Ametek 7280 User manual

Model 7280
Wide Bandwidth
DSP Lock-in Amplifier
Instruction Manual
190398-A-MNL-C
Copyright © 2005 AMETEK ADVANCED MEASUREMENT TECHNOLOGY, INC

Firmware Version
The instructions in this manual apply to operation of a Model 7280 DSP Lock-in Amplifier that is fitted with
revision 5.0 or later operating firmware. Users of instruments that are fitted with earlier firmware revisions
can update them to the current revision free of charge by downloading an Update Pack from our website
at www.signalrecovery.com The pack includes full instructions for use.
Trademarks
AMETEK® and the b® and alogos are registered trademarks of AMETEK, Inc
Microsoft is a registered trademark, and Windows a trademark, of Microsoft Corporation. National
Instruments is a registered trademark of National Instruments Corporation
FCC Notice
This equipment generates, uses, and can radiate radio-frequency energy and, if not installed and used in
accordance with this manual, may cause interference to radio communications. As temporarily permitted
by regulation, operation of this equipment in a residential area is likely to cause interference, in which case
the user at his own facility will be required to take whatever measures may be required to correct the
interference.
Company Names
SIGNAL RECOVERY is part of Advanced Measurement Technology, Inc, a division of AMETEK, Inc. It
includes the businesses formerly trading as EG&G Princeton Applied Research, EG&G Instruments
(Signal Recovery), EG&G Signal Recovery and PerkinElmer Instruments (Signal Recovery).
Declaration of Conformity
This product conforms to EC Directives 89/336/EEC Electromagnetic Compatibility Directive, amended by
92/31/EEC and 93/68/EEC, and Low Voltage Directive 73/23/EEC amended by 93/68/EEC.
This product has been designed in conformance with the following IEC/EN standards:
EMC: BS EN55011 (1991) Group 1, Class A (CSPIR 11:1990)
BS EN50082-1 (1992):
IEC 801-2:1991
IEC 801-3:1994
IEC 801-4:1988
Safety: BS EN61010-1: 1993 (IEC 1010-1:1990+A1:1992)

Table of Contents
Table of Contents
i
Chapter One, Introduction
1.1 How to Use This Manual.................................................................................................................................. 1-1
1.2 What is a Lock-in Amplifier?........................................................................................................................... 1-2
1.3 Key Specifications and Benefits....................................................................................................................... 1-3
Chapter Two, Installation & Initial Checks
2.1 Installation ........................................................................................................................................................ 2-1
2.1.01 Introduction ............................................................................................................................................. 2-1
2.1.02 Rack Mounting ........................................................................................................................................ 2-1
2.1.03 Inspection ................................................................................................................................................ 2-1
2.1.04 Line Cord Plug ........................................................................................................................................ 2-1
2.1.05 Line Voltage Selection and Line Fuses ................................................................................................... 2-1
2.2 Initial Checks.................................................................................................................................................... 2-3
2.2.01 Introduction ............................................................................................................................................. 2-3
2.2.02 Procedure................................................................................................................................................. 2-3
2.3 Line Frequency Filter Adjustment.................................................................................................................... 2-6
2.3.01 Introduction ............................................................................................................................................. 2-6
2.3.02 Procedure................................................................................................................................................. 2-6
Chapter Three, Technical Description
3.1 Introduction ...................................................................................................................................................... 3-1
3.2 Operating Modes .............................................................................................................................................. 3-1
3.2.01 Introduction ............................................................................................................................................. 3-1
3.2.02 Single Reference / Dual Reference.......................................................................................................... 3-1
3.2.03 Single Harmonic / Dual Harmonic .......................................................................................................... 3-1
3.2.04 Internal / External Reference Mode......................................................................................................... 3-2
3.2.05 Virtual Reference Mode .......................................................................................................................... 3-2
3.3 Principles of Operation..................................................................................................................................... 3-2
3.3.01 Block Diagram......................................................................................................................................... 3-2
3.3.02 Signal Channel Inputs.............................................................................................................................. 3-3
3.3.03 Line Frequency Rejection Filter .............................................................................................................. 3-4
3.3.04 AC Gain and Dynamic Reserve............................................................................................................... 3-4
3.3.05 Anti-Aliasing Filter.................................................................................................................................. 3-6
3.3.06 Main Analog-to-Digital Converter .......................................................................................................... 3-7
3.3.07 Reference Channel................................................................................................................................... 3-7
3.3.08 Phase-Shifter............................................................................................................................................ 3-8
3.3.09 Internal Oscillator - General .................................................................................................................... 3-9
3.3.10 Internal Oscillator - Update Rate............................................................................................................. 3-9
3.3.11 Internal Oscillator - Frequency & Amplitude Sweeps............................................................................. 3-9
3.3.12 Demodulators......................................................................................................................................... 3-10
3.3.13 Output Processor - Output Filters.......................................................................................................... 3-11
3.3.14 Output Processor - Output Offset and Expand ...................................................................................... 3-12
3.3.15 Output Processor - Vector Magnitude and Phase .................................................................................. 3-12
3.3.16 Output Processor - Noise Measurements............................................................................................... 3-13

TABLE OF CONTENTS
ii
3.3.17 Auxiliary Analog Inputs and Outputs (ADCs and DACs) .................................................................... 3-14
3.3.18 Main Microprocessor - Spectral Display............................................................................................... 3-15
3.3.19 Main Microprocessor - User Settings.................................................................................................... 3-15
3.3.20 Main Microprocessor - General............................................................................................................. 3-15
3.3.21 Main Microprocessor - Auto Functions ................................................................................................ 3-15
3.4 General ........................................................................................................................................................... 3-17
3.4.01 Accuracy................................................................................................................................................ 3-17
3.4.02 Power-up Defaults................................................................................................................................. 3-18
Chapter Four, Front and Rear Panels
4.1 Front Panel ....................................................................................................................................................... 4-1
4.1.01 A and B/I Signal Input Connectors ......................................................................................................... 4-1
4.1.02 OSC OUT Connector .............................................................................................................................. 4-1
4.1.03 REF IN Connector................................................................................................................................... 4-1
4.1.04 Electroluminescent Screen ...................................................................................................................... 4-2
4.1.05 HELP Key ............................................................................................................................................... 4-5
4.1.06 MENU Key.............................................................................................................................................. 4-5
4.1.07 SELECT CONTROL Key....................................................................................................................... 4-5
4.2 Rear Panel......................................................................................................................................................... 4-6
4.2.01 Line Power Switch .................................................................................................................................. 4-6
4.2.02 Line Power Input Assembly .................................................................................................................... 4-6
4.2.03 RS232 Connector .................................................................................................................................... 4-6
4.2.04 AUX RS232 Connector........................................................................................................................... 4-6
4.2.05 GPIB Connector ...................................................................................................................................... 4-7
4.2.06 DIGITAL I/O Connector......................................................................................................................... 4-7
4.2.07 PRE-AMP POWER Connector ............................................................................................................... 4-7
4.2.08 REF MON Connector.............................................................................................................................. 4-7
4.2.09 REF TTL Connector................................................................................................................................ 4-7
4.2.10 DAC 1 and DAC 2 Connectors ............................................................................................................... 4-7
4.2.11 CH 1 and CH 2 Connectors..................................................................................................................... 4-7
4.2.12 ADC 1, ADC 2, ADC 3 and ADC 4 Connectors .................................................................................... 4-8
4.2.13 TRIG Connector ...................................................................................................................................... 4-8
4.2.14 SIG MON Connector............................................................................................................................... 4-8
Chapter Five, Front Panel Operation
5.1 Introduction ...................................................................................................................................................... 5-1
5.2 Menu Structure................................................................................................................................................. 5-2
5.3 Menu Descriptions - Single Reference Mode .................................................................................................. 5-3
5.3.01 Main Display ........................................................................................................................................... 5-3
5.3.02 Control Selection Menu........................................................................................................................... 5-5
5.3.03 Main Menu 1 ........................................................................................................................................... 5-7
5.3.04 Signal Channel Menu .............................................................................................................................. 5-8
5.3.05 Reference Channel Menu ...................................................................................................................... 5-11
5.3.06 Output Filters Menu .............................................................................................................................. 5-12
5.3.07 Output Offset & Expand Menu ............................................................................................................. 5-13
5.3.08 Output Equations Menu......................................................................................................................... 5-15
5.3.09 Oscillator Menu..................................................................................................................................... 5-16
5.3.10 Frequency Sweep Menu ........................................................................................................................ 5-17

TABLE OF CONTENTS
iii
5.3.11 Amplitude Sweep Menu ........................................................................................................................ 5-20
5.3.12 Auto Functions Menu ............................................................................................................................ 5-23
5.3.13 Configuration Menu .............................................................................................................................. 5-25
5.3.14 Communications Menu.......................................................................................................................... 5-28
5.3.15 RS232 Settings Menu ............................................................................................................................ 5-28
5.3.16 GPIB Settings Menu.............................................................................................................................. 5-30
5.3.17 Communications Monitor...................................................................................................................... 5-32
5.3.18 Analog Outputs Menu - Single & Virtual Reference Modes................................................................. 5-33
5.3.19 Options Menu ........................................................................................................................................ 5-38
5.3.20 Spectral Display..................................................................................................................................... 5-39
5.3.21 Main Menu 2 ......................................................................................................................................... 5-41
5.3.22 Curve Buffer Menu................................................................................................................................ 5-42
5.3.23 Curve Select Menu ................................................................................................................................ 5-45
5.3.24 Single Graph Menu................................................................................................................................ 5-46
5.3.25 Double Graph Menu .............................................................................................................................. 5-48
5.3.26 User Settings Menu ............................................................................................................................... 5-49
5.3.27 Auxiliary I/O Menu ............................................................................................................................... 5-50
5.3.28 Digital Port Menu .................................................................................................................................. 5-53
5.4 Menu Descriptions - Virtual Reference Mode................................................................................................ 5-54
5.4.01 Virtual Reference Menus....................................................................................................................... 5-54
5.4.02 Main Display - Virtual Reference Mode ............................................................................................... 5-56
5.4.03 Configuration Menu - Virtual Reference Mode .................................................................................... 5-57
5.5 Menu Descriptions - Dual Reference Mode ................................................................................................... 5-57
5.5.01 Dual Reference Setup Menu.................................................................................................................. 5-57
5.5.02 Dual Reference Main Display ............................................................................................................... 5-58
5.5.03 Reference Channel Menu ...................................................................................................................... 5-62
5.5.04 Dual reference Output Filters Menu...................................................................................................... 5-64
5.5.05 Output Offset Ref 1 Menu ..................................................................................................................... 5-65
5.5.06 Output Offset Ref 2 Menu ..................................................................................................................... 5-66
5.5.07 Auto Functions Menu ............................................................................................................................ 5-67
5.5.08 Configuration Menu - Dual Reference Mode........................................................................................ 5-68
5.5.09 Analog Outputs Menu - Dual Reference and Dual Harmonic Modes................................................... 5-68
5.6 Menu Descriptions - Dual Harmonic Mode ................................................................................................... 5-75
5.6.01 Dual Harmonic Setup Menu .................................................................................................................. 5-75
5.6.02 Dual Harmonic Main Display................................................................................................................ 5-76
5.6.03 Reference Channel Menu ...................................................................................................................... 5-80
5.6.04 Dual Harmonic Output Filters Menu..................................................................................................... 5-82
5.6.05 Output Offset Harm 1 Menu.................................................................................................................. 5-83
5.6.06 Output Offset Harm 2 Menu.................................................................................................................. 5-84
5.6.07 Auto Functions Menu ............................................................................................................................ 5-85
5.6.08 Configuration Menu - Dual Harmonic Mode ........................................................................................ 5-86
5.7 Typical Lock-in Amplifier Experiment.......................................................................................................... 5-87

TABLE OF CONTENTS
iv
Chapter Six, Computer Operation
6.1 Introduction ...................................................................................................................................................... 6-1
6.2 Capabilities....................................................................................................................................................... 6-1
6.2.01 General .................................................................................................................................................... 6-1
6.2.02 Curve Storage.......................................................................................................................................... 6-1
6.2.03 Curve Display.......................................................................................................................................... 6-1
6.3 RS232 and GPIB Operation ............................................................................................................................. 6-2
6.3.01 Introduction ............................................................................................................................................. 6-2
6.3.02 RS232 Interface - General Features ........................................................................................................ 6-2
6.3.03 Choice of Baud Rate................................................................................................................................ 6-3
6.3.04 Choice of Number of Data Bits ............................................................................................................... 6-3
6.3.05 Choice of Parity Check Option ............................................................................................................... 6-3
6.3.06 Auxiliary RS232 Interface....................................................................................................................... 6-4
6.3.07 GPIB Interface - General Features .......................................................................................................... 6-4
6.3.08 Handshaking and Echoes......................................................................................................................... 6-5
6.3.09 Terminators ............................................................................................................................................. 6-6
6.3.10 Command Format.................................................................................................................................... 6-6
6.3.11 Delimiters ................................................................................................................................................ 6-7
6.3.12 Compound Commands ............................................................................................................................ 6-7
6.3.13 Status Byte, Prompts and Overload Byte ................................................................................................ 6-7
6.3.14 Service Requests...................................................................................................................................... 6-9
6.3.15 Communication Monitor Menu............................................................................................................... 6-9
6.4 Command Descriptions .................................................................................................................................... 6-9
6.4.01 Signal Channel ...................................................................................................................................... 6-10
6.4.02 Reference Channel ................................................................................................................................ 6-12
6.4.03 Signal Channel Output Filters ............................................................................................................... 6-14
6.4.04 Signal Channel Output Amplifiers ........................................................................................................ 6-16
6.4.05 Instrument Outputs ................................................................................................................................ 6-18
6.4.06 Internal Oscillator.................................................................................................................................. 6-21
6.4.07 Auxiliary Outputs.................................................................................................................................. 6-23
6.4.08 Auxiliary Inputs..................................................................................................................................... 6-24
6.4.09 Output Data Curve Buffer ..................................................................................................................... 6-26
6.4.10 Computer Interfaces (RS232 and GPIB)............................................................................................... 6-31
6.4.11 Instrument Identification ....................................................................................................................... 6-33
6.4.12 Front Panel ............................................................................................................................................ 6-33
6.4.13 Auto Default.......................................................................................................................................... 6-33
6.4.14 Dual Mode Commands.......................................................................................................................... 6-34
6.5 Programming Examples ................................................................................................................................. 6-36
6.5.01 Introduction ........................................................................................................................................... 6-36
6.5.02 Basic Signal Recovery........................................................................................................................... 6-36
6.5.03 Frequency Response Measurement ....................................................................................................... 6-36
6.5.04 X and Y Output Curve Storage Measurement....................................................................................... 6-37
6.5.05 Transient Recorder ................................................................................................................................ 6-38
6.5.06 Frequency Response Measurement using Curve Storage and Frequency Sweep ................................. 6-38

TABLE OF CONTENTS
v
Appendix A, Specifications
Appendix B, Pinouts
B1 RS232 Connector Pinout .................................................................................................................................B-1
B2 Preamplifier Power Connector Pinout ..............................................................................................................B-1
B3 Digital Output Port Connector..........................................................................................................................B-2
Appendix C, Demonstration Programs
C1 Simple Terminal Emulator................................................................................................................................C-1
C2 RS232 Control Program with Handshakes .......................................................................................................C-1
C3 GPIB User Interface Program ...........................................................................................................................C-3
Appendix D, Cable Diagrams
D1 RS232 Cable Diagrams......................................................................................................................................D1
Appendix E, Default Settings
Auto Default Function............................................................................................................................................. E1
Appendix F, Alphabetical Listing of Commands
Index
Warranty...................................................................................................................................... End of Manual

TABLE OF CONTENTS
vi

Introduction
Chapter 1
1-1
1.1 How to Use This Manual
This manual gives detailed instructions for setting up and operating the
SIGNAL RECOVERY Model 7280 Digital Signal Processing (DSP) dual phase,
wide bandwidth, lock-in amplifier. It is split into the following chapters:-
Chapter 1 - Introduction
Provides an introduction to the manual, briefly describes what a lock-in amplifier is
and the types of measurements it may be used for, and lists the major specifications
of the model 7280.
Chapter 2 - Installation and Initial Checks
Describes how to install the instrument and gives a simple test procedure which may
be used to check that the unit has arrived in full working order.
Chapter 3 - Technical Description
Provides an outline description of the design of the instrument and discusses the
effect of the various controls. A good understanding of the design will enable the
user to get the best possible performance from the unit.
Chapter 4 - Front and Rear Panels
Describes the instrument’s connectors, controls and indicators as referred to in the
subsequent chapters.
Chapter 5 - Front Panel Operation
Describes the capabilities of the instrument when used as a manually operated unit,
and shows how to operate it using the front panel controls.
Chapter 6 - Computer Operation
This chapter provides detailed information on operating the instrument from a
computer over either the GPIB (IEEE-488) or RS232 interfaces. It includes
information on how to establish communications, the functions available, the
command syntax and a detailed command listing.
Appendix A
Gives the detailed specifications of the unit.
Appendix B
Details the pinouts of the multi-way connectors on the rear panel.
Appendix C
Lists three simple terminal programs which may be used as the basis for more
complex user-written programs.

