Instrument not visible in software when connected using Ethernet

If you are able to connect and the instrument is performing as expected, the problem may be related to your computer firewall settings. In this case, you’ll need to create an exception that allows the gas analyzer through the firewall. If you are using the Windows firewall, follow the instructions provided by Microsoft at If you are using another firewall, refer to documentation provided with that software. After allowing the software through your firewall, you should be able to connect over Ethernet.

LI-7700 will not power up

Power supply inadequate? Be sure the power supply is 10.5 to 30 VDC, 3 Amps.

Power supply connected improperly? This will blow the fuse. Connect the power supply correctly and replace the fuse.

Blown fuse? Replace the fuse.

Signal strength (RSSI) excessively low

Mirrors dirty? Clean the upper and lower mirrors with water and a mild soap solution or commercial glass cleaner. If this does not work, see Cleaning the mirrors for more tips.

Check the reference signal strength (click the Diagnostics Page 1 tab on the software main screen). Typically, the reference signal strength is between 40 and 60%. If it is lower than this, check the Laser Control Status on the main page. If the indicator is a blue dot, click it and change the temperature range setting to Warm (see Operating temperature range).

If this does not bring the signal strength up, contact technical support.

Lower mirror spin motor runs loudly at start-up

Power supply inadequate? Be sure the power supply is 10.5 to 30 VDC, 3 Amps.

Temperature readings are unreasonable

Thermocouple damaged. Replace the optical path thermocouple with the spare.

LI-7700 not visible on the network

Check the Ethernet data cable connections. Wiggle the cable connectors

Enable TCP/IP v6 on Windows® XP computers.

Ensure that the correct version of mDNS responder is installed on your computer.

Pressure measurements noisy

The mirror washer causes perturbations in the pressure measurement due to the proximity of the pressure sensor to the lower mirror. One way to reduce this effect is to set the cleaner to operate less frequently.

Optics RH warning in the software or diagnostic data

Desiccant needs to be replaced. The RH warning turns on if the relative humidity in the head is over 30%.

Data loss during night/morning hours

Mirrors may be covered in condensation. Check the signal strength (RSSI) data during those periods. If the signal strength drops in condensing conditions, turn on the mirror heaters or boost the power delivered to the mirror heaters during those time periods.

Washer fluid used up too quickly

Leaky tube? As the tube ages, it may develop leaks. Inspect the tubing, with special attention given to the connections and cable ties that may strain the tube. You may need to manually activate a wash cycle via software controls while looking for leaks. You can remove leaky sections of tubing or replace it. It is Tygon F-4040A 1/8-ID; 1/4-OD, which can be purchased from LI-COR as part number 222-19304.

Washer activated more often than needed? Check the washer mirror settings. Try lowering the signal strength threshold, setting the stop time close to the start time, or reducing the duration of the cleaning cycle.

Larger reservoir needed? Attach an auxiliary reservoir to the washer assembly.

No methane data stream

If your computer enters standby mode, the methane graph will not update when it exits standby mode. Click the Clear Charts button.

Be sure the Pause/Resume button has not been clicked.

Methane density data near zero, negative, or otherwise unbelievable

Check the Diagnostics Page 1 tab. If the graph does not make a nice bell curve shape, check the Laser control: in the Status frame. If the indicator is red, the reference signal is unlocked. Click the red indicator or press Ctrl + Alt + L to open the Laser Temperature Control window. Follow the steps described on page Laser temperature control to re-enable the line locking.

Check the zero and span using the procedure described in User calibration: zero and span. Restore the factory settings using the procedure described there.

If these do not work, contact technical support.

Instrument does not keep time when disconnected from power supply

The internal battery needs to be replaced. Contact technical support.