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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...
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...
2.1.05 Line Voltage Selection and Line Fuses Before plugging in the line cord, ensure that the model 7220 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.
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.
INSTRUMENTS or the nearest authorized representative for assistance. 2.2.02 Procedure 1) Ensure that the model 7220 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 at the extreme left-hand side of the instrument when viewed from the rear) set to 0 (off), plug in the line cord to an appropriate line source.
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.
Chapter 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.
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.
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.
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.
Chapter 3, TECHNICAL DESCRIPTION This alias signal is indistinguishable from the output generated when a genuine signal at frequency f is sampled. Hence if the frequency of the unwanted signal were alias such that the alias signal frequency produced from it was close to, or equal to, that of the wanted signal then it is clear that a spurious output would result.
Chapter 3, TECHNICAL DESCRIPTION There is one situation where this automatic correction might not be sufficient to give good performance. Consider the case where the signal being measured is at 73 kHz, which is 10 kHz away from half the sampling frequency. If there were also a strong interfering signal at 93 kHz (i.e.
The model 7220, 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 7220 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, 1 mHz to 120 kHz.
Chapter 3, TECHNICAL DESCRIPTION and Y channel output filters. The outputs of these in turn drive two 16-bit digital to analog converters (DACs) which generate the instrument’s FAST X and FAST Y analog outputs. In addition, the signals are fed to further low-pass filters before subsequent processing by the instrument’s host microprocessor.
A new feature of the model 7220 is the introduction of a separate control function (“AC Gain”) for the gain of the signal channel. Where appropriate, this can be set to accommodate the existing noise level and subsequent changes in the instrument’s full-...
DR( in dB) = 20 log(DR( as a ratio)) Applying this formula to the model 7220 we may put in the maximum value of INPUT LIMIT (3 V) and the smallest available value of FULL-SCALE SENSITIVITY (20 nV) to reach a value of about 1E8 or 160 dB for the maximum available dynamic reserve.
7220 to apply to the envelope of the frequency response function of the digital FIR (finite impulse response) output filters. Accordingly the front panel display control which selects the configuration of the output filters is labelled SLOPE and the options are labelled 6, 12, 18, 24 dB/octave.
Chapter 3, TECHNICAL DESCRIPTION The 6 dB/octave filters are not satisfactory for most purposes because they do not give good rejection of periodic components in the demodulator output, including the inevitable component at double the reference frequency. However, the 6 dB/octave filter finds use where the lock-in amplifier is incorporated in a feedback control loop, and in some situations where the form of the time-domain response is critical.
Chapter 3, TECHNICAL DESCRIPTION with respect to the reference input) and is computed by the output processor in the lock-in amplifier and made available as the “magnitude” output. The phase angle between V (t) and the X demodulation function is called the “signal phase”: this is equal to the angle of the complex quantity (V + jV ) (where j is the square root of -1)
Chapter 3, TECHNICAL DESCRIPTION 3.10 Noise Measurements The noise measurement facility is available only in the baseband mode (i.e. at reference frequencies less than 60 kHz) and uses the output processor to perform a noise computation on the Y output where it is assumed that the waveform is Gaussian with zero mean.
Chapter 3, TECHNICAL DESCRIPTION 3.12.02 Auto-Sensitivity This function only operates when the reference frequency is above 1 Hz. A single Auto-Sensitivity operation consists of increasing the full-scale sensitivity range if the magnitude output is greater than 90 % of full-scale, or reducing the range if the magnitude output is less than 30 % of full-scale.
Auto-Measure and to make subsequent modifications to individual controls. 3.12.06 Default Setting With an instrument of the design of the model 7220, 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.
As shown in figure 4-1 there are four BNC connectors with associated LED indicators, two LCD display panels, an edge-indicating analog meter, eight double and three single keys mounted on the model 7220’s front panel. The following sections describe the function and location of these items.
Chapter 4, FRONT AND REAR PANELS 4.1.03 REF IN Connector This is the input connector for a general purpose external reference signal. When external reference mode is selected the LED adjacent to the connector will be lit (see figure 4-3). Under unlock conditions the LED will flash. Figure 4-3, OSC OUT and REF IN Connectors 4.1.04 Left-hand LCD Display Panel This panel and the two pairs of keys on each side of it are normally used to select and...
Chapter 4, FRONT AND REAR PANELS precision. In these cases a significant number of keypresses are required to make adjustments. Adjustment of the latter type of control is made easier by the use of one or other of the two methods described below. Auto Repeat If an up or down ADJUST key is pressed and held, then its action is automatically repeated such that the displayed control setting will increment or decrement at a rate...
Chapter 4, FRONT AND REAR PANELS Figure 4-6, Active Cursor Operation The double keypress action can also be performed with one finger by firmly pressing the center of the up and down ADJUST key rocker which will deform to press both keys.
Chapter 4, FRONT AND REAR PANELS Figure 4-8, Setup Menu Mode - Left and Right-hand LCD Displays In the setup menu mode, the left-hand SELECT keys adjacent to the left-hand display cycle through a series of twelve setup menus. In general each menu allows three controls to be adjusted, one via the right-hand side of the left-hand display and the other two via the right-hand display.
