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
Designed to meet joint services military ATE program requirements. Supports external arming sources and VXI TTL trigger lines for system integration.
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