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Company:Signal Recovery
Product:DSP Lock-in Amplifier
Model7124
InformationSignal Recovery
Since their invention back in the 1960's, lock-in amplifiers have been used whenever the need arises to measure the amplitude and/or phase of a signal of known frequency in the presence of noise. Unlike other AC measuring instruments they have the ability to give accurate results even when the noise is much larger than the signal - in favorable conditions even up to a million times larger.

Since their invention back in the 1960's, lock-in amplifiers have been used whenever the need arises to measure the amplitude and/or phase of a signal of known frequency in the presence of noise. Unlike other AC measuring instruments they have the ability to give accurate results even when the noise is much larger than the signal - in favorable conditions even up to a million times larger.

Early instruments used analog technology, with manual controls and switches, and with output readings being taken from large panel meters. Later, microprocessors were added to give more user-friendly operation, digital output displays, and to support computer control. More recently the analog phase sensitive detectors forming the heart of the instrument have been replaced by DSP (digital signal processing) designs, further improving performance.

But the addition of this digital technology has had one unfortunate side effect, which is that the instrument itself can act as a source of digital clock and switching noise, which is typically coupled back into the experiment via the signal or internal oscillator connectors. This noise is of course rejected by the lock-in and generally does not impair its performance, but the power it dissipates in the sample or device under test can cause serious problems. This is particularly the case in low temperature physics experiments.

SIGNAL RECOVERY is therefore proud to introduce the model 7124 precision lock-in amplifier, which is particularly suited to such work. It uses a unique analog fiber optic link to interconnect a remote connection unit (RCU), to which the experiment is connected, and a main instrument console. In normal operation there are no digital clock signals within the RCU, and so it can emit no switching noise.

This architecture gives an instrument with all the advantages of the latest DSP technology for signal detection, and a powerful processor for easy user operation, as well as the low noise performance that until now has only been available in instruments of all-analog design. 

Specifications

The table gives the specifications for the Model 7124 Precision Lock-in Amplifier. A printable PDF brochure is also available - see the link on the left.

General Dual-phase DSP lock-in amplifier operating over a reference frequency range of 0.5 Hz to 150 kHz. All-analog front-end generating no digital clock or switching noise with fiber optic connections to a powerful DSP based instrument console.

Wide range of extended measuring modes and auxiliary inputs and outputs. 

User-upgradeable firmware.

