Astronics / EADS / Racal 2681 Frequency/Time Interval Counter + Load

The Astronics / EADS / Racal 2681 is a 2-channel universal timer/counter delivering high-precision frequency and time interval measurements up to 200 MHz. Built for military ATE programs and demanding calibration environments, this instrument combines five automatic measurement functions with programmable triggering, integrated load control, and noise rejection in a single platform.

Technical Specifications Frequency Measurement

Range: DC to 200 MHz (Channel 1)

Resolution: Up to 9 digits per second Time Interval Measurement

Single-shot resolution: 1 ns

Average mode resolution: 100 ps

Time Error Correction (TEC) minimizes measurement time without performance loss Triggering

Programmable trigger level: −5.1 V to +5.1 V (or −51 V to +51 V in x10 mode)

Trigger resolution: 2.5 mV (or 25 mV in x10 mode)

Four standard sensitivity settings with switchable hysteresis to prevent false triggering Filtering

Independent 50 kHz low-pass filters on each channel for measurements in noisy environments Programmable Load

Type: Integrated five-watt resistive load

Range: 1 Ω to 100 kΩ with 0.1 Ω resolution

Built-in protection: over-current, over-voltage, over-power, and over-temperature Dynamic Range

x1 attenuation, below 50 MHz: 5 Vpk-pk minimum

Key Features

Five measurement functions: Frequency, Period, Time Interval, Time Interval Delay, and Totalize

Programmable measurement timeout for absent input signals

Nine arming modes with external arming input and VXI TTL trigger line selection

Support for external arming sources and VXI TTL triggering

Typical Applications Precision frequency and time interval analysis in calibration labs, military ATE systems, and test environments requiring sub-nanosecond timing resolution and programmable load simulation.

Compatibility & Integration joint services military ATE program requirements. Supports external arming sources and VXI TTL trigger lines for system integration.