AI brand diving sensors ship with the documentation of a final pressure test for each sensor. The sensor is tested at approximately one ATA in air and 100% oxygen, then tested again at 1.6 ATA in oxygen, and the millivolt readings are recorded for all measurements. The results document that the cell is within specifications for current and linearity up to a PO2 exceeding 1.6 ATA. The dated test results are included in the package with each individual sensor.

These diving grade sensors are widely used in handheld oxygen analyzers for verifying scuba cylinder oxygen content, but many handheld oxygen analyzers use a medical grade oxygen sensor. The oxygen sensors for diving have a "hydrophobic membrane," which is a necessity for rebreather applications, but will slightly slow (by two or three seconds) the response time of handheld O2 analyzers. This is true for any diving sensor, not just ours and to be clear does not affect the accuracy of the analysis, just the response time of the sensor. The medical versions are often more difficult to find and much more expensive. If you have been using a diving sensor in your handheld analyzer and have been satisfied with it, by all means order a sensor from us. Our R-17DR will work in the Dive Rite VTI, Mini-Ox brand, Spectrum brand, Vandagraph VN202, El Cheapo/Expedition, and Teledyne AD300/MD300. Our R-22DR will work in the Cochran Lifeguard, DiveTek Oz, Mares EANx, and OxySpy.

Our R-22DR with a 3-pin Molex gold plated connector is our part number for the Analytical Industries PSR-11-39-MD, compatible with the Teledyne R-22D and Maxtec MAX-305. This type of connector is used in the Dive Rite O2ptima, Jetsam KISS Classic, Innerspace Megalodon, Hammerhead, rEvo, and other brands of rebreathers. Our R-17DR with the 3.5mm mini-jack is our part number for the Analytical Industries PSR-11-39-JD, compatible with the Teledyne R-17D and Maxtec MAX-301. This type of connector is used in the CIS-Lunar, and the VR Technology Ouroboros and Sentinel rebreathers. Dive Gear Express has not done any verification or validation of these sensors and disclaims any responsibility and liability for use in rebreather applications. Verification and validation for use in rebreather applications is the responsibility of the equipment user and/or manufacturer.

Oxygen Sensor Life in Rebreathers

When any new oxygen sensor is removed from the sealed package, it can take anywhere from a few minutes to a few hours for it to acclimate and the millivolt output to stabilize. We recommend waiting 12 hours before calibrating your rebreather with a freshly opened sensor. Also, as oxygen sensors reach end-of-life they can become unpredictable, causing problems that are sometimes difficult to diagnose. Because oxygen sensors are so critical to the operational safety of rebreathers, we recommend discontinuing the use of oxygen sensors that have been in-service over 12 months, or have a total age of over 18 months.

Three conditions are particularly notable for drastically shortening the life of an oxygen sensor, regardless of brand.

• Impact - Inside the oxygen sensor is a tiny gold wire and seals on the face membrane that are very fragile. Sensors subjected to g-force shocks explains why a new sensor will come out of the package DOA, reading zero millivolts (broken wire) or with erratic readings (ruptured seal).
• Heat - The warmer the sensor, the shorter the life. That can happen during shipping or storage, but can also happen when the rebreather sits in the sun and gets very hot.
• Prolonged Oxygen Exposure - Leaving elevated oxygen mixtures in the breathing loop, which often happens following a calibration, will drastically reduce the life of a sensor. Heavy use of your rebreather will also shorten the life of the sensor.

to read Oxygen Sensor Handling - Best Practices

Maxtec markets their 'Scuba Sensors' for use in handheld oxygen analyzers associated with scuba. The Maxtec sensor package label contains the following statement: "Maxtec warrants the sensor to work according to the stated specifications under normal operating conditions. For sensors used in rebreather applications, Maxtec has not performed validation or verification testing and therefore cannot promote our sensors for use in this application and disclaims any liability for off-label use. Verification and validation for use in these applications is the responsibility of the equipment user and/or manufacturer." Dive Gear Express also has not done any verification or validation of this sensor and disclaims any responsibility and liability for use in rebreather applications.

Mixing Brands or Ages of Oxygen Sensors

Many electronically controlled rebreathers use an array of three sensors together with a system of 'voting' to avoid calculating a PO2 with a failing sensor. Rebreather electronics can temporarily or permanently 'vote out' a sensor with characteristics that are different than the other two. This is an important safety feature enabled by the multi-sensor array.

However, if the sensor array contains a mix of brands or ages of sensors you may experience unexpected behavior of the sensor array as a result of the voting algorithm. For example, installing a single new sensor in an array with two older sensors may cause the perfectly good new sensor to be voted out simply because it responds faster than the older sensors. This will cause a situation where the reported PO2 is less accurate because the most accurate sensor information has been discarded. There are numerous other circumstances in which a mixture of brands or ages in an oxygen sensor array can cause an otherwise acceptable sensor to be voted out, solely due to differences between the sensors. You might see transient sensor alarms while the different sensors catchup to each other and auto calibrating rebreathers might even fail to calibrate in such situations.

If you are considering switching brands of sensors, it's tempting to want to just 'try one out', rather than replace the whole array. When only one sensor in an array is due for replacement, it's tempting to just replace that sensor alone. While best practice is for the array to contain a mix of sensors selected from differing lots, you should not mix brands or very old sensors with very new sensors.

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