Figure 4-9, Main Display - Right-hand LCD 4.2 Rear Panel Figure 4-10, Model 7220 Rear Panel Layout As shown in figure 4-10, the line power switch, line power voltage selector, two RS232 connectors, a GPIB (IEEE-488) connector, digital output port, preamplifier power connector and twelve BNC signal connectors are mounted on the rear panel of the instrument.
Chapter 4, FRONT AND REAR PANELS 4.2.03 RS232 Connector This 9-pin D type RS232 interface connector implements pins 1, 2, 3 and 7 (Earth Ground, Transmit Data, Receive Data, Logic Ground) of a standard DTE interface. To make a connection to a PC-compatible computer, it is normally sufficient to use a three-wire cable connecting Transmit Data to Receive Data, Receive Data to Transmit Data, and Logic Ground to Logic Ground.
Chapter 4, FRONT AND REAR PANELS 4.2.11 CH1, CH2 Connectors The signal at these connectors is an analog voltage corresponding to a selected output, such as X, Y, R, θ, etc., as specified in the Output Setup menu. The minimum time constant that can be used is 5 ms.
Chapter 5.1 Introduction This chapter describes how to operate the model 7220 using the front panel controls, and describes its capabilities when used in this way. Chapter 6 provides similar information in the situation where the unit is operated remotely using one of the computer interfaces.
Chapter 5, FRONT PANEL OPERATION the right-hand display. The setup menu description is shown on the left-hand side of the left-hand display. Figure 5-1 makes this clear. One further press of the MENU key causes the instrument to leave the setup menu mode and return to the main display mode.
Chapter 5, FRONT PANEL OPERATION the front panel BNC connector marked “B/I”, and uses a low-noise (LN) current to voltage converter. Input This control has four settings:- Flt/DC The shells of the “A” and “B/I” connectors are connected to chassis ground via a 1 kΩ...
Chapter 5, FRONT PANEL OPERATION 5.2.02 Reference Setup Menu Figure 5-3, Reference Setup Menu In this menu, shown in figure 5-3, there are three controls affecting the reference channel of the instrument. They are:- Ref Source This control allows selection of the source of reference signal used to drive the reference circuitry, and has three settings:- INTERNAL The lock-in amplifier’s reference is taken from the instrument’s internal oscillator.
Chapter 5, FRONT PANEL OPERATION When the Demodulator Monitor is switched ON and the instrument is operating in External Reference mode, the signal at the OSC OUT connector changes from that of the internal oscillator to an analog representation of the drive from the reference channel to the X output demodulator.
Chapter 5, FRONT PANEL OPERATION Output expansion is turned off. X ONLY A ×10 output expansion is applied to the X output only. Y ONLY A ×10 output expansion is applied to the Y output only. X & Y A ×10 output expansion is applied to both the X and Y outputs. OUTPUTS This control, shown on the right-hand LCD, allows the two rear panel analog outputs CH1 and CH2 to be connected to the required instrument outputs.
Chapter 5, FRONT PANEL OPERATION MAG %fs CH1/2 Voltage +120 12.0 V +100 10.0 V 0.0 V -100 -10.0 V -120 -12.0 V PHASE1 When set to PHASE1 the corresponding rear panel CH1/CH2 connector will output a voltage related to the PHA deg front panel display as follows:- PHA deg CH1/2 Voltage +180...
Chapter 5, FRONT PANEL OPERATION 5.2.04 Control Options Menu Figure 5-5, Control Options Setup Menu This menu, shown in figure 5-5, has three controls affecting the line frequency rejection filter, AC Gain control and output time constants, as follows:- Linefilt This control sets the mode of operation of the internal line frequency rejection filter.
Chapter 5, FRONT PANEL OPERATION MANUAL In this setting the AC Gain may be manually adjusted from the main display. AUTOMATIC In this setting the AC Gain value is automatically selected by the instrument, depending on the full-scale sensitivity. TCs This control affects the output time constants, and has two settings:- SYNC When set to SYNC, the actual time constant used is chosen to be some multiple...
Chapter 5, FRONT PANEL OPERATION 5.2.05 Miscellaneous Options Menu Figure 5-6, Miscellaneous Options Setup Menu This menu, shown in figure 5-6, has three controls affecting the auxiliary ADC trigger rate and the front panel display as follows:- Trigger This control selects the trigger which is used to initiate the conversion of voltages applied to the rear panel ADC1 and ADC2 connectors, as follows:- 200Hz In this setting, ADC conversions occur at a 200 Hz rate.
Chapter 5, FRONT PANEL OPERATION 5.2.06 RS232 Setup 1 Menu Figure 5-7, RS232 Setup 1 Menu This menu, shown in figure 5-7, has three controls affecting the RS232 computer interface, as follows:- BaudRate Thirteen values of Baud Rate are available in the range 75 to 19200 bits per second. Format There are four data formats available: 7D + 1P...
