Keysight / Agilent / HP 53131A Universal Counter

The Keysight 53131A Universal Counter is a high-performance instrument for precise frequency, time interval, and phase measurements across research, manufacturing, and service applications. It delivers 10-digit frequency resolution, 500 ps time interval resolution, and real-time digital signal processing that simultaneously analyzes incoming data while capturing new measurements. The instrument supports dual standard channels at 225 MHz bandwidth, with optional third-channel capability up to 12.4 GHz. Flexible input impedance (50 ohm or 1 megohm), AC/DC coupling, and adjustable trigger levels accommodate diverse signal environments. Built-in statistics track average, minimum, maximum, and standard deviation in real time. Automated limit testing with out-of-limit flagging and trigger outputs enables production screening. The 53131A includes GPIB (IEEE-488) and RS-232 interfaces with SCPI compatibility, plus optional USB connectivity. IntuiLink connectivity software supports instrument setup and data monitoring. Time base options range from standard (<3 × 10⁻⁷/month aging) to high-stability oven references (5 × 10⁻¹⁰ per day or 2 × 10⁻⁸ per year aging rates). The instrument stores up to 20 front-panel setups for rapid recall. Compact form factor (89 mm H × 213 mm W × 348 mm D, 7 lb) with removable handle and bumpers supports benchtop or rack-mount operation. Measurement functions include frequency, period, ratio, time interval, pulse width, rise/fall time, phase angle, duty cycle, and totalize.