Ametek 7124 User manual

Model 7124
Precision
Lock-in Amplifier
Instruction Manual
197776-A-MNL-F
Copyright © 2017 AMETEK ADVANCED MEASUREMENT TECHNOLOGY, INC

Firmware Version
The instructions in this manual apply to operation of a Model 7124 Precision Lock-in Amplifier that is fitted
with Version 2.20 or later operating firmware. Users of instruments that are fitted with earlier firmware
versions can update them to the current version 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
Other product and company names mentioned are trademarks or trade names of their respective
companies.
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).

Table of Contents Table of Contents
i
General Safety Precautions..............................................................................................................vii
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 and 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 Plugs....................................................................................................................................... 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 ................................................................................................................... 2-7
2.3.01 Introduction ............................................................................................................................................. 2-7
2.3.02 Procedure................................................................................................................................................. 2-7
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 Tandem Demodulation............................................................................................................................ 3-1
3.2.04 Single Harmonic / Dual Harmonic.......................................................................................................... 3-2
3.2.05 Internal / External Reference Mode ........................................................................................................ 3-2
3.2.06 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 - 7124 RCU......................................................................................................... 3-4
3.3.03 Line Frequency Rejection Filter.............................................................................................................. 3-5
3.3.04 AC Gain and Dynamic Reserve............................................................................................................... 3-5
3.3.05 Anti-Aliasing Filter ................................................................................................................................. 3-6
3.3.06 Analog Fiber Links.................................................................................................................................. 3-7
3.3.07 Auxiliary Signal Input - Main Console................................................................................................... 3-7
3.3.08 Main Analog-to-Digital Converter.......................................................................................................... 3-8
3.3.09 Reference Channel Inputs - 7124 RCU................................................................................................... 3-8
3.3.10 Reference Channel Inputs- Main Console............................................................................................... 3-8
3.3.11 Reference Channel .................................................................................................................................. 3-8
3.3.12 Phase-Shifter ........................................................................................................................................... 3-9

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ii
3.3.13 Internal Oscillator - General...................................................................................................................3-10
3.3.14 Internal Oscillator - Update Rate ...........................................................................................................3-10
3.3.15 Internal Oscillator - Frequency & Amplitude Sweeps...........................................................................3-10
3.3.16 Internal Oscillator - Voltage Control .....................................................................................................3-11
3.3.17 Demodulators - Dual Phase Multipliers.................................................................................................3-11
3.3.18 Demodulators - Output Filters................................................................................................................3-11
3.3.19 Fast Curve Buffer...................................................................................................................................3-12
3.3.20 Main Output Processor - General...........................................................................................................3-12
3.3.21 Main Output Processor - Output Offset and Expand.............................................................................3-12
3.3.22 Main Output Processor - Vector Magnitude and Phase.........................................................................3-13
3.3.23 Main Output Processor - Noise Measurements......................................................................................3-14
3.3.24 Main Output Processor - Standard Curve Buffer...................................................................................3-15
3.3.25 Analog Outputs (DACs).........................................................................................................................3-15
3.3.26 Auxiliary Analog Inputs (ADCs)...........................................................................................................3-15
3.3.27 Main Microprocessor - General.............................................................................................................3-16
3.3.28 Main Microprocessor - Spectral Display ...............................................................................................3-16
3.3.29 Main Microprocessor - Auto Functions.................................................................................................3-16
3.3.30 Main Microprocessor - User Settings ....................................................................................................3-18
3.4 General............................................................................................................................................................3-18
3.4.01 Accuracy.................................................................................................................................................3-18
3.4.02 Power-up Defaults..................................................................................................................................3-18
Chapter Four, Front and Rear Panels
4.1 Front Panel - Main Console ..............................................................................................................................4-1
4.1.01 AUX Signal Input Connector...................................................................................................................4-1
4.1.02 MON Connector.......................................................................................................................................4-1
4.1.03 REF IN Connector....................................................................................................................................4-1
4.1.04 OSC OUT Connector ...............................................................................................................................4-2
4.1.05 LCD Screen..............................................................................................................................................4-2
4.1.06 HELP Key................................................................................................................................................4-5
4.1.07 MENU Key ..............................................................................................................................................4-5
4.1.08 SELECT CONTROL Key........................................................................................................................4-5
4.2 Rear Panel - Main Console................................................................................................................................4-6
4.2.01 Line Power Switch...................................................................................................................................4-6
4.2.02 Line Power Input Assembly.....................................................................................................................4-6
4.2.03 DIGITAL I/O Connector..........................................................................................................................4-6
4.2.04 USB Connector ........................................................................................................................................4-6
4.2.05 LAN Connector........................................................................................................................................4-7
4.2.06 RS232 Connector .....................................................................................................................................4-7
4.2.07 AUX RS232 Connector............................................................................................................................4-7
4.2.08 PRE-AMP POWER Connector................................................................................................................4-7
4.2.09 ADC TRIG IN Connector ........................................................................................................................4-7
4.2.10 ADC 1, ADC 2, ADC 3 and ADC 4 Connectors .....................................................................................4-7
4.2.11 REF MON Connector...............................................................................................................................4-7
4.2.12 TTL REF IN Connector ...........................................................................................................................4-7
4.2.13 TRIG IN Connector..................................................................................................................................4-8
4.2.14 TRIG OUT Connector..............................................................................................................................4-8
4.2.15 DAC 1, DAC 2, DAC 3, and DAC 2 Connectors ....................................................................................4-8
4.2.16 FIBER LINKS Connectors.......................................................................................................................4-8
4.3 Front Panel - 7124 RCU....................................................................................................................................4-8

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iii
4.3.01 A and B/I Signal Input Connectors ......................................................................................................... 4-8
4.3.02 REF IN Connector................................................................................................................................... 4-9
4.3.03 OSC OUT Connector .............................................................................................................................. 4-9
4.3.04 STATUS LED......................................................................................................................................... 4-9
4.4 Rear Panel - 7124 RCU.................................................................................................................................... 4-9
4.4.01 Line Power Switch .................................................................................................................................. 4-9
4.4.02 Line Power Input Assembly.................................................................................................................... 4-9
4.4.03 DIGITAL OUTPUT Connector............................................................................................................... 4-9
4.4.04 TTL REF IN Connector......................................................................................................................... 4-10
4.4.05 POWER IN/OUT Connector................................................................................................................. 4-10
4.4.06 CONTROL, REF OUT, OSC IN, and SIG OUT Fiber Optic Connectors............................................ 4-10
4.4.07 SIG MON Connector............................................................................................................................. 4-10
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 1........................................................................................................................... 5-7
5.3.05 Reference Channel Menu...................................................................................................................... 5-11
5.3.06 Output Filters Menu .............................................................................................................................. 5-13
5.3.07 Output Offset & Expand Menu ............................................................................................................. 5-14
5.3.08 Output Equations Menu......................................................................................................................... 5-15
5.3.09 Oscillator Menu..................................................................................................................................... 5-16
5.3.10 Frequency Sweep Menu........................................................................................................................ 5-18
5.3.11 Amplitude Sweep Menu........................................................................................................................ 5-21
5.3.12 Amplitude Modulation Menu................................................................................................................ 5-23
5.3.13 Frequency Modulation (VCO) Menu.................................................................................................... 5-24
5.3.14 Auto Functions Menu............................................................................................................................ 5-25
5.3.15 Configuration Menu .............................................................................................................................. 5-27
5.3.16 Communications Menu ......................................................................................................................... 5-29
5.3.17 RS232 Settings Menu............................................................................................................................ 5-30
5.3.18 Ethernet Settings Menu......................................................................................................................... 5-32
5.3.19 USB Status Menu.................................................................................................................................. 5-34
5.3.20 Communications Monitor...................................................................................................................... 5-35
5.3.21 Options Menu........................................................................................................................................ 5-35
5.3.22 Configuration Menu 2 ........................................................................................................................... 5-36
5.3.23 Spectral Display .................................................................................................................................... 5-37
5.3.24 Main Menu 2 ......................................................................................................................................... 5-39
5.3.25 Curve Buffer Menu ............................................................................................................................... 5-41
5.3.26 Curve Trigger Menu.............................................................................................................................. 5-42
5.3.27 Curve Select Menu................................................................................................................................ 5-44
5.3.28 Single Graph Menu ............................................................................................................................... 5-46
5.3.29 Double Graph Menu.............................................................................................................................. 5-47
5.3.30 User Settings Menu ............................................................................................................................... 5-48
5.3.31 ADC Menu ............................................................................................................................................ 5-49
5.3.32 DAC Menu ............................................................................................................................................ 5-51