Chapter 5, FRONT PANEL OPERATION 5.2.07 RS232 Setup 2 Menu Figure 5-8, RS232 Setup 2 Menu This menu, shown in figure 5-8, has three controls affecting the RS232 computer interface, as follows:- Prompt This function can be switched ON or OFF:- The prompt character is sent out by the lock-in amplifier after each command response to indicate that the response is finished and the instrument is ready for a new command.
Chapter 5, FRONT PANEL OPERATION MP command (report Magnitude and Phase). Hence it is necessary for the controlling program to be able to determine when all of the first value has been sent. The delimiter is a separator character sent between each response which may be used for this purpose.
Chapter 5, FRONT PANEL OPERATION 5.2.09 GPIB Setup 1 Menu Figure 5-10, GPIB Setup 1 Menu This menu, shown in figure 5-10, has two controls affecting the GPIB computer interface, as follows:- Address Each instrument used on the GPIB interface must have a unique address, in the range 0 to 31, and this control is used to set this address.
Chapter 5, FRONT PANEL OPERATION 5.2.10 GPIB Setup 2 Menu Figure 5-11, GPIB Setup 2 Menu This menu, shown in figure 5-11, has two controls affecting the GPIB computer interface, as follows:- SRQ Mask The instrument includes the ability to generate a Service Request on the GPIB interface, to signal to the controlling computer that urgent attention is required.
Chapter 5, FRONT PANEL OPERATION 5.2.11 Digital Outputs Setup Menu Figure 5-12, Digital Outputs Setup Menu This menu, shown in figure 5-12, is used to control the 8 TTL lines of the rear panel digital output port, used for controlling external equipment. Decimal The bit pattern appearing at the digital output port is set by an unsigned eight-bit binary number, the decimal equivalent of which can range from 0 to 255.
Chapter 5, FRONT PANEL OPERATION 5.2.12 Control Setup Menu Figure 5-13, Control Setup Menu The final setup menu, shown in figure 5-13, is used to set the instrument to a known state and to adjust the sampling rate of the main analog to digital converter. Default Setting Pressing a key adjacent to this label will set all of the instrument’s controls to a known state.
Chapter 5, FRONT PANEL OPERATION 5.3 Auto Functions Menu When in the Main Display mode, one press of the MENU key accesses the AUTO MENU showing four auto functions that are built into the instrument. The left-hand LCD changes to that shown in figure 5-14. Figure 5-14, Auto Functions Menu - Left-hand Display To activate one of the auto functions press one of the keys adjacent to it, as shown in figure 5-14.
Chapter 5, FRONT PANEL OPERATION are steady, implying the signal phase is stable, when the procedure is called. If a zero error is present on the outputs, such as may be caused by unwanted coupling between the reference and signal channel inputs, then the following procedure should be adopted:- 1) Remove the source of input signal, without disturbing any of the connections to the signal input which might be picking up interfering signals from the reference...
Chapter 5, FRONT PANEL OPERATION The line filter is disabled; AC coupling is established; the voltage measurement mode is entered, using the single-ended, A, input; the FET input devices are enabled; the FLOAT mode is set. If the reference frequency is more than 10 Hz the output time constant is set to 100 ms, otherwise it is set to the lowest synchronous value;...
Chapter 5, FRONT PANEL OPERATION Figure 5-15, Sensitivity Control - Voltage Input Mode When set to current input mode, the instrument’s full-scale current sensitivity may be set to any value between 20 fA and 1 µA (wide bandwidth mode) or 20 fA and 10 nA (low-noise mode), in a 1-2-5 sequence.
Chapter 5, FRONT PANEL OPERATION AC Gain If the AC Gain control is set to Manual (using the Input Setup menu), then this control allows it to be adjusted from 0 dB to 90 dB in 10 dB steps, although not all settings are available at all full-scale sensitivity settings.
Chapter 5, FRONT PANEL OPERATION 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. Note this control does not affect the roll-off of outputs at the FAST X and FAST Y connectors which are fixed at 6 dB/octave.
Chapter 5, FRONT PANEL OPERATION Oscillator Amplitude The amplitude of the instrument’s internal oscillator may be set, using this control, to any value between 1 mV and 5 V rms with a 1 mV resolution. Adjustment is faster if use is made of the Active Cursor control - see section 4.1.04. Figure 5-22, Internal Oscillator Amplitude Control DAC 1 This control sets the voltage appearing at the rear panel DAC1 output connector to...
Chapter 5, FRONT PANEL OPERATION DAC 2 This control sets the voltage appearing at the rear panel DAC2 output connector to any value between +10 V and -10 V with a resolution of 1 mV. Adjustment is faster if use is made of the Active Cursor control - see section 4.1.04. Figure 5-24, DAC 2 Output Control Offset This control allows an output offset to be added to the X output, Y output, neither or...
