LI-7500 Software and Data Output

The LI-7500 Open Path CO₂/H₂O Gas Analyzer supports three data output options:

• Linearized analog voltages via the Digital-to-Analog Converters (DACs)
• RS-232 serial data
• Synchronous Device for Measurement (SDM) output for Campbell Scientific Inc. (Logan, Utah, USA) dataloggers.

Selectable output bandwidths of 5, 10, or 20 Hz are available (response times of approximately 0.1, 0.05 and 0.025 seconds, respectively).

The LI-7500 has a user-programmable feature known as Delay Time to allow synchronization of the LI-7500 CO₂ or H₂O data with data from sonic anemometers.  This delay time applies to all LI-7500 outputs (SDM, RS-232, and DAC).

RS-232 Output

Serial data output is available at baud rates to 38400, at rates of up to 20 times per second.  A software command is also available to query the LI-7500 for individual data records.

Digital-to-Analog Output

The LI-7500 uses a simple Windows® interface software for setup and calibration.  Two user-configurable linear DACs are updated 300 times per second by Digital Signal Processing (DSP) electronics.

SDM Output

Serial data can also be output at rates of up to 40 Hz using the SDM interface of Campbell Scientific Inc. dataloggers.  The SDM interface offers the advantage of polling the LI-7500 on demand for measurement or diagnostic information.  This allows the user to see real-time measurements and LI-7500 status information in the field without the aid of a computer.  Polling also allows a method for synchronizing CO₂, water vapor, and vertical wind speed data with a Campbell Scientific Inc. Sonic Anemometer.