Most Eddy Covariance Flux Systems use the LI-7500 CO2/H2O Analyzer in conjunction with a Campbell Scientific Data Logger. The Campbell Data Logger communicates with a computer using a straight through type serial cable. This means pin 2 connects to pin 2, pin 4 to pin 4, etc. LI-COR, however, uses a combination of two serial cables for calibrating the LI-7500 CO2/H2O Analyzer, and for observing real-time values; a standard null modem cable (part no. 9975-016), and a second null modem cable (part no. 9975-015) with a connector on one end that mates with a connector inside the LI-7500 Control Box (see Typical LI-7500 Communication Cabling below).
If the 9975-016 is not available, and only a Campbell Scientific straight through type RS-232 serial cable is available, then the wires on a connector inside the LI-7500 Control Box that mate with the 9975-015 Serial Adapter Cable can be swapped to convert the communication path so that it can be used with the Campbell Scientific cable (or any other straight through serial cable) to connect directly to your computer.
To modify the connector inside the LI-7500 Control Box, refer to the diagram below. Simply swap the wires on the Serial Interface connector inside the Control Box as shown. The 9975-015 Serial Adapter Cable can then be used as shown in the diagram above with any straight through type serial cable to connect to your computer.