Tech Note 442 Detail

CO2 Gas Sensor Theory, Calibration & Troubleshooting

Affected Products:

PS-2110 PASPORT Carbon Dioxide Gas Sensor

Problem/Symptom:
CO2 Gas Sensor Theory, Calibration & Troubleshooting

PASCO Solution:

Theory of Operation

The PS-2110 pulses the power to an incandescent light, which emits a broad spectrum of electromagnetic radiation. An interference filter placed in front of a broad-spectrum pyroelectric (lithium tantalate) detector limits the transmitted radiation to a wavelength that is absorbed strongly by CO2, but by no other gases that would normally be found in air (4268 nm) . The intensity of the radiation is always measured at the same point in the pulsed power cycle of the light source. Since the intensity of the infrared radiation and the path length is fixed, the absorbance of detected radiation is directly proportional to the concentration of CO2 (Beer-Lambert law).

When the PS-2110 is calibrated, it is presumed that the concentration of CO2 in outdoor air away from sources of CO2 is 400 ppm.

Calibration

  1. If you are using an interface on batteries, check that you have at least 90% charge with the PS-2000 Xplorer Datalogger or at least 50% charge with other PASPort interfaces.
  2. Take a standard air sample.
    1. Go outdoors and away from any local sources of CO2, such as streets with busy traffic.
    2. Open the sample bottle and turn it with the opening pointed down.
    3. Shake the bottle vigorously outdoors to create turbulent mixing of the air in the sample bottle. (This will be assumed to be 400 ppm.)
    4. Cap the bottle with by placing it on the CO2 sensor.
  3. Go indoors away from windows or intense incandescent lighting. (The intensity of infrared radiation emitted by the CO2 gas sensor is small compared to that of the sun or intense incandenscent lights and may saturate the sensor it the radiation gets in through the gas holes to the detector, making it unresponsive. Fluorescent and LED lights emit little radiation in the infrared and are compatible with the sensor.)
  4. Keep sources of heat, such as your hands, away from the base of the black probe and shield the sensor from strong air currents. (The output of pyroelectric sensors is influenced by changes in relative junction temperature.)
  5. Connect the CO2 sensor to a powered PASPort interface.
  6. Select a graph display.
  7. Begin recording data.
  8. Wait until the value has stabilized to within a satifactory level. (Stabilization to within 20 ppm takes ~500 s. Stabilization to within 10 ppm of a value will take ~1500 seconds.)
  9. Depress the calibrate button for at least 3 seconds. (The calibration LED should turn solid green .)
  10. Release the calibrate button. (The calibration LED should begin flashing after approximately 1 minute.)

Troubleshooting

The CO2 is unresponsive or is reporting obviously inaccurate values.

This can be the result of an incorrect calibration. Recalibrate being careful not to place the sensor near intense sources of infrared radiation such as incandescent lights, heat lamps, or direct sunlight, being sure to wait until the value has had at least 500 seconds to stabilize, and keeping any heat sources such as hands away from the base of the probe. If you continue to experience problems, please contact Teacher Support.

The value of the CO2 slowly changes under constant conditions.

This can occur if insufficient power is getting to the sensor, especially when using the sensor with the PS-2000 Xplorer interface. Please be sure to have at least 80% charge when connecting a PS-2000 Xplorer Datalogger or PS-2005 AirLink SI, or PS-2010 PASPORT AirLink 2 and at least 50% charge when connecting to the PS-2002 Xplorer GLX or PS-2008(A) Spark Science Learning System.

The value of the CO2 concentration is systematically inaccurate by tens to hundreds of ppm.

When the PS-2110 is calibrated, it is presumed that the concentration of CO2 in outdoor air is 400 ppm; however, the accuracy of this presumption may vary depending on a number of ambient factors, such as temperature inversions, proximity to producers of CO2 (urban centers, volcanos, ..), time of day, etc. If you know that the concentration of CO2 is different from the presumed value, then you can make a calculation in DataStudio to correct for this; otherwise, you can use an environment with a controlled 400 ppm concentration for calibration.

Refer to the table below for typical ground-level concentrations of CO2:

Environment Typical CO2 Concentration [ppm]
Rural Outdoors 350-400
Urban Outdoors 350-650
Indoor Air (Well Ventilated) 400-1000
Indoor Air (Poorly Ventilated) 1000-2700

Creation Date: 09/19/2003
Last Modified: 09/19/2003
Mod Summary: