General information

The LI-7700 is a high-speed, high-precision open path methane analyzer designed for use in eddy covariance flux and atmospheric monitoring applications. It uses Wavelength Modulation Spectroscopy (WMS) to make high-speed, precise measurements of methane concentrations at ambient pressure and temperature. It is designed to withstand environmental extremes expected during outdoor deployments. Some features of the LI-7700 include fast response (data are output at up to 20 Hz bandwidth), low power requirements (8 W during normal operation), withstands outdoor environmental extremes, including freezing weather and high temperatures (-25 to 50 °C) and rain without damage or calibration shifts.

When used in conjunction with an LI-7500A/RS/DS or LI-7200/RS CO2/H2O gas analyzer and the SmartFlux System, measurements from the gas analyzers and sonic anemometer are logged in self-contained data files and flux results computed in real-time by EddyPro on the SmartFlux 2 or 3 System.

Contact LI-COR if you have questions about the suitability of the LI-7700 in your application.

Suggested Reference: When referring to this instruction manual in scientific literature or other publications, we recommend the following citation:

LI-COR, Inc. 2020. LI-7700 Open Path CH4 Analyzer Instruction Manual. LI-COR, Inc. Lincoln, NE.

What’s what

If you have just taken delivery of your LI-7700, check the packaging list to verify that you received everything that was ordered. The standard LI-7700 will include:

The LI-7700 Open Path CH4 Gas Analyzer

LI-7700 Analyzer - Includes the laser, detector, sampling path, mirrors, heaters, and laser control electronics. The radiation shield (not shown) is attached to the upper housing prior to shipment.

Figure 1‑1. Representations of the LI-7700 upper housing and Herriott cell.

LI-7700 components

  1. Radiation Shield: Reduces condensation on the upper mirror. It is in place when the instrument is shipped and it should be kept in place during normal operation, especially in high-humidity environments.

  2. Upper Housing: Encloses the laser source, sensor, and laser control electronics.

  3. Upper Mirror: This is the upper mirror in the optical path. It can be configured to remain slightly above ambient temperatures in condensing conditions.

  4. Fine-wire Thermocouple: Measures the ambient temperature near the optical path. There is a plastic sleeve over the thermocouple. It protects the thermocouple and should be left in place.

  5. Desiccant Cap: This seals the desiccant bottle. Only remove the desiccant cap to replace the internal chemical bottle. The desiccant cap removal screw is in place and can be left in place during normal operation.

  6. Sample Path: The optical path is 0.5 m in length. The laser makes 60 passes in a Herriott cell pattern for a total path length of 30 m. The laser beam is about 1.5 mm in diameter.

  7. Lower Mirror: The lower mirror features automated cleaning and temperature controls to prevent condensation on the mirror surface.

  8. Pressure Transducer: High-speed ambient pressure measurements. The transducer is below the lower mirror.

  9. Lower Housing: Houses the digital signal processing electronics and spin motor.

  10. Stand: Mount the instrument in the stand when using indoors.

Cable connections

The connection panel on the bottom of the analyzer includes the following components:

LI-7700 connector panel.
  1. Power In: Provide a +10.5 to 30 VDC 3 Amp power supply.
  2. The LI-7700 powers on when a suitable power supply is connected. It always starts up with the most recent settings.
  3. Fuse Housing: Use only a 8A FAST 250V TR5 UL fuse.
  4. An extra fuse is included in the spares kit (part number 438-15034). Early models used a 5 amp fuse. Contact LI-COR if you have questions about the fuse.
  5. Status LED: Stays solid green when the LI-7700 has finished starting up.
  6. Power LED: Stays solid green when a suitable power supply is connected.
  7. Analog Inputs: Connector for the analog input cable or 7550-101.
  8. Washer Power: Supplies power to the external washer unit accessory.
  9. Ethernet Connection: Port for Ethernet communication.
  10. Ethernet LED: Blinks at about 4 Hz when the Ethernet connection is active.
  11. Network Reset: Depress this button to reset the network connection.
  12. Mounting Post: The mounting post is attached with two ¼”-20 bolts (5/8”).

