 |
How They Work
At the heart of every O2 analyzer is a sensor similar to a small fuel cell. These sensors contain materials that react to oxygen by producing an electrical current in voltages that are directly proportional to the amount of oxygen present. By measuring the current produced when gas flows past the sensor, O2 analyzers can reliably display the percentage of oxygen in a diver's cylinder.All but one of the analyzers in this review have user-replaceable sensors--and for good reason: Even when not in use, the sensor is in contact with air and reacting to ambient oxygen levels, which is why most sensors have a life expectancy of just two or three years. When the sensor degrades, it offers erratic readings and must be replaced, so the details of a unit's warranty (some sensor warranties are pro-rated, covering less replacement cost over time) and the cost of replacing the sensor should be considered when making a buying decision.
The pressure of the gas flowing past the sensor can also affect the accuracy of analyzer readings; too much pressure and you'll get an artificially high reading. All of the units reviewed here are designed to work best with a flow rate in the .5- to 2-liter-per-minute range.
There are generally two different types of analyzers, distinguished by how they regulate gas flow across the sensor. Direct-flow analyzers usually have a small dome-shaped fitting designed to rest against a tank valve opening, allowing gas into the analyzer via a small hole. Others incorporate a flow hose with a restrictor that connects to your BC inflator hose via a quick-disconnect fitting. Some units reviewed here have the hardware to do both. What does the difference mean to you? A flow hose samples at a constant pressure for greater accuracy, but takes longer to set up and your regulator has to be attached to the tank. Direct-flow analyzers may be more convenient, but the accuracy of readings can be affected by how well the user controls the gas flow. The process of sampling also wastes a certain amount of gas.
If you're like most occasional nitrox users, the direct-flow analyzers are generally the best choice. For technical divers who use multiple mixes in complicated decompression schedules, the flow-restrictor type that samples from a BC hose would be better for the job.
In the following reviews, we look at both types and focus on their ease of use and maintenance. We then put them to real-world use by analyzing four different cylinders (air, 32 percent nitrox, 36 percent nitrox, and pure oxygen). We found them all to be accurate within the manufacturers' specifications--generally +/- 1 percent. Here are the individual reviews in alphabetical order.
Analox O2 EII
Sensor warranty: 3 years pro-rated Sensor Replacement Cost: $130 The O2 EII is the most ergonomic and feature-rich of all the direct-flow analyzers we reviewed. It's well made and water-resistant, and our test unit came with the optional padded hard case that houses both the analyzer and the sensor saver cap. The analyzer fits nicely in the hand with the on/off button conveniently located under the thumb. It has an auto-off feature, which powers down after 10 minutes to conserve the user-replaceable 9-volt battery. Calibration is quick and easy thanks to an adjustment dial, and the LCD screen on top of the analyzer--though small--is easy to read. Analox claims the unit is water-resistant and it looks pretty well sealed up except for the tiny sampling hole. To analyze what's in your cylinder, simply turn the unit on, calibrate to ambient air, put the sample dome against the valve opening and crack open the cylinder. Two vent holes on the dome prevent overpressurization of the sensor. Once the reading stabilizes, press the on/off button to freeze the reading. The O2 EII also comes with a wrist lanyard and a waterproof reference chart for adjusting for humidity during calibration. MSRP: $325. Optional hard case, $36. www.analox.net |
Maxtec Handi
Sensor warranty: N/A (2 years entire unit) Sensor Replacement Cost: N/A (entire unit must be replaced) The Handi is the smallest analyzer in this review. It's also the only disposable model. So, while it's maintenance-free, when the sensor or battery go, you need a whole new analyzer, and replacing the unit costs more than replacing a sensor alone. The Handi fits nicely in your hand with the display screen and calibration knob facing up. A button turns the unit on, but it automatically shuts itself off after 80 seconds to conserve battery power, which was a little too quick for our liking. The Handi comes with both a flow hose to sample from your BC inflator hose and a Quick-Ox flow adapter that can be used to sample directly from a tank valve. We got a stable reading in only a few seconds with either method, but sometimes we had to turn the unit back on a few times to complete the process. MSRP: $225. www.maxtecinc.com |
Maxtec MaxO2+A