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5.3.33 Digital Port Menu...................................................................................................................................5-55
5.3.34 RCU Digital Port Menu..........................................................................................................................5-56
5.3.35 Fiber Calibration Menu..........................................................................................................................5-56
5.4 Menu Descriptions - Virtual Reference Mode................................................................................................5-57
5.4.01 Virtual Reference Menus .......................................................................................................................5-57
5.4.02 Virtual Reference Main Display ............................................................................................................5-60
5.4.03 Virtual Reference Configuration Menu .................................................................................................5-61
5.5 Menu Descriptions - Dual Reference Mode....................................................................................................5-61
5.5.01 Dual Reference Setup Menu ..................................................................................................................5-61
5.5.02 Dual Reference Main Display................................................................................................................5-62
5.5.03 Dual Reference Channel Menu..............................................................................................................5-66
5.5.04 Dual Reference Channel Menu 2...........................................................................................................5-68
5.5.05 Dual Reference Output Filters Menu 1..................................................................................................5-68
5.5.06 Dual Reference Output Filters Menu 2..................................................................................................5-70
5.5.07 Dual Reference Output Offset Ref 1 Menu............................................................................................5-70
5.5.08 Dual Reference Output Offset Ref 2 Menu............................................................................................5-72
5.5.09 Dual Reference Auto Functions Menus.................................................................................................5-73
5.5.10 Dual Reference Configuration Menu.....................................................................................................5-74
5.5.11 Dual Reference and Dual Harmonic Modes Curve Select Menu ..........................................................5-74
5.5.12 Dual Reference and Dual Harmonic Modes DAC Menu.......................................................................5-75
5.6 Menu Descriptions - Dual Harmonic Mode....................................................................................................5-79
5.6.01 Dual Harmonic Setup Menu...................................................................................................................5-79
5.6.02 Dual Harmonic Main Display................................................................................................................5-80
5.6.03 Dual Harmonic Reference Channel Menu.............................................................................................5-84
5.6.04 Dual Harmonic Output Filters Menu .....................................................................................................5-86
5.6.05 Dual Harmonic Output Filters Menu 2 ..................................................................................................5-87
5.6.06 Dual Harmonic Output Offset Harm 1 Menu.........................................................................................5-88
5.6.07 Dual Harmonic Output Offset Harm 2 Menu.........................................................................................5-89
5.6.08 Dual Harmonic Auto Functions Menus .................................................................................................5-90
5.6.09 Dual Harmonic Configuration Menu .....................................................................................................5-91
5.7 Typical Lock-in Amplifier Experiment...........................................................................................................5-91
Chapter Six, Computer Operation
6.1 Introduction.......................................................................................................................................................6-1
6.2 Capabilities........................................................................................................................................................6-1
6.2.01 General.....................................................................................................................................................6-1
6.2.02 Operation..................................................................................................................................................6-1
6.2.03 Communications Monitor Menu..............................................................................................................6-1
6.2.04 Compound Commands.............................................................................................................................6-1
6.3 RS232 Operation...............................................................................................................................................6-1
6.3.01 Introduction..............................................................................................................................................6-1
6.3.02 General Features.......................................................................................................................................6-2
6.3.03 Choice of Baud Rate ................................................................................................................................6-2
6.3.04 Choice of Number of Data Bits................................................................................................................6-2
6.3.05 Choice of Parity Check Option ................................................................................................................6-3
6.3.06 Auxiliary RS232 Interface .......................................................................................................................6-3
6.3.07 Handshaking and Echoes .........................................................................................................................6-3
6.3.08 Terminators ..............................................................................................................................................6-4
6.3.09 Delimiters.................................................................................................................................................6-4
6.3.10 Status Byte, Prompts and Overload Byte.................................................................................................6-4

