Terrible, Horrible, No Good, Very Bad Data

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Instructions for identifying the cause of bad readings from the LI-820, LI-830, LI-840, LI-840A, LI-850, LI-870, LI-8100, and LI-8100A.

There are four common causes for bad readings from the LI-820, LI-830, LI-840, LI-840A, LI-850, LI-870, LI-8100, and LI-8100A, listed below:

Incorrect zero and span calibration parameters

Check: these values using the LI-COR interface software for each instrument by going to:

  • For LI-830, LI-850, and LI-870: Settings > Calibrations > Advanced

  • For LI-820, LI-840, and LI-840A: View > Calibration > Advanced
  • For the LI-8100 and LI-8100A: Utilities > Calibration > Manual

The typical values for these parameters are as follows:

Calibration Parameter Normal range of values
CO2 Zero, CO2 Span,
H2O Zero, H2O Span		 0.8 - 1.2
CO2 Span 2 (Span Slope),
H2O Span 2		 ~0 (example: 0.005)

Solution: If the values are outside this range:

  1. Reset them back to factory calibration values, which can be found at licor.com/env/support
  2. Reset them to ‘1’ and perform a zero and span for each gas you adjust.

IR light source that is failing or has failed

The light source used in these instruments has a typical life time of 18,000 hours (2 years continuous use). If the unit has a failed light source it will typically report readings that oscillate between -50 ppm and some large value (2000 ppm or millions) for CO2.

Check: For LI-820, LI-830, LI-840, LI-840A, LI-850, and LI-870: Remove the cover and inspect the IR light source assembly.

  • For the LI-820, LI-840, and LI-840A, it is located on the left side of the optical bench.
  • For the LI-830, LI-850, and LI-870, it is located on the right side of the optical bench.
  • For LI-8100 and LI-8100A: Using the LI-COR interface software go to View > Instrument Status and review the field Operating Hours. If it indicates more than 18,000 hours the light source most likely needs replacement.

Solution: For all instruments the light source is a user replaceable component.

  • 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. A user calibration (set zero and span for both CO2 and H2O) should be performed after the light source replacement.

Contamination (dirt, corrosion, liquids) in the optical path

Check: Check the optical path for each instrument by following the instructions given in the respective manual.

Solution: Cleaning the optical path by following the instructions given in the respective manual.

Failed Detector

Check: If the detector has failed, the instrument will be unresponsive to changes in concentration. You may also observe unresponsive or zero readings for pressure and bench temperature. After checking for contamination, infrared source, and the zero and span settings, run a zero and span (ambient) gas through the instrument. If it is not responsive, most likely the detector has failed.

Solution: For all instruments the detector is a user replaceable component.

  • For the LI-820, the part number is 800-903.
  • For the LI-840, LI-840A, LI-8100 and LI-8100A the part number is 800-906.
  • For the LI-830 the part number is 800-916.
  • For the LI-850 and LI-870 the part number is 800-918.