Chapter 5, FRONT PANEL OPERATION Reference Phase This control allows the reference phase to be adjusted over the range -360° to + 360° in 10m° steps, although readers will appreciate that a setting of -180° is equivalent to +180°, and that ±360° is equivalent to 0°. The Auto-Phase function also affects the value displayed here.
Chapter 5, FRONT PANEL OPERATION X %fs Figure 5-27, X Output as % Full-Scale Shows the X output as a percentage of the selected full-scale sensitivity setting. Hence if the sensitivity setting were 100 mV and a 50 mV signal were applied, with the instrument’s reference phase adjusted for maximum X output, the display would read 50.00 % Y %fs...
Chapter 5, FRONT PANEL OPERATION MAG %fs Figure 5-29, Magnitude Output as % Full-Scale Shows the signal magnitude, where magnitude = √((X output) + Y output) ), as a percentage of the selected full-scale sensitivity setting. Hence if the sensitivity setting were 100 mV and a 50 mV signal were applied, regardless of the setting of the instrument’s reference phase, the display would read 50.00 % Noise %fs...
Chapter 5, FRONT PANEL OPERATION Phase in Degrees Figure 5-31, Phase Output in Degrees Shows the relative phase, where phase = tan (Y output/X output), in degrees. Reference Frequency Figure 5-32, Reference Frequency Display Shows the reference frequency at which the lock-in amplifier is operating. Note that the display shows values in kHz only when the frequency is greater than 3 kHz.
Chapter 5, FRONT PANEL OPERATION X Volts (or Amps) Figure 5-33, X Output in Volts or Amps Shows the X output directly in terms of volts or amps (depending on whether voltage or current input mode is selected). Hence if the sensitivity setting were 100 mV and a 50 mV signal were applied, with the instrument’s reference phase adjusted for maximum X output, the display would read 50.00 mV Y Volts (or Amps)
Chapter 5, FRONT PANEL OPERATION MAG Volts (or Amps) Figure 5-35, Magnitude Output in Volts or Amps Shows the signal magnitude, where magnitude = √((X output) + (Y output) directly in terms of volts or amps (depending on whether voltage or current input mode is selected).
Chapter 5, FRONT PANEL OPERATION Ratio Figure 5-37, Ratio Output Shows the ratio, where ratio = (X output / ADC1 Input), usually used to compensate for source intensity fluctuations in optical experiments. Log Ratio Figure 5-38, Log Ratio Output Shows the logarithm to base 10 of the ratio, where ratio = (X output / ADC1 Input), usually used to compensate for source intensity fluctuations in optical experiments.
Chapter 5, FRONT PANEL OPERATION ADC1 Volts Figure 5-39, ADC 1 Input Shows the voltage applied to the rear panel ADC1 auxiliary input. ADC2 Volts Figure 5-40, ADC 2 Input Shows the voltage applied to the rear panel ADC2 auxiliary input. 5-33...
Chapter 5, FRONT PANEL OPERATION X Offset Figure 5-41, X Output Offset Control This control allows the X output offset to be adjusted, using the lower ADJUST keys adjacent to the displayed value. Note that although this control adjusts the level of the offset, it is only applied if the OFFSET control on the left-hand LCD is set to X or BOTH.
Chapter 5, FRONT PANEL OPERATION warning message OFFSET! The instrument provides a quick way to switch between the following pairs of outputs, by simply pressing simultaneously both ends of the SELECT keys adjacent to their description:- ↔ X %fs X volts or amps ↔...
Computer Operation Chapter 6.1 Introduction The model 7220 includes both RS232 and IEEE-488 (also known as GPIB for General Purpose Interface Bus) interface ports, designed to allow the lock-in amplifier to be completely controlled from a remote computer. All the instrument’s controls may be operated, and all the outputs read, via these interfaces.
BASIC code (see appendix C.1). 6.3.02 RS232 Interface - General Features The RS232 interface in the model 7220 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.
7-bit option can result in slightly faster communication. 6.3.05 Choice of Parity Check Option Parity checks are not required at the baud rates available in the model 7220, 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 7220 for dealing with parity errors.
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 7220 the address is set using the GPIB SETUP 1 setup menu or by means of the GP command.
RD input). However, these lines are not capable of implementing the handshaking function required by the model 7220 on a byte-by-byte basis and are not connected in the model 7220 apart from the RTS and DTR outputs which are constantly asserted.
The function of the individual bits in the status byte is instrument dependent, apart from bit 6 (the request service bit) whose functions are defined by the standard. In the model 7220, bits 0 and 7 signify ‘command complete’ and ‘data available’...
Chapter 6, COMPUTER OPERATION respectively. In GPIB communications, the use of these bits can lead to a useful simplification of the control program by providing a response subroutine which is the same for all commands, whether or not they send a response over the bus. The principle is that after any command is sent, serial poll operations are repeatedly executed.
In the model 7220 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. If any bit in the status byte becomes asserted, and the corresponding bit in the mask byte has a non-zero value, the SRQ line is automatically asserted.