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v
6.4 USB Operation ................................................................................................................................................. 6-5
6.4.01 Introduction ............................................................................................................................................. 6-5
6.4.02 General Features...................................................................................................................................... 6-5
6.4.03 Terminator, Status Byte, and Overload Byte .......................................................................................... 6-5
6.4.04 Delimiters................................................................................................................................................ 6-6
6.5 Ethernet Operation ........................................................................................................................................... 6-7
6.5.01 Introduction ............................................................................................................................................. 6-7
6.5.02 IP Address ............................................................................................................................................... 6-7
6.5.03 Home Page............................................................................................................................................... 6-7
6.5.04 Sockets..................................................................................................................................................... 6-8
6.5.05 Terminator, Status Byte, and Overload Byte .......................................................................................... 6-8
6.5.06 Delimiters................................................................................................................................................ 6-9
6.6 Command Format............................................................................................................................................. 6-9
6.7 Command Descriptions .................................................................................................................................. 6-10
6.7.01 Signal Channel ...................................................................................................................................... 6-10
6.7.02 Reference Channel ................................................................................................................................ 6-12
6.7.03 Signal Channel Output Filters............................................................................................................... 6-14
6.7.04 Signal Channel Output Amplifiers........................................................................................................ 6-15
6.7.05 Instrument Outputs................................................................................................................................ 6-17
6.7.06 Internal Oscillator.................................................................................................................................. 6-19
6.7.07 Analog Outputs...................................................................................................................................... 6-23
6.7.08 Digital I/O.............................................................................................................................................. 6-24
6.7.09 Auxiliary Inputs..................................................................................................................................... 6-24
6.7.10 Output Data Curve Buffer..................................................................................................................... 6-25
6.7.11 Computer Interfaces .............................................................................................................................. 6-32
6.7.12 Instrument Identification....................................................................................................................... 6-34
6.7.13 Front Panel ............................................................................................................................................ 6-34
6.7.14 Auto Default and Calibration................................................................................................................ 6-34
6.7.15 Dual Mode Commands.......................................................................................................................... 6-35
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
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, Cable Diagrams
C1 RS232 Cable Diagrams......................................................................................................................................C1
Appendix D, Default Settings
Auto Default Function.............................................................................................................................................D1

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vi
Appendix E, 7124/99 DC Power Option for 7124 RCU
E.1 Introduction....................................................................................................................................................... E1
E.2 7124 RCU POWER Connector......................................................................................................................... E1
E.3 7124/99 DC Power Input Cable........................................................................................................................ E1
E.4 Operation .......................................................................................................................................................... E2
E.5 DC Power Over- and Under- Voltage Protection ............................................................................................. E2
E.6 Line Power/DC Input Power Switching ........................................................................................................... E3
Appendix F, Alphabetical Listing of Commands
Index
Warranty...................................................................................................................................... End of Manual

TABLE OF CONTENTS
vii
GENERAL SAFETY PRECAUTIONS
The equipment described in this manual has been designed in accordance with EN61010 "Safety
requirements for electrical equipment for measurement, control and laboratory use", and has been
supplied in a safe condition. To avoid injury to an operator or service technician the safety precautions
given below, and throughout the manual, must be strictly adhered to, whenever the equipment is
operated, serviced or repaired. For specific safety details, please refer to the relevant sections within
the manual.
The equipment is intended solely for electronic measurement and should be used for no other purpose.
SIGNAL RECOVERY accepts no responsibility for accidents or damage resulting from any failure to
comply with these precautions.
Grounding
To minimize the hazard of electrical shock, it is essential that the equipment be connected to a
protective ground through the AC supply cable. The continuity of the ground connection should be
checked periodically.
AC Supply Voltage
Never operate the equipment from a line voltage or frequency in excess of that specified. Otherwise,
the insulation of internal components may break down and cause excessive leakage currents.
Fuses
Before switching on the equipment check that the fuses accessible from the exterior of the equipment
are of the correct rating. The rating of the AC line fuse must be in accordance with the voltage of the
AC supply.
Should any fuse continually blow, do not insert a fuse of a higher rating. Switch the equipment off,
clearly label it "unserviceable" and inform a service technician.
Explosive Atmospheres
This equipment must NEVER BE OPERATED in a potentially explosive atmosphere. The equipment is
NOT designed for use in these conditions and could possibly cause an explosion.
Safety Symbols
For the guidance and protection of the user, the following safety symbols may appear on the
equipment, together with details of the hazard where appropriate:
Symbol
Meaning
General safety hazard. Refer to the operating manual for detailed instructions.
Electrical safety hazard. This symbol may appear alongside the general safety
hazard symbol, together with a voltage.
Notes and Cautions
For the guidance and protection of the user, Notes and Cautions appear throughout the manual. The
significance of these is as follows:
NOTES highlight important information for the reader’s special attention.
CAUTIONS guide the reader in avoiding damage to the equipment.