Measurement Modes
Outputs The instrument can simultaneously show any four of these outputs on the front panel display:
X In-phase
Y Quadrature
R Magnitude
Θ Phase Angle
Noise
Harmonic Detection nF, n ≤ 127
Dual Harmonic Simultaneously measures the signal at two different harmonics F1 and F2 of the reference frequency
Dual Reference Simultaneously measures the signal at two different reference frequencies, F1 and F2 where F1 is the external and F2 the internal reference
Tandem Demodulation Demodulates the signal using the internal reference frequency F1, and then passes the resulting X channel output to a second demodulator running at an external reference frequency F2
Virtual Reference Locks to and detects a signal without a reference (100 Hz ≤ F ≤ 150 kHz)
Noise Measures noise in a given bandwidth centered at the reference frequency F
Spectral Display Gives a visual indication of the spectral power distribution of the input signal in a user-selected frequency range lying between  0.5 Hz and 250 kHz. Note that although the display is calibrated in terms of frequency, it is not calibrated for amplitude. Hence it is only intended to assist in choosing the optimum reference frequency
Display 320 x 240 pixel (¼ VGA) color TFT display panel giving digital, analog bar-graph and graphical indication of measured signals. Menu system with dynamic key function allocation.
Signal Channel - Remote Connection Unit (7124RCU)
Voltage Input
Modes A only, -B only or Differential (A-B)
Frequency Response 0.5 Hz < F < 150 kHz (–3dB)
Full-scale Sensitivity 2 nV to 1 V in a 1-2-5 sequence (e.g. 2 nV, 5 nV, 10 nV, 20 nV, etc.)
Impedance - FET input 10 MΩ // 25 pF, AC or DC coupled
Impedance - Bipolar input 10 kΩ // 25 pF, input must be DC coupled
Max safe input ±12.0 V
Voltage Noise 5 nV/√Hz @ 1 kHz
C.M.R.R. > 100 dB @ 1 kHz degrading by no more than 6 dB/octave with increasing frequency
Gain Accuracy ±1.0% typ, ±2.0% max
Distortion -90 dB THD (60 dB AC gain, 1 kHz)
Current Input
Mode Low Noise (10E8 V/A) or Wide Bandwidth (10E6 V/A)
Full-scale Sensitivity
  Low Noise 2 fA to 10 nA in a 1-2-5 sequence
  Wide Bandwidth 2 fA to 1 µA in a 1-2-5 sequence
Frequency Response (-3 dB):
  Low Noise 0.5 Hz < F < 500 Hz minimum
  Wide Bandwidth 0.5 Hz < F < 5 kHz minimum
Impedance
  Low Noise < 2.5 kΩ @ 100 Hz
  Wide Bandwidth < 250 Ω @ 1 kHz
Noise
  Low Noise 13 fA/√Hz @ 500 Hz
  Wide Bandwidth 130 fA/√Hz @ 1 kHz
Gain Accuracy ±2.0% typ, midband
Either Input Mode
Line Filter Filter can be set to attenuate 50/60 Hz, 100/120 Hz, or both frequency bands
Max. Dynamic Reserve > 100 dB
Grounding BNC shield can be grounded or floated via 1 kΩ to ground
Signal Monitor
  Amplitude  ±1 V FS. This is the signal after preamplification and filtering, but before transmission over the optical link
  Output Impedance 1 kΩ
Signal Channel - Main Console
Auxiliary Input
  Mode Single-ended voltage mode input
  Impedance  10 MΩ // 25 pF
  Maximum Safe
  Input
±12.0 V
  Full-scale
  Sensitivity
1 V
Signal Monitor
  Amplitude ±1 V FS. This is the signal received from the Remote Connection Unit immediately prior to conversion by the main ADC
  Output Impedance 1 kΩ
Reference Channel
Reference Input - Remote Connection Unit or Main Console
TTL Input (rear panel)
Frequency Range 0.5 Hz to 150 kHz
Analog Input (front panel)
  Impedance 1 MΩ // 30 pF
  Sinusoidal Input
    Level 1.0 V rms*
    Frequency Range 0.5 Hz to 150 kHz
  Squarewave Input
    Level 250 mV rms
Frequency Range 2 Hz to 150 kHz
Reference Channel
Phase Set Resolution 0.001° increments
Phase Noise at 100 ms TC, 12 dB/octave slope:
  Internal Reference < 0.0001° rms
  External Reference < 0.01° rms @ 1 kHz
Orthogonality 90° ± 0.0001°
Acquisition Time
