Electro-galvanic fuel cell

The galvanic DO sensor is a particular type of fuel cell. It is an electrical device that is used to measure the concentration of oxygen in the scuba diving and medical equipment.

When the potassium hydroxide contained therein comes into contact with oxygen, there is a chemical reaction in the fuel cell. This results in an electrical current flowing between a lead anode and a gold cathode through a load resistor. The voltage produced in this case is proportional to the existing oxygen concentration.

One uses galvanic sensors in oxygen meters while diving to check breathing gas mixtures before a dive the oxygen content Nitrox or Trimix in. Likewise, the use of it in electronic rebreathers, so-called rebreathers to monitor the partial pressure of oxygen during a dive.

Galvanic oxygen sensors have a limited service life, reduced if they are exposed to high concentrations of oxygen. In the reaction of oxygen at the anode lead and lead is consumed, which eventually leads to measurement errors at high oxygen concentrations. Normally, a cell that is used for diving, over a period of approximately three years working correctly if you keep them in an airtight bag. The period is reduced, however, to only 4 months if they are stored in pure oxygen.

Disadvantages

The described form of fuel cell is similar to a battery, because it has depending on the application a limited life. The chemical reaction of the cell can generate a current having a predictable voltage which depends on the particular material used. In theory, should provide this voltage from the date of manufacture on until it is self- consumed, unless you remove the oxygen component of the intended response from the unit. , A cell

Oxygen is one of the fuels of the cell, thus more electricity is produced the more, the more oxygen is available. The chemical properties of all the materials determine the voltage, the amount of available oxygen on the other hand, how much electric power can be produced. When connecting a circuit with a corresponding consumption of such a cell, one can use a specific electrical power. However, when one increases the consumption, can be according to the performance of the cell.

Malfunction of the sensors can be used for diving, especially for users of rebreathers, be life-threatening. The usual failure modes galvanic sensors are:

• Excessive readings caused by leaks in the electrolyte container,
• Limited current in depleted cells,
• Non-linear power within the measurement range.

Have any malfunction caused normally. To mechanical damage, contamination or defects during the manufacture in the manufacturing process

Excessive readings are invariably caused by manufacturing defects or mechanical damage. In a rebreather they have an overestimation of the oxygen content in the circulation results in causing the unit replaced too little oxygen, which usually leads to hypoxia.

Sensors with reduced amperage produce a lower measured value despite high oxygen levels. The rebreather is therefore constantly being added due to the underestimation of the oxygen content in the circulation of oxygen to reach a value that the sensor already can not represent. The result is known as the Paul Bert effect of hyperoxia in the rule.

For non- linear power, the sensor in the intended measuring range of oxygen partial pressure does not behave as expected. During calibration the error is generally not detected, leading to a defective level of the rebreather. This can potentially cause decompression sickness.

Accidents due to malfunction of the sensors in rebreathers can be prevented in most cases by properly checked the cells before each use. Some divers carry out tests in the water through by increasing the partial pressure of oxygen in the circulation to a level above that of pure oxygen at sea level, to determine whether the sensor high values ​​can still be processed. This test, however, is only selectively and can provide reliable information about the possible inaccuracy of a sensor to. The only way to check a sensor properly, therefore exists in a calibrated test chamber which can both maintain a static pressure without deviations, as also has the ability to record measured values ​​and graphically evaluated.

Review

One of the first commercially available device for checking galvanic oxygen sensors was brought in 2005 by narked at 90 on the market, but without much success. A heavily revised model followed in 2007 and won the " Gordon Smith Award" for innovation during the trade fair in the diving equipment in Florida. Meanwhile, the devices worldwide by organizations such as NOAA ( National Oceanic and Atmospheric Administration ), NURC (NATO Underwater Research Centre) and DDRC ( Diving Diseases Research Centre) are used.

Credentials

Oxygen Measurement for Divers

Helge Weber: textbook recommended eV from Rebreather Advisory Board. Books on Demand GmbH, 2006, ISBN 978-3-8334-6795-0

Oxygen measurements for OC and Rebrather Diver

Helge Weber: textbook recommended eV from Rebreather Advisory Board. Books on Demand GmbH, 2009, ISBN 978-3-8370-3307-6