Catalog excerpts
Analog Lock-In Amplifiers SR124 — Analog lock-in amplifier SR124 Analog Lock-In Amplifier 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). Remote computer control, digital readouts and user-friendly front panels all resulted. · 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) The capabilities of the modern DSP lock-in amplifier in stability, dynamic reserve, and flexibility were revolutionary, making it a mainstay for researchers and engineers across multiple fields. But in moving forward, something was left behind. For a core group of users, including low-temperature researchers in particular, the new instruments became a potential source of high-frequency interference. This is best reflected in the persistence of one instrument — the PAR124A — still actively used by many researchers decades after discontinuation by its long-gone manufacturer. · Selectable input filtering Recognizing that one size shouldn’t have to fit all, SRS is proud to introduce the SR124 Analog Lock-In Amplifier. Inspired by the best of an earlier generation’s lock-ins, but availing itself of today’s low-noise analog components and design methodologies, the SR124 is an uncompromising tour de force in low-noise, high-performance analog instrumentation. Stanford Research Systems
Open the catalog to page 1SR124 Analog Lock-In Amplifier Architecture The SR124 design follows two basic themes. First, the signal path is entirely built from low-noise analog electronics: the best JFETs, transistors, op-amps, and discrete components. Second, configuration control is managed by a microcontroller whose system clock only oscillates during the brief moments needed to change gains or filter settings. This “clock-stopping” architecture, first introduced by SRS in the SR560 Voltage Preamplifier, eliminates the inconvenience and reliability issues associated with mechanical panel controls, and makes full...
Open the catalog to page 2SR124 Analog Lock-In Amplifier first chosen in the reference section of the front panel — either manually or by the auto Ref Range feature. be measured at a range of different bias values. Bias values can be set up to ±1000× the reference amplitude, depending on amplitude. In external reference mode, the SR124 will lock to external signals with at least 100 mVpp amplitude. The reference oscillator will phase-lock to the positive zero-crossings of the external reference input. Locking at f, 2f (second harmonic), or 3f (3rd harmonic) is supported. Phase Control The SR124 is a single phase...
Open the catalog to page 3Frequency accuracy 0.1 % Frequency resolution 3½ digits or 1 mHz, whichever is greater Amplitude 1 µV to 20 Vpp into 10 kΩ, 50 Ω output impedance. Amplitude stability 50 ppm/°C 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 MΩ + 35 pF, AC or DC coupled Current 1 kΩ to virtual ground Gain accuracy ±1 % Gain stability 100 ppm/°C (flat mode, normal reserve) Noise (rms) 2.5 nV/√Hz at 1 kHz 0.14 pA/√Hz at 1 kHz (106 V/A) 0.014 pA/√Hz at 100 Hz (108 V/A) Signal filters (Tunable from 0.2 Hz to 200 kHz)...
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