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Ametek 7280 Instruction Manual

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

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Summary of Contents for Ametek 7280

  • Page 1 Model 7280 Wide Bandwidth DSP Lock-in Amplifier Instruction Manual 190398-A-MNL-C Copyright © 2005 AMETEK ADVANCED MEASUREMENT TECHNOLOGY, INC...
  • Page 2 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.

  • Page 3: Table Of Contents

    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........................1-3 Chapter Two, Installation & Initial Checks 2.1 Installation ................................ 2-1 2.1.01 Introduction ............................. 2-1 2.1.02 Rack Mounting ............................
  • Page 4 TABLE OF CONTENTS 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 ................................
  • Page 5 TABLE OF CONTENTS 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 ............................
  • Page 6 TABLE OF CONTENTS 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..........................
  • Page 7 TABLE OF CONTENTS 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...
  • Page 8 TABLE OF CONTENTS...

  • Page 9: How To Use This Manual

    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...

  • Page 10: What Is A Lock-In Amplifier

    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...

  • Page 11: Key Specifications And Benefits

    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.
  • Page 12 Chapter 1, INTRODUCTION 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...

  • Page 13: Installation

    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.
  • Page 14 Chapter 2, INSTALLATION & INITIAL CHECKS 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.

  • Page 15: Initial Checks

    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.
  • Page 16 Chapter 2, INSTALLATION & INITIAL CHECKS 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.
  • Page 17 Chapter 2, INSTALLATION & INITIAL CHECKS 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...

  • Page 18: Line Frequency Filter Adjustment

    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...
  • Page 19 Chapter 2, INSTALLATION & INITIAL CHECKS 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.
  • Page 20 Chapter 2, INSTALLATION & INITIAL CHECKS...

  • Page 21: Introduction

    3.2.02 Single Reference / Dual Reference Conventionally, a lock-in amplifier makes measurements such as signal magnitude, phase, etc. on the applied signal at a single reference frequency. In the model 7280 this is referred to as the single reference mode.

  • Page 22: Internal / External Reference Mode

    3.3 Principles of Operation 3.3.01 Block Diagram The model 7280 uses digital signal processing (DSP) techniques implemented in field-programmable gate arrays (FPGA), a microprocessor and very low-noise analog circuitry to achieve its specifications. A block diagram of the instrument is shown in figure 3-1.

  • Page 23: Signal Channel Inputs

    Chapter 3, TECHNICAL DESCRIPTION Figure 3-1, Model 7280 - Block Diagram 3.3.02 Signal Channel Inputs The signal input amplifier can be set 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 using an FET input device.

  • Page 24: Line Frequency Rejection Filter

    Chapter 3, TECHNICAL DESCRIPTION single-ended signals, subject to the limitation that the user must allow for the signal inversion (equivalent to a 180° phase-shift) which it introduces when reading the outputs. Input Connector Shell, Ground / Float The input connector shells may be connected either directly to the instrument's chassis ground or floated via a 1 kΩ...
  • Page 25 Chapter 3, TECHNICAL DESCRIPTION parameter, which is the maximum instantaneous (peak) voltage or current that can be applied to the input without causing input overload, as shown in table 3-1 below. AC Gain (dB) INPUT LIMIT (mV) 1600 Table 3-1, Input Limit vs. AC Gain It is a basic property of the digital signal processing (DSP) lock-in amplifier that the best demodulator performance is obtained by presenting as large a signal as possible to the main analog-to-digital converter (ADC).

  • Page 26: Anti-Aliasing Filter

    For the benefit of users who prefer to have the AC Gain value expressed in decibels, the model 7280 displays the current value of Dynamic Reserve (DR) in this form, on the input full-scale sensitivity control, for values up to 100 dB. Above 100 dB the legend changes to “DR>100”.

  • Page 27: Main Analog-To-Digital Converter

    Chapter 3, TECHNICAL DESCRIPTION bandwidth. It should be noted that the dynamic range of a lock-in amplifier is normally so high that practical anti-alias filters are not capable of completely removing the effect of a full-scale alias. For instance, even if the filter gives 100 dB attenuation, an alias at the input limit and at the reference frequency will give a one percent output error when the dynamic reserve is set to 60 dB, or a ten percent error when the dynamic reserve is set to 80 dB.

  • Page 28: Phase-Shifter

    Chapter 3, TECHNICAL DESCRIPTION waveform at the selected harmonic of the reference frequency. Dual harmonic mode operates in a similar way to dual reference mode, but in this case the reference circuit generates phase values for both of the selected harmonics of the reference frequency. Dual harmonic mode may therefore be used with either internal or external references.

  • Page 29: Internal Oscillator - General

    The model 7280, in common with many other lock-in amplifiers, incorporates an internal oscillator which may be used to drive an experiment. However, unlike most other instruments, the oscillator in the model 7280 is digitally synthesized with the result that the output frequency is extremely accurate and stable. The oscillator operates over the same frequency range as the lock-in amplifier, that is 500 mHz to 2.0 MHz, and is implemented using a dedicated direct digital synthesis circuit.

  • Page 30: Demodulators

    Chapter 3, TECHNICAL DESCRIPTION It is important to note that this type of phase-locked loop, unlike a conventional edge- triggered type using a clean reference, does not automatically re-acquire lock after it has been lost. Lock can be lost as a result of a signal channel transient or a phase reversal of the signal, in which case it may be necessary to repeat the lock acquisition procedure.

  • Page 31: Output Processor - Output Filters

    12 dB per octave. These terms have become part of the accepted terminology relating to lock-in amplifier output filters and are used in the model 7280 to apply to the envelope of the frequency response function of the digital finite impulse response (FIR) output filters. Accordingly the front-panel control which selects the configuration of the output filters is labeled SLOPE and the options are labeled 6, 12, 18, 24 dB/octave.

  • Page 32: Output Processor - Output Offset And Expand

    Chapter 3, TECHNICAL DESCRIPTION Where random noise is relatively small, synchronous filter operation gives a major advantage in low-frequency measurements by enabling the system to give a constant output even when the output time constant is equal to only 1 reference cycle. 3.3.14 Output Processor - Output Offset and Expand Following the output filter, an output offset facility enables ±300% full-scale offset to be applied to the X, Y or both displays and to the analog outputs.

  • Page 33: Output Processor - Noise Measurements

    Chapter 3, TECHNICAL DESCRIPTION as a result of the inherent non-linearity of the magnitude formula: this error is always positive and its value, expressed as a fraction of the signal level, is half the ratio of the mean-square value of the noise to the square of the signal. These considerations lead to the conclusion that when the magnitude output is being used, the time constants of the demodulator should be set to give the required signal- to-noise ratio at the X channel and Y channel demodulator outputs;...

  • Page 34: Auxiliary Analog Inputs And Outputs (Adcs And Dacs)

    3.3.17 Auxiliary Analog Inputs and Outputs (ADCs and DACs) The model 7280 incorporates four auxiliary ADC inputs of conventional sampled design offering a resolution of 1 mV in ±10.000 V. These converters may be used at slow sample rates for digitizing slowly changing or DC signals which are associated...

  • Page 35: Main Microprocessor - Spectral Display

    In some cases it can be useful to determine the spectral power distribution of the input signal. The model 7280 can do this, since when the Spectral Display menu is selected, the output processor performs a discrete Fourier transform on the digitized input signal and displays the resulting spectrum.
  • Page 36 Chapter 3, TECHNICAL DESCRIPTION Auto-Sensitivity This function only operates when the reference frequency is above 1 Hz. A single Auto-Sensitivity operation consists of decreasing the full-scale sensitivity range if the magnitude output is greater than 90% of full-scale, or increasing the full-scale sensitivity range if the magnitude output is less than 30% of full-scale.

  • Page 37: General

    Auto-Sensitivity followed by Auto-Phase functions. Auto-Default With an instrument of the design of the model 7280, where there are many controls of which only a few are regularly adjusted, it is very easy to overlook the setting of one of them.

  • Page 38: Power-Up Defaults

    Chapter 3, TECHNICAL DESCRIPTION signal channel and the reference channel. The resulting typical accuracy is ±0.3 percent of the full-scale sensitivity and ±0.25 degree respectively. When the higher values of AC Gain are in use, the errors tend to increase above 25 kHz. 3.4.02 Power-up Defaults All instrument settings are retained when the unit is switched off.

  • Page 39: Front Panel

    4.1 Front Panel Figure 4-1, Model 7280 Front Panel Layout As shown in figure 4-1, the model 7280's front panel has four BNC connectors, a 320 × 240 pixel electroluminescent screen, ten double and four single keys positioned adjacent to the screen, four cursor-movement keys and a 12-button keypad.