Chapter 6, COMPUTER OPERATION 6.4 Command Descriptions This section lists the commands in logical groups, so that, for example, all commands associated with setting controls affecting the signal channel are shown together. Appendix E gives the same list of commands but in alphabetical order. 6.4.01 Signal Channel IMODE [n] Controls whether the instrument input is connected to a current or a voltage preamplifier...
Chapter 6, COMPUTER OPERATION CP [n] Input coupling control The value of n sets the input coupling mode according to the following table: Coupling mode SEN[.] [n] Full-scale sensitivity control The value of n sets the full-scale sensitivity according to the following table, depending on the setting of the IMODE control: full-scale sensitivity IMODE=0...
Chapter 6, COMPUTER OPERATION Perform an Auto-Measure operation The instrument adjusts its full-scale sensitivity so that the magnitude output lies between 30 % and 90 % of full-scale, and then performs an auto-phase operation to maximize the X output and minimize the Y output. ACGAIN [n] AC Gain control Sets the gain of the signal channel amplifier.
Chapter 6, COMPUTER OPERATION Notch filter mode 60 Hz (and/or 120 Hz) 50 Hz (and/or 100 Hz) Units made prior to June 1996 generate an Invalid Command (bit 1 of the serial poll status byte is asserted) to the LINE50 command. SAMPLE [n] Main analog to digital converter sample rate control The sampling rate of the main analog to digital converter, which is nominally...
Chapter 6, COMPUTER OPERATION FRQ[.] Reference frequency meter If the lock-in amplifier is in the EXT or EXT LOGIC reference source modes, the FRQ command causes the lock-in amplifier to respond with 0 if the reference channel is unlocked, or with the reference input frequency if it is locked. If the lock-in amplifier is in the INT reference source mode, it responds with the frequency of the internal oscillator.
Chapter 6, COMPUTER OPERATION 10 s 20 s 50 s 100 s 200 s 500 s 1 ks 2 ks 5 ks The TC. command is only used for reading the time constant, and reports the current setting in seconds. Hence if a TC 11 command were sent, TC would report 11 and TC.
Chapter 6, COMPUTER OPERATION Auto-Offset The X and Y output offsets are turned on and set to levels giving zero X and Y outputs. Any changes in the input signal then appear as changes about zero in the outputs. EX [n] Output expansion control Expands X and/or Y outputs by a factor of 10.
Chapter 6, COMPUTER OPERATION XY[.] X, Y outputs Equivalent to the compound command X[.];Y[.] MAG[.] Magnitude In fixed point mode causes the lock-in amplifier to respond with the magnitude value in the range 0 to 30000, full-scale being 10000. In floating point mode causes the lock-in amplifier to respond with the magnitude value in the range +3.000E0 to +0.001E-9 volts or +3.000E-6 to +0.001E-15 amps.
The first transfer takes a little longer than subsequent ones because some overhead time is required for the model 7220 to get into the high speed transfer mode. When in this mode, the front panel controls are inactive and display is frozen.
Chapter 6, COMPUTER OPERATION Caution: Check that the computer program does not automatically add a carriage return or carriage return-line feed terminator to the * command, since these characters will slow down communications. 6.4.06 Internal Oscillator OA[.] [n] Oscillator amplitude control In fixed point mode n sets the oscillator amplitude in mV.
Chapter 6, COMPUTER OPERATION FSTEP[.] [n Oscillator frequency sweep step size and type The frequency may be swept either linearly or logarithmically, as specified by parameter n . The step size is specified by parameter n Log sweep n In fixed point mode, n is the step size in thousandths of a percent.
Chapter 6, COMPUTER OPERATION BYTE [n] Digital output port control The value of n, in the range 0 to 255, determines the bits to be output on the rear panel digital output port. When n = 0, all outputs are low, and when n = 255, all are high.
Chapter 6, COMPUTER OPERATION TADC parameter Effect on CBD parameter none none automatically set to 32 automatically set to 96 automatically set to 32 automatically set to 96 automatically set to 32 automatically set to 96 automatically set to 32 automatically set to 96 The maximum sampling rate depends on the number of ADC inputs used and whether the sampling is timed or simply runs as fast as possible.
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) or TDC (take data continuously) commands are issued. Up to 16 curves, or outputs, may be acquired, as specified by the CBD parameter.
Chapter 6, COMPUTER OPERATION and HC commands. It also interacts with the LEN command and affects the values reported by the M command. LEN [n] Curve length control The value of n sets the curve buffer length in effect for data acquisition. The maximum allowed value depends on the number of curves requested using the CBD command, and a parameter error results if the value given is too large.
Chapter 6, COMPUTER OPERATION Halt curve acquisition Halts curve acquisition in progress. It is effective during both single (data acquisition initiated by TD command) and continuous (data acquisition initiated by TDC command) curve acquisitions. The curve may be restarted by means of the TD or TDC command, as appropriate.
Chapter 6, COMPUTER OPERATION The computer program’s subroutine which reads the responses to the DC command needs to run a FOR...NEXT loop of length equal to the value set by the LEN (curve length) command. Note that when using this command with the GPIB interface the serial poll must be used.
