Temporary Fix for a Bad IR Source

The infrared (IR) source for the LI-8xx1 and LI-8100/A series instruments has an operational life of better than 20,000 hours, or about two years of continuous use. The IR source is essentially an incandescent light bulb, and fails as a result of the filament thinning with use as it burns away. Eventually the filament becomes thin enough that it cracks and breaks, at which point the source no longer works.

The permanent fix for a failed source is to replace it with a new one. Replacement sources can be ordered from LI-COR and are field installable. For the LI-820, LI-830, LI-840, LI-840A, LI-850, and LI-870, the part number is 800-902. For LI-8100 and LI-8100A the part number is 8100-902.

In situations where a quick fix is needed to complete measurements it is often possible to get the source temporarily working again using percussive maintenance; simply lift one end of the instrument an inch or so above the work surface and let it drop. This can cause a momentary contact between the broken ends of the source filament. If the instrument is powered up when this happens, that momentary contact will cause an electrical arc that can weld the filament ends back together. This fix is temporary; it does nothing to reverse the thinning that led to the failure, and the filament will break again eventually. However, it can provide anywhere from a few hours to a few weeks of operation out of the source.