  • Page 40: Electroluminescent Screen

    The model 7280 is a very sophisticated instrument with many features and consequently had the traditional approach of using one button per control been adopted the front panel would have been very large.
  • Page 41 In some cases it is useful to be able to quickly adjust a control in equal increments, for example when monitoring the effect of changing the oscillator frequency about a given value. This is easily done in the model 7280 using a control setting feature known as Active Cursor operation.
  • Page 42 Chapter 4, FRONT AND REAR PANELS Step 3 Press the key to change the digit to the required value. Figure 4-3, Active Cursor Activation As an example of this operation, suppose that the oscillator frequency is 1000.000 Hz and it is required to change it to 1001.000 Hz. Simultaneously press both keys adjacent to the oscillator frequency display.

  • Page 43: Help Key

    To exit the Help screens and return to normal operation press the HELP key again. 4.1.06 MENU Key The model 7280 is controlled by a series of on-screen menus. When the Main Display is shown the MENU key is used to access Main Menu 1, from which other menus may be accessed.

  • Page 44: Rear Panel

    Brief descriptions of these are given in the following text. 4.2.01 Line Power Switch 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.

  • Page 45: Gpib Connector

    Chapter 4, FRONT AND REAR PANELS way. Each unit must be set to a unique address (see section 5.3.22). Pinouts for this connector are given in appendix B. 4.2.05 GPIB Connector The GPIB interface connector conforms to the IEEE-488 1978 Instrument Bus Standard.

  • Page 46: Adc 1, Adc 2, Adc 3 And Adc 4 Connectors

    Chapter 4, FRONT AND REAR PANELS to provide up to 3 × full-scale overload capability. 4.2.12 ADC 1, ADC 2, ADC 3 and ADC 4 Connectors The input voltages at these connectors may be digitized using the auxiliary ADCs and read either from the front panel or by the use of a computer command. The input voltages are sampled and held when the ADC is triggered, and several different trigger modes are available.

  • Page 47: Introduction

    20 kHz, but units fitted with the 7280/99 option allow operation to 800 kHz and those with the 7280/98 option allow operation to 2.0 MHz The sections which follow describe the menus as they appear when the unit is being...

  • Page 48: Menu Structure

    Chapter 5, FRONT PANEL OPERATION the time for instrument control and display of data, through to those menus accessing controls which typically only need changing occasionally. The menus for the other three operating modes are then described, since in some cases these differ from those used in single reference mode to accommodate the additional controls and displays that are needed.

  • Page 49: Menu Descriptions - Single Reference Mode

    Chapter 5, FRONT PANEL OPERATION Some menus, such as the Oscillator menu, have further sub-menus which are discussed later. These have been omitted from figure 5-1 for the sake of clarity. 5.3 Menu Descriptions - Single Reference Mode 5.3.01 Main Display Figure 5-2, Main Display - Single Reference Mode The Main Display always appears on power-up and is similar to that shown in figure 5-2 above.
  • Page 50 Chapter 5, FRONT PANEL OPERATION Output Description Title Numeric Displays only: Resultant (Magnitude) output as a percentage of full-scale sensitivity Noise output as a percentage of full-scale sensitivity θ° Phase output in degrees X channel output as a percentage of full-scale sensitivity Y channel output as a percentage of full-scale sensitivity Resultant (Magnitude) output in volts or amps Numeric and Bar-Graph Displays:...

  • Page 51: Control Selection Menu

    Chapter 5, FRONT PANEL OPERATION Controls AC GAIN The AC Gain control is always displayed in the top left-hand corner of the Main Display. If the automatic AC Gain control is turned off (using the Signal Channel menu - see section 5.3.04), then this control allows the AC Gain to be adjusted from 0 dB to 66 dB in 6 or 8 dB steps, although not all settings are available at all full-scale sensitivity settings.
  • Page 52 Chapter 5, FRONT PANEL OPERATION full-scale current sensitivity may be set to any value between 1 pA and 100 µA (wide bandwidth mode), 10 fA and 1 µA (normal mode), or 10 fA and 10 nA (low-noise mode), in a 1-2-5 sequence. The number reported after the letters DR is the instrument's Dynamic Reserve, expressed in decibels, as calculated by the following equation:- ACGain (in dB)

  • Page 53: Main Menu 1

    Chapter 5, FRONT PANEL OPERATION RELOCK EXT. REFERENCE The 7280 includes frequency-dependent calibration parameters. When operating in Internal reference mode the correct parameters can be chosen because the reference frequency is equal to the specified oscillator frequency. In External reference mode the applied frequency is measured, and the measured value is used to select the correct parameters.

  • Page 54: Signal Channel Menu

    Chapter 5, FRONT PANEL OPERATION Figure 5-4, Main Menu Main Menu 1 is used to access all of the remaining instrument controls via a series of sub-menus, which are selected simply by pressing the key adjacent to the required menu. These sub-menus are described in the following sections. 5.3.04 Signal Channel Menu When Main Menu 1 is displayed, pressing a key adjacent to the Signal Channel item accesses the Signal Channel menu, which is shown in figures 5-5 and 5-6.
  • Page 55 Chapter 5, FRONT PANEL OPERATION Figure 5-6, Signal Channel Menu - Current Input Mode The Signal Channel menu has five controls affecting the instrument's signal input channel. Changes to the setting of these controls can be made by using the adjacent keys, with the currently active selection being shown in reversed text.
  • Page 56 Chapter 5, FRONT PANEL OPERATION The signal channel input is an inverting single-ended voltage input to the BNC connector on the front panel marked B/I. In this setting the signal channel input is a differential voltage input connected to the BNC connectors on the front panel marked A and B/I. NONE The input is disconnected in this setting.

  • Page 57: Reference Channel Menu

    Chapter 5, FRONT PANEL OPERATION AUTO AC GAIN OFF In this setting the AC Gain may be manually adjusted from the Main Display. AUTO AC GAIN ON In this setting the AC Gain value is automatically selected by the instrument, depending on the full-scale sensitivity.

  • Page 58: Output Filters Menu

    Chapter 5, FRONT PANEL OPERATION EXT-F In this setting the reference channel is configured to accept a suitable external reference source applied to the front panel REF IN input connector REF HARMONIC This control allows selection of the harmonic of the reference frequency at which the lock-in amplifier will detect.

  • Page 59: Output Offset & Expand Menu

    Chapter 5, FRONT PANEL OPERATION channel output filters. Changes to the setting of these controls can be made by using the adjacent keys. TIME CONSTANT This control, which duplicates the Main Display TIME CONSTANT control, is used to set the time constant of the output filters. SLOPE The roll-off of the output filters is set, using this control, to any value from 6 dB to 24 dB/octave, in 6 dB steps.
  • Page 60 Chapter 5, FRONT PANEL OPERATION The Offset & Expand menu has five controls affecting the instrument's X channel and Y channel outputs. Changes to the setting of these controls can be made by using the adjacent keys, with the currently active selection being highlighted. X OFFSET and Y OFFSET These controls, which duplicate the Main Display X OFFSET and YOFFSET controls, allow manual adjustment of the X channel and Y channel output offsets.

  • Page 61: Output Equations Menu

    Chapter 5, FRONT PANEL OPERATION 5.3.08 Output Equations Menu When Main Menu 1 is displayed, pressing a key adjacent to the Output Equations item opens the Output Equations Menu, shown in figure 5-10. Figure 5-10, Output Equations Menu The Output Equations menu is used to define more complex calculations on the instrument outputs than are possible using the basic ratio and log ratio options.

  • Page 62: Oscillator Menu

    Chapter 5, FRONT PANEL OPERATION The select keys are used to highlight the required variable, and then the adjust keys are used to change it. The values C1 and C2 within each equation are user-defined integer constants and are adjusted using the two corresponding keys.

  • Page 63: Frequency Sweep Menu

    Chapter 5, FRONT PANEL OPERATION figure 5-12. Note that as with the main menu structure, shown in figure 5-1, it is possible to return to the Main Display from any menu by pressing the Main Display key, but this has been omitted from figure 5-12 for the sake of clarity. Figure 5-12, Oscillator Menu Structure Changes to the setting of the controls on the Oscillator menu can be made by using the adjacent...
  • Page 64 Chapter 5, FRONT PANEL OPERATION Figure 5-13, Frequency Sweep Menu The Frequency Sweep menu has nine controls affecting the instrument's internal oscillator, and one link to the Curve Buffer menu (see section 5.3.22). Changes to the setting of the controls can be made by using the adjacent keys.
  • Page 65 Chapter 5, FRONT PANEL OPERATION TIME/STEP This control defines the time that the oscillator frequency remains at each step of the complete frequency sweep. The range of available values depends on the setting of the OPERATING MODE control on the Analog Outputs Menu (section 5.3.18), as follows: Operating Mode Time/Step...

  • Page 66: Amplitude Sweep Menu

    Chapter 5, FRONT PANEL OPERATION present frequency. The control changes to PAUSE Note that if the oscillator amplitude sweep (see section 5.3.11) is also armed then the controls that start, pause, continue and stop on the Frequency Sweep menu will also control the amplitude sweep.
  • Page 67 Chapter 5, FRONT PANEL OPERATION Figure 5-14, Amplitude Sweep Menu The Amplitude Sweep menu has eight controls affecting the instrument's internal oscillator, and one link to the Curve Buffer menu (see section 5.3.22). Changes to the setting of the controls can be made by using the adjacent keys.
  • Page 68 Chapter 5, FRONT PANEL OPERATION TIME/STEP This control defines the time that the oscillator frequency remains at each step of the complete frequency sweep. The range of available values depends on the setting of the OPERATING MODE control on the Analog Outputs Menu (section 5.3.18), as follows: Operating Mode Time/Step...

