Model 441 lock-in amplifier

Dual phase OEM analogue lock-in amplifier

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  • A dual phase lock-in amplifier with manual setting, using jumpers, of input mode, sensitivity, low pass filter time constant and reference signal course phase control. Can be used in any of the following three modes:
  1. Dual phase operation – one input signal with two demodulators operating 90° apart providing both X and Y (or real and imaginery) components of the input signal.
  2. R calculation – on board circuitry provides the modulus of the X and Y components.
  3. Single channel 1F and 2F operation – one input signal and two demodulators operating at 1x and 2x the reference frequency to measure the first and second harmonics of the input signal.
  • Differential or single-ended input
  • Sensitivities from 3 µV to 10 V for 1 V output
  • High performance wide bandwidth input gain stage
  • Low pass filter output time constants from 100 µs to 30 s
  • 1F and 2F reference signal operation
  • 90° step and fine phase control
  • Power: -15 V, 0 V, +15 V and +5 V dc, at 50 mA per supply rail.

Input Signal Channels

The input signal channel amplifies the input signal to a level suitable for the demodulator. High performance, low-noise, broad-band amplifiers are used throughout. The input circuits can accept differential or single-ended inputs via the input SMB connectors. Options within the unit allow the outer SMB contact or screen to act as a high impedance differential input or allow it to be connected to ground for single-ended operation.

  • Input: Differential or single ended voltage via SMB socket
  • Input Gain: x0.1 to x330 in 1, 3.3, 10 steps
  • Input Impedance: 10¹² // 1 nF, dc coupled
  • Frequency: 10 Hz to 100 kHz
  • Maximum Inputs: ±10 V before saturation occurs
  • Input Noise Voltage: Other lock-in amplifier manufacturers give input noise values but without providing any definition of this specification. Indeed there is no meaningful definition of this specification in relation to lock-in amplifiers. As such, Scitec Instruments does not provide noise values and other manufacturers data sheets are considered misleading. Further details about input noise are available on request
  • Gain Accuracy: 1%
  • Gain Stability: 200ppm/°C
  • Dynamic Reserve: 0dB to 80dB


  • The input stage drives high bandwidth demodulators to recover the input signal.


  • The demodulator outputs are passed through low pass filters before being amplified for output.
  • Output Gain: x1, x10, x100, x1000
  • Low Pass Filter Time Constants: 100 µs to 30 s in 1, 3, 10 steps
  • Outputs – SMB connectors: +/-100 mV to +/-10 V full scale

Reference Channel

A single reference channel is used to generate the signals that drive the demodulator(s). A fine phase shifting circuit allows the reference signal to be phase shifted from 0° to 150° relative to the signal input. A second circuit then produces signals that are phase shifted by 0°, 90°, 180° and 270° at both the reference frequency and twice the reference frequency.

  • Frequency: 10 Hz to 100 kHz Trigger: Standard TTL, mark to space ratio in the range 20:1 to 1:20. Rising edge triggered
  • Acquisition Time: 10 s max.
  • Phase Control: 90° steps + fine shift of 0° – 150°
  • Phase Drift: 0.1°/C
  • 1F and 2F operation


  • Power connections are made via a 64 pin type C DIN41612 connector. Signal connections are not possible via this connector. Mechanical: 100 x 160 mm
  • Temperature Range: 0 – 50°C
  • Warranty: 1 year from date of shipment
  • Phase Drift: 0.1°/C
  • 1F and 2F operation