LI-7200 Key Features

Advantages

The LI-7200 CO2/H2O Analyzer is a high-performance non-dispersive infrared gas analyzer designed for demanding applications, such as eddy covariance measurements. It maximizes the strengths of traditional open-path and closed-path instruments.

Unlike closed-path instruments, the LI-7200 mounts on a flux tower or measurement platform right next to other measurement devices. It uses a short intake tube and an energy efficient flow module (optional) to draw sample air through the optical path. The tube can be as short as few centimeters or as long as many meters, but the optimal length is 0.5 m to 1 m. The 1 m intake tube provided with the instrument minimizes attenuation of CO2/H2O, while attenuating temperature by 90-95%. The remaining fluctuations are measured in the cell with two fast temperature sensors and a fast pressure sensor. This virtually eliminates the complications that result from long tubing runs.

Benefits of Closed Path

• Minimal data loss due to precipitation and icing
• No surface heating issues - fast cell temperature measurementes
• Possibility of automated calibrations on tower
• Minimal-to-negligible WPLH correction
• Possible to heat the system to prevent ice build up in extremely cold environments

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Benefits of Open Path

• Good frequency response for both CO2 and H2O measurements
• Small and easily corrected flux attenuation in short intake tube
• Tool-free optical cell cleaning
• Low power requirements
• System simplicity, small size, light weight, and weather-proof design

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LI-7200 CO2/H2O Analyzer

System Integration

The LI-7200 enables the collection of integrated data sets during long-term eddy covariance deployments. CO2/H2O density, sonic anemometer, and auxiliary data can be logged together to an onboard USB data storage device or output to an external storage device.
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The LI-7200 uses an intuitive Windows® interface for set-up and calibration. The software provides complete control over instrument settings and data logging options. The inexpensive 7550-101 Auxiliary Sensor Interface accessory provides weatherproof connections for a sonic anemometer and additional thermocouples.

7200-101 Flow Module

The 7200-101 Flow Module (optional) is an energy efficient, durable blower unit designed to provide a precisely controlled airflow rate through the LI-7200 optical path. With an internal precision mass flow sensor and intelligent feedback controls, the flow module actively regulates flow to ensure a stable, carefully monitored airflow rate.

The 7200-101 Flow Module outputs mass flow rate, volume flow rate, and pressure drops with the data record, and it provides diagnostic data to indicate when filters need to be cleaned or replaced.

The LI-7200 provides versatile data output options, including:

• 6 High speed Digital-to-Analog converters (20 Hz bandwidth)
• SDM (Synchronous Devices for Measurement) for logging to Campbell Scientific, Inc. data loggers (>40 Hz)
• Ethernet (20 Hz)
• RS-232 (20 Samples/Sec.)

Eddy Covariance

The LI-7200 is optimized for the eddy covariance technique. With the eddy covariance method, the flux, Fc of gas C (e.g. CO2) is given by where c' is the density fluctuations of the gas (mmol/m3), and w' is the vertical wind velocity fluctuations (m/s). The LI-7200 has the high speed and precision required for this method. The flux of CO2 and H2O is obtained from the vertical wind speed (measured with a sonic anemometer) and the concentration of the gas (measured with the LI-7200).

Advantages of the LI-7200 for Eddy Covariance Measurements

• Based on the proven LI-7500 Open Path CO2/H2O Analyzer.
• Provides continuous measurements through rain, fog, and snow.
• The LI-7200 integrates and stores data from any fast sonic anemometer (ATI, CSI, Gill, Kaijo, Metek, RM Young).
• Includes the LI-7550 Analyzer Interface Unit for datalogging.
• The 7200-101 Flow Module provides an efficient, integrated air-flow solution for the enclosed analyzer.

Software

Intuitive Windows® software provides versatile, yet simple instrument set-up. Configuring the instrument is accomplished using either the RS-232 or Ethernet connection. When using Ethernet, any LI-7200 that is connected to the network can be configured from any computer on the network (with the LI-7200 configuration software installed).

The graphical controls window provides easy access to instrument settings, including auxiliary sensor inputs, flow rate (with the 7200-101 Flow Module) live data charting, and data logging settings.