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Galvanic Electrode
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Measuring dissolved oxygen with either sensor type
For both electrochemical and optical dissolved oxygen sensor, they do not measure the concentration of dissolved oxygen in mg/L or ppm (parts per million which is equivalent to mg/L). Instead, the pressure of oxygen that is dissolved in the sample is being measured. To interpret the readings from the measurement, the pressure of the dissolved oxygen is expressed as DO % Saturation. To explain this in detail, the instrument converts the dissolved oxygen pressure value from the sensor to % Saturation by dividing the sensor output in mmHg by 160*** (the pressure of oxygen in air at 760 mmHg) and then multiplying 38 39by 100. For example, a measured oxygen pressure of 150 mmHg would be displayed by a sensor as 93.8 % Saturation (150/160 * 100). Source: https://www.fondriest.com/pdf/ysi_do_handbook.pdf
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Cleaning and Maintenance
[need to be paraphrased]
The component The membrane of the sensor that sensors is sensitive to contamination is the membrane. Contamination results in lower readings when measuring or lesser slopes when calibrating because a portion of the membrane surface is not available which caused by inappropriate cleaning. Contamination affects the reading (usually lowering the reading) when measuring small DO amount due to the damage on the membrane surface for the diffusion of oxygen. The attempt to compensate for deal with the contamination by adjusting the instrument does not agree with the water principle. It is preferable to clean the membrane. Acetic or citric acid with a concentration of 5--10% (percent in weight!) is used for calcium and iron oxide deposits and warm (<50C) household detergent is used for fats and oils.Avoid rinsing it with water is not sufficient enough. Acids such as acetic or citric acid (concentration of 5~10% by weight) are preferable for cleaning the membrane. It should draw attention from avoid using strong mechanical treatment of the membrane during all cleaning activities because its thickness is on the order of m and it is easily destroyed. It is best to use a soft paper towel. Dissolved oxygen not clean the sensor in an ultrasound bath as this Also, it is not appropriate to clean the sensor by using ultrasonic water bath which may cause the coating of the anodes to peel off. In addition, it is best to use a soft paper towel instead.
Regeneration of the sensor becomes necessary is required when the function responds or when the slope (S) < 0.6 has decreased markedly when calibrating.Basically, regeneration is required when the electrolyte solution is depleted, when the gold cathode has become coated with lead or silver, when the reference electrode is to xified or when the has dropped remarkably when calibration. This is caused by the depletion of electrolyte solution when the membrane is damaged or contaminated. It consists of To maintain the sensor, exchanging the electrolyte solution , cleaning the electrodes and exchanging the membrane head .It is important to follow the operating manual exactly! Mistakes are then easily avoidedand cleaning the electrodes are needed.
The following points should be emphasized :when carrying out the cleaning process. Source: http://www.eidusa.com/Theory_DO.htm#Cleaning of sensors
- The sensor must be disconnected from the meter. When the sensor is connected and submersed in the cleaning solution, no chemical reaction takes place between the solution and the oxidized reference electrode surface; instead, the cleaning solution may become electrolyzed!
- Use the cleaning or electrolyte solution suitable for the particular sensor as stated in the operating manual! A solution that is suitable for silver electrodes cannot regenerate lead electrodes!
- Only the gold cathode should be polished; the counter electrode is merely wiped clean with a soft cloth to wipe away easily removable salt deposits! A spotty coating after regeneration of the lead or silver electrodes does not impair measurements!
- When polishing the gold electrode, only use the moistened EID abrasive film that has a special grain that polishes and do not scratch!
- It is also recommended to use a new membrane head since the used membrane cannot necessarily guarantee that the membrane fits correctly against the gold cathode which is ensured by a spacing lattice on the inside of the membrane. Baggy clothing don't fit either!
Please noteNote:
- The spacing lattice is clearly visible when the membrane head is held up against the light.
The result of an oxygen measurement can be documented in several ways:
Display of the concentration: The instrument requires the appropriate data of the calibration curve and uses them to calculate the concentration in mg/L (ppm is identical in this case), allowing for the temperature dependency of the individual parameters
- Display of the percentage of oxygen saturation: The instrument measures the sensor current and calculates the partial pressure of oxygen according to the calibration. The current air pressure is measured for the calculation of the saturation partial pressure. The display corresponds to the quotient, converted into a percentageAlways re-calibrate an instrument after changing a membrane.
Applications
A. Foods and Beverages
Many foodstuffs are packed in a Modified Atmosphere Packaging where a low or controlled oxygen level is necessary. Dissolved oxygen levels in some drinks, such as beer, should be kept in specific range. Practice of adding oxygen under pressure to bottled water to make oxygenated water has become more common. These dissolved oxygen measurements required dissolved oxygen probes that can be cleaned at elevated temperatures without being removed from the application.
B. Environmental monitoring
EID's dissolved oxygen data loggers can be left to record dissolved oxygen fluctuations in lakes, rivers etc. Deep sea oxygen probes are used in oceans and deep lakes. EId's dissolved oxygen electrodes with fast response are used to map the dissolved oxygen content of lakes and fishing waters. EId's dissolved oxygen probes are not only raised and lowered in the water, but also towed through the water at different depths to give a total picture of the state of the area concerned.
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