Chapter 1, INTRODUCTION
1-2
Appendix D
Shows the connection diagrams for suitable RS232 null-modem cables to couple the
unit to an IBM-PC or 100% compatible computer.
Appendix E
Provides a listing of the instrument settings produced by using the Auto-Default
functions.
Appendix F
Gives an alphabetical listing of the computer commands for easy reference.
New users are recommended to unpack the instrument and carry out the procedure in
chapter 2 to check that it is working satisfactorily. They should then make themselves
familiar with the information in chapters 3, 4 and 5, even if they intend that the unit
will eventually be used under computer control. Only when they are fully conversant
with operation from the front panel should they then turn to chapter 6 for information
on how to use the instrument remotely. Once the structure of the computer commands
is familiar, appendix F will prove convenient as it provides a complete alphabetical
listing of these commands in a single easy-to-use section.
1.2 What is a Lock-in Amplifier?
In its most basic form the lock-in amplifier is an instrument with dual capability. It
can recover signals in the presence of an overwhelming noise background or
alternatively it can provide high resolution measurements of relatively clean signals
over several orders of magnitude and frequency.
Modern instruments, such as the model 7280, offer far more than these two basic
characteristics and it is this increased capability which has led to their acceptance in
many fields of scientific research, such as optics, electrochemistry, materials science,
fundamental physics and electrical engineering, as units which can provide the
optimum solution to a large range of measurement problems.
The model 7280 lock-in amplifier can function as a:-
AC Signal Recovery Instrument Transient Recorder
Vector Voltmeter Precision Oscillator
Phase Meter Frequency Meter
Spectrum Analyzer Noise Measurement Unit
These characteristics, all available in a single compact unit, make it an invaluable
addition to any laboratory.

Chapter 1, INTRODUCTION
1-3
1.3 Key Specifications and Benefits
The SIGNAL RECOVERY Model 7280 represents a significant advance in the
application of DSP technology in the design of a lock-in amplifier. Until now,
limitations in the available semiconductor devices have restricted the operating
frequency range of such instruments to at most a few hundred kilohertz. The model
7280, with its use of the latest technology, extends this limit to 2 MHz. What is more,
it does this without compromising any other important specifications.
Key specifications include:
Frequency range: 0.5 Hz to 2.0 MHz
Voltage sensitivity: 10 nV to 1 V full-scale
Current input mode sensitivities: 1 pA to 100 µA full-scale
10 fA to 1 µA full-scale
10 fA to 10 nA full-scale
Line frequency rejection filter
Dual phase demodulator with X-Y and R-θoutputs
Very low phase noise of < 0.0001°rms
Output time constant: 1 µs to 100 ks
5-digit output readings
Dual reference mode - allows simultaneous measurement of two signals at
different reference frequencies up to 20 kHz, or 800 kHz with option 7280/99 or
2.0 MHz with option 7280/98
Single and dual harmonic mode - allows simultaneous measurement of up to two
different harmonics of a signal at up to 20 kHz, or 800 kHz with option 7280/99
or 2.0 MHz with option 7280/98
Virtual reference mode - allows reference free measurement of signals up to
2.0 MHz
Spectral Display mode shows frequency spectrum of the signal prior to the
demodulators to help in selecting a reference frequency
Direct Digital Synthesizer (DDS) oscillator with variable amplitude and
frequency
Oscillator frequency and amplitude sweep generator
8-bit programmable digital I/O port for external system control
Four auxiliary ADC inputs and two auxiliary DAC outputs

Chapter 1, INTRODUCTION
1-4
Full range of auto-modes
Non-volatile memory for 8 complete instrument settings
Standard IEEE-488 and RS232 interfaces with RS232 daisy-chain capability for
up to 16 instruments
Large high-resolution electroluminescent display panel with menus for control
and display of instrument outputs in both digital and graphical formats
Easy entry of numerical control settings using keypad
32,768 point internal curve storage buffer