  • Page 69: Auto Functions Menu

    Chapter 5, FRONT PANEL OPERATION CONTINUE Pressing the adjacent key restarts the paused amplitude sweep from the present amplitude. The control changes to PAUSE Note that if the oscillator frequency sweep (see section 5.3.10) is also armed then the controls that start, pause, continue and stop on the Amplitude Sweep menu will also control the frequency sweep.
  • Page 70 Chapter 5, FRONT PANEL OPERATION AUTO PHASE In an Auto-Phase operation the value of the signal phase with respect to the reference is computed and an appropriate phase-shift is then introduced into the reference channel so as to bring the difference between them to zero. The intended result is to null the output of the Y channel while maximizing the output of the X channel.

  • Page 71: Configuration Menu

    Auto-Phase. AUTO DEFAULT With an instrument of the design of the model 7280, where there are many controls of which only a few are regularly adjusted, it is very easy to overlook the setting of one of them.
  • Page 72 Chapter 5, FRONT PANEL OPERATION Figure 5-16, Configuration Menu, Single Reference Mode The Configuration menu has three controls used to set the instrument’s basic operating mode and controls to adjust the line-frequency rejection filter’s center frequency, the Noise Measurement mode and the Noise Buffer Length. Changes to the setting of these controls can be made by using the adjacent keys.
  • Page 73 Chapter 5, FRONT PANEL OPERATION The controls on the Configuration menu operate as follows. LINE FREQUENCY This control is used to set the center frequency of the line frequency rejection filter, and so should be set to the prevailing line frequency, i.e. 50 or 60 Hz. NOISE MEASUREMENT This control is used to configure the instrument for noise measurements.

  • Page 74: Communications Menu

    Chapter 5, FRONT PANEL OPERATION Turn display off Pressing this key turns off the display panel. Press any key to turn it back on, when the display reverts to the Main Display. Pressing the Previous Menu key returns control to the Main Menu 1 The Virtual Reference, Dual Reference and Dual Harmonic modes are discussed later in sections 5.4, 5.5 and 5.6 respectively.
  • Page 75 Chapter 5, FRONT PANEL OPERATION Figure 5-19, RS232 Settings Menu This menu has seven controls affecting the RS232 computer interface, as follows:- BAUD RATE This control sets the baud rate to one of the following values:- Baud Rate (bits per second) 134.5 1200 1800...

  • Page 76: Gpib Settings Menu

    ECHO This control, when switched on, causes the model 7280 to echo each character received over the RS232 interface back to the controlling computer. The computer should wait until the echoed character is returned before it sends the next character.
  • Page 77 Chapter 5, FRONT PANEL OPERATION Figure 5-20, GPIB Settings Menu This menu has five controls affecting the GPIB computer interface and a key for accessing the Communications Monitor display, as follows:- GPIB ADDRESS This control sets the GPIB communications address to any value between 0 and 31. Each instrument used on the GPIB bus must have a unique address setting.

  • Page 78: Communications Monitor

    Chapter 5, FRONT PANEL OPERATION Decimal Value Status Byte command complete invalid command command parameter error reference unlock overload new ADC values available after external trigger asserted SRQ data available Hence, for example, if the SRQ mask byte is set to decimal 16 (i.e. bit 4 asserted), a service request would be generated as soon as an overload occurred;...

  • Page 79: Analog Outputs Menu - Single & Virtual Reference Modes

    Chapter 5, FRONT PANEL OPERATION Figure 5-21, Communications Monitor The monitor is useful when attempting to establish communications via the computer interfaces for the first time, or if a problem is suspected. The Input side of the display shows all of the characters that have been received from the interface, whether valid or not.
  • Page 80 Chapter 5, FRONT PANEL OPERATION Figure 5-22, Analog Outputs Menu, Normal Operating Mode, Single/Virtual Reference Modes The Analog Outputs menu has three controls, changes to the setting of which can be made by using the adjacent keys. OPERATING MODE This control determines the position from which the analog outputs are derived in the circuit (see figure 3-1), and hence the rate at which they are updated.
  • Page 81 Chapter 5, FRONT PANEL OPERATION Y% (2.5V fs) When set to Y% the corresponding CH1/CH2 connector on the rear panel will output a voltage related to the Y%fs front panel display as follows:- CH1/2 Voltage +300 7.5 V +100 2.5 V 0.0 V -100 -2.5 V...
  • Page 82 Chapter 5, FRONT PANEL OPERATION Note: When NOISE is selected as an output, the Noise Measurement Mode (Configuration Menu) must be ON. If it is not, a warning message is displayed which offers the option of turning it on or deselecting NOISE as an analog output.
  • Page 83 Chapter 5, FRONT PANEL OPERATION input, then the value of LOG RATIO would be:- RATIO 1.000 RATIO 0.301 The relationship between the voltage at the CH1/CH2 connector and the LOG RATIO value is defined as follows:- LOG RATIO CH1/2 Voltage +2.000 2.000 V 0.0 V...

  • Page 84: Options Menu

    Chapter 5, FRONT PANEL OPERATION The available options for the CH1 ANALOG OUTPUT and CH2 ANALOG OUTPUT controls are reduced to the following: CH1 ANALOG OUTPUT In the Fast mode, this can only be set to: X% (2.5V fs) The CH1 connector on the rear panel will output a voltage related to the X%fs front panel display as follows:- CH1/2 Voltage +300...

  • Page 85: Spectral Display

    Chapter 5, FRONT PANEL OPERATION Figure 5-23, Options Menu The options menu is used to install additional firmware options and shows which options are already fitted. If an option is purchased at the same time as the instrument, then the factory will install it and no further action is required. If however it is bought at a later date then the user will need to provide details of the instrument's serial number with his order.
  • Page 86 15 kHz, the nominal range is 0 kHz to 3.43 MHz, although frequencies above 2 MHz are not usually of interest since they lie outside the frequency range of signals that the 7280 can measure. With the finest resolution of 3 kHz, the display range is nominally 687 kHz.

  • Page 87: Main Menu 2

    Chapter 5, FRONT PANEL OPERATION RUN FFT When the key adjacent to the Run FFT control is pressed, the instrument acquires a new set of data, performs an FFT on it and displays the resulting spectrum. A change in the reference frequency also causes the displayed spectrum to be updated.

  • Page 88: Curve Buffer Menu

    Chapter 5, FRONT PANEL OPERATION Figure 5-25, Main Menu 2 Main Menu 2 has keys used to access the extended features found in the model 7280, via a series of sub-menus. The relationship of these sub-menus to Main Menu 2 is shown in figure 5-26.
  • Page 89 Chapter 5, FRONT PANEL OPERATION Figure 5-27, Curve Buffer Menu The curve buffer menu has three controls affecting the instrument's internal 32768 point curve buffer, two status indicators and keys to access the Curve Select sub- menu and menus associated with the oscillator.. TIME PER POINT This control defines the interval between each data point in the curve buffer.
  • Page 90 Chapter 5, FRONT PANEL OPERATION sweep, in single-sweep mode, the number will be the same as the Curve Length control, whereas in multi-sweep mode the number increments continuously. SWEEPS COMPLETED This shows the number of completed sweeps, where one sweep is equal to the Length control setting.

  • Page 91: Curve Select Menu

    Chapter 5, FRONT PANEL OPERATION by pressing Cont. Multi Sweep. CONT. MULTI SWEEP This key restarts data acquisition from the current point. STOP MULTI SWEEP This key stops data acquisition at the current point. Data already acquired remains in the curve buffer. One of the following links to other menus will also be shown, allowing quick access between the oscillator frequency and amplitude sweep setup menus and the curve buffer, which is useful when defining oscillator sweeps linked to the curve buffer.

  • Page 92: Single Graph Menu

    Chapter 5, FRONT PANEL OPERATION that can be stored to the curve buffer, arranged in four rows of four columns. Three controls allow between one and sixteen of these data types to be selected for storage, with those that are selected being indicated by being shown in reversed text. MOVE POINTER This control allows the pointer to be moved to any one of the possible data types.
  • Page 93 Chapter 5, FRONT PANEL OPERATION representing zero. If curve storage is already running, or if there is data in the curve buffer, then a curve will be displayed with the most recent value at the right-hand side of the screen. Figure 5-27 shows the layout of the Single Graph menu.

  • Page 94: Double Graph Menu

    Chapter 5, FRONT PANEL OPERATION moved fully to the left then the displayed data scrolls to the right in groups of ten points, allowing earlier data to be shown. If acquisition is in progress then the cursor is automatically positioned at the right- hand side of the display area and cannot be moved.

