» On-line Process Monitoring » Dissolved Oxygen
On-line Dissolved Oxygen Monitoring and Analysis
Clark polarographic method
Using this method, the sensors consist of a working electrode (cathode), a counter/reference electrode (anode) and an oxygen-permeable membrane. Once the oxygen has permeated through the membrane it is reduced at the cathode whilst at the anode silver is oxidized and liberated into the electrolyte, which closes the electric circuit. The current produced by the reactions is proportional to the partial pressure of oxygen of the sample medium. This current may be converted to a concentration of oxygen.
Mettler Toledo membranes feature two layer construction (PTFE/silicon) as well as an integrated stainless steel mesh for improved durability, minimal distortion and to hold the electrolyte layer constant for continuous and reliable on-line measurements. The current produced by the reactions is measured by a transmitter and then converted to a concentration of oxygen, generally expressed in parts per million (ppm) or parts per billion (ppb).
Fluorescent / Optical method
Using this method, oxygen associates with a fluorescent silicone rubber compound that emits red light when stimulated with a blue laser diode. The amount of oxygen affects the amount of red light emitted. Neither the oxygen nor the compound are consumed in this process. The amount of red light emitted is measured and converted to a dissolved oxygen value.
This method has the following advantages over the Clark and Galvanic methods:
- Measurement of oxygen is optical with the rubber in contact with the water only.
- Clark and Galvanic probes require flow across the probe. The fluorescent / optical method does not.
- Clark and Galvanic probes consume oxygen and any water borne organisms that also consumes oxygen, and coats the membrane causes rapid O2 depletion behind the membrane. The fluoroprobe, when coated with Bio-Mass can simply be wiped off and immediately returned to service with NO need for recalibration.
We supply the patented Flouroprobe on-line dissolved oxygen analyser.
We also supply the Centec Oxytec-TR on-line dissolved oxygen analyser. This analyser uses a variation of the fluorescent/optical method that is insensitive to variations in turbidity and colour of the water, and to variations in the intensity of the stimulating light.
For further information or enquiries please contact us.
