General Description

What's What

This procedure should be followed if you have just taken delivery of your LI-840A. Check the packing list to verify that you have received everything that was ordered and that you have also received the following items:

  • RS-232 Cable - (Part #392-04993), used to connect the LI-840A to your computer. This cable is a null modem (cross-over) type cable; a straight through type cable will not work with the LI-840A. Appendix C shows the pin assignments for the DB-9 connector on the LI-840A front panel. An RS-232-to-USB converter is provided as well (Part # 6400-27)
  • Data Communications Software - This Windows® 7, 8/8.1, and 10 compatible software is used for communication between the LI-840A and a computer. The software is provided on CD. A complete description of this software can be found in Operation.
  • Standard Spare Parts Kit (9980-021) - This kit contains replacement parts for the LI-840A. As you become familiar with the analyzer you will learn which items to keep close at hand and which items can be stored away. The spare parts kit contains these items:
Description Qty. LI-COR Part No.
Spares Kit: 1 9980-021
Polyurethane Mounting Feet 4 234-02268
Mounting Screws 4 149-02610
Terminal Block 1 331-05273
Bev-a-line Tubing 12' 222-01824
Gelman Air Filter 2 9967-008
Quick Connect Unions 2 300-03123
Rapid Tube Fitting Nut 2 9861-036
2A Fuse 2 439-03952
Cleaning Kit: 1 9980-013
5" Cleaning Swabs 5 610-05315
O-Rings 4 192-00226
Pre-formed Optical Bench Tubing 4 6580-010


The LI-840A is an economical, high performance, non-dispersive infrared gas analyzer designed to be used for a wide variety of applications. Some of the LI-840A's important features include:

  • A 14 cm (5.5") optical bench is used to obtain a CO2 measurement range of 0-20,000 ppm (parts per million, or µmol/mol) and an H2O measurement range of 0-60 mmol/mol.
  • The optical bench is fully serviceable by the user; cleaning the optical bench is a simple process, and does not affect the instrument's factory calibration.
  • Simple Windows® software provides for easy user calibration and data output.


  • Avoid storing the LI-840A in humid conditions while powered off. Doing so can cause the optical sensor to become saturated with humidity, which will temporarily affect measurements when the instrument is removed from storage. See Storing the LI-840A for more details.
  • The optical bench is maintained at a constant temperature of about 50 °C. Avoid direct exposure to sunlight or extremely high temperatures that may elevate the temperature inside the LI-840A case.
  • The optical source is sensitive to vibration, and can be damaged by strong vibrations or jarring. Do not drop the LI-840A or expose it to severe mechanical shock.
  • Do not use abrasive cleansers when cleaning the optical bench, as damage to the gold plating may result. Instructions for cleaning the optical bench can be found in Section 5.
  • Always filter air entering the LI-840A. Two Gelman filter assemblies (p/n 9967-008) are included in the spares kit.