BRUEL & KJAER 2732 User manual

Technical
Documentation
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Power Amplifier
Type 2732
User Manual
English BE 1662 – 12
ËBE-1662---'Î
Cover_BE166212.fm Page 1 Tuesday, October 4, 2005 3:16 PM

BE 1662−12 October 2005
Power Amplifier Type 2732
User Manual

Trademarks
Neutrik and Speakon are registered trademarks of Neutrik AG.
Copyright ©2002 – 2005, 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 written consent from Brüel & Kjær Sound & Vibration Meas-
urement A/S, Nærum, Denmark
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 Laboratory Use. This manual contains information and warnings which must be fol-
lowed 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.
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
• In order to avoid injury, it is recommended that two persons share the weight when lifting,
positioning and installing the power amplifier.
• 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.
• Do not dispose of electronic equipment as unsorted municipal waste
• It is your responsibility to contribute to a clean and healthy environment by using
the appropriate local return and collection systems
• Hazardous substances in electronic equipment may have detrimental effects on the
environment and human health
• The symbol shown to the left indicates that separate collection systems must be used
for any discarded equipment marked with that symbol
• Waste electrical and electronic equipment may be returned to your local Brüel & Kjær
representative or to Brüel & Kjær Headquarters for disposal

Contents
CHAPTER 1
Introduction......................................................................................................... 1
CHAPTER 2
Controls............................................................................................................... 3
Front Panel................................................................................................................................ 3
Back Panel ................................................................................................................................ 4
CHAPTER 3
Operation............................................................................................................. 7
Preliminary ................................................................................................................................ 7
Environment......................................................................................................................... 7
Rack Mounting ..................................................................................................................... 7
System Checks and Connections ............................................................................................. 7
Exciter Connections ............................................................................................................. 7
Mains Supply Connections .................................................................................................. 8
Fuse Check and Replacement............................................................................................. 8
Operating Procedure ................................................................................................................. 9
Warning Lamps and Fault Detection.................................................................................. 10
CHAPTER 4
Characteristics.................................................................................................. 11
Signal Inputs............................................................................................................................ 11
Power Output .......................................................................................................................... 11
Frequency Response......................................................................................................... 13
Distortion ................................................................................................................................. 13
CHAPTER 5
Specifications ................................................................................................... 15
CHAPTER 6
Service and Repair ........................................................................................... 17

1
Chapter 1
Introduction
Power Amplifier Type 2732 has been especially designed to drive Modal Exciter Type 4824 but
can be used with any vibration or modal exciter requiring a 120 VA power amplifier. The rated
AC output is 120 VA into a 4 Ωexciter or resistive load. The power amplifier has a usable
frequency range from 40 Hz to 15 kHz (full capacity) or DC to 150 kHz (reduced capacity). The
maximum voltage gain at 1 kHz is 7.7 V/V in low-impedance mode. Harmonic content of the
output is very small as heavy negative feedback is used. The instrument can tolerate tempera-
ture and supply-line variations while maintaining excellent stability. Type 2732 can be used as a
voltage generator with low output impedance and a flat voltage frequency response, or as a
current generator with high output impedance and a flat current frequency response. The RMS
output-current limit is adjustable.

Power Amplifier Type 2732 – User Manual2

3
Chapter 2
Controls
Front Panel
Fig.2.1 Front panel of Type 2732
Power: Mains On/Off push-button switch.
Display: The display shows output AC current and voltage on a LCD display
– The LED Indicator for State lights green when the amplifier power is switched on
– The LED Indicator for Output Phase lights green when indicating phase shift from input
to output
– The LED Indicator for Distortion lights yellow when output voltage or current clipping
take place
– The LED Indicator for Temperature lights red if the Power MOS Output Transistors over-
heat. Power Amplifier Type 2732 is then put in the Reset State
– The LED Indicator for Current lights red when output current to the load exceeds the
current
– Limit value set. Power Amplifier Type 2732 is then put in the Reset State
– The LED Indicator for Output V/C Mode lights green showing the Output Mode, Current
Mode or Voltage Mode – whichever is applicable
– The LED Indicator for Interlock lights red when the interlock circuit is activated
Variable Gain (dB): Single-turn, logarithmic potentiometer for continuous adjustment of input
signal level. To prevent a power surge, turn the knob fully anticlockwise for maximum attenua-
tion before switching the power on or off. Turning the knob fully anticlockwise past the click
and back again activates reset.

