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: A failed detector will be unresponsive to changes in concentration. After the above three items have been checked, run a zero and span (ambient) gas through the instrument if no response then 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.