Stanford Research Systems Model SR540 Chopper Controller

The SR540 is a precision‑engineered optical chopper — a device that periodically interrupts a light beam to modulate it. It’s widely used in lock‑in amplification, spectroscopy, and other signal recovery experiments due to its low phase jitter and wide frequency range (4 Hz–3.7 kHz.

📊 Key Specifications

• Chopping Frequency:

  • 4–400 Hz (using 5/6‑slot blade)

  • 400 Hz–3.7 kHz (using 25/30‑slot blade)

• Frequency Stability: ~250 ppm/°C; Drift <2% between 100 Hz and 3.7 kHz

• Phase Jitter: 0.2° rms at 50–400 Hz; 0.5° rms up to 3.7 kHz

• Reference Outputs: Dual BNC ports supporting inner/outer, sum, difference, and 5× outer modes

• Control:

  • Digital 4‑digit display, 1 Hz resolution

  • 10‑turn front‑panel potentiometer (spanning three ranges)

  • External 0–10 V VCO input overrides manual control