Chapter 6, COMPUTER OPERATION <X output value ><delim><Magnitude value ><term> <X output value ><delim><Magnitude value ><term> <X output value ><delim><Magnitude value ><term> <X output value ><delim><Magnitude value ><term> <X output value ><delim><Magnitude value ><term> etc, where <delim> and <term> are the delimiter and terminator characters respectively.
\N n Address command When the model 7220 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.
0, the front panel control functions normally. 6.4.11 Instrument Identification Identification Causes the lock-in amplifier to respond with the number 7220. Report firmware revision Causes the lock-in amplifier to respond with the firmware revision number. This gives a four line response which the controlling program must be able to accept.
Chapter 6, COMPUTER OPERATION 6.4.12 Front Panel LTS [n] Lights on/off control The value of n controls the front panel LEDs and LCD backlights according to the following table: Selection All lights off Normal operation 6.4.13 Default Setting Default Setting command This command will automatically set all the instrument controls and displays to the factory set default values.
Chapter 6, COMPUTER OPERATION The controlling program would send a new output command each time a new reading were required. Note that a good “rule of thumb” is to wait for a period of five time- constants after the input signal has changed before recording a new value. Hence in a scanning type experiment, the program should issue the commands to whatever equipment causes the input signal to the lock-in amplifier to change, wait for five time-constants, and then record the required output.
Chapter 6, COMPUTER OPERATION 6.5.04 X and Y Output Curve Storage Measurement In this example, the lock-in amplifier is measuring a current input signal applied to the B input connector and the measured X output and Y output are recorded for 10 seconds at a 100 Hz sampling rate.
Chapter 6, COMPUTER OPERATION Clear and reset curve buffer LEN 20000 500 ms recording time at 40 kHz = 20,000 points TADC 6 Set ADC1 sampling to burst mode, fixed rate (≈ 40 kHz), external trigger, and arm trigger As soon as a trigger occurs, the acquisition starts. Once it completes the acquired data may be transferred to the computer using:- DC.
Chapter 6, COMPUTER OPERATION Clear and reset curve buffer CBD 49180 Stores Magnitude, Phase, Sensitivity and Frequency (i.e. bits 2, 3, 4, 14 and 15) LEN 100 Number of points = 100 STR 100 Store a point every 100 ms - must match SRATE parameter The data may now be acquired by issuing the compound command: TD;...
Specifications Appendix Measurement Modes X In-phase Y Quadrature The unit can simultaneously present any R Magnitude two of these as outputs θ Phase Angle Noise Harmonic 2F or 3F Noise Measures noise in a given bandwidth centered on frequency F Displays Two LED backlit, two-line, 16-character alphanumeric dot-matrix LCDs giving...
Appendix A, SPECIFICATIONS Current Input Mode Low Noise or Wide Bandwidth Full-scale Sensitivity Low Noise 20 fA to 10 nA in a 1-2-5 sequence Wide Bandwidth 20 fA to 1 µA in a 1-2-5 sequence Dynamic Reserve > 100 dB (with no signal filters) Frequency Response Low Noise -3 dB at 500 Hz...
Appendix A, SPECIFICATIONS Orthogonality 90º ±0.0001º Drift < 0.01º/ºC below 10 kHz < 0.1º/ºC above 10 kHz Acquisition Time Internal Reference instantaneous acquisition External Reference 2 cycles + 50 ms Reference Frequency Meter Accuracy 120 kHz > F > 40 kHz ±4 Hz 40 kHz >...
Appendix A, SPECIFICATIONS Amplitude Range 1 mV to 5 V Setting Resolution 1 mV to 500 mV 1 mV 501 mV to 2 V 4 mV 2.001 V to 5 V 10 mV Accuracy 0.001 Hz to 60 kHz ±0.3 % 60 kHz to 120 kHz ±0.5 % Stability...
Appendix A, SPECIFICATIONS Signal Monitor Amplitude ±10 V FS Impedance 1 kΩ Aux D/A Output 1, 2 Maximum Output ±10 V Resolution 1 mV Accuracy ±0.1 % Output Impedance 1 kΩ 8-bit Digital Output 8 TTL compatible lines that can be independently set high or low to activate external equipment Reference Output...
Appendix A, SPECIFICATIONS General Dimensions Width 432 mm (17 ") Depth 415 mm (16.4 ") Height With feet 74 mm (2.9 ") Without feet 60 mm (2.4 ") Weight 7.4 kg (16.3 lb)
Pinouts Appendix B.1 RS232 Connector Pinout Figure B-1, RS232 and AUX RS232 Connector (Female) FUNCTION COMMENT Data In Data Out Signal Ground (Always at +12 V) All other pins are not connected. B.2 Preamplifier Power Connector Pinout Figure B-2, Preamplifier Power Connector FUNCTION -15 V GROUND...
Appendix B, PINOUTS B.3 Digital Output Port Connector Figure B-3, Digital Output Port Connector 8-bit TTL-compatible output set from the front panel or via the computer interfaces; each line can drive 3 LSTTL loads. This connector mates with a 20-pin IDC Header Plug.