Installation &
Initial Checks
Chapter 2
2-1
2.1 Installation
2.1.01 Introduction
Installation of the model 7280 in the laboratory or on the production line is very
simple. It can be operated on almost any laboratory bench or be rack mounted, using
the optional accessory kit, at the user's convenience. With an ambient operating
temperature range of 0 °C to 35 °C, it is highly tolerant to environmental variables,
needing only to be protected from exposure to corrosive agents and liquids.
The instrument uses forced-air ventilation and as such should be located so that the
ventilation holes on the sides and rear panels are not obstructed. This condition is
best satisfied by leaving a space of at least 2" (5 cm) between the side and rear panels
and any adjacent surface.
2.1.02 Rack Mounting
An optional accessory kit, part number K02004, is available from
SIGNAL RECOVERY to allow the model 7280 to be mounted in a standard 19-inch
rack.
2.1.03 Inspection
Upon receipt the model 7280 Lock-in Amplifier should be inspected for shipping
damage. If any is noted, SIGNAL RECOVERY should be notified immediately and
a claim filed with the carrier. The shipping container should be saved for inspection
by the carrier.
2.1.04 Line Cord Plug
A standard IEC 320 socket is mounted on the rear panel of the instrument and a
suitable line cord is supplied.
2.1.05 Line Voltage Selection and Line Fuses
Before plugging in the line cord, ensure that the model 7280 is set to the voltage of
the AC power supply to be used.
A detailed discussion of how to check and, if necessary, change the line voltage
setting follows.
CAUTION: The model 7280 may be damaged if the line voltage is set for 110 V AC
operation and it is turned on with 220 V AC applied to the power input connector.
The model 7280 can operate from any one of four different line voltage ranges, 90-
110 V, 110-130 V, 200-240 V, and 220-260 V, at 50-60 Hz. The change from one
range to another is made by repositioning a plug-in barrel selector internal to the Line

Chapter 2, INSTALLATION & INITIAL CHECKS
2-2
Input Assembly on the rear panel of the unit. Instruments are normally shipped from
the factory with the line voltage selector set to 110-130 V AC, unless they are
destined for an area known to use a line voltage in the 220-260 V range, in which
case, they are shipped configured for operation from the higher range.
The line voltage setting can be seen through a small rectangular window in the line
input assembly on the rear panel of the instrument (figure 2-1). If the number
showing is incorrect for the prevailing line voltage (refer to table 2-1), then the barrel
selector will need to be repositioned as follows.
Observing the instrument from the rear, note the plastic door immediately adjacent to
the line cord connector (figure 2-1) on the left-hand side of the instrument. When the
line cord is removed from the rear-panel connector, the plastic door can be opened
outwards by placing a small, flat-bladed screwdriver in the slot on the right-hand side
and levering gently. This gives access to the fuse and to the voltage barrel selector,
which is located at the right-hand edge of the fuse compartment. Remove the barrel
selector with the aid of a small screwdriver or similar tool. With the barrel selector
removed, four numbers become visible on it: 100, 120, 220, and 240, only one of
which is visible when the door is closed. Table 2-1 indicates the actual line voltage
range represented by each number. Position the barrel selector such that the required
number (see table 2-1) will be visible when the barrel selector is inserted and the door
closed.
Figure 2-1, Line Input Assembly
VISIBLE # VOLTAGE RANGE
100 90 - 110 V
120 110 - 130 V
220 200 - 240 V
240 220 - 260 V
Table 2-1, Range vs. Barrel Position
Next check the fuse rating. For operation from a nominal line voltage of 100 V or
120 V, use a 20 mm slow-blow fuse rated at 2.0 A, 250 V. For operation from a
nominal line voltage of 220 V or 240 V, use a 20 mm slow-blow fuse rated at 1.0 A,
250 V.
To change the fuse, first remove the fuse holder by pulling the plastic tab marked
with an arrow. Remove the fuse and replace with a slow-blow fuse of the correct
voltage and current rating. Install the fuse holder by sliding it into place, making sure
the arrow on the plastic tab is pointing downwards. When the proper fuse has been
installed, close the plastic door firmly. The correct selected voltage setting should
now be showing through the rectangular window. Ensure that only fuses with the