Power Amplifier Type 2732 – User Manual4
Current Limit A (RMS): Single-turn potentiometer for limiting RMS current output.
Phase: Push-button switch to set the phase shift, output/input, 0 or 180 degrees.
V/C Mode: Push-button switch for selection of feedback and output-impedance modes. The
positions are:
•Voltage Mode: Provides constant voltage characteristics independent of changes of test object
on the exciter. Gives the best acceleration waveform and is therefore preferable for most vibra-
tion tests
•Current Mode: Provides constant current characteristics, keeping the generated force inde-
pendent of changes of test object. This is the preferred setting for most modal-test applications
Back Panel
Fig.2.2 Back panel of Type 2732
Signal Input DC: BNC socket providing a direct-coupled input to the amplifier. It enables a
DC offset voltage to be applied for centring the exciter's armature. The input impedance is
>10 k Ω. If DC Static Centering Unit Type 1056 (optional) is used, the output from Type 1056 –
using a BNC to BNC cable – must be connected to the Signal Input DC socket of Type 2732.
Signal Input AC: BNC socket providing a capacitive-coupled input to the amplifier.
Output: Power output Neutrik®Speakon®socket accepting a 4-pin Neutrik Speakon plug or
connecting cable for connection of an exciter. For a full power output of 120 VA, the moving
coil of the exciter or load should have a nominal load impedance of 4 Ω.
Mains Voltage Selector and Fuse: Voltage selector for operation of the amplifier from a 100,
120, or 230 V ±10% (50 to 60 Hz) single phase, AC mains supply. To select the correct voltage
setting or to change the fuse, see “Mains Supply Connections” on page 8.
Mains Input: Input socket accepting the power cable provided. For connection of a mains
supply, see “Mains Supply Connections” on page 8.
Mains Output: Output socket accepting a power cord from DC Static Centering Unit Type
1056 (optional).
Voltage Monitor: BNC socket providing an output of the amplifier voltage waveform (includ-
ing DC component) for display on an oscilloscope. The monitor signal is the amplifier output
voltage attenuated 20 dB or 0.1 V/V.

CHAPTER 2
Controls 5
Current Monitor: BNC socket providing output of the amplifier output waveform (including
DC component) for display on an oscilloscope. The monitor signal is the amplifier output
current as 0.1 V/A.

Power Amplifier Type 2732 – User Manual6

7
Chapter 3
Operation
Preliminary
Environment
Power Amplifier Type 2732 is designed for operation at ambient temperatures between 5 and
40°C (41 to 104°F). Operation at full power will cause the Power MOS Output Transistors’ heat
sink to heat up. This is normal. However, it is important to ensure a free flow of cooling air
through the input vent in the front panel to the output vent in the back panel, otherwise the
input drive signal will be automatically blocked and Type 2732 will be put in Reset State to
prevent overheating of the transistors.
Rack Mounting
Power Amplifier Type 2732 is designed to fit into a 19-inch standard rack system with its
rubber feet removed. It may also be used free standing on its four rubber feet.
System Checks and Connections
Before connecting a mains supply, the following system checks and connections should be
carried out to ensure the correct function and safe operation of the apparatus.
Exciter Connections
The amplifier’s power socket accepts a 4-pin Neutrik®Speakon®plug. The pin connections are
shown in Fig.3.1.

Power Amplifier Type 2732 – User Manual8
Fig.3.1
Output socket for
Type 2732
For connection to Modal Exciter Type 4824, use Drive Cable AQ 0649 provided with the exciter.
The pin connections are shown in Fig.3.2.
Fig.3.2
Drive Cable AQ 0649.
Soldering side of plug
shown
Mains Supply Connections
Mains Voltage Setting
Type 2732 can be powered from a 100 V, 120 V or 230 V ± 10% (50 – 60 Hz), single-phase AC
mains supply. To select the correct mains voltage setting, use a small screwdriver to remove the
voltage selector with integrated fuse holder from the combined voltage selector and mains inlet,
then put it back again so that the white arrow is aligned with the appropriate voltage printed on
the selector.
Fuse Check and Replacement
The mains fuse is contained in the fuse holder, immediately beneath the voltage selector. It can
be released using a screwdriver. For 100 V or 120 V operation, the fuse should be a T6.3A slow
blow, whilst for 230 V operation it should be a T2.5 A slow blow. Make sure that only fuses of
the required rated current and of the specified type are used for replacement. Do not use
mended fuses or short-circuit the fuse holder.
Drive Signal
(Coil Start)
Neutral
(Coil Finish)
-1 -2
+2
+1
010166/3
Brown
Yellow/Green
Blue
Black
-1
-2
+2
+1
-1
-2
+2
+1
010113/2
AQ 0649: Soldering side of Plug shown

