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do_measurementprinciple [31/03/2015 13:33]
pieter [Temperature effects on the probe output]
do_measurementprinciple [31/03/2015 13:35]
pieter [Measurement probe]
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 The dissolved Oxygen electrode is a galvanic MPOD (Membrane-covered Polarographic Oxygen Detector) system.  They provide a convenient approach to an essential direct measurement of molecular oxygen. The membrane isolates the electrode from the sample and the oxygen is detected as it diffuses across the membrane. The probe can be used to measure any system where oxygen is present. Calibration of the sensor is readily achieved if the oxygen concentration or solubility at a specific condition is known. The dissolved Oxygen electrode is a galvanic MPOD (Membrane-covered Polarographic Oxygen Detector) system.  They provide a convenient approach to an essential direct measurement of molecular oxygen. The membrane isolates the electrode from the sample and the oxygen is detected as it diffuses across the membrane. The probe can be used to measure any system where oxygen is present. Calibration of the sensor is readily achieved if the oxygen concentration or solubility at a specific condition is known.
  
-=====Measurement probe=====+=====Galvanic probe=====
 A galvanic MPOD consists internally of two metals of different nobility which serve as electrodes. The more noble metal is the cathode (Silver, Platinum or Gold), the other (Lead or Zinc) is the anode. In the presence of an electrolyte, a voltage around 800 mV is produced between the two metals.  A galvanic MPOD consists internally of two metals of different nobility which serve as electrodes. The more noble metal is the cathode (Silver, Platinum or Gold), the other (Lead or Zinc) is the anode. In the presence of an electrolyte, a voltage around 800 mV is produced between the two metals. 
  
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 There are two factors related to temperature which must be recognised in order to correlate the output of the dissolved oxygen probe with concentration of molecular oxygen in the sample. There are two factors related to temperature which must be recognised in order to correlate the output of the dissolved oxygen probe with concentration of molecular oxygen in the sample.
  
-  * As the temperature of water decreases, kinetic energy of water and oxygen molecules decreases and molecular attraction increases. As a result, the concentration of oxygen which must be present in the water to establish a particular concentration of oxygen at the water-to-Teflon interface increases.// +  * As the temperature of water decreases, kinetic energy of water and oxygen molecules decreases and molecular attraction increases. As a result, the concentration of oxygen which must be present in the water to establish a particular concentration of oxygen at the water-to-Teflon interface increases. 
-  * The resistance to oxygen diffusion through the Teflon membrane increases as temperature decreases.//+  * The resistance to oxygen diffusion through the Teflon membrane increases as temperature decreases.
  
 Both of the temperature factors serve to decrease the rate at which oxygen molecules reach the surface of the cathode as temperature decreases. Therefore, if the read-out from the dissolved oxygen meter is to display the correct reading of oxygen concentration for all samples which have the same concentration of oxygen but are at different temperatures, compensation for the overall temperature effect must be accomplished. Both of the temperature factors serve to decrease the rate at which oxygen molecules reach the surface of the cathode as temperature decreases. Therefore, if the read-out from the dissolved oxygen meter is to display the correct reading of oxygen concentration for all samples which have the same concentration of oxygen but are at different temperatures, compensation for the overall temperature effect must be accomplished.
do_measurementprinciple.txt · Last modified: 31/03/2015 13:35 by pieter