Chapter 2, INSTALLATION & INITIAL CHECKS
2-3
required current and voltage ratings and of the specified type are used for
replacement. The use of makeshift fuses and the short-circuiting of fuse holders is
prohibited and potentially dangerous.
2.2 Initial Checks
2.2.01 Introduction
The following procedure checks the performance of the model 7280. In general, this
procedure should be carried out after inspecting the instrument for obvious shipping
damage.
NOTE: Any damage must be reported to the carrier and to SIGNAL RECOVERY
immediately. In addition the shipping container must be retained for inspection by
the carrier.
Note that this procedure is intended to demonstrate that the instrument has arrived in
good working order, not that it meets specifications. Each instrument receives a
careful and thorough checkout before leaving the factory, and normally, if no
shipping damage has occurred, will perform within the limits of the quoted
specifications. If any problems are encountered in carrying out these checks, contact
SIGNAL RECOVERY or the nearest authorized representative for assistance.
2.2.02 Procedure
1) Ensure that the model 7280 is set to the line voltage of the power source to be
used, as described in section 2.1.05.
2) With the rear-panel mounted power switch (located to the right of the line power
input connector) set to 0(off), plug in the line cord to an appropriate line source.
3) Turn the model 7280 power switch to the I (on) position.
4) The instrument's front panel display will now briefly display the following:-

Chapter 2, INSTALLATION & INITIAL CHECKS
2-4
Figure 2-2, Opening Display
5) Wait until the opening display has changed to the Main Display and then press the
key under the bottom right hand corner of the display identified by the legend
MENU on the display. This enters the first of the two main menus, Main Menu 1,
shown below in figure 2-3.
Figure 2-3, Main Menu 1
6) Press one of the keys adjacent to the Auto functions menu item to enter the Auto
Functions menu, shown below in figure 2-4.

Chapter 2, INSTALLATION & INITIAL CHECKS
2-5
Figure 2-4, Auto Functions Menu
7) Press one of the keys adjacent to the Auto Default menu item. This will set all of
the instrument's controls and the display to a defined state. The display will
revert to the Main Display, as shown below in figure 2-5, with the right-hand
side showing the vector magnitude, R, and the phase angle, θ, of the measured
signal in digital form, with two bar-graphs showing the X channel output and Y
channel output expressed in millivolts. The left-hand side shows five instrument
controls, these being the AC Gain in decibels, full-scale sensitivity, output time
constant, reference phase and internal oscillator frequency. The resulting
dynamic reserve (DR), in decibels, is also shown.
Figure 2-5, Main Display
8) Connect a BNC cable between the OSC OUT and Ainput connectors on the
front panel.

Chapter 2, INSTALLATION & INITIAL CHECKS
2-6
9) The right-hand side of the display should now indicate R, the vector magnitude,
close to 100% of full-scale (i.e. the sinusoidal oscillator output, which was set to
1 kHz and a signal level of 0.5 V rms by the Auto-Default function, is being
measured with a full-scale sensitivity of 500 mV rms) and θ, the phase angle, of
near zero degrees, if a short cable is used.
This completes the initial checks. Even though the procedure leaves many functions
untested, if the indicated results were obtained then the user can be reasonably sure
that the unit incurred no hidden damage in shipment and is in good working order.
2.3 Line Frequency Filter Adjustment
2.3.01 Introduction
The model 7280 incorporates a line-frequency rejection filter which is normally
supplied set to 60 Hz. If the power line frequency of the country in which the
instrument is to be used is also 60 Hz then the setting does not need to be changed. If,
however, the unit is to be used in an area with a 50 Hz power line frequency the
setting should be changed using the following procedure.
2.3.02 Procedure
1) Turn the model 7280’s power switch to the I(on) position.
2) The instrument's front panel display will now briefly display the following:-
Figure 2-6, Opening Display
3) Wait until the opening display has changed to the Main Display and then press
the key under the bottom right hand corner of the display identified by the legend
MENU on the display once. This enters the first of the two main menus, Main
Menu 1, shown below in figure 2-7.

Chapter 2, INSTALLATION & INITIAL CHECKS
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Figure 2-7, Main Menu 1
4) Press one of the keys adjacent to the Configuration menu item to enter the
Configuration menu, shown below in figure 2-8.
Figure 2-8, Configuration Menu
5) The present line frequency setting is shown in reversed text under the
LINE FREQUENCY label and is either 50 or 60 Hz. In figure 2-8, the filter is set
to 60 Hz. If this setting does not match the prevailing line frequency, then press a
key adjacent to this item once to change it.
6) Press the key marked MAIN DISPLAY once to return to the Main Display.
This completes the procedure for adjusting the line frequency filter.

Chapter 2, INSTALLATION & INITIAL CHECKS
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