SRS
SR124 & SR2124 – analog lock-in amplifiers
Overview
For over a half century, the lock-in amplifier has been the instrument of choice for measuring small AC signals in the presence of noise. Early instruments were designed with analog electronics, multi-gang mechanical switches, needle indicators, etc., and measurements were often monitored with chart recorders. Microprocessor based designs emerged in the 1980s, and by the early 1990s even the lock-in’s analog demodulators were replaced by high-resolution ADCs and digital signal processors (DSP).
Feature
• Low noise, all analog design
• No digital interference
• 0.2 Hz to 200 kHz measurement range
• Low noise current and voltage inputs
• Harmonic detection (f, 2f, or 3f)
• Selectable input filtering
Technical Specifications
Signal Channel
Voltage inputs: Single-ended or differential
Sensitivity: 100 nV to 500 mV
Current input: 106 or 108 V/A
Input impedance
Voltage: 10 M?+ 35 pF, AC or DC coupled
Current input: 1 k? to virtual ground
Gain accuracy: ?1 %
Gain stability: 100 ppm/?C
(flat mode, normal reserve)
Noise (rms): 2.5 nV/?Hz at 1kHz
0.14 pA/?Hz at 1 kHz (106 V/A)
0.014 pA/?Hz at 100 Hz (108 V/A)
Signal filters: (Tuneable from 0.2 Hz to 200 kHz)
Flat: Flat response to within ?1% from 10 Hz to 100 kHz, ?2 % from 100 kHz to 200 kHz, and ?10% below 10 Hz.
Band pass: Bandwidth adjustable from 1% to 100% of center frequency (Q from 100 to 1).
High pass: ?12 dB/oct rolloff
Low pass: ?12 dB/oct rolloff
Notch: Up to 80 dB attenuation
CMRR: 100 dB at 10 kHz, decreasing by 6 dB/oct above 10 kHz
Dynamic reserve: (without band pass filter)
Low noise: 20 dB
Normal: 40 dB
High reserve: 60 dB
Reference Channel
Frequency range: 0.2 Hz to 200 kHz
Reference input: TTL or sine (100 mVpp min.)
Input impedance: 1 M?
Phase resolution: 0.01?
Phase accuracy: ?1? (2 to 20 kHz),
?5? (20 kHz to 200 kHz)
Harmonic detection: F, 2F and 3F (ext. ref)
Demodulator
Output stability:
Low noise: 20 ppm/?C
Normal: 100 ppm/?C
High reserve: 1000 ppm/?C
Time constants: 1ms to 300 s (6 or 12 dB/oct rolloff). Minimum time position, typically 500 ?s, is determined by stray capacitance. ?10% (to 200 kHz)
Internal Oscillator
Range: 0.2 Hz to 200 kHz
Outputs: Sine, square. (When using an external reference, output is phase locked to the external reference.)
Frequency accuracy: 0.1%
Frequency resolution: 3? digits or 1mHz, whichever is greater
Amplitude: 1?V to 20 Vpp into 10 k?, 50 ? output impedance.
Amplitude stability: 50 ppm/?C
VCO
VCO input: A 0 to 10 V signal corresponds to the beginning and ending frequencies in the range set on the front panel.
Displays
Panel meter: Center-zero, mirror-backed (a single meter for SR124, two meters for SR2124)
Offset: Output can be offset up to ?1000% of full scale
Reference: 3?-digit LED display
Inputs and Outputs
Lock-In/AC Volt: Instrument can be operated as a lock-in amplifier or as a frequency selective AC voltmeter.
Output
Lock-in: X (Rcos?), ?10 V
Y (Rsin?), ?10 V, SR2124 only
AC Volt: ?10 V
Ref. Out: Analog output. Sine or square wave, up to ?20 Vpp
Remote preamp: Provides power to the optional SR550, SR552 and SR554 preamps
Fiber optic interface: Connection for SX199 Remote Computer Interface Unit. The SX199 has GPIB (IEEE-488.2), RS-232, and Ethernet interfaces for remotely controlling the SR124.
RS-232 interface: RS-232 interface is standard. All instrument functions can be controlled and read through the interface.
Quadrant outputs: Four phase-shifted outputs at 0?, 90?, 180? and 270? from the reference. Output levels are 1Vrms sinewaves.
General
Power: 40 W, 100/120/220/240 VAC, 50/60 Hz
Dimensions: 17″” ? 5.25″” ? 19.5″” (WHD)
Weight: 23 lbs.
Warranty: One year parts and labor on defects in materials and workmanship
Others
N/A
