9
3
Cleaning
Proper maintenance of a probe is important. If the probe is not cleaned properly and regularly, probe
malfunction can occur due to a polluted diaphragm or ISFET. The cause for this pollution is usually the
sample.
Pollution on/or blockage of the sensor and reference electrode diaphragm surface is the most likely
cause for probe failure. If any of the following events occur: low slope, drift, instability of the reading,
slow calibration, probe will not calibrate, pH value doesn’t change as expected when changing samples,
start the cleaning procedure as described below and perform a revitalization.
Probe wear is another cause for probe failure. Probe wear is often, but not necessarily, preceded by a
period of declining calibration slope values. Probe wear is dependent on how the probe is used, stored.
Worn probes need to be replaced.
3.1 Daily cleaning
The appropriate cleaning frequency is dependent on the type of sample being measured. A good rule
of thumb to use when sampling colored liquids is when the reference diaphragm is no longer white,
the probe should be cleaned.
Both the surface of the chip (the shiny dot at the probe’s tip) and the diaphragm (the white surface on
the probe tip) are to be cleaned with a brush. Place the probe in warm tap water (around 60°C / 140°F)
with a mild detergent for 5 minutes, stir periodically. Scrub the probe tip with a soft brush and water
with a mild detergent. After scrubbing rinse with deionized water.
Never brush the probe tip, especially the ISFET chip, before rinsing and flushing thoroughly with water
(tap water, demi-water etc). Before rinsing debris and particles may be on the sensor surface and
brushing them into the senor may damage it. When in doubt, soak the probe for a while in warm water
with a mild detergent.
3.2 Revitalizing
Revitalization is performed to regenerate the diaphragm in the pH probe. The diaphragm is part of the
so called reference electrode and necessary for pH measurements.
For best results, clean the probe first as described in section 3.1 before revitalizing. Make sure the
probe is still warm (around 60°C / 140°F) and place the probe directly (without flushing it with
deionized water or cooling it down) in a saturated KCl-solution at room temperature and let it stand
for 20 minutes. This ‘cold’ KCl-dip will regenerate the reference system and the diaphragm.
To prepare saturated KCl (potassium chloride) solution: Add KCl-granules to distilled water until
no more KCl will dissolve. Adding 38 grams of KCl to 100 ml water is sufficient. Let this stand for at
least two hours and decant the clear solution. Now you have saturated KCl.
Summary of Contents for ConeFET
Page 5: ...5 1 3 Specifications...
