AP200 series
Rugged pH/Redox (ORP) sensor systems with rapid temperature response for critical processes
5 Maintenance
14
IM/AP200 Rev. S
5 Maintenance
5.1 General Cleaning
To ensure accurate monitoring, keep the electrodes free of
contaminants by periodic cleaning. The frequency of cleaning
depends on the particular application.
Automatic cleaning using the optional jetwash system and
controlling the cleaning solution using a suitable controller or
analyzer, will reduce the amount of manual cleaning.
Methods of removing various types of deposit are detailed
below. Replace the sensor if the performance of the sensor
does not improve after cleaning.
5.1.1 General Sludge and Loosely Adhering Matter
Rinse off the excess matter and wipe the sensor with a soft cloth
or tissue before calibrating.
5.1.2 Heavy, Non-Greasy Deposits
For example: lime, salts, etc.
Immerse the sensor in 1 to 2 M hydrochloric acid until the
deposit has dissolved. Rinse with demineralized water before
calibrating.
5.1.3 Greasy or Organic Deposits
Wipe the glass membrane with a detergent or acetone-based
solvent. Rinse with demineralized water before calibrating.
5.2 Fault Finding
Listed
below
are
some
common
symptoms
of
sensor
malfunction together with possible cures.
Short scaling (Low Slope) or sluggish response
1. Glass sensor membrane dirty or coated – refer to Section
5.1 for cleaning.
2. Poor insulation on cable connectors, possibly due to
moisture – dry connectors with warm air.
Replace sensor if no improvement is seen. (It may also be
necessary to replace the extension cable if used.)
No response to pH buffer or sample
1. Sensor incorrectly connected – see Section 3.1, page 11
and the analyzer user guide for connection details.
2. Glass sensor membrane broken or cracked – replace
sensor.
Unstable readings or drift
1. Sensor incorrectly connected – see Section 3.1, page 11
and the analyzer user guide for connection details.
2. Dry or dirty reference junction – clean junction as detailed
in Section 5.1. Leave to soak in a buffer solution for
several hours.
Replace sensor if no improvement is seen.
Stable but incorrect readings
1. Incorrect calibration – recalibrate using fresh buffer
solutions.
2. Incorrect temperature compensation settings – enter
correct manual temperature or check that automatic
temperature compensation is reading correctly.
3. Sensor responds correctly to pH changes, but there is an
offset of <1.0 pH and >0.2 pH – perform a one-point
process calibration – see Section 4.1, page 13.
5.3 Storing the Electrode
If it is necessary to remove the electrode from the sample line, fill
the retained protective cap with buffer solution and cotton wool,
or equivalent, and fit it to the sensor.
Warning.
Close all isolating valves before removing an
electrode from a flow line.
Note.
All the above symptoms could be caused by a faulty
extension cable. Check and replace it, if necessary.
Note.
Allowing the glass membrane and reference junction
to dry out irreversibly affects the response of the electrode.