CHAPTER 3
Operation 9
Mains Socket Connection
Once the mains voltage setting and fuse are correct, use the power cable provided to connect
the mains to the mains input socket of the amplifier. Note that for maximum operating safety,
the protective (green/yellow) conductor of the cable should be connected to a suitable earth,
such as the earth contact of a mains outlet socket. The use of an extension cable without
protective conductor should be avoided for safety reasons. In countries where use of mains
socket outlets without protective conductor is standard, the mains supply should incorporate an
authorised earth-leakage current circuit breaker (Residual Current Circuit Breaker or RCCB).
Operating Procedure
Use the following procedure to commence operation:
1) Set the amplifier controls as shown below:
2) Connect the output of a signal generator to the AC or DC input on the back panel of the
amplifier
3) Turn the Variable Gain (dB) control knob fully anticlockwise.
4) Set the power amplifier as shown below:
5) Set the generator to the required frequency. Then, slowly increase the output voltage until
the exciter reaches the required level of vibration. With setups where the vibration level is
controlled by a feedback circuit, the voltage level will be increased automatically. If the
amber Distortion lamp lights or the maximum displacement limit of the exciter is exceeded,
causing the armature to knock against its end-stops, reduce the generator output voltage to
a lower level in order to resume operation. For frequency sweep vibration testing, adjust
the generator to the lowest frequency of interest to check that the exciter’s low frequency
limit is not exceeded.
6) To set the amplifier to standby during a test, turn the Amplifier Gain (dB) to Reset. At the
end of the test, switch the Power Off.
Power Off
Variable Gain (dB) Reset click-stop position
Current Limit A (RMS) Maximum current limit of the exciter’s moving coil. Consult the manufacturer’s
data for the exciter in use
V/C Mode Select Voltage Mode for the best acceleration waveform or Current Mode
for force-related tests. See “Power Output” on page 13
Power On. The Status, Mode and Phase LED in the display unit will light up green
Variable Gain (dB) Fully clockwise to position Cal

Power Amplifier Type 2732 – User Manual10
Warning Lamps and Fault Detection
If one of the red warning lamps lights, a fault has occurred in the system. Under such circum-
stances, the test is automatically stopped to protect the amplifier and exciter. To help establish
the cause of the shut-down, some probable faults are given in Table 3.1.
Table 3.1
If incorrect amplifier control settings or exciter connections cause shutdown, turn the Amplifier
Gain (dB) to Reset and make the necessary adjustments. Normal operation can then be resumed
by returning Amplifier Gain (dB) to the position used for test. If a shutdown is caused by an
internal fault in the amplifier or exciter, stop the test by setting Amplifier Gain (dB) to Reset
and switch the amplifier off. Then consult your Brüel & Kjær service representative.
Warning Lamp/LCD Display Probable Fault
Current Input drive level too high for Current Limit A (RMS) setting
Wrong output connections to exciter
Temperature Overdrive at low frequencies
Wrong output connections to exciter
Vibration laboratory temperature too high
Forced air-cooling system of amplifier blocked
Air Control Insufficient forced air cooling of exciter

11
Chapter 4
Characteristics
Signal Inputs
The signal inputs of Type 2732 have a minimum input impedance of 10 kΩ. The AC signal
input is for connecting an exciter controller or generator and is capacitive coupled giving a
±0.5 dB lower limiting frequency of approximately 15 Hz. The DC signal input is direct coupled
enabling a DC offset voltage to be applied for centering the exciter armature. At high input
levels, the drive signal is clipped causing the Distortion lamp to light.
Power Output
In Voltage Mode (low impedance), a fraction of the voltage developed across the moving coil
of the exciter is used as feedback. This gives the amplifier constant voltage characteristics –
very low output impedance and constant output voltage with frequency – producing the best
acceleration waveform. It is therefore suited to most single-exciter applications as well as to
multiple-exciter applications at low frequencies where it is important that the exciters have the
same motion.
In Current Mode (high impedance), feedback is proportional to the current flowing in the
exciter’s moving coil. This gives the amplifier constant current characteristics – high output
impedance and constant output current with frequency – necessary to obtain a constant force
with the exciter regardless of changes in the test object. This is useful for single-exciter fatigue
tests and multiple-exciter resonant mode studies of structural test objects.

Power Amplifier Type 2732 – User Manual12
Fig.4.1 Output impedance of Type 2732 as a function of frequency and output impedance
switch mode
The power output of Type 2732 is direct coupled. Its output impedance, shown in Fig.4.1,
depends on the feedback setting selected using the V/C Mode switch.
Fig.4.2 Maximum output current rating of Type 2732 as a function of frequency
High Impedance Specification LIMIT
Low Impedance Specification LIMIT
Output Impedance (ohms)
Frequency (Hz)
1K
500
200
100
50
20
10
5
2
1
0.5
0.2
0.1
0.05
0.02
0.01
0.005
0.002
0.001 12510 20 50 100 200 500 1k 2k 5k 10k 20k 50k 100k
010219
5A 5.5A
Maximum current
Maximum Output Voltage (V) and Current (A)
20
18
16
14
12
10
8
6
4
2
0
DC1 25 10 20 50 100 200 500 1k 2k 5k 10k 20k 50k 100k
Frequency (Hz) 010218

