Astronics / EADS / Racal 2251 VXI Counter Timer

The Astronics / EADS / Racal 2251 is a single-slot, C-size VXI counter timer module engineered for precision measurement applications requiring extensive arming and triggering control. Installed in a VXIbus-compatible mainframe and controlled remotely over VXIbus, it delivers frequency, period, time interval, pulse width, rise/fall time, frequency ratio, phase, and totalizing measurements across multiple input channels with nanosecond-level resolution.

Technical Specifications Form Factor & Control

Single-slot, C-size VXI module

VXIbus System Specification Revision 1.4 compatible

Remote VXIbus control only; no local control

NSN: 6625-01-371-8269 Frequency Measurement

Channel A: DC to 200 MHz

Channel B: DC to 160 MHz

Channel C (Option 41): 40 MHz to 1.3 GHz

Resolution: Up to 9 digits per second at 1 GHz; 10 nHz at 10 Hz in one second Time & Period Measurement

Period: 5 nS (Channel A), 6.25 nS (Channel B)

Time Interval: −2 ns to 1 × 10⁹ sec; 1 ns (single-shot), 100 ps (average mode)

Pulse Width: 5 ns to 20 ms Input Conditioning

Sensitivity: <100 MHz: 25 mVrms, 75 mVp-p

Input Voltage Range: ±5.1 V or ±42 V

Trigger Resolution: 2.5 mV (manual mode)

Low Pass Filters: 50 kHz per channel Measurement Functions

Frequency Ratio: Channel A/B; Channel C/B (Option 41, to 1.3 GHz)

Phase Measurement: Phase A relative to B; 0.10 to 360 degrees

Totalizing: Total A by B; manual totalize modes

Rise/Fall Time: Programmable trigger level −5.1 V to +5.1 V

Check Mode operation Accuracy & Performance

Accuracy: ± Resolution ± Timebase Error × Frequency

VXIbus CLK10: 100 ppm typ.

Typical Applications Frequency and period measurement; time interval and pulse width characterization; rise/fall time analysis; phase relationship determination; event counting and frequency ratio computation.

Compatibility & Integration Operates within VXIbus mainframe environments. No standalone operation.