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 GW-BASIC 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"...
Appendix C, DEMONSTRATION PROGRAMS B$=B$+CR$ ' append a carriage return GOSUB 180 ' output the command B$ GOSUB 310: PRINT Z$; ' read and display response IF A$="?" THEN GOSUB 410: GOSUB 470 ' if "?" prompt fetch STATUS% ' and display message 150 WEND ' return to start of loop 160 '...
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 GW-BASIC 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.
Appendix C, DEMONSTRATION PROGRAMS 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........340 WHILE 1 ' infinite loop INPUT "command (00 to exit) ";A$ IF A$="00"...
Appendix D.1 RS232 Cable Diagrams Users who choose to use the RS232 interface to connect the model 7220 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.
Alphabetical Listing of Commands Appendix ACGAIN [n] AC Gain control Sets the gain of the signal channel amplifier. Values of n from 0 to 9 can be entered corresponding to the range 0 dB to 90 dB in 10 dB steps. ADC[.] n Read auxiliary analog to digital inputs Reads the voltage appearing at the rear panel ADC1 (n = 1) and ADC2 (n = 2)
Appendix E, ALPHABETICAL LISTING OF COMMANDS Auto-Offset The X and Y output offsets are turned on and set to levels giving zero X and Y outputs. Any changes in the input signal then appear as changes about zero in the outputs.
Appendix E, ALPHABETICAL LISTING OF COMMANDS Decimal value Output and range X Output (±10000 FS) Y Output (±10000 FS) Magnitude Output (±10000 FS) Phase (±18000 = ±180°) Sensitivity setting (4 to 27) + IMODE (0, 1, 2 = 0, 32, 64) ADC1 (±10000 = ±10.0 V) ADC2 (±10000 = 10.0 V) Unassigned...
Appendix E, ALPHABETICAL LISTING OF COMMANDS CH n Analog output control Defines what outputs appear on the rear panel CH1 and CH2 connectors according to the following table: Signal X %FS Y %FS Magnitude %FS Phase 1: +9 V = +180°, -9 V = -180° Phase 2: +9 V = 360°, -9 V = 0°...
Appendix E, ALPHABETICAL LISTING OF COMMANDS The computer program’s subroutine which reads the responses to the DC command needs to run a FOR...NEXT loop of length equal to the value set by the LEN (curve length) command. Note that when using this command with the GPIB interface the serial poll must be used.
Appendix E, ALPHABETICAL LISTING OF COMMANDS <X output value ><delim><Magnitude value ><term> <X output value ><delim><Magnitude value ><term> <X output value ><delim><Magnitude value ><term> <X output value ><delim><Magnitude value ><term> <X output value ><delim><Magnitude value ><term> etc, where <delim> and <term> are the delimiter and terminator characters respectively.
Appendix E, ALPHABETICAL LISTING OF COMMANDS EX [n] Output expansion control Expands X and/or Y outputs by a factor of 10. Changes meter, CH1 and CH2 outputs full-scale to ±10 % if X or Y selected. The value of n has the following significance: Expand mode Expand X...
Appendix E, ALPHABETICAL LISTING OF COMMANDS FSTART[.] [n] Oscillator frequency sweep start frequency Sets the start frequency for a subsequent sweep of the internal oscillator frequency. In fixed point mode, n is in millihertz. In floating point mode n is in hertz. FSTEP[.] [n Oscillator frequency sweep step size and type The frequency may be swept either linearly or logarithmically, as specified by...
The curve may be restarted by means of the TD or TDC command, as appropriate. Identification Causes the lock-in amplifier to respond with the number 7220. IE [n] Reference channel source control (Internal/External) The value of n sets the reference input mode according to the following table:...
Appendix E, ALPHABETICAL LISTING OF COMMANDS LF [n] Signal channel line frequency rejection filter control In instruments manufactured prior to June 1996, the value of n sets the mode of the line frequency notch filter according to the following table: Selection On (i.e.
Appendix E, ALPHABETICAL LISTING OF COMMANDS LTS [n] Lights on/off control The value of n controls the front panel LEDs and LCD backlights according to the following table: Selection All lights off Normal operation Curve acquisition status monitor Causes the lock-in amplifier to respond with four values that provide information concerning data acquisition, as follows.
Appendix E, ALPHABETICAL LISTING OF COMMANDS \N n Address command When the 7220 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.
Appendix E, ALPHABETICAL LISTING OF COMMANDS OA[.] [n] Oscillator amplitude control In fixed point mode n sets the oscillator amplitude in mV. The range of n is 0 to 5000 representing 0 to 5 V rms. In floating point mode n sets the amplitude in volts. OF[.] [n] Oscillator frequency control In fixed point mode n sets the oscillator frequency in mHz.
Appendix E, ALPHABETICAL LISTING OF COMMANDS RS [n Set/read RS232 interface parameters The values of n set the baud rate of the RS232 interface according to the following table: Baud rate (bits per second) 134.5 1200 1800 2000 2400 4800 9600 19200 The lowest five bits in n...