CHAPTER 4
Characteristics 13
As shown in Fig.4.2, the maximum output current is frequency dependent. The maximum pow-
er output is 120 VA, which can be obtained using exciters with a nominal load impedance of
4Ω.
Frequency Response
The full power output of 120 VA is available in the frequency range from 40 Hz to 15 kHz. At
lower power levels, the amplifier has a useful frequency range from DC to 150 kHz. This
depends on the signal input socket used and the setting of the V/C Mode switch, as shown by
the response curves for small signals given in Fig.4.3.
Fig.4.3 Frequency response in Voltage Mode of Type 2732 for small power output levels
Distortion
The percentage of harmonic distortion produced by Type 2732 is shown in Fig.4.4. Considering
the 120 VA power output rating of the amplifier, the amount of distortion is very low. This can
be attributed to the generous amount of feedback applied and the use of a direct-coupled input.
Low Impedance DC Input Specification LIMIT
Low Impedance AC Input Specification LIMIT
DC Input
AC Input Low Impedance
Voltage
251020 50 100 200 500 1k 2k 5k 10k 20k 50k 100k
010217
Frequency (Hz)
-10
-9
-3
-2
-1
0
1
2
3
4
5
Relative Amplitude (dB)
-4
-5
-6
-7
-8
1200k 500k 1M

Power Amplifier Type 2732 – User Manual14
Fig.4.4 Typical harmonic distortion percentage curves for Voltage Mode (Low) and Current
Mode (High) output impedance – 120 VA in a 4 Ω load
12510 20 50 100 200 500 1k 2k 5k 10k 20k 50k 100k
01021
6
Frequency (Hz)
0
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
Output Distortion (%)
High Impedance
Specification
Low Impedance
Specification
H
L
Low
High

15
Chapter 5
Specifications
COMPLIANCE WITH STANDARDS
compliance with EMC Directive
compliance with EMC Requirements of
Australia and New Zealand
Safety, EMC Emission and Immunity: According to
relevant standards:
EN/IEC 61010 –1, UL 61010–1, EN/IEC 61000–6–2,
EN/IEC 61000–6–4, CISPR22 Class A limit, FCC
Rules Part 15, EN/IEC 61326
Temperature: According to IEC 60068–2–1 and
IEC 60068–2–2
Operating temperature:
+5 to +40°C (41 to 104°F)
Storage temperature:
–25 to +70°C (–13 to 158°F)
Humidity: According to IEC 60068–2–78, Damp
Heat: 90% RH (non-condensing at 40°C (104°F))
Mechanical: Non-operating according to IEC 60068–
2–6, IEC60068–2–27, IEC60068–2–29
POWER OUTPUT CAPACITY
120 VA into a 4 Ωexciter or resistive load, at 25°C and
nominal mains voltage.
(4-pin Neutrik®Speakon®socket at rear panel)
OUTPUT VOLTAGE CAPACITY
22 V RMS, DC to 15 kHz (without load)
OUTPUT CURRENT CAPACITY
5.5 A RMS, 40 Hz to 15 kHz
5.0 A RMS, 15 Hz to 15 kHz
MAX. VOLTAGE GAIN
17 dB ±2 dB @ 1 kHz
FREQUENCY RANGE
Full Capacity: 40 Hz to 15 kHz
Reduced Capacity: DC to 150 kHz (–20 dB)
FREQUENCY RESPONSE
Typical small signal response (–20 dB) in low
impedance mode:
DC Input: DC to 15 kHz ±0.5 dB; DC to 150 kHz ±3 dB
AC Input: 15 Hz to 15 kHz ±0.5 dB
(2 separate BNC sockets at rear panel)
HARMONIC DISTORTION
<0.1% (40 Hz to 5 kHz) Low Impedance Mode
<0.2% (5 kHz to 15 kHz) Low Impedance Mode
<0.2 % (40 Hz to 2 kHz) High Impedance Mode
<0.8% (2 kHz to 15 kHz) High Impedance Mode
INPUT IMPEDANCE
>10kΩ
DC STABILITY
Less than ± 100 mV drift from 0 V for ±10% variation
of mains supply from nominal, and for 10°C to 40°C
(50°F to 104°F) variation in ambient temperature
CONTROLS
• Power on/off
• Continuously variable gain control, 0 to Cal. (17 dB)
with integral reset
• Continuously variable current limit control 1 to 5.5 A
(RMS)
• Switch for voltage mode or current mode operation
• Switch for phase inversion (0° or 180°)
INDICATOR LAMPS
•Clipping
• Temperature overload
• Current overload
•State
• Voltage mode
• Current mode
• Interlock
• Phase (0°or 180°)
MULTIFUNCTION DISPLAY (LCD)
• Voltage, RMS, readout accuracy ±5% ±1 digit (40 Hz
to 15 kHz)