Tech Note 553 Detail

Oxygen Gas Sensor Troubleshooter

Affected Products:

PS-2126 PASPORT Oxygen Gas Sensor
CI-6562 Oxygen Gas Sensor

Oxygen Gas Sensor Troubleshooter

PASCO Solution:

Theory of Operation

The MAX-250 is a galvanic, partial pressure sensor that is specific to oxygen. It consists of two electrodes (a cathode and an anode), a teflon membrane and an electrolyte. Oxygen diffuses through the teflon membrane and immediately reacts electrochemically at a gold cathode. Concurrently, oxidation occurs electrochemically at a lead anode, generating an electrical current and providing a voltage output. Electrodes are immersed in a unique gelled weak acid electrolyte which is responsible for the sensors long life and motion insensitive characteristic. The current generated is proportional to the amount of oxygen present in the sample gas.


Oxygen gas sensor reports < 18% oxygen concentration before calibration in ambient outdoor air.

This usually indicates that the probe needs to be replaced. Please follow the steps in the calibration procedure below to determine whether the probe needs to be replaced:


  1. Max 250 Probe users: Remove the protective pink tape from oxygen gas sensing probe.
  2. Thread the deflector onto end of the probe.
  3. Attach the probe to the blue PS-2126(A) sensor box.
  4. Connect the sensor to a powered PASPort interface.
  5. Place the sensor in a well-ventilated environment either indoors or outdoors, but away from sources of CO2 such as motor vehicle exhaust or animal breath.
  6. Monitor the oxygen concentration.
  7. If the concentration stabilizes within +/- 0.5 % of a value between 18 - 23% (~ 20 seconds), press the CAL (20.9%) button on the sensor and hold it for 3 seconds. (The green light will flash on and off for 4 seconds, indicating that calibration is in progress. After 4 seconds, the reading should stabilize at 20.9%.)
  8. If the oxygen sensor does not read >18.0% oxygen concentration, replace the probe with a known working probe. (See viablity.)
  9. If the oxygen sensor still does not read >18.0% oxygen concentration and the sensor is within the 5-year warranty, contact PASCO Teacher Support for a replacement sensor.


The ambient concentration of oxygen outdoors at least 10 cm from local heavy consumers of oxygen (animal breath, fires, vehicle exhaust) varies over a narrow range between 20-21%. If the oxygen gas sensor reads an outdoor oxygen gas concentration lower than 18% before calibration, the probe should be replaced. Responsive oxygen gas probes reading above 18% concentration outdoors should be calibrated.

The probe included with the PS-2126 is expected to last 1-3 years under normal use and is warranted by the manufacturer for 1 year.

The probe included with the PS-2126A, which is also compatible with the PS-2126, is expected to last 4-5 years under normal use (900,000 % oxygen-hours under standard temperature, pressure and humidity) and is warranted by the manufacturer for 2 years. A replacement probe can be purchased as PS-6524 Oxygen Sensor Replacement Electrode.


Probes from PS-2126 and PS-2126A Oxygen Gas sensors are interchangeable.


To extend the shelf life of the probe, cover the probe with the protective pink tape and store the probe in the refrigerator . (optimal storage temperature: 5 - 25 C).

General Specifications


Interfering Gases

Interfering Gas

Gas Concentration % Required to Produce a Maximum Full Scale Error of 2 %







Carbon Dioxide








Nitrous Oxide


· Operating temperature: 5- 40 C

· Storage temperature: -15 to 50 C

· Optimal storage temperature: 5 to 25 C

· Response Time (90% of reading): 15 seconds at 23 +/-2

· Linearity: +/-2%

· Stability: 1% of full scale over 8 hours at constant temperature, pressure and humidity

· Temperature Error: < +/- 3% from 15 to 40 C

· Expected Life: 900,000 % oxygen-hours under standard temperature, pressure and humidity (5 years in atmospheric conditions)

· Humidity: 4 -59% non-condensing

· Warranty: 2 years

Creation Date: 10/20/2005
Last Modified: 10/6/2011
Mod Summary: