Sensor Cap Life - palintest Macro 900 Operation Manual

Macro 900 Operation Manual V3

21.2. Sensor Cap Life

All optical dissolved oxygen sensors work on the same principle, and all must
have the sensor cap containing the luminophore replaced periodically due to a
phenomenon known as photo bleaching.
When a sensor cap is new, the luminophore will return a large number of red
photons when excited. As time goes on, a bleaching effect takes place and the
number of red photons returned reduces to a point where they are no longer
detectable.
The amount of photo bleaching that the luminophore suffers is in direct
proportion to the amount of time it is excited by the sensor's blue light source.
It therefore follows that the faster a reading can be taken, the less time the
luminophore needs to be excited and the longer it will last.
The high-speed circuitry within the Optical DO module requires just eleven
milliseconds to take a reading! This incredibly fast reading time increases the
useful life of the luminophore considerably.
Another technique used to prolong the life of the luminophore in the Optical DO
module is variable excitation brightness. When the luminophore is new, the
brightness of the excitation is reduced to a minimum in order to prevent
unnecessary photo bleaching. As the output from the luminophore gradually
reduces, the brightness of the excitation is increased in order to squeeze the
maximum possible life from the sensor cap.
The combination of low duty cycle and variable excitation brightness can stretch
the useful life of a sensor cap as far as several years.
© 2013 Palintest Ltd. www.palintest.com Page 134 of 147