1 General
From time to time some minor changes may be made to improve the performance
and serviceability of NEXUS amplifiers. All information concerning these changes, or
any other changes to the Service manual, will be released in the form of a Service
Note.
Note: The Service Note is renewed as a whole, meaning:
Discard the previous Service Note every time you receive a new one
The new edition of the Service Note must be placed in the binder in this section.

The NEXUS Range of Conditioning Amplifiers
Service Manual
BI 5042 -12 13
Chapter 3
Checking Procedure

Chapter 3 — Checking Procedure
Introduction
The NEXUS Range of Conditioning Amplifiers
Service Manual Brüel & Kjær
14
3.1 Introduction
The Checking procedure is divided up into 2 different modes.
●A built-in Self-test program that checks the digital parts of NEXUS.
●A Manual Checking Procedure that checks most of the analogue circuit based on
the factory checks of NEXUS.
Note: The Manual Checks of the analogue circuit are only a limited and selective part
of the complete factory check. This checking procedure only ensures that the NEXUS
unit is functional, not that it is within the tolerances described in the PD. The toler-
ance on the test equipment used is in many instances worse than the actual toleranc-
es of NEXUS. To check and test the analogue circuitry to ensure it complies with the
tolerances in the PD, an ATAC system is required.
3.1.1 Results Not Achieved
If the expected result is not achieved when a certain check is done, the defective
part must be identified and replaced using the FRP scheme (see Chapter 1).
3.1.2 Special Tools and Equipment
See Chapter 1.
3.1.3 Preparation
Please refer to User Manual Vol. 1 for information about the operation of NEXUS.
3.2 Self-test Procedure
A comprehensive self-test can be made of all the digital circuits in a NEXUS amplifier,
including the display and the soft-keys. It is not normally necessary to run the self-
test, only if you suspect there is something wrong with the instrument. Simply select
the Self Test field and press to initiate the self test. Follow the instructions on
the screen to complete the self-test procedure. If an error is indicated during the test
you should contact your local Brüel & Kjær representative and inform about the error
type. If no errors are found, the amplifier will boot again and display the NEXUS log
3.3 Manual Checking Procedure
This part of the checking procedure mainly checks the analogue circuitry of NEXUS
with use of the external test equipment.