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viii
Avoid Unsafe Equipment
The equipment may be unsafe if any of the following statements apply:
Equipment shows visible damage.
Equipment has failed to perform an intended operation.
Equipment has been stored in unfavorable conditions.
Equipment has been subjected to severe physical stress.
If in any doubt as to the serviceability of the equipment, don't use it. Get it properly checked out by a
qualified service technician.
Live Conductors
When the equipment is connected to its measurement inputs or supply, the opening of covers or
removal of parts could expose live conductors. The equipment must be disconnected from all power
and signal sources before it is opened for any adjustment, replacement, maintenance or repair.
Adjustments, maintenance or repair must only be done by qualified personnel, who should refer to the
relevant maintenance documentation.
Equipment Modification
To avoid introducing safety hazards, never install non-standard parts in the equipment, or make any
unauthorized modification. To maintain safety, always return the equipment to your
SIGNAL RECOVERY service provider for service and repair.
European WEEE Directive
This product is subject to Directive 2002/96/EC of the European Parliament and the Council of the
European Union on waste electrical and electronic equipment (WEEE) and, in jurisdictions adopting
that Directive, is marked as being put on the market after August 13, 2005, and should not be disposed
of as unsorted municipal waste. Please use your local WEEE collection facilities for the disposal of this
product and otherwise observe all applicable requirements.
FCC Notice
This equipment generates, uses, and can radiate radio frequency energy and, if not installed and used
in accordance with this instruction manual, may cause harmful interference with radio communications.
Operation of this equipment in a residential area is likely to cause harmful interference, in which case
the user is required to correct the interference at his own expense.
Acknowledgment
Operation of the Ethernet interface in the model 7270 relies on software code developed by the
Swedish Institute of Computer Science, copyright 2001-2004, all rights reserved. In accordance with
the license under which it is used, we reproduce here the following disclaimer:
THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

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ix
DECLARATION OF CONFORMITY
The directives covered by this declaration
73/23/EEC Low Voltage Equipment Directive, amended by 93/68/EEC
89/336/EEC Electromagnetic Compatibility Directive, amended by 92/31/EEC
& 93/68/EEC
Product(s)
Model 7124 Precision Lock-in Amplifier
Basis on which conformity is being declared
The product(s) identified above comply with the requirements of the EU directives by
meeting the following standards:
BS EN61326:1998 Electrical equipment for measurement control and laboratory use -
EMC requirements; including amendments A1:1998 and A2:2001.
BS EN61010-1:2001 Safety requirements for electrical equipment for measurement,
control and laboratory use.
Accordingly the CE mark has been applied to this product.
Signed
For and on behalf of SIGNAL RECOVERY
Authority: Business Element Manager
Date: January 2009

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x

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 7124 Precision Lock-in Amplifier. It is split into the
following chapters:-
Chapter 1 - Introduction
Provides an introduction to the manual, briefly describes the function of a lock-in
amplifier and the types of measurements it may be used for, and lists the major
specifications of the model 7124.
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 via the built-in 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 panels of both the main
console and the remote connection unit.
Appendix C
Shows the connection diagrams for suitable RS232 null-modem cables to couple the
unit to a compatible computer.
Appendix D
Provides a listing of the instrument settings produced by using the Auto-Default
functions.
Appendix E
Describes how to use the 7124/99 option that allows the 7124 RCU unit to be
powered from external DC power supplied (e.g. batteries).