Appendix E, ALPHABETICAL LISTING OF COMMANDS SEN[.] [n] Full-scale sensitivity control The value of n sets the full-scale sensitivity according to the following table, depending on the setting of the IMODE control: full-scale sensitivity IMODE=0 IMODE=1 IMODE=2 20 nV 20 fA 50 nV 50 fA 100 nV...
The first transfer takes a little longer than subsequent ones because some overhead time is required for the model 7220 to get into the high speed transfer mode. When in this mode, the front panel controls are inactive and display is frozen.
Appendix E, ALPHABETICAL LISTING OF COMMANDS return or carriage return-line feed terminator to the * command, since these characters will slow down communications. STR [n] Storage interval control Sets the time interval between successive points being acquired under the TD or TDC commands.
Appendix E, ALPHABETICAL LISTING OF COMMANDS SYNCOSC [n] Synchronous oscillator (demodulator monitor) control This control operates only in external reference mode. The parameter n has the following significance: Effect Synchronous Oscillator (Demodulator Monitor) disabled Synchronous Oscillator (Demodulator Monitor) enabled When enabled and in external reference mode, the instrument’s OSC OUT connector functions as a demodulator monitor of the X channel demodulation function.
Appendix E, ALPHABETICAL LISTING OF COMMANDS The maximum sampling rate depends on the number of ADC inputs used and whether the sampling is timed or simply runs as fast as possible. In the modes above described as Fixed Rate, sampling runs at the maximum possible rate, nominally 20 kHz when sampling both ADC1 and ADC2 or 40 kHz when sampling ADC1 only.
Appendix E, ALPHABETICAL LISTING OF COMMANDS Take data continuously Initiates data acquisition. Acquisition starts at the current position in the curve buffer and continues at the rate set by the STR command until halted by an HC command. The buffer is circular in the sense that when it has been filled, current data overwrites earlier points.
Appendix E, ALPHABETICAL LISTING OF COMMANDS YOF [n Y output offset control The value of n sets the status of the Y offset facility according to the following table: Selection Disables offset facility Enables offset facility The range of n is ±30000 corresponding to ±300 % full-scale.
Appendix E, ALPHABETICAL LISTING OF COMMANDS E-22...
Default Settings Appendix Default Setting Function The default setting function sets the model 7220’s controls and output displays as follows:- Left-hand LCD Displays the AC Gain control on the upper line and the full-scale sensitivity control on the lower line.
Appendix F, DEFAULT SETTINGS Line frequency rejection filter Off AC Gain control Manual Time constant mode Sync ADC trigger rate 200 Hz Front panel lights Display contrast RS232 interface settings Baud rate 9600 Data bits Stop bits Parity Even Prompt character Character echo Delimiter , (044)
Index Index * command 6-18, E-16 AUTO menu 4-4 \N n command 6-28, E-12 Auto repeat 4-3 2F reference mode 3-7, 5-4 AUTOMATIC [n] command 6-12, E-1 8-bit programmable output port 3-8 AUX RS232 connector 4-7 90° Key 4-5 Auxiliary ADCs 3-8 Auxiliary RS232 interface 6-4 Absolute accuracy 3-8 AXO command 6-16, E-2...
INDEX Computer control, sample programs 6-30 FAST X connector 4-8 Contrast control 5-10 output 3-7 Control options menu 5-8 FAST Y Control setup menu 5-17 connector 4-8 CP [n] command 6-11, E-4 output 3-7 Current input mode 3-2, 5-2 FET [n] command 6-10, E-7 Current to voltage converter 5-2 FET input device 3-2, 5-3 Current/voltage input mode selection 3-3...
INDEX Ratio display 5-32 SET key 4-5 RATIO output 5-7 Setup menu mode 4-4, 5-1 Rear panel layout 4-6 SIG MON connector 3-4, 4-7 REF IN connector 3-10, 4-2, 5-4 Signal channel inputs 3-2 REF MON connector 4-7 Signal channel overload 3-9 REF TTL connector 4-7, 5-4 Signal input connectors 4-1 Reference channel DSP 3-6...
INDEX Update program 3-8 Vector magnitude 3-8 Ventilation 2-1 VER command 6-29, E-20 VMODE [n] command 6-10, E-20 Voltage input mode 3-2 What is a lock-in amplifier? 1-2 X % output 5-6 X %fs display 5-27 X & Y demodulation functions 3-7 X in volts/amps display 5-30 X output offset level control 5-34 X[.] command 6-16, E-20...
WARRANTY EG&G Instruments Corporation warrants each instrument of its own manufacture to be free of defects in material and workmanship for a period of ONE year from the date of delivery to the original purchaser. Obligations under this Warranty shall be limited to replacing, repairing or giving credit for the purchase, at our option, of any instruments returned, shipment prepaid, to our Service Department for that purpose, provided prior authorization for such return has been given by an authorized representative of EG&G Instruments Corporation.