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7124 Precision DSP Lock-in Amplifier

7124 Lock-in Amplifier
Model 7124 - Overview
The 7124 is the only DSP lock-in with a fiber optically separated analog front end giving you the best of both technologies.  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 More recently the analog phase sensitive detectors forming the heart of the instrument have been replaced by DSP (digital signal processing) designs, further improving performance.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 the next generation amplifier from the widely popular PARC-124. 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 be available in instruments of all-analog design.

Signal and Reference Connections
In normal use the 7124's signal and reference connections are made at the RCU. The signal input can be switched to operate in single ended or differential voltage mode, or in current mode with a choice of two transimpedance settings. It can also be used to switch between two single-ended voltage signals, for simple sequential measurement, under computer control, of two inputs. In cases where further preamplification is needed then one of the SIGNAL RECOVERY remote preamplifiers can be used, with its output connected to the 7124's single ended voltage input. This flexible choice of input modes allows the best possible connection to be made to the experiment. The RCU also has both general purpose analog and TTL logic reference inputs, as well as the output for a precision DDS oscillator that generates a sinewave signal of adjustable frequency and amplitude.

The RCU is connected to the main instrument console via a 16ft (5 m) fiber cable bundle that carries the applied signal and oscillator outputs in analog form, and control signals to the RCU and the reference signal from it, in digital format. However, the RCU contains no digital clocks or oscillators that are running continuously, and so unlike all other lock-in amplifiers that use any form of logic control, there is no digital switch noise present at the signal connectors.

  • Documents +

  • Specifications +

    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
    Indepance - 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 < 50 kHz minimum
    Low Noise < 2.5 kΩ @ 100 Hz
    Wide Bandwidth < 250 Ω @ 1 kHz
    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 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
    Range 0.5 Hz to 150 kHz
    Setting Resolution 1 mHz
    Absolute Accuracy ± 50 ppm
    Range 1 mV to 5 V
    Setting Resolution 1 mV
    Output Impedance 50 Ω
    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
    Accuracy ±1.0% typ
    Stability 100 ppm/ºC
    Distortion (THD) -80 dB @ 1 kHz and 100 mV rms
    Oscillator Output - Main Console
    Accuracy ±0.2% typ
    Stability 50 ppm/ºC
    Distortion (THD) -80 dB @ 1 kHz and 100 mV rms
    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)

    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
    RCU with option 7124/99
    Voltage ±24.0 V DC
    Current +300 mA / –170 mA
    Width 15½" (390 mm) 15½" (390 mm)
    Depth 7¼" (185 mm) 7¼" (185 mm)
    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)
    Preliminary specifications subject to change without notice

  • Software +

    Item Model Number
    Acquire Software
    The software includes a powerful plotting engine that lets you show data just as you want it using a variety of line styles, allows data export to both text and CSV files, offers comprehensive clipboard support, and includes a context-sensitive help system
    Active X Control SRINSTCOMMS