Chapter 1, INTRODUCTION
1-2
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?
Since their invention back in the 1960's, lock-in amplifiers have been used whenever
the need arises to measure the amplitude and/or phase of a signal of known
frequency in the presence of noise. Unlike other AC measuring instruments they
have the ability to give accurate results even when the noise is much larger than the
signal - in favorable conditions even up to a million times larger.
Early instruments used analog technology, with manual controls and switches, and
with output readings being taken from large panel meters. Later, microprocessors
were added to give more user-friendly operation, digital output displays, and to
support computer control. More recently the analog phase sensitive detectors
forming the heart of the instrument have been replaced by DSP (digital signal
processing) designs, further improving performance.
But the addition of this digital technology has had one unfortunate side effect, which
is that the instrument itself can act as a source of digital clock and switching noise,
which is typically coupled back into the experiment via the signal or internal
oscillator connectors. This noise is of course rejected by the lock-in and generally
does not impair its performance, but the power it dissipates in the sample or device
under test can cause serious problems. This is particularly the case in low
temperature physics experiments.
The model 7124 precision lock-in amplifier is designed to address this problem. It
uses a unique analog fiber optic link to interconnect a remote connection unit (the
7124 RCU), to which the experiment is connected, and a main instrument console. In
normal operation there are no digital clock signals within the 7124 RCU, and so it
can emit no switching noise.
This architecture gives an instrument with all the advantages of the latest DSP
technology for signal detection, and a powerful processor for easy user operation, as
well as the low noise performance that until now has only been available in
instruments of all-analog design.
The model 7124 is therefore particularly suited to work in low temperature physics,
but will be equally useful in many other fields of scientific research, such as optics,
electrochemistry, materials science, fundamental physics and electrical engineering.
In these and other experiments it can function as a:-
AC Signal Recovery Instrument Transient Recorder
Vector Voltmeter Precision Oscillator
Phase Meter Frequency Meter
Spectrum Analyzer Noise Measurement Unit

Chapter 1, INTRODUCTION
1-3
These characteristics, all available in a compact system, make it an invaluable
addition to any laboratory.
1.3 Key Specifications and Benefits
In addition to its unique fiber optic link to isolate the experiment from digital
switching noise, the SIGNAL RECOVERY Model 7124 represents a further
significant advance in the application of DSP technology in the design of a lock-in
amplifier.
Key specifications include:
Analog fiber optic link to eliminate digital switching noise being emitted from
the 7124 RCU connectors
Frequency range: 0.5 Hz to 150.000 kHz
Voltage sensitivity: 10 nV to 1 V full-scale
Current input mode sensitivities: 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-outputs
Very low phase noise of < 0.0001°rms
Output time constant: 10 µs to 100 ks
5-digit output readings
Dual reference mode - allows simultaneous measurement of two signals at
different reference frequencies.
Single and dual harmonic mode - allows simultaneous measurement of up to two
different harmonics of a signal
Tandem demodulation capability - suitable for double demodulation experiments
that would previously have required two lock-in amplifiers
Spectral Display mode shows frequency spectrum of the signal prior to the
demodulators to help in selecting a reference frequency
Virtual reference mode - allows reference free measurements
Direct Digital Synthesizer (DDS) oscillator with variable amplitude and
frequency
Oscillator frequency and amplitude sweep generator
Voltage controlled oscillator frequency and amplitude
8-bit programmable digital I/O port for external system control on the main
console; 8-bit programmable digital output port on the 7124 RCU
Four configurable DAC outputs which can be used as analog signal outputs
and/or as auxiliary DAC outputs
Four auxiliary ADC inputs
Full range of auto functions
Non-volatile memory for 8 complete instrument settings

Chapter 1, INTRODUCTION
1-4
Standard USB, Ethernet, and RS232 interfaces with RS232 daisy-chain
capability for up to 16 instruments.
Large high-resolution color LCD 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
100,000 point internal curve storage buffer

Installation and
Initial Checks Chapter 2
2-1
2.1 Installation
2.1.01 Introduction
Installation of the model 7124 is very straightforward. The main console can be
operated on almost any laboratory bench or be rack mounted, using the optional
accessory kit, at the user's convenience, while the remote connection unit
(7124 RCU) is compact enough to be located close to the experiment. With an
ambient operating temperature range of 0 C to 35 C, both units are highly tolerant
to environmental variables, needing only to be protected from exposure to corrosive
agents and liquids.
The main console 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 these panels and any
adjacent surface.
The 7124 RCU does not use cooling fans and therefore simply needs to be located so
that there is a free flow of air around the unit.
2.1.02 Rack Mounting
An optional accessory kit, part number K02005, is available from
SIGNAL RECOVERY to allow the model 7124 main console to be mounted in a
standard 19-inch rack.
2.1.03 Inspection
Upon receipt the model 7124 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 Plugs
Both the main console and the 7124 RCU are fitted with standard IEC 320 sockets
on their rear panels and suitable line cords are supplied.
2.1.05 Line Voltage Selection and Line Fuses
Before plugging in the line cords, ensure that both the main console and the 7124
RCU are 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 7124 main console and 7124 RCU may be damaged if the
line voltage is set for 110 V AC operation and they are turned on with 220 V AC
applied to the power input connector.
The model 7124 main console and 7124 RCU 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 plug-in

