Signal Recovery Model 7230 Dual Phase DSP Lock-in Amplifier

Overview

The model 7230 is a new concept in general-purpose DSP lock-in amplifiers. It offers the excellent signal recovery performance that users expect from our instruments but at a lower price than many competitive models. We’ve achieved this improvement in price/performance ratio by replacing traditional control buttons and display with easy-to-use control panels that can be operated from any computer via your favorite browser. No longer do you need to be in front of the instrument to operate it - now you can set up your experiment in the lab but return to the office while it runs, monitoring what is happening via your computer. And if you need to make a change to a setting then it’s as easy as clicking a button on a web page.

You can use any web compatible device to operate the model 7230, ranging from a simple netbook to the most powerful development machine, from an Android smartphone to the latest iPad. No special software is needed, since the panels work directly through the device’s browser. All that is necessary is that the computer and instrument be connected to the same Ethernet network.

The instrument is also much more compact than traditional designs, making it easier to accommodate in crowded laboratories, and as it does not include any cooling fans it is completely silent, which is especially useful for acoustic research.

It is normally configured for operation over a frequency range extending from 1 mHz to 120 kHz. However, for a small extra charge it can also be delivered, or upgraded via a firmware update pack, to allow operation at frequencies of up to 250 kHz.

Specifications

Note: † In the following specifications, the upper frequency limit for the standard model 7230 is 120 kHz; when fitted with the model 7230/99 it is 250 kHz

Measurement Modes

  • X In-phase, Y Quadrature, R Magnitude, θ Phase Angle, Noise: The instrument can simultaneously show any four of these outputs via the web control pages
  • Harmonic: n × F, 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 one is the internal and the other the external reference
  • Tandem Demodulation: Demodulates the signal using the internal reference frequency, and then passes the resulting X channel output to a second demodulator running at an external reference frequency
  • Virtual Reference: Locks to and detects a signal without a reference (100 Hz ≤ F ≤ 120/250 kHz †)
  • Noise: Measures noise in a selected bandwidth centered at the reference frequency F

Signal Channel

Voltage Input
  • Modes: A only, –B only or Differential (A–B)
  • Frequency Response: 1 mHz ≤ F ≤ 120/250 kHz †
  • Full-scale Sensitivity: 10 nV to 1 V in a 1-2-5 sequence (e.g. 10 nV, 20 nV, 50 nV, 100 nV, etc.)
  • Input Impedance
    • FET Input: 10 MΩ // 25 pF, AC or DC coupled
    • Bipolar Input: 10 kΩ // 25 pF, input must be DC coupled
  • Maximum Safe Input: ±12.0 V
  • Voltage Noise
    • FET Input: 5 nV/√Hz @ 1 kHz
    • Bipolar Input: 2 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: ±0.5% typ, ±1.0% max.
  • Distortion: -90 dB THD (60 dB AC gain, 1 kHz)
Current Input
  • Mode
    • Low Noise (108 V/A)
    • Wide Bandwidth (106 V/A)
  • Full-scale Sensitivity
    • Low Noise: 10 fA to 10 nA in a 1-2-5 sequence
    • Wide Bandwidth: 10 fA to 1 μA in a 1-2-5 sequence
  • Frequency Response (-3dB)
    • Low Noise: 1 mHz ≤ F ≤ 500 Hz minimum
    • Wide Bandwidth: 1 mHz ≤ F ≤ 50 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 @ 50 kHz
  • Gain Accuracy: ± 2.0% typ, midband
Either Input Mode
  • Max. Dynamic Reserve: > 100 dB
  • Line Filter: Filter can be set to attenuate 50/60 Hz, 100/120 Hz, or both frequency bands
  • Grounding: BNC shields can be grounded or floated via 1 kΩ to ground
Signal Monitor
  • Amplitude: ±1 V FS. This is the signal after preamplification and filtering immediately prior to conversion by the main ADC
  • Output Impedance: 1 kΩ

Reference Input

  • TTL setting
    • Frequency Range: 1 mHz to 120/250 kHz †
  • Analog setting
    • Impedance: 1 MΩ // 30 pF
    • Sinusoidal Input:
      • Level: 1.0 V rms
      • Frequency Range: 0.5 Hz to 120/250 kHz †
    • Squarewave Input
      • Level: 250 mV rms
      • Frequency Range: 2 Hz to 120/250 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

Demodulators 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/Manual on X and/or Y: ±300% F.S.
  • Phase Measurement Resolution: ≤ 0.01°
  • Reference Monitor: TTL signal at current reference frequency, internal or external

Oscillator

  • Frequency
    • Range: 1 mHz to 120/250 kHz †
    • Setting Resolution: 1 mHz
    • Absolute Accuracy: ± 50 ppm
  • Amplitude
    • Range: 1 μV to 5 V
    • Max Setting Resolution: 1 μV
  • Output Impedance: 50 Ω
  • Sweep
    • Frequency
      • Output Range: 1 mHz to 120/250 kHz †
      • Law: Linear or Logarithmic
      • Step Rate: 1000 Hz maximum (1 ms/step)
    • Amplitude Sweep
      • Output Range: 0.000 to 5.000 V rms
      • Law: Linear
      • Step Rate: 20 Hz maximum (50 ms/step)

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: 200 kHz maximum (one ADC only)
    • Trigger Mode: Internal, External or burst
    • Trigger Input: TTL compatible, rising or falling edge

Outputs

Analog Outputs
DAC1
DAC2
DAC3
DAC4
Output Functions
X, X1, Mag2, User DAC1, Output function
Y, Y1, Pha2, User DAC2, Output function
X2, Mag, Mag1, User DAC3, Output
function
Y2, Pha, Pha2, User DAC4, Output
function
Noise, Ratio, Log Ratio and User Equa-
tions 1 & 2.
Amplitude
X(1), Y(1), Mag(1), Pha(1)
±2.5 V full-scale; linear to ±300% F.S.
User DACs and Output Functions
±10.0 V full-scale
Impedance
1 kΩ