Time is measured and correlated to oxygen concentration. The more oxygen present, the shorter the time it takes for red light emission. The elapsed time from excitation till return to steady state is measured. This blue light excites the luminescent material which in turn emits red light as it returns to its unexcited state. Blue light is transmitted to the sensor from an LED on the surface. Probes utilize a sensor coated with luminescent material. This results in emission of red light which is correlated to oxygen content. ![]() As oxygen molecules encounter the sensor surface, they react with the luminescent material, causing it to return to its un-excited state. This blue light excites the luminescent material which in turn emits red light as it encounters oxygen and is returned to its unexcited state. Blue light is transmitted to the probe sensor from an LED on the surface. Luminescence technology I: Initially Blue light from an LED inside the probe excites luminescent material on the sensor surface.Ĭoming into vogue around 2005, luminescence represented a whole new technology for environmental chemistry, but which had been in use in medical field for many years. Bottom Line: provides for more accurate & consistent calibrations. Double thermistor monitors differential between air and electrolyte and does not lock in calibration until the two are equal in temperature. People have tendency to calibrate too quickly when doing AIR calibrations. Air is poor heat sink (think of cooking in a copper vs. This allows temperature measurement in sample (water or air) AND in electrolyte. Dual ThermistorĪdded thermistor to electrolyte (in addition to sample sensor). Other than greater stability and longer probe membrane life, one key advantage with "electro-optical" probes is that oxygen is not consumed. Those little fingertip oxygen sensors use the same technology. This technology has been used for years in the medical field. Changes in fluorescence activity are proportional to the concentration of oxygen in the sample. The fluorescence is sensitive to the presence of oxygen. ![]() Luminescence method:Ī fluorescent film is applied to the tip of a probe. Since oxygen is "consumed" the sample needs to be stirred to ensure accurate readings. This process produces a current flow, which is detected by the meter and is proportional to the partial pressure of oxygen. Oxygen diffuses through the membrane and is reduced at the cathode by the voltage. ![]() A constant voltage is placed across the cathode and anode. Oxygen Measurement Techniques DO Probe Electrochemical method:Ĭomposed of two metal electrodes in contact with supporting electrolyte and separated from the test solution by a gas permeable membrane. While polarographic type DO probes used to be the most common style in use, they are quickly being outpaced by the newer, more rugged electro-optical (LDO, RDO) probes.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |