Installation
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BPD17 pH / Redox Monitor
Operating Guide
Installation and Choice of pH / Redox Electrodes
The choice of the correct type of pH / Redox electrode, how and where to mount it, so that it has a
representative sample of solution are probably the two most important considerations when installing
a pH / Redox system.
The following criteria are of great importance during selection:
The chemical makeup, temperature and the viscosity of the sample.
The use of the correct materials for corrosion resistance.
Position of electrode for robustness and service access.
Ensuring a representative, uncontaminated solution sample.
The following tips might be useful. High temperature samples will restrict your choice to electrodes
with high temperature references, note that low temperatures will also affect the response time of the
electrode. When measuring high viscosity samples, it is important that the junction is easy to clean.
Samples with high pH or salt concentrations require electrodes with alkali-resistant membranes.
To ensure correct electrode mounting the following conditions should be observed:
The electrode system can only measure what is in the immediate vicinity of the sensor area of the
probe.
A moderate flow is maintained to provide an “up to date” sample. Excessive flow rates, however, can
cause certain electrodes to rapidly deplete, which will result in inaccurate readings. In this case a
sealed reference is recommended.
Ensure that both the glass electrode and reference are in contact with the sample.
Avoid points where air can be trapped.
Avoid points of high turbulence as air bubbles will affect the measurement.
If the sample has solids present then use a guard or filter to protect the glass electrode. Alternatively
use a flat pH bulb.
The glass electrode contains a liquid, ensure that the probe is mounted so that the internal filling
solution is in contact with the glass bulb.
When a new pH electrode is first fitted or changed it must be calibrated (see page 32). Depending on
the application it may also need periodic re-calibration, the BPD17 provides an inbuilt count down
timer which will trigger an alarm when calibration interval has expired (see page 38).
Care and Maintenance of pH / Redox Electrodes
All pH and Redox electrodes contain an electrolyte solution, gel or polymer that has a limited life in
both operation and on the shelf. The electrode shelf life depends on its storage conditions, it is
recommended that the electrode should be used within six to twelve months after purchase.
For gel filled, non-flow electrodes the storage boot may become dried out during storage. This can
result in evaporation of the water inside the electrode causing high impedance in the reference cell. If
allowed to fully dry out the operation of the electrode will be