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Model 7220
DSP Lock-in Amplifier
Instruction Manual
190171-A-MNL-C
Copyright © 1996 EG&G INSTRUMENTS CORPORATION
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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. Declaration of Conformity This product conforms to EC
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Table of Contents Table of Contents 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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TABLE OF CONTENTS 3.3.02 Relative Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9 3.4 Full-Scale Sensitivity and AC Gain Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9 3.5 Dynamic Reserve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9 3.6 System Updates and R
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TABLE OF CONTENTS 4.2.07 PREAMP POWER Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7 4.2.08 REF MON Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7 4.2.09 REF TTL Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7 4.2.10 SIG MON Connector . . . . . . . . . . . .
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TABLE OF CONTENTS 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 . .
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TABLE OF CONTENTS Appendix B, Pinouts B.1 RS232 Connector Pinout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1 B.2 Preamplifier Power Connector Pinout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1 B.3 Digital Output Port Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2 Appendix C, Dem
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TABLE OF CONTENTS vi
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Introduction Chapter 1 1.1 How to Use This Manual This manual gives detailed instructions for setting up and operating the EG&G Instruments Model 7220 Digital Signal Processing (DSP) dual phase 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 7220. Chapter 2 - Installation and I
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Chapter 1, INTRODUCTION 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 Gives an alphabetical listing of the computer commands for easy reference. Appendix F Provides a listing of the instrument settings produced by using the default setting function. If you are a new user, it is suggested that you unpack the instrument and carry out the procedure in chapter 2 to check that it is working satisf
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Chapter 1, INTRODUCTION 1.3 Key Specifications and Benefits The EG&G Instruments Model 7220 represents the latest in DSP Lock-in Amplifier technology at an affordable price, and offers:- n Frequency range: 0.001 Hz to 120 kHz n Voltage sensitivity: 20 nV to 1 V full-scale n Current input mode sensitivities: 20 fA to 1 μA full-scale 20 fA to 10 nA full-scale n Line frequency rejection filter n Dual phase demodulator with X-Y and R-θ θ θ θ θ outputs o rms n Very low phase noise of < 0.0001 n 5-di
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Chapter 1, INTRODUCTION 1-4
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Installation & Initial Checks Chapter 2 2.1 Installation 2.1.01 Introduction Installation of the model 7220 in the laboratory or on the production line is very simple. Because of its low power consumption, the model 7220 does not incorporate forced-air ventilation. 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 o o operating temperature range of 0 C to 35 C, it is highly tolerant to environmental
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Chapter 2, INSTALLATION AND INITIAL CHECKS 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 fo
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Chapter 2, INSTALLATION AND INITIAL CHECKS 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 required current rating 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 7220. In
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Chapter 2, INSTALLATION AND INITIAL CHECKS the CONTROL SETUP menu is displayed, which will look similar to the following:- Figure 2-3, Control Setup Menu 7) Press one of the keys on the right-hand side of the left-hand display once. This will set all the instrument’s controls and displays to a known state. The displays will revert to the normal mode, with the left-hand panel showing the AC Gain and Full Scale Sensitivity controls and the right-hand one the instrument’s outputs in the form of mag
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Technical Description Chapter 3 3.1 Introduction The model 7220 lock-in amplifier is capable of outstandingly good signal recovery performance, provided that it is operated correctly. This chapter describes the design of the instrument, enabling the best use to be made of its facilities. Of particular importance is the correct adjustment of the AC Gain parameter, described in section 3.2.04. 3.2 Principles of Operation 3.2.01 Block Diagram The model 7220 utilizes two digital signal processors, a
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Chapter 3, TECHNICAL DESCRIPTION 3.2.02 Signal-Channel Inputs The signal input amplifier may be configured for either single-ended or differential voltage mode operation, or single-ended current mode operation. In voltage mode a choice of AC or DC coupling is available and the input may be switched between FET and bipolar devices. In current mode two conversion gains are selectable to allow for optimum matching to the signal input. In both modes the input connector “shells” may be either floated
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Chapter 3, TECHNICAL DESCRIPTION The primary purpose of the DC coupling facility is to enable the use of the instrument at reference frequencies below 0.5 Hz. It may also be used to reduce the effect of phase and magnitude errors introduced by the AC coupling circuitry below a few hertz. However, the use of DC coupling introduces serious problems where the source has a DC offset or is of such high impedance that bias currents cause significant offsets. In these cases it may be necessary to inclu
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Chapter 3, TECHNICAL DESCRIPTION 3.2.04 AC Gain The signal channel contains a number of analog filters and amplifiers, the gain of which are defined by the “AC Gain” parameter, which is specified in terms of decibels (dB). For each value of AC Gain there is a corresponding value of the INPUT LIMIT parameter, which is the maximum instantaneous (peak) voltage or current that can be applied to the input without input overload, as shown in table 3-1 below. It is a basic property of the DSP lock-in a