  • Page 95: User Settings Menu

    Chapter 5, FRONT PANEL OPERATION As in single graph mode, there is no facility for adjusting the x-axis scale, which always shows up to 243 points. Furthermore both the upper and lower curves are shown over the same range of points; it is not possible, for example, to show Curve 1 for data points 1 to 243 and Curve 2 for points 243 to 486.

  • Page 96: Auxiliary I/O Menu

    Chapter 5, FRONT PANEL OPERATION Pressing the Save settings, Restore settings or Delete memory keys causes Select Memory Number and the Memory keys to be displayed. For example, when the Save settings key is pressed, the menu changes to that shown in figure 5-31. Figure 5-31, User Settings Menu - Save Settings To use the user settings feature, proceed as follows:...
  • Page 97 Chapter 5, FRONT PANEL OPERATION Figure 5-32, Auxiliary I/O Menu The Auxiliary I/O menu has five controls, which are used to set the voltages appearing at the DAC1 and DAC2 connectors on the rear panel and configure the auxiliary ADC trigger mode, four displays to show the voltages at the rear-panel ADC1 to ADC4 inputs and a key access a further sub-menu.
  • Page 98 Chapter 5, FRONT PANEL OPERATION BURST ADC1&2 A burst of conversions at exactly 56 µs/point (approximately 18 kHz) is performed on both ADC1 and ADC2, either on receipt of the TADC3 computer command or when the Trigger Burst Mode key is pressed. The results are stored to the curve buffer, with the number of conversions being set by the curve length control on the Curve Buffer menu - see section 5.3.22.

  • Page 99: Digital Port Menu

    Chapter 5, FRONT PANEL OPERATION 5.3.28 Digital Port Menu When the Auxiliary I/O menu is displayed, pressing a key adjacent to the Digital Port item accesses the Digital Port menu, shown in figure 5-33. Figure 5-33, Digital Port Menu The Digital Port menu allows the operating mode of each of the eight pins of the DIGITAL I/O connector on the rear panel to be set and its logic status to be set and read.

  • Page 100: Menu Descriptions - Virtual Reference Mode

    Chapter 5, FRONT PANEL OPERATION 5.4 Menu Descriptions - Virtual Reference Mode 5.4.01 Virtual Reference Menus The virtual reference mode is very similar to the single reference mode with internal reference, and is the simplest of the three additional modes of operation. NOTE: This mode is only suitable for signals at frequencies between 100 Hz and 2.0 MHz.
  • Page 101 Chapter 5, FRONT PANEL OPERATION This menu has six controls affecting the virtual reference mode, a single display, and two keys to establish virtual lock. The left-hand side of the display is used for the semi-automatic method of establishing Virtual Reference mode, with the right-hand side being used for the manual mode.

  • Page 102: Main Display - Virtual Reference Mode

    Chapter 5, FRONT PANEL OPERATION NOTE: If the full-scale sensitivity is set so that the signal is less than 50% full- scale then it will not be found. START FREQUENCY Once the Time Constant and Sensitivity Controls have been set to suitable values, the Start Frequency control should be slowly adjusted from below the expected signal frequency, until the Magnitude display reads in excess of 50%.

  • Page 103: Configuration Menu - Virtual Reference Mode

    5.5 Menu Descriptions - Dual Reference Mode 5.5.01 Dual Reference Setup Menu The dual reference mode allows the model 7280 to measure simultaneously signals applied to the signal input at two different reference frequencies. One reference must be supplied to the external reference input, and the second has to be the internal oscillator.

  • Page 104: Dual Reference Main Display

    Chapter 5, FRONT PANEL OPERATION During dual reference mode operation, some of the control and display menus differ from those used for single reference mode, so these are described in the following sections. The remaining menus operate in the same way as in single reference mode, as already described in section 5.3.
  • Page 105 Chapter 5, FRONT PANEL OPERATION internal oscillator is set to 15 kHz, the unit will measure signals at both 1 kHz and 15 kHz. The Sensitivity 1, Time Constant 1 and Ref Phase 1 controls will affect the signal being measured at 1 kHz, while the Sensitivity 2, Time Constant 2 and Ref Phase 2 controls will affect the signal being measured at 15 kHz.
  • Page 106 32 nd. RELOCK EXT. REFERENCE The 7280 includes frequency-dependent calibration parameters. In Dual reference mode the correct parameters can be chosen for the internal reference channel because its frequency is equal to the specified oscillator frequency. The parameters for the external reference channel are selected by measuring the applied frequency.
  • Page 107 Chapter 5, FRONT PANEL OPERATION OSC AMPLITUDE This control may be set to any value between 1 mV and 1 V rms. Adjustment is faster using the Keypad or Active Cursor controls - see section 4.1.04. Since the instrument is now generating two sets of outputs (one for the external and one for the internal reference signals) there are more output display choices in this mode than in single reference mode, and these are listed in table 5-2.

  • Page 108: Reference Channel Menu

    In standard instruments, the maximum detection frequency for either regference reference is 20 kHz; units fitted with the 7280/99 option allow operation to 800 kHz and those with the 7280/98 option allow operation to 2.0 MHz 5.5.03 Reference Channel Menu...
  • Page 109 Chapter 5, FRONT PANEL OPERATION Main Menu 1 accesses the Dual Reference Channel menu, shown in figure 5-39. Figure 5-40, Dual Reference Channel Menu The Dual Reference Channel menu has five controls affecting the instrument's reference channel. Changes to the setting of these controls can be made by using the adjacent keys.

  • Page 110: Dual Reference Output Filters Menu

    Chapter 5, FRONT PANEL OPERATION The Auto-Phase1 and Auto-Phase 2 functions (see section 5.5.07) also affect the settings of these controls. Pressing the Previous Menu key returns control to Main Menu 1. 5.5.04 Dual reference Output Filters Menu In dual reference mode, pressing the Output Filters key on Main Menu 1 access the Dual Reference Output Filters Menu, shown in figure 5-41.

  • Page 111: Output Offset Ref 1 Menu

    Chapter 5, FRONT PANEL OPERATION In this setting, the actual time constant used is chosen to be some multiple of the reference frequency period, giving a much more stable output at low frequencies than would otherwise be the case. Note that, depending on the reference frequency, output time constants shorter than 100 ms cannot be used.

  • Page 112: Output Offset Ref 2 Menu

    Chapter 5, FRONT PANEL OPERATION level controls, to be switched on to either or both outputs, or to be switched off. It therefore has four settings, as follows:- NONE Both X1 channel and Y1 channel output offsets are switched off. The X1 channel output offset is switched on.

  • Page 113: Auto Functions Menu

    Chapter 5, FRONT PANEL OPERATION The offset level set by the controls, which can be any value between -300% and +300% in 0.01% steps, is added to the X2 channel or Y2 channel output when the X2 channel or Y2 channel offset is switched on. Adjustment is faster using the Keypad or Active Cursor controls - see section 4.1.04.

  • Page 114: Configuration Menu - Dual Reference Mode

    5.5.09 Analog Outputs Menu - Dual Reference and Dual Harmonic Modes When operating in Dual Reference or Dual Harmonic modes the 7280 can generate analog outputs representing the in-phase components of the two detected signals updated at a rate of 7.5 MHz, making it possible to use output time constants in the range 1 µs to 200 µs...
  • Page 115 Chapter 5, FRONT PANEL OPERATION and the range of output time constants and filter slopes available. The Analog Outputs menu is used to select the outputs to be converted, which in dual reference or dual harmonic modes appears as shown in figure 5.46 below. Figure 5-46, Analog Outputs Menu, Normal Operating Mode, Dual Reference/Dual Harmonic Modes The Analog Outputs menu has three controls, changes to the setting of which can be...
  • Page 116 Chapter 5, FRONT PANEL OPERATION CH1/2 Voltage +300 7.5 V +100 2.5 V 0.0 V -100 -2.5 V -300 -7.5 V Y1% (2.5V fs) When set to Y1% the corresponding CH1/CH2 connector on the rear panel will output a voltage related to the Y1%fs front panel display as follows:- CH1/2 Voltage +300 7.5 V...
  • Page 117 Chapter 5, FRONT PANEL OPERATION NOISE1 (2.5V fs) When set to NOISE1 the corresponding CH1/CH2 connector on the rear panel will output a voltage related to the N %fs front panel display as follows:- CH1/2 Voltage +300 7.5 V +100 2.5 V 0.0 V Note: When NOISE1 is selected as an output, the Noise Measurement Mode...
  • Page 118 Chapter 5, FRONT PANEL OPERATION output RATIO1 ADC1 input where X1 output is the X1 channel output as a percentage of the full-scale sensitivity and ADC 1 is the voltage applied to the ADC1 input connector on the rear panel expressed in volts. Hence, for example, if the instrument were measuring a 100 mV signal when set to the 500 mV sensitivity setting, the X1 channel output were maximized and a 1 V signal were applied to the ADC1 input, then the value of LOG RATIO1 would be:-...
  • Page 119 Chapter 5, FRONT PANEL OPERATION X2% (2.5V fs) When set to X2% the corresponding CH1/CH2 connector on the rear panel will output a voltage related to the X2%fs front panel display as follows:- CH1/2 Voltage +300 7.5 V +100 2.5 V 0.0 V -100 -2.5 V...
  • Page 120 Chapter 5, FRONT PANEL OPERATION PHA or θ deg CH1/2 Voltage +180 0.0 V -4.5 V -9.0 V 9.0 V 4.5 V -180 0.0 V FAST In dual reference or dual harmonic mode when the analog outputs operating mode is set to Fast, the CH1 and CH2 analog outputs are derived either from the first stage of output filtering or from the output processor.

