Page 47
Addendum to YSI Dissolved Oxygen sensor instructions.
WARNING: FAILURE TO READ THIS NOTE CAN RESULT IN
DAMAGE TO YOUR NEW SENSOR
The YSI 5739 dissolved sensor is shipped dry from the YSI factory.
Before the sensors are despatched from TPS, they are fully tested.
Therefore the sensor should be already filled, with a correctly fitted and
tested membrane when you receive it. This is part of the TPS Quality
Control Program.
NOTE:
During storage and transport after the sensor has been tested by
TPS, some bubbles may appear behind the membrane. This may be due
to a number of factors, non of which affect the performance of the
sensor. If in doubt, refill the sensor and fit a new membrane before use.
Why is correct membrane fitting SO IMPORTANT ?
There are two reasons why the membrane must form a perfect seal…
1. It stops the internal fluid leaking out and causing air bubbles to form
behind the membrane.
2. Most important: It resists contamination from outside getting INTO the
sensor. Substances such as Sulphides will poison the Silver anode.
(This is triangular-shaped piece behind the sensor membrane.)
How to fit the membrane correctly...
Section "d." of the YSI "SENSOR PREPARATION" of the enclosed
instruction leaflet, says to stretch the membrane up and over the end of
the sensor.
This point cannot be overstated. The act of physically stretching the
membrane is what forms the correct shape to seal the sensor from the
outside world. The "O" ring itself DOES NOT guarantee a correct seal of
the sensor membrane. It only helps to hold a correctly formed membrane
in place.
The correct stretching technique will form a "CUP" shape in the
membrane. Note that the membrane will stretch up to twice its original
length without breaking. It is better to tend to over-stretch the membrane
than not to form this "CUP" shape correctly.