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LI-7700 Open Path CH4 Analyzer

The LI-7700 is designed specifically for eddy covariance flux measurements to evaluate methane emissions from the terrestrial landscape. It provides low-maintenance long-term operation in demanding field deployments.

  • SKU : E473-LI-7700
  • Manufacturer: Li-Cor
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Integrates with LI-COR Eddy Covariance Systems

The LI-7700 integrates easily with LI-COR eddy covariance systems without requiring any additional components. Using GPS clocks and the Precision Time Protocol (PTP), methane data are synchronized with wind speed and other measurements with sub-microsecond accuracy. Methane fluxes are computed on the SmartFlux® System at the same time as CO2 and H2fluxes.

For other applications, the LI-7700 can be ordered with the optional LI-7550 Analyzer Interface Unit, which provides analog, RS-232 serial, and SDM data outputs, as well as other functions.

The LI-7700 instrument
How it works

The only open path methane analyzer designed for field deployment in eddy covariance systems, the LI-7700 features innovations that ensure high performance, low-maintenance operation in the most demanding environments. A technological marvel, the LI-7700 maintains accuracy over a wide range of temperature and pressure fluctuations. The LI-7700 is capable of 40 measurements per second.

Wavelength Modulation Spectroscopy

The LI-7700 optical source is a single-mode tunable near-infrared laser, which operates at ambient temperature. Using Wavelength Modulation Spectroscopy (WMS), the laser scans across a single absorption feature of methane with high resolution. The wavelength is modulated across the absorption band at sub-MHz frequency. The LI-7700 demodulates the resulting signal at twice the modulation frequency. It compares the demodulated signal to a reference signal shape to determine CH4 concentration.

Pressure- and temperature-induced changes in line shape and population distribution, as well as changes in laser power and mirror reflectivity, are compensated using computational fitting algorithms. This ensures that measurements remain accurate over a wide range of pressure and temperature conditions.

LI-7700 Specifications
  • Resolution (RMS noise): 5 ppb @ 10 Hz and 2000 ppb CH4
  • Measurement Range: 0 to 25 ppm @ -25 °C, 0 to 40 ppm @ 25 °C
  • Data Communication: Ethernet (up to 40 Hz)
  • Detection Method: Wavelength Modulation Spectroscopy 2f detection
  • Linearity: Within 1% of reading
  • Operating Pressure Range: 50 to 110 kPa
  • Output Bandwidth: up to 20 Hz
  • Operating Temperature Range: -25 to 50 °C
  • Power Requirements: 10.5 to 30 VDC
  • Power Consumption: 8 W nominal, 16 W during cleaning cycle
  • Dimensions:
    • Sensor: 14.33 cm dia (5.64 inches), 82.8 cm height (32.6 inches)
    • Optical Path: 0.5 m physical path (1.65 ft), 30 m measurement path (98.4 ft)
  • Weight: 5.2 kg (11.5 lbs)
  • User Interface: Windows®based software supports all setup, configuration, and calibration functions through Ethernet connection
7700-101 Mirror Cleaner Specifications
  • Pump Operating Temperature Range: -10 °C to 50 °C
  • Weight: 3.2 kg (7 lbs)
  • Dimensions: 44.5 × 32.8 × 15 cm (17.5 × 12.9 × 6 inches)
  • Fluid Capacity: 4 liters (1.1 U.S. Gallon)
LI-7550 Specifications
  • Data Storage: Removable USB Storage Device. 16 Gigabyte Provided (expandable with user supplied Industrial Grade USB Flash Drive)
  • Data Communication:
    • Ethernet: up to 40 Hz
    • Synchronous Devices for Measurement (SDM): up to 33.3 Hz
    • RS-232: 57,600 baud, 20 records per second max.
    • DAC: 0-5 V, 40 Hz
  • Bandwidth: Up to 20 Hz
  • Inputs: Ethernet, 4 analog inputs, differential ±5 V, 16 bit
  • Operating Temperature Range: -25° to 50° C
  • Power Requirements: 10.5 to 30 VDC
  • Power Consumption: 10 W nominal
  • Dimensions: 35 × 30 × 15 cm (13.8 × 12 × 6 inches) external dimensions
  • Weight: 4.4 kg (10 lbs)

Specifications subject to change without notice.