  • Page 121: Menu Descriptions - Dual Harmonic Mode

    5.6 Menu Descriptions - Dual Harmonic Mode 5.6.01 Dual Harmonic Setup Menu The dual harmonic mode allows the model 7280 to measure signals, applied to the signal input, at two different harmonics of the reference frequency simultaneously. The reference may be either externally supplied or derived from the internal oscillator.

  • Page 122: Dual Harmonic Main Display

    Chapter 5, FRONT PANEL OPERATION Figure 5-47, Dual Harmonic Setup Menu 5.6.02 Dual Harmonic Main Display Once dual harmonic has been activated, the Main Display - Dual Harmonic Mode is displayed, as shown in figure 5-48. Figure 5-48, Main Display - Dual Harmonic Mode In dual harmonic mode, controls and displays relating to the first detection harmonic carry the suffix "1"...
  • Page 123 Chapter 5, FRONT PANEL OPERATION SENSITIVITY 1 SENSITIVITY 2 When set to voltage input mode, using the Signal Channel menu, the instrument's full-scale voltage sensitivity may be set to any value between 10 nV and 1 V in a 1-2-5 sequence. When set to current input mode, using the Signal Channel menu, the instrument's full-scale current sensitivity may be set to any value between 1 pA and 100 µA (wide bandwidth mode), 10 fA and 1 µA (normal mode), or 10 fA and 10 nA (low-noise...
  • Page 124 3 kHz and 5 kHz. RELOCK EXT. REFERENCE The 7280 includes frequency-dependent calibration parameters. When operating in Internal reference mode the correct parameters can be chosen because the reference frequency is equal to the specified oscillator frequency. In External reference mode the applied frequency is measured, and the measured value is used to select the correct parameters.
  • Page 125 Chapter 5, FRONT PANEL OPERATION Output Description Title Numeric Displays only: Resultant (Magnitude) output, harmonic 1, %FS Resultant (Magnitude) output, harmonic 2, %FS Noise output about harmonic 1, % FS Noise output about harmonic 2, % FS θ ° Phase output, harmonic 1, in degrees θ...

  • Page 126: Reference Channel Menu

    In standard instruments, the maximum detection frequency for either harmonic harmonic is 20 kHz; units fitted with the 7280/99 allow operation to 800 kHz and those with th2 7280/98 allow operation to 2.0 MHz 5.6.03 Reference Channel Menu...
  • Page 127 Chapter 5, FRONT PANEL OPERATION Figure 5-50, Dual Harmonic Reference Menu The Dual Harmonic Reference menu has five controls affecting the instrument's reference channel. Changes to the setting of these controls can be made by using the adjacent keys. REF SOURCE This control allows selection of the source of reference signal used to drive the reference circuitry, and has three settings:- The lock-in amplifier's reference is taken from the instrument's internal oscillator.

  • Page 128: Dual Harmonic Output Filters Menu

    Chapter 5, FRONT PANEL OPERATION faster using the Keypad or Active Cursor controls - see section 4.1.04. The Auto-Phase1 and Auto-Phase 2 functions (see section 5.6.06) also affect the settings of these controls. Pressing the Previous Menu key returns control to Main Menu 1. 5.6.04 Dual Harmonic Output Filters Menu In dual harmonic mode, pressing the Output Filters key on Main Menu 1 access the Dual Harmonic Output Filters Menu, shown in figure 5-51.

  • Page 129: Output Offset Harm 1 Menu

    Chapter 5, FRONT PANEL OPERATION reference frequency period. In this setting, the actual time constant used is chosen to be some multiple of the reference frequency period, giving a much more stable output at low frequencies than would otherwise be the case. Note that, depending on the reference frequency, output time constants shorter than 100 ms cannot be used.

  • Page 130: Output Offset Harm 2 Menu

    Chapter 5, FRONT PANEL OPERATION OFFSET 1 STATUS This control allows the X1 channel and Y1 channel output offsets, set by the above level controls, to be switched on to either or both outputs, or to be switched off. It therefore has four settings, as follows:- NONE Both X1 channel and Y1 channel output offsets are switched off.

  • Page 131: Auto Functions Menu

    Chapter 5, FRONT PANEL OPERATION X2 OFFSET and Y2 OFFSET These controls, which duplicate the Main Display X2 OFFSET and Y2 OFFSET controls, allow manual adjustment of the X2 channel and Y2 channel output offsets. The offset level set by the controls, which can be any value between -300% and +300% in 0.01% steps, is added to the X2 channel or Y2 channel output when the X2 channel or Y2 channel offset is switched on.

  • Page 132: Configuration Menu - Dual Harmonic Mode

    Chapter 5, FRONT PANEL OPERATION Figure 5-54, Auto Functions Menu - Dual Harmonic Mode This menu is virtually identical to the normal single reference mode Auto Functions menu, except that the an additional key appears in the lower left-hand corner, marked Harmonic3 menu or Harmomic1 menu.

  • Page 133: Typical Lock-In Amplifier Experiment

    This completes the description of the dual harmonic mode menus. 5.7 Typical Lock-in Amplifier Experiment The model 7280 is a complex instrument which has many controls and the following basic checklist may be helpful in setting up the instrument for manual operation in single reference mode.
  • Page 134 Chapter 5, FRONT PANEL OPERATION 5-88...

  • Page 135: Introduction

    Chapter 6.1 Introduction The model 7280 includes both RS232 and GPIB (IEEE-488) interface ports, designed to allow the lock-in amplifier to be completely controlled from a remote computer. Virtually all of the instrument's controls may be operated, and all of the outputs can be read, via these interfaces.

  • Page 136: Rs232 And Gpib Operation

    BASIC code (see appendix C.1). 6.3.02 RS232 Interface - General Features The RS232 interface in the model 7280 is implemented with three wires; one carries digital transmissions from the computer to the lock-in amplifier, the second carries digital transmissions from the lock-in amplifier to the computer and the third is the Logic Ground to which both signals are referred.

  • Page 137: Choice Of Baud Rate

    6.3.05 Choice of Parity Check Option Parity checks are not required at the baud rates available in the model 7280, that is up to 19,200 baud, with typical cable lengths of up to a few meters. Therefore no software is provided in the model 7280 for dealing with parity errors.

  • Page 138: Auxiliary Rs232 Interface

    By means of internal hardware or software switches, each instrument is set to a different address on the bus, usually a number in the range 0 to 31. In the model 7280 the address is set using the GPIB Settings menu or by means of the GP command.

  • Page 139: Handshaking And Echoes

    RD input). However, these lines are not capable of implementing the handshaking function required by the model 7280 on a byte-by-byte basis and are not connected in the model 7280 apart from the RTS and DTR outputs which are constantly asserted.

  • Page 140: Terminators

    In the model 7280 there are three input termination options for GPIB communications, selected from the front panel under the GPIB Settings menu or by means of the GP command.

  • Page 141: Delimiters

    6 (the request service bit) whose functions are defined by the standard. In the model 7280, bits 0 and 7 signify "command complete" and "data available" respectively. In GPIB communications, the use of these bits can lead to a useful...
  • Page 142 Chapter 6, COMPUTER OPERATION command and a slow computer were being used then the instrument may actually clear and then reset bit 0 (i.e. actually complete the command) before the first serial poll operation were executed. Hence the loop must include the provision to timeout under these conditions;...

  • Page 143: Service Requests

    In the model 7280 the assertion of the SRQ line is under the control of a byte called the SRQ mask byte which can be set by the user with the MSK command or via the GPIB Settings menu.

  • Page 144: Signal Channel

    Chapter 6, COMPUTER OPERATION 6.4.01 Signal Channel IMODE [n] Current/Voltage mode input selector The value of n sets the input mode according to the following table: Input mode Current mode off - voltage mode input enabled Normal current mode enabled - connect signal to B input connector Low noise current mode enabled - connect signal to B input connector High bandwidth current mode enabled - connect signal to B input connector If n = 0 then the input configuration is determined by the VMODE command.
  • Page 145 Chapter 6, COMPUTER OPERATION full-scale sensitivity IMODE=0 IMODE=1 IMODE=2 IMODE=3 10 nV 10 fA 1 pA 20 nV 20 fA 2 pA 50 nV 50 fA 5 pA 100 nV 100 fA 10 pA 200 nV 200 fA 20 pA 500 nV 500 fA 50 pA...