Chapter 2, INSTALLATION AND INITIAL CHECKS
2-2
barrel selectors internal to the line input assemblies on the rear panels of the two
units. Instruments are normally shipped from the factory with the line voltage
selectors 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 assemblies on the rear panels of the instruments (figure 2-1). If the number
showing is incorrect for the local line voltage (refer to table 2-1), then the barrel
selectors will need to be repositioned as follows.
Observing the instrument from the rear, note the plastic door forming part of the
input assembly (figure 2-1). When the line cord is removed from the rear-panel
connectors, the plastic door can be opened outwards by placing a small, flat-bladed
screwdriver in the slot and levering gently. This gives access to the fuse and to the
voltage barrel selector. 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 Assemblies (Left - Main Console; Right - 7124 RCU)
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 1.0 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 0.5 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 AND 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 7124. 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 both the 7124 main console and the 7124 RCU are set to the line
voltage of the power source to be used, as described in section 2.1.05.
2) The Main Console and the RCU are connected together using fiber optic cables.
Before connecting the fiber cables place the main console and RCU in the
locations they are to be used. Always disconnect the fiber cables when relocating
either unit.
3) CAUTION: The tips of the fiber optic cables must be cleaned before attaching
them to the units. This only takes a few seconds and should be repeated every
time they are connected to ensure consistent results.
4) Pre-saturated wipes are supplied for cleaning the fiber optic cables. Make sure
everything is near to hand before opening a pre-saturated wipe as they tend to
dry out fairly quickly.
5) At this point it is a good idea to wash and dry your hands before trying to clean
the fibers.
6) Remove the dust caps from the optical connectors on the rear panels of the main
console and RCU and put them somewhere safe. You will need to replace them
on the sockets whenever you disconnect the fibers.
7) Identify the duplex cable labeled with OSC and SIG. Remove the ferrule caps
and clean the tips of the ferrules with a pre-saturated wipe. Give the connector a
quick wave in the air to ensure the solvent has evaporated and connect to the
corresponding sockets on the rear of the main console, as follows:
Fiber End 1 Label 7124 Console
#1-2 OSC OSC OUT
#1-2 SIG SIG IN

Chapter 2, INSTALLATION AND INITIAL CHECKS
2-4
The connectors have a spring bayonet action, similar to that of a BNC connector
8) Repeat using the duplex cable labeled REF and CON, as follows:
Fiber End 1 Label 7124 Console
#2-1 CON CONTROL
#2-2 REF REF IN
9) Use the same cleaning procedure with the connectors at the other ends of the two
duplex cables, and then connect them to corresponding sockets on the rear of the
RCU, as follows:
Fiber End 2 Label 7124 RCU
#1-2 OSC OSC IN
#1-2 SIG SIG OUT
#2-1 CON CONTROL
#2-2 REF REF OUT
NOTE: Handle the fiber optic cables with care. Do not touch or otherwise
contact the exposed ends of the fiber connectors, and always fit the connector
covers when the fibers are not connected. Any dirt or contamination of the
fibers will impair instrument calibration and may prevent satisfactory
operation. Such contamination is not covered under the instrument warranty.
Retain the connector covers from the 7124 main console and the 7124 RCU for
use when needed.
10) With both rear-panel mounted power switches set to 0(off), plug in the line
cords to an appropriate line power source.
11) Turn the model 7124 RCU power switch to the I (on) position.
12) Turn the 7124 main console power switch to the I (on) position.
13) The main console 's front panel display will now briefly display the following:-
Figure 2-2, Opening Display
14) 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.