The LI-7550 Analyzer Interface Unit (AIU) is an integral component of the LI-7200 and LI-7500A CO₂/H₂O Analyzers. Each analyzer is shipped with a compatible LI-7550 AIU. The following table compares the capabilities of an LI-7550 equipped with various embedded software versions, including the latest version.

Feature	Version 4 (April, 2010)	Version 5 (April, 2011)	Version 6 (July, 2012)	Version 7.5 (July, 2015)
Digital Signal Processing for CO2 and H2O data	Yes	Yes	Yes	Yes
Regulation and control of critical components on the sensor head	Yes	Yes	Yes	Yes
Integration of sonic anemometer data through auxiliary inputs	Yes	Yes	Yes	Yes
Integrate and time align CH4 data from the LI-7700 through the Ethernet port for on board data logging to a USB drive	CH4 data on a separate file on USB drive (not time aligned)	Yes	Yes	Yes
Record metadata along with raw data and compress it to .ghg format for processing with EddyPro® data processing software	Data on USB drive recorded as text files; no compression, no metadata	Yes	Yes	Yes
Integrate biological and meteorological measurements from a LI-COR Biomet System through Ethernet port	No		Yes	Yes
Provide on board data logging to a USB memory stick for integrated CO2, H2O, CH4, sonic (u, v, w, Ts, or SOS), and biomet variables (net radiation, PAR, RH, Tair, etc.)	Two files; one for CO2/H2O and sonic and one for CH4 and sonic. No biomet data	All in one file	Yes	Yes
View LI-7700s on remote network. View, graph, and log CH4 values in the Windows application software	No	No	No	Yes
New help system and support for SmartFlux® System. Vin visible in Diagnostics, auto GPS coordinates in site setup, graphing of flux results, flux results to USB	No	No	No	Yes
CO2/H2O mass densities and efficiency improvements	No	No	No	Yes

The LI-7200/RS Software Change Log can be found here.

The LI-7500A/RS Software Change Log can be found here.

The LI-7550 AIU with a modified software version can optionally be used with the LI-7700 CH₄ analyzer. An LI-7550 that was purchased solely for use with an LI-7700 is designated as part number LI-7550-1. When the modified version (LI-7550-1) is used with LI-7700 CH₄ analyzers, the LI-7550-1 AIU serves the following functions:

1. Handles all CH₄ data output on the DACs, Ethernet, Serial (RS-232), and SDM channels.
2. Integrates sonic anemometer data through Auxiliary Inputs
3. Integrates CH₄ data from the LI-7700 through the Ethernet Port.
4. Provides on-board data logging for CH₄ and sonic (u, v, w, Ts, or SOS) data.

The LI-7700 outputs Ethernet data, so the LI-7550-1 AIU is intended for use with the LI-7700 and data loggers or data collection devices that require RS-232, SDM or analog outputs. However, it doesn’t integrate CO₂ and H₂O data or biomet data. In addition, it doesn’t record metadata and doesn’t compress raw data into the .ghg file format.

The LI-7550 AIU that comes with the LI-7200 or LI-7500A can integrate CH₄ data from the LI-7700 into the same file as CO₂/H₂O data as long as it is running version 5.0 or higher. You can view the Quick Start Guide that details how to set up the LI-7200 or LI-7500A and LI-7700 here:

https://licor.app.boxenterprise.net/s/82ktruk14saiyt435d03

Earlier firmware versions (4.0) of the LI-7550 that came with the LI-7200 or LI-7500A logged CH₄ data to a separate file. At that point it was necessary to split the sonic signal to go to LI-7700 and LI-7200 or LI-7500A to make sure both data sets contained sonic and gas analyzer data. As of version 5.0, released in April, 2011, there is no need to split the sonic signal. All CO₂/H₂O data from the LI-7200 or LI-7500A, CH₄ data from LI-7700, and sonic anemometer data through the auxiliary inputs of the LI-7550 can be logged to the same file with synchronized time stamps. An LI-7550-1 that was purchased solely for use with the LI-7700 can be converted to be used as a LI-7550 for CO₂/H₂O (similar to the LI-7550 that is purchased with a LI-7200 or LI-7500A). This conversion allows the LI-7550 to provide the integration capability mentioned earlier when connected to an LI-7200 or LI-7500A and LI-7700. However, this conversion will also dedicate the other output channels (RS-232, SDM, and DAC) to only CO₂/H₂O data and not CH₄ data. If you would like to convert your LI-7550, follow the instructions given in the following document:

https://licor.app.boxenterprise.net/s/dl7gqsbw0nr2yz5od2fqhe8lj8eba1rl

Alternatively, an LI-7550 that was purchased for an LI-7200 or LI-7500A can be converted to be used as an LI-7500-1 for CH₄ outputs on the DACs, Ethernet, Serial (RS-232), and SDM channels. Keep in mind however, that once converted, it will not function with the LI-7200 or LI-7500A without reinstalling the software.