  • Page 146: Reference Channel

    Chapter 6, COMPUTER OPERATION AC Gain 0 dB 6 dB 14 dB 20 dB 26 dB 34 dB 40 dB 46 dB 54 dB 60 dB 10 66 dB AUTOMATIC [n] AC Gain automatic control The value of n sets the status of the AC Gain control according to the following table: Status AC Gain is under manual control, either using the front panel or the ACGAIN command...
  • Page 147 Chapter 6, COMPUTER OPERATION IE [n] Reference channel source control (Internal/External) The value of n sets the reference input mode according to the following table: Selection INT (internal) EXT LOGIC (external rear panel TTL input) EXT (external front panel analog input) REFN [n] Reference harmonic mode control The value of n sets the reference channel to one of the NF modes, or restores it to the...

  • Page 148: Signal Channel Output Filters

    Chapter 6, COMPUTER OPERATION 6.4.03 Signal Channel Output Filters NOISEMODE [n] Noise Measurement Mode control The value of n sets the noise measurement mode according to the following table: Function Noise measurement mode off Noise measurement mode on. When the noise measurement mode is turned on, the output filter time constant is automatically adjusted until it lies in the range 500 µs to 10 ms inclusive, the synchronous time constant control is turned off, and the output filter slope is set to 12 dB/octave if it had previously been 18 or 24 dB/octave.
  • Page 149 Chapter 6, COMPUTER OPERATION When the fast analog output mode is turned on (FASTMODE 1) and the instrument is in dual harmonic or dual reference mode, the selection is according to the following table: Slope 6 dB/octave TC [n] Filter time constant control The value of n sets the output filter time constant in accordance with the following table: FASTMODE = 0,...

  • Page 150: Signal Channel Output Amplifiers

    Chapter 6, COMPUTER OPERATION The TC. command is only used for reading the time constant, and reports the current setting in seconds. Hence if a TC 15 command were sent and the noise measurement mode was turned off, TC would report 15 and TC. would report 1.0E-01, i.e. 0.1 s or 100 ms.
  • Page 151 Chapter 6, COMPUTER OPERATION FASTMODE [n] Analog Output Mode Control The value of n sets the fast analog output mode control according to the following table: Function Fast mode off Fast mode on When the fast analog output mode is turned on, the available settings for the CH1/CH2 analog output controls are restricted, and hence affect the allowable parameter range for CH1 and CH2 commands.

  • Page 152: Instrument Outputs

    Chapter 6, COMPUTER OPERATION is in single or virtual reference mode, the selection is according to the following tables: = 1 (i.e. CH1 output) Signal X % (2.5 V FS) 2 (i.e. CH2output) Signal Y % (2.5 V FS) Magnitude % (2.5 V FS) When the fast analog output mode is turned on (FASTMODE 1) and the instrument is in dual harmonic or dual reference mode, the selection is fixed according to the following tables:...
  • Page 153 Chapter 6, COMPUTER OPERATION XY[.] X, Y channel outputs Equivalent to the compound command X[.];Y[.] XYER X, Y channel outputs - enhanced resolution Equivalent to the compound command XER;YER. Active only when both X and Y × 10 output expansion is turned ON. MAG[.] Magnitude In fixed point mode causes the lock-in amplifier to respond with the magnitude value...
  • Page 154 Chapter 6, COMPUTER OPERATION In floating point mode, reports the equivalent noise bandwidth of the output low-pass filters at the current time constant setting in hertz. NN[.] Noise output In fixed point mode causes the lock-in amplifier to respond with the mean absolute value of the Y channel output in the range 0 to 12000, full-scale being 10000.

  • Page 155: Internal Oscillator

    Chapter 6, COMPUTER OPERATION EQU n Output result of equation #1 or equation #2 The value returned is the output of the user equation #1 (n = 1) or equation #2 (n = 2), where the equations are defined using the Equation Setup menus (see section 5.3.09).
  • Page 156 Chapter 6, COMPUTER OPERATION FSTART[.] [n] Oscillator frequency sweep start frequency Sets the start frequency for a subsequent sweep of the internal oscillator frequency, in the range 0 to 2.000 MHz. In fixed point mode, n is in millihertz and in floating point mode n is in hertz. FSTOP[.] [n] Oscillator frequency sweep stop frequency Sets the stop frequency for a subsequent sweep of the internal oscillator frequency,...

  • Page 157: Auxiliary Outputs

    Chapter 6, COMPUTER OPERATION 10 Link amplitude sweep to curve buffer acquisition 11 Link frequency and amplitude sweep to curve buffer acquisition This command is used to start or stop the internal oscillator frequency or amplitude sweep, or to specify that the sweep should be linked to the curve buffer data acquisition.

  • Page 158: Auxiliary Inputs

    Chapter 6, COMPUTER OPERATION BYTE [n] Digital port output control The value of n, in the range 0 to 255, determines the bits to be output on those lines of the rear panel digital port that are configured as outputs. Hence, for example, if PORTDIR = 8 and BYTE = 0, all outputs are low, and when BYTE = 255, all are high.
  • Page 159 Chapter 6, COMPUTER OPERATION In the burst modes, data is stored in the curve buffer. Use the LEN command to set the number of points required. Note that it may be necessary to enter CBD 256 before setting the length, if the curve buffer has previously been used for more than one data type.

  • Page 160: Output Data Curve Buffer

    Chapter 6, COMPUTER OPERATION 6.4.09 Output Data Curve Buffer CBD [n] Curve buffer define Defines which data outputs are stored in the curve buffer when subsequent TD (take data), TDT (take data triggered) or TDC (take data continuously) commands are issued.
  • Page 161 Chapter 6, COMPUTER OPERATION The reason why bit 4 and, for dual reference modes, bit 21, which store both the sensitivity and the IMODE setting, are needed, is to allow the instrument to transfer the acquired curves to the computer in floating point mode. Without this information, the unit would not be able to determine the correct calibration to apply.
  • Page 162 Chapter 6, COMPUTER OPERATION store a complete curve or set of curves, the number of triggers applied must equal the number of points specified by the LEN command parameter. Note that in this mode the maximum trigger rate is 1000 Hz and the storage interval control setting has no effect.
  • Page 163 Chapter 6, COMPUTER OPERATION Fourth value, Number of Points Acquired: This number is incremented each time a point is taken. It is zeroed by the NC command and whenever CBD or LEN is applied without parameters. DC[.] n Dump acquired curve(s) to computer In fixed point mode, causes a stored curve to be dumped via the computer interface in decimal format.
  • Page 164 Chapter 6, COMPUTER OPERATION Bit Decimal value Output and range X Output (±10000 FS) Y Output (±10000 FS) Magnitude Output (0 to +10000 FS) Phase (±18000 = ±180°) Sensitivity setting (3 to 27) + IMODE (0, 1, 2, 3 = 0, 32, 64, 128) Noise (0 to +10000 FS) Ratio (±10000 FS)

  • Page 165: Computer Interfaces (Rs232 And Gpib)

    Chapter 6, COMPUTER OPERATION Magnitude outputs would be stored. The permitted values of n would therefore be 0 and 2, so that DCB 0 would transfer the X channel output curve and DCB 2 the Magnitude curve. Curves 15 and 16 store the reference frequency in millihertz. When using the DCB command (although not with the other curve transfer commands), both curves need to be transferred separately.
  • Page 166 Each instrument must be set to a unique address. \N n Address command When the model 7280 is daisy-chained with other compatible instruments this command will change which instrument is addressed. All daisy-chained instruments receive commands but only the currently addressed instrument will implement or respond to the commands.

  • Page 167: Instrument Identification

    0, the front panel controls function normally. 6.4.11 Instrument Identification Identification Causes the lock-in amplifier to respond with the number 7280. Report firmware version Causes the lock-in amplifier to respond with the firmware version number. The firmware version number is the number displayed on the Configuration menu.

  • Page 168: Dual Mode Commands

    Chapter 6, COMPUTER OPERATION predefined states. The value of n is used to define what controls are affected, according to the following table: effect Complete reset to factory set default values (listed in appendix E), equivalent to using the front-panel Auto Default function. However, if this command is used when the interface parameters are at values other than their default settings, then communication will be lost.
  • Page 169 Chapter 6, COMPUTER OPERATION AXO1 AXO2 6-35...

  • Page 170: Programming Examples

    Chapter 6, COMPUTER OPERATION 6.5 Programming Examples 6.5.01 Introduction This section gives some examples of the commands that need to be sent to the lock-in amplifier for typical experimental situations. 6.5.02 Basic Signal Recovery In a typical simple experiment, the computer is used to set the instrument controls and then to record the chosen outputs, perhaps as a function of time.

  • Page 171: And Y Output Curve Storage Measurement

    Chapter 6, COMPUTER OPERATION FLOAT 1 Float input connector shell using 1 kΩ to ground LF 0 Turn off line frequency rejection filter OA. 1.0E0 Set oscillator amplitude to 1.0 V rms OF. 100.0 Set oscillator frequency to 100 Hz (starting frequency) SEN 27 Set sensitivity to 1 V full-scale TC 14...