Spares kit and cables

Part Number: 9977-019

The items in Table 1‑1 are included in the LI-7700 spares kit. Some may be shipped in separate boxes.

Table 1‑1. LI-7700 spares and additional components.
Description Part Number
Ethernet Cable, Eurofast (0.3 M) 8-pin female to RJ45 392-10107
Ethernet Cable, Eurofast (5 M) 8-pin male to 8-pin male 392-10108
Power Cable, Eurofast (5 M), 4-pin female 9975-030
8 Amp Fuse (5 Amp on earlier instruments) 438-15034
Desiccant Cap Removal Screw (attached to analyzer) 125-09760
Solar Shield Assembly (attached to analyzer) 9877-085
Thermocouple Assembly (attached to analyzer) 9977-038
Mounting Post (attached to analyzer) 9977-018
Mounting Post Screws (1/4”-20, 5/8” long, attached) 140-04320
Washer Reservoir Assembly 7700-101
Washer Power Cable 392-10211
Spray Nozzle Assembly 9977-032
Indoor Instrument Stand 9977-067
Calibration Shroud (optional) 9977-033
  • Ethernet Data Cables – Two Ethernet cables are included: part number 392-10108 is a 5 m cable terminated on both ends with male Turck connectors; one end attaches to the LI-7700 Ethernet output, while the end attaches to either the 0.3 m Ethernet adapter cable (part number 392-10107), or to an LI-7550 Analyzer Interface Unit. When both cables are used, the LI-7700 can be connected to an Ethernet wall socket, Ethernet hub, or the Ethernet port on your computer.
  • Power Cable – (part number 9975-030) Used to connect the LI-7700 to a 10.5 to 30 VDC power supply. The power cable has 4 wires: brown and white are tied to a black lead, which connects to the negative (-) power supply terminal; blue and black are tied to a red lead, which connects to the positive power supply terminal (+).
  • Washer Assembly – The washer assembly includes a reservoir, pump, hose, washer nozzle, and mounting hardware.
  • Calibration Certificate – This documents the performance characteristics of your particular instrument when it left the factory. Keep this sheet for future reference.

Optional accessories

Several accessories are available for the LI-7700.

Data cables

Optional data cables with 8-pin Eurofast-to-RJ45 connectors are available in 5-, 25-, and 50-meter lengths. These cables connect the external Ethernet terminal on the LI-7550, LI-7500DS, or LI-7700 to a network switch.

Description Part Number
5 meter data cable (optional) 392-13977
25 meter data cable (optional) 392-16699
50 meter data cable (optional) 392-13767

Mounting hardware

The LI-7700 can be mounted directly to a tripod cross arm with one 1" × ¾" crossover fitting (part number 7900-342).

Figure 1‑2. The LI-7700 can be mounted with a simple 1" × ¾" crossover fitting.

For a range of height adjustment options, use the mounting kit (7900-340).

Figure 1‑3. The mounting kit (7900-340) provides a range of height adjustments.

7550-101 Auxiliary Sensor Interface

The 7550-101 is an optional weatherproof junction for analog inputs on the LI-7700 and for the analog outputs from the LI-7550. Detailed instructions for using the 7550-101 are provided later (see Analog inputs (LI-7700), Analog inputs (LI-7550), or Analog outputs (LI-7550)).

Table 1‑2. Components of the 7550-101 Auxiliary Sensor Interface Spare Kit (part number 9975-032).
Description Qty. LI-COR Part No.
U-Bolt, ¼" by 20 2 184-09842
Hex Nuts 4 798-01788
Quick Connect Plug 10 300-07393
Santoprene Tubing 2 ft (60 cm) 222-08325

LI-7550 Analyzer Interface Unit

The optional LI-7550 enhances the functionality of the LI-7700 by providing compatibility with other data logging and communication systems. Detailed instructions for using the LI-7550 with the LI-7700 are provided later (see Operation with the LI-7550).

Calibration Shroud

The optional calibration shroud (part number 9977-033) is used to isolate the LI-7700 optical path during calibration verification. Contact LI-COR or your distributor to purchase the shroud.