Maintenance

The LI-830 and LI-850 will require little maintenance. Typical maintenance procedures are described in this section.

User calibration

If the instrument is not measuring as expected, or if you have disassembled the optical bench for any reason, you should check the zero and span settings and set them if necessary. The zero and span are an offset and slope. The zero value ensures that the instrument shows zero when the gas has a zero concentration. A change in the zero will affect every measurement. The span setting ensures a correct measurement at a known non-zero concentration. A change in the span affects higher concentration measurements more than lower ones.

Setting the CO2 zero

Always perform the zero first. To set the zero, you'll need either a tank of dry air that is free of CO2 or a CO2 scrubbing chemical such as wet soda lime and a desiccant such as Drierite.

  1. Plumb the zero-gas tank or scrubber to the air inlet.
  2. Be sure to use an air filter to prevent contaminants from entering the optical path.
    • If using tank air, the pressure of the tank is sufficient to flow the gas through the analyzer. Allow at least 0.75 liters per minute to flow through the cell (no more than 1.0 lpm).
    • Caution: Disable the pump to allow tank pressure to drive the flow of calibration gases.
    • If using a scrubbing chemical, use the internal pump or a user-supplied pump to draw air through the analyzer.
  4. Install a 10 to 20 cm length of tubing to the air outlet.
  5. This vent prevents ambient air from diffusing upstream into the optical cell.
  6. When the CO2 concentration has stabilized, click the Zero CO2 button.

Setting the primary CO2 span

When choosing a span gas, we recommend a gas concentration that is close to the upper limit of what you expect to measure. For example, if you are measuring near-ambient levels, choose a span gas that is near 400 ppm CO2 (as opposed to 18,000 ppm). Similarly, if you are measuring concentrations near 15,000 ppm CO2, a span gas with 100 ppm would not be ideal.

  1. After zeroing, flow a gas with a known CO2 concentration through the analyzer at a rate of 0.5 liters per minute.
  2. Caution: Disable the pump to allow tank pressure to drive the flow of calibration gases.
  3. Enter the CO2 concentration of the span gas into the software
  4. When the CO2 reading has stabilized, click Span CO2.

Setting the secondary CO2 span

You can set a second span (using a gas that has a CO2 concentration that is higher or lower than the primary span gas) to improve the precision of the analyzer. The process is exactly the same as setting the primary span, only you'll enter a different concentration and click Span2 CO2.

Setting the H2O zero and spans (LI-850 only)

The water vapor span can be set with a dew point generator such as the LI-610. The procedure is the same as setting the CO2 zero and spans, only this uses known concentrations of water vapor rather than CO2.

Caution: Setting the zero and span incorrectly for either CO2 or H2O will adversely impact the performance of your instrument. If you do not have the proper equipment to span the analyzer, it is best to leave it alone.

Recovering from a bad zero or span

If your attempt to zero or span does not go as planned, you can restore the factory default zero and span settings. The information you need is provided on the calibration sheet (included with the instrument or available for download from www.licor.com/env/support/). Under Settings > Calibrations > Advanced, enter the factory zero and span values for your instrument.

Cleaning the optical bench

The optical bench can be removed and cleaned if necessary. If, for example, you are unable to set the span, the optics may be contaminated. Generally speaking, don't undertake this procedure unless you've ruled out other potential problems. You'll have to set the instrument zero and span after reassembling the optical bench.

  1. Turn off the instrument.
  2. Unplug the power cable.
  3. Remove the top cover.
  4. It is attached with 6 captive screws. Loosen each of the screws until the top cover is free of the bottom. If your instrument has a display, carefully rotate the top cover out of the way without straining the cable, and then unplug the display cable. Set the cover aside, being careful not to strain the ribbon cable.
  5. Remove the cables from the source and detector.
  6. Gently grasp the plug and pull it free of the assembly. Leave the tubes in place.
  7. Carefully lift the optical bench out of the foam.
  8. Remove the screws that secure the source and detector (4 each), then separate the source and detector housings (with circuit boards attached) from the optical path.
  9. Clean the parts.
  10. Retrieve an optical path swab from the accessories kit. Dip one end into a 50:50 ethanol-water mixture (mild dish washing soap and water will work too) and carefully swab both ends of the optical path. Dip a Source/Detector swab into the solution and then swab around the source and detector to remove any residue.

Caution: Do not use abrasive cleansers. Abrasive cleaners can irreparably damage the gold plating on the optical path, source, or detector.

  1. Inspect the hose barbs and tubing.
  2. If the tubes are dirty or damaged, replace them with new tubes (available from LI-COR, part number 6580-041). Carefully remove them from the hose barbs. If the tubes are in good condition and clean, you may be able to reuse them. If the hose barbs are dirty, remove them and clean them with rubbing alcohol or soapy water. Use caution: Do not scratch the hose barbs because scratches may cause leaks.
  3. Inspect the O-rings.
  4. If they are smashed flat or damaged in any way, replace them with new O-rings (part number 192-00226) from the accessories kit.
  5. Let the optical bench components dry.
  6. Reassemble the optical bench.
  7. Attach the source and detector. The orientation of the optical path cylinder is unimportant — either end can be inserted into the source and detector housing. Tighten each of the screws snugly.
  8. Place the optical bench in the foam, plug in the source and detector connectors, and re-assemble the case.
  9. Be sure the foam insulation on the top cover is positioned over the optical bench. It is required for thermal stability.
  10. Perform a zero and span calibration. See User calibration.

Replacing a fuse

The power supply and terminal strip are both protected by fuses. The instrument has one extra fuse (Littelfuse 476 Series Nano2® 3 amp 125 V fuse) that can be used in the event that one of the fuses blows. If you are able to power on the instrument using one of these two ways—but not the other—a fuse may be blown. If you can't power the instrument using either way, both fuses may be blown (or you may have a power supply issue).

Before simply replacing a fuse, be sure to identify the problem that caused the fuse to blow in the first place. Otherwise, you'll just blow the spare fuse, in which case, you'll still have the problem and you'll be out of spare fuses. After identifying and solving the problem that caused the fuse to blow, replace the fuse:

  1. Open the case.
  2. Loosen each of the six top cover screws until the top cover is free of the bottom. If your instrument has a display, carefully rotate the top cover out of the way without straining the cable, and then unplug the display cable. Set the cover aside.
  3. Locate the fuses.
  4. With the air-in and -out ports facing away from you, the fuses are mounted to the lower left corner of the lowest circuit board. In the image, ribbon cables and tubes have been removed for clarity.
  5. Using a needle-nose pliers, grasp the blown fuse and remove it from the holder.
  6. Replace it with a spare fuse.
  7. Power on the instrument to verify that the issue is resolved.