Sensor warranty: 2 years Sensor Replacement Cost: $79 Of all the units we tested, the MaxO2+A was the easiest analyzer to use. It fits nicely in the hand with a compact design, finger grooves and soft rubber trim, and the unit calibrates easily with a touch of a button at ambient air or 100 percent oxygen. It offers two methods for sampling gas (a flow hose and a Quick-Ox direct-flow attachment) and runs on two AA batteries, which are inexpensive and easy to replace. Multiple screen warnings alert you to low-battery conditions and calibration errors. The display screen was the easiest to read with the largest numbers of any analyzer in this review. It's priced higher than some of the other sensors in this review, but for analyzing made easy, it's probably worth the extra dough. MSRP: $350. www.maxtecinc.com |
Nuvair O2 Quickstick
Sensor warranty: 3 years pro-rated Sensor Replacement Cost: $85 Simplicity is the hallmark of the O2 Quickstick. The unit comes housed in a solid aluminum tube and is one of the easiest portable analyzers to maintain. The O-ring-sealed cap on the lanyard end pulls open to access the battery compartment (it runs on a simple 9-volt battery); the sample end cap also pops off when it's time to replace the sensor. As long as the battery is connected, the unit is on. When it's time to analyze, the unit must be calibrated by turning the recessed adjustment screw with the small flathead screwdriver provided. Then open the tank valve slowly to achieve a slight, steady hiss of gas. Hold the sensor end directly against the valve opening, being careful not to block the vent holes on the sides. We got a stable, accurate reading in 15 seconds. Nuvair says you can also place the sensor end of the Quickstick directly against the mouthpiece opening of a regulator second stage and sample the gas by gently depressing the purge button. It's a bit more challenging, but we were able to get an accurate reading using this method, too. The display uses large numbers for a quick read, but with no off button, you'll need to disconnect the battery to conserve power. MSRP: $250. www.nuvair.com |
Nuvair Pro O2
Sensor warranty: 3 years pro-rated Sensor Replacement Cost: $85 The Pro O2 analyzer was the most versatile model in this review, offering three different ways to sample gas: An optional BC quick-disconnect fitting ($30) with a flexible flow tube, or you can sample gas directly through a small hole in the cap either from a tank valve or second-stage mouthpiece. The 9-volt battery and O2 sensor can be accessed by removing four screws in the case--not as easy to access as the Quickstick, and not as water-resistant either. To analyze, push the on/off button to power up and calibrate using the dial. We were able to get stable, accurate readings with all three sampling methods. The display was easiest to read when using the BC connector method, allowing us to hold the screen face up. Display warnings include a low-battery icon. Bottom line: The Pro O2 has the versatility to make a tech diver happy, plus a great price. MSRP: $250. www.nuvair.com |
TDL OxySpy
Sensor warranty: 1 year Sensor Replacement Cost: $85 The OxySpy is a unique direct-flow analyzer with some neat features, such as push-button calibration and an MOD (maximum operating depth) calculator that uses any PPO2 you choose from 1.2 to 1.8 (default setting: 1.4). Instead of a small sampling hole, the OxySpy uses a gas capture tube. To analyze, place either end of the tube against the valve and open the tank to provide a slight, steady flow of gas. Its hand-grip design allows for a good view of the display screen, and once the reading has stabilized, you press the button once to freeze the screen; press it again for the MOD. The analyzer turns off automatically within 30 minutes to conserve battery power, and the display was large and easy to read with icons for low battery, calibration and sensor warnings. The OxySpy also comes in a foam-padded soft case for transport and storage. MSRP: $375. www.techdivinglimited.com |
TDL O2 Check
Sensor warranty: 2 years Sensor Replacement Cost: $75 The O2 Check is a tough little black box that's O-ring-sealed for wet conditions, and it samples gas both directly from the valve or with a flow hose. It comes in a padded case for travel and is pre-loaded with a sensor and three AAA batteries. An extra feature not available on other analyzers in this review is a backlight for low-light conditions. The three-position switch (on/off/on with backlight) lets you run the unit with or without the backlight, thus conserving battery power in bright conditions. To sample a gas, just turn on the analyzer and calibrate with ambient air, then either place the dome against the valve or attach the flow-restrictor hose to your BC inflator hose. Both methods resulted in fast and accurate readings of our test gases. The display features icons that warn you when batteries are low and when the sensor needs replacing. MSRP: $350. www.techdivinglimited.com |