  • Page 172: Transient Recorder

    Chapter 6, COMPUTER OPERATION As the acquisition is running, the M command reports the status of the curve acquisition. Once this indicates the acquisition is complete (i.e. parameter 1 = 0, parameter 2 = 1), the acquired data may be transferred to the computer using: DC.
  • Page 173 Chapter 6, COMPUTER OPERATION LF 0 0 Turn off line frequency rejection filter OA. 1.0E0 Set oscillator amplitude to 1.0 V rms OF. 100.0 Set initial oscillator frequency to 100 Hz so that AQN runs correctly SEN 27 Set sensitivity to 1 V full-scale TC 12 Set time constant to 10 ms Auto-Phase...
  • Page 174 Chapter 6, COMPUTER OPERATION 6-40...
  • Page 175 Specifications Appendix Measurement Modes ⎫ X In-phase ⎪ The unit can simultaneously present any Y Quadrature ⎬ four of these as outputs R Magnitude θ ⎪ Phase Angle ⎭ Noise nF, n ≥ 32 Harmonic Simultaneously measures the signal at two different Dual Harmonic harmonics F and F...

  • Page 176: Appendix A, Specifications

    Appendix A, SPECIFICATIONS Signal Channel Voltage Inputs Modes A only, -B only or Differential (A-B) Full-scale Sensitivity 0.5 Hz ≤ F ≤ 250 kHz 10 nV to 1 V in a 1-2-5 sequence 250 kHz ≤ F ≤ 2.0 MHz 100 nV to 1 V in a 1-2-5 sequence Dynamic Reserve >...
  • Page 177 Appendix A, SPECIFICATIONS Reference Channel TTL Input (rear panel) Frequency Range 0.5 Hz to 2.0 MHz Analog Input (front panel) Impedance 1 MΩ // 30 pF Sinusoidal Input Level 1.0 V rms** Frequency Range 0.5 Hz to 2.0 MHz Squarewave Input Level 250 mV rms** Frequency Range...
  • Page 178 Appendix A, SPECIFICATIONS Auto and Manual on X and/or Y: ±300% FS Offset Absolute Phase Measurement Accuracy ≤ 0.01° Oscillator Frequency Range 0.5 Hz to 2.0 MHz Setting Resolution 1 mHz Absolute Accuracy 25 ppm -80 dB at 1 kHz and 100 mV rms Distortion (THD) Amplitude (rms) Range...
  • Page 179 Appendix A, SPECIFICATIONS Outputs CH1 CH2 Outputs X, Y, R, θ, Noise, Ratio, Log Ratio and User Function Equations 1 & 2. Amplitude ±2.5 V full-scale but capable of operating to ±300 % full-scale Impedance 1 kΩ Update Rate: X, Y or R TC ≤...
  • Page 180 Appendix A, SPECIFICATIONS saved or recalled at will from non-volatile memory. Interfaces RS232, IEEE-488. A second RS232 port is provided to allow "daisy-chain" connection and control of up to 16 units from a single RS232 computer port. General Power Requirements Voltage 110/120/220/240 VAC Frequency...

  • Page 181: Appendix B, Pinouts

    Pinouts Appendix B.1 RS232 Connector Pinout Figure B-1, RS232 and AUX RS232 Connector (Female) Function Description Data In Data Out Signal Ground Request to Send - always +12 V All other pins are not connected B.2 Preamplifier Power Connector Pinout Figure B-2, Preamplifier Power Connector Function –15 V...

  • Page 182: B3 Digital Output Port Connector

    Appendix B, PINOUTS B.3 Digital I/O Port Connector Figure B-3, Digital I/O Port Connector 8-bit TTL-compatible input/output port with each bit being configurable as an input or output. If configured as an output, the bit status can be set, and if configured as an input it can be read, from the front panel or via the computer interfaces.

  • Page 183: Appendix C, Demonstration Programs

    Demonstration Programs Appendix C.1 Simple Terminal Emulator This is a short terminal emulator with minimal facilities, which will run on a PC-compatible computer in a Microsoft GWBASIC or QuickBASIC environment, or can be compiled with a suitable compiler. 10 'MINITERM 9-Feb-96 20 CLS : PRINT "Lockin RS232 parameters must be set to 9600 baud, 7 DATA bits, 1 stop bit and even parity"...
  • Page 184 Appendix C, DEMONSTRATION PROGRAMS IF A$ = "?" THEN GOSUB 410: GOSUB 470 ' if "?" prompt fetch STATUS% ' and display message 150 WEND ' return to start of loop 160 ' 170 ' 180 '...output the string B$....190 ON ERROR GOTO 510 ' enable error trapping 200 IF LOC(1) >...

  • Page 185: C3 Gpib User Interface Program

    Appendix C, DEMONSTRATION PROGRAMS C.3 GPIB User Interface Program GPCOM.BAS is a user interface program which illustrates the principles of the use of the serial poll status byte to coordinate the command and data transfer. The program runs under Microsoft GWBASIC or QuickBASIC on a PC-compatible computer fitted with a National Instruments IEEE-488 interface card and the GPIB.COM software installed in the CONFIG.SYS file.
  • Page 186 Appendix C, DEMONSTRATION PROGRAMS 270 CALL IBCLR(DEV%) 280 '..set timeout to 1 second...... 290 V% = 11: CALL IBTMO(DEV%, V%) 300 '..set status print flag......310 INPUT "Display status byte y/n "; R$ 320 IF R$ = "Y" OR R$ = "y" THEN DS% = 1 ELSE DS% = 0 330 '..main loop........

  • Page 187: Appendix D, Cable Diagrams

    Appendix D.1 RS232 Cable Diagrams Users who choose to use the RS232 interface to connect the model 7280 lock-in amplifier to a standard serial port on a computer will need to use one of two types of cable. The only difference between them is the number of pins used on the connector which goes to the computer.
  • Page 188 Appendix D, CABLE DIAGRAMS Figure D-2, Interconnecting RS232 Cable Wiring Diagram...

  • Page 189: Appendix E, Default Settings

    Default Settings Appendix Auto Default Function The Auto-Default computer command ADF 1 sets the model 7280's controls and output displays as follows:- Main Display Displays the AC Gain, full-scale sensitivity, reference phase, time constant, reference phase and oscillator frequency controls on the left-hand side. On the right-hand side,...
  • Page 190 D0 to D7 status Logic zero The Auto-Default function on the front-panel Auto Functions menu and the ADF 0 computer command set the model 7280's controls and output displays as above, and in addition sets the communications interface parameters as follows:-...
  • Page 191 Appendix E, DEFAULT SETTINGS RS232 Settings Baud rate 9600 Data bits 7 + 1 Parity Delimiter , (044) Address Character echo Parity Even Prompt character GPIB Settings GPIB Address Terminator [CR],[LF] Test Echo SRQ mask byte Delimiter , (044)
  • Page 192 Appendix E, DEFAULT SETTINGS...

  • Page 193: Appendix F, Alphabetical Listing Of Commands

    Alphabetical Listing of Commands Appendix ACGAIN [n] AC Gain control Sets the gain of the signal channel amplifier according to the following table:- AC Gain 0 dB 6 dB 14 dB 20 dB 26 dB 34 dB 40 dB 46 dB 54 dB 60 dB 10 66 dB...
  • Page 194 Appendix F, ALPHABETICAL LISTING OF COMMANDS ASTEP[.] [n] Oscillator amplitude sweep step size Sets the amplitude step size for a subsequent sweep of the internal oscillator amplitude, in the range 0 to 1.000 V In fixed point mode, n is in millivolts rms and in floating point mode n is in volts rms ASTOP[.] [n] Oscillator amplitude sweep stop amplitude Sets the stop amplitude for a subsequent sweep of the internal oscillator amplitude, in...
  • Page 195 Appendix F, ALPHABETICAL LISTING OF COMMANDS storage. When a bit is negated, the output is not stored. The bit function and range for each output are shown in the table below: Bit Decimal value Output and range X Output (±10000 FS) Y Output (±10000 FS) Magnitude Output (0 to +10000 FS) Phase (±18000 = ±180°)
  • Page 196 Appendix F, ALPHABETICAL LISTING OF COMMANDS NOTE: At least one of the curves selected for storage in the curve buffer must be chosen from those marked with an asterisk(*) in the above table. CH n Analog output control Defines what outputs appear on the CH1 and CH2 connectors on the rear panel. When the fast analog output mode is turned off (FASTMODE 0), the selection is according to the following table: Signal...
  • Page 197 Appendix F, ALPHABETICAL LISTING OF COMMANDS = 1 (i.e. CH1 output) Signal X1 % (2.5 V FS) 2 (i.e. CH2output) Signal 10 X2 % (2.5 V FS) CP [n] Input connector coupling mode control The value of n sets the input coupling mode according to the following table: Coupling mode Fast Slow...
  • Page 198 Appendix F, ALPHABETICAL LISTING OF COMMANDS value is available. The loop should continue until bit 1 is set, indicating that the transfer is completed. DCB n Dump acquired curve(s) to computer in binary format This command causes a stored curve to be dumped via the computer interface in binary format, using two bytes per point.
  • Page 199 Appendix F, ALPHABETICAL LISTING OF COMMANDS Bit Decimal value Output and range X Output (±10000 FS) Y Output (±10000 FS) Magnitude Output (0 to +10000 FS) Phase (±18000 = ±180°) Sensitivity setting (3 to 27) + IMODE (0, 1, 2, 3 = 0, 32, 64, 128) Noise (0 to +10000 FS) Ratio (±10000 FS)
  • Page 200 Appendix F, ALPHABETICAL LISTING OF COMMANDS Parameter n is used to set the addition/subtraction operator in the numerator according to the following table:- Operator Subtraction Addition The parameters n and n specify the variables A, B, C and D respectively according to the following table: Variable Range...
  • Page 201 Appendix F, ALPHABETICAL LISTING OF COMMANDS EX [n] Output expansion control Expand mode Expand X Expand Y Expand X and Y FASTMODE [n] Analog Output Mode Control The value of n sets the fast analog output mode control according to the following table: Function Fast mode off...
  • Page 202 [CR,LF], test echo enabled no terminator, test echo disabled no terminator, test echo enabled Halt curve acquisition Identification Causes the lock-in amplifier to respond with the number 7280. IE [n] Reference channel source control (Internal/External) Selection INT (internal) EXT LOGIC (external rear panel TTL input)
  • Page 203 Appendix F, ALPHABETICAL LISTING OF COMMANDS IMODE [n] Current/Voltage mode input selector Input mode Current mode off - voltage mode input enabled Normal current mode enabled - connect signal to B input connector Low noise current mode enabled - connect signal to B input connector High bandwidth current mode enabled - connect signal to B input connector If n = 0 then the input configuration is determined by the VMODE command.
  • Page 204 The value of n sets the SRQ mask byte in the range 0 to 255 \N n Address command When the model 7280 is daisy-chained with other compatible instruments this command will change which instrument is addressed. All daisy-chained instruments receive commands but only the currently addressed instrument will implement or respond to the commands.
  • Page 205 Appendix F, ALPHABETICAL LISTING OF COMMANDS Report overload byte Causes the lock-in amplifier to respond with the overload byte, an integer between 0 and 255, which is the decimal equivalent of a binary number with the following bit- significance: Bit 0 not used Bit 1 CH1 output overload (>...
  • Page 206 Appendix F, ALPHABETICAL LISTING OF COMMANDS 12 dB/octave if it had previously been 18 or 24 dB/octave. OA[.] [n] Oscillator amplitude control In fixed point mode n sets the oscillator amplitude in mV. The range of n is 0 to 1000 representing 0 to 1 V rms.
  • Page 207 Appendix F, ALPHABETICAL LISTING OF COMMANDS REFMODE [n] Reference mode selector Mode Single Reference / Virtual Reference mode Dual Harmonic mode Dual Reference mode NOTE: When in either of the dual reference modes the command set changes to accommodate the additional controls. These changes are detailed in section 6.4.14 REFN [n] Reference harmonic mode control The value of n sets the reference channel to one of the NF modes, or restores it to the...
  • Page 208 Appendix F, ALPHABETICAL LISTING OF COMMANDS RSADDR [n] Set/read RS232 address The value of n sets the RS232 address in the range 0 to 15. This is relevant only when using more than one instrument connected via the RS232 “daisy-chain” method.
  • Page 209 Appendix F, ALPHABETICAL LISTING OF COMMANDS Slope 6 dB/octave 12 dB/octave (TC ≥ 500 µs) 18 dB/octave (TC ≥ 500 µs) 24 dB/octave When: a) The fast analog output mode is turned on (FASTMODE 1) and the instrument is in single or virtual reference mode, or b) Noise measurement mode is turned ON (NOISEMODE 1) the selection is according to the following table: Slope...
  • Page 210 Appendix F, ALPHABETICAL LISTING OF COMMANDS Fast Data Transfer command The ? command offers a method of reading a combination of instrument outputs which are sampled at the same time, thereby ensuring that they are correlated. The response to the ? command is the output(s), expressed in floating point mode, specified by the present setting of the Curve Buffer Define (CBD) command (see section 6.4.09) and separated by delimiter character(s) defined by the DD command.
  • Page 211 Appendix F, ALPHABETICAL LISTING OF COMMANDS amplitude) commands. SYNC [n] Synchronous time constant control Effect Synchronous time constant disabled Synchronous time constant enabled TADC [n] Auxiliary ADC trigger mode control The value of n sets the trigger mode of two of the auxiliary ADC inputs according to the following table: Trigger mode Asynchronous (5 ms intervals)
  • Page 212 Appendix F, ALPHABETICAL LISTING OF COMMANDS TADC parameter Effect on CBD parameter automatically set to 256 automatically set to 768 automatically set to 256 automatically set to 768 automatically set to 256 automatically set to 768 automatically set to 256 automatically set to 768 The maximum sampling rate depends on the number of ADC inputs used, and is either 25 µs when sampling ADC1 only, or 56 µs when sampling both ADC1 and...
  • Page 213 Appendix F, ALPHABETICAL LISTING OF COMMANDS FASTMODE = 0, FASTMODE = 1, FASTMODE = 0, FASTMODE = 1, NOISEMODE = 0 NOISEMODE = 0 NOISEMODE = 1 NOISEMODE = 1 time constant time constant time constant time constant 24 100 s 100 s 25 200 s 200 s...
  • Page 214 Appendix F, ALPHABETICAL LISTING OF COMMANDS firmware version number is the number displayed on the Configuration menu. VMODE [n] Voltage input configuration Input configuration Both inputs grounded (test mode) A input only -B input only A-B differential mode Note that the IMODE command takes precedence over the VMODE command. VRLOCK [n] Virtual reference mode lock The Seek option of the frequency sweep mode must be used before issuing this...
  • Page 215 Appendix F, ALPHABETICAL LISTING OF COMMANDS demodulator output in volts or amps. Y channel output - enhanced resolution This command, which is only active when the Y channel × 10 output expansion is turned ON, causes the lock-in amplifier to respond with the Y demodulator output in the range ±300000, full-scale being ±100000.
  • Page 216 Appendix F, ALPHABETICAL LISTING OF COMMANDS F-24...
  • Page 217 Index Index ? command 6-21, F-18 Auxiliary I/O Menu 5-50 \N n command 6-32, F-12 AXO command 6-16, F-2 8-bit programmable output port 3-15 Burst mode control 5-52 AC Gain BURSTTPP [n] command 6-25 and Auto-Measure 3-17, 5-25 BYTE [n] command 6-24, F-2 and Auto-Sensitivity 5-25 CBD [n] command 6-26, F-2 and dynamic reserve 5-6, 5-59, 5-77...
  • Page 218 INDEX Curve Buffer Menu 5-42 Output Filters Menu 5-82 Curve Select Menu 5-45 Output Offset Harm 1 Menu 5-83 Curve storage Output Offset Harm 2 Menu 5-84 additional curves with dual modes 6-1 Reference Channel Menu 5-80 commands for 6-26 Setup Menu 5-75 Curve Buffer Menu 5-43 signal channel restrictions 3-1...
  • Page 219 INDEX general features 6-4 MAG[.] command 6-19, F-12 handshaking and echoes 6-5 Main Menu 1 5-7 service request mask byte control 5-31 Main Menu 2 5-41 service requests 6-9 Main Menu structure 5-2 status byte 6-7 MENU Key 4-5, 5-2 terminator selection 5-31 Menu structure 5-2 terminators 6-6...
  • Page 220 INDEX Overload terminators 6-6 input overload indicator 5-4 RS232 Settings Menu 5-28 output overload indicator 5-4 RSADD [n] command 6-32 PHA[.] command 6-19, F-14 RSADDR [n] command F-16 PORTDIR [n] command 6-23, F-14 RT[.] command 6-19, F-16 PREAMP POWER connector 4-7 SEN [n] command 6-10, F-16 Rack mounting 2-1 SEN.
  • Page 221 INDEX Terminators 6-6 virtual lock key 5-56 Time constant control 5-6, 5-59, 5-77 Virtual Reference Menu 5-54 TRIG connector 4-8 VMODE [n] command 6-10, F-22 Typical Lock-in Amplifier Experiment 5-87 VRLOCK [n] command 6-13, F-22 User Setttings Menu 5-49 Warning indicators 5-4 Vector magnitude 3-12 What is a lock-in amplifier? 1-2 VER command 6-33, F-21...
  • Page 222 INDEX INDEX-6...
  • Page 223 This Warranty shall not apply to any instrument or component not manufactured by AMETEK Advanced Measurement Technology, Inc. When products manufactured by others are included AMETEK Advanced Measurement Technology, Inc equipment, the original manufacturers Warranty is extended to AMETEK Advanced Measurement Technology, Inc customers.

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