  Internal Reference instantaneous acquisition
  External Reference 2 cycles + 1 s
Reference Frequency Meter Resolution 4 ppm or 1 mHz, whichever is the greater
Demodulator and Output Processing
Output Zero Stability
  Digital Outputs No zero drift on all settings
  Displays No zero drift on all settings
  DAC Analog Outputs <  100 ppm/°C
Harmonic Rejection -90 dB
Output Filters
  Time Constant 10 µs to 100 ks in a 1-2-5 sequence
  Slope (roll-off):
    TC < 5 ms 6 or 12 dB/octave
    TC > 5 ms 6, 12, 18 or 24 dB/octave
Synchronous Filter Available for F < 20 Hz
Offset Auto and Manual on X and/or Y: ±300% full-scale
Phase Measurement Resolution <  0.01º
Reference Monitor TTL signal at current reference frequency, internal or external
Oscillator - General
Frequency
  Range 0.5 Hz to 150 kHz
  Setting Resolution 1 mHz
  Absolute Accuracy ± 50 ppm
Amplitude
  Range 1 mV to 5 V
  Setting Resolution 1 mV
Output Impedance 50 Ω
Sweep
  Frequency Sweep
    Output Range 0.5 Hz to 150 kHz
    Law Linear or Logarithmic
    Step Rate 1 kHz maximum (1 ms/step)
  Amplitude Sweep
    Output Range 0.000 to 1.000 V rms
    Law Linear
    Step Rate
       Main
       Console       
20 Hz maximum (50 ms/step)
       RCU        1 Hz maximum (1 s/step)
Oscillator Output - Remote Connection Unit
Amplitude
  Accuracy ±1.0% typ
  Stability 100 ppm/ºC
  Distortion (THD)  -80 dB @ 1 kHz and 100 mV rms
Oscillator Output - Main Console
Amplitude
  Accuracy ±0.2% typ
  Stability 50 ppm/ºC
  Distortion (THD)   -80 dB @ 1 kHz and 100 mV rms
Auxiliary Inputs
ADC 1, 2, 3 and 4
  Maximum Input ±11 V
  Resolution 1 mV
  Accuracy ±20 mV
  Input Impedance 1 MΩ // 30 pF
  Sample Rate 250 kHz maximum (one ADC only)
  Trigger Mode Internal, External or burst
  Trigger Input TTL compatible, rising or falling edge
Outputs
Analog Outputs
DAC1 X, X1, Mag2, User DAC1, Output function
DAC2 Y, Y1, Pha2, User DAC2, Output function
DAC3 X2, Mag, Mag1, User DAC3, Output function
DAC4 Y2, Pha, Pha2, User DAC4, Output function
Output Functions Noise, Ratio, Log Ratio and User Equations 1 & 2
Amplitude
  X(1), Y(1), Mag(1),
  Pha(1)
±2.5 V full-scale; linear to ±300% full-scale
  User DACs and
  Output Functions
±11.0 V full-scale
  Impedance 1 kΩ
  Update Rate
    X(1/2), Y(1/2),
    Mag(1/2), Pha(1/2)
    @ TC < 1 s
1.0 MHz
    User DACs, Output
    Functions and
    TC’s > 1 s
1 kHz
8-bit Digital Port - 7124RCU
  Mode 8 TTL outputs
  Status Each output line can be set high or low
8-bit Digital Port - Main Console 
  Mode 0 to 8 , lines can be configured as inp, uts,, with the remainder being outputs
  Status Each output line can be set high or low and the status of each input line read
Power - Low Voltage ±15 V at 100 mA 5-pin 180° DIN connectors on both main console and remote connection unit for powering compatible SIGNAL RECOVERY preamplifiers
Data Storage Buffer
Size 100,000 data points
Max. Storage Rate
  Fast Mode up to 1 MHz (X1, Y1, X2, Y2, ADC1, Demod I/P 1, Demod I/P 2)
  Normal Mode 1 kHz
User Settings
Up to 8 complete instrument settings can be saved or recalled at will from non-volatile memory
Interfaces
USB 2.0, Ethernet, and RS232 on main console allow complete control of instrument settings, and data readout. Four channel 5 m (16ft) fiber optic link between main console and remote connection unit.
General
Main Console 7124 RCU
Power Requirements
  Voltage 110/120/220/240 VAC 110/120/220/240 VAC
  Frequency 50/60 Hz 50/60 Hz
  Power 40 VA max 15 VA max
Dimensions
  Width 15½" (390 mm) 15½" (390 mm)
  Depth 7¼" (185 mm) 7¼" (185 mm)
  Height
    With feet 7¼" (185 mm) 3" (75 mm)
    Without feet 6½" (170 mm) 2½" (64 mm)
Weight 12.8 lb (5.8 kg) 7.9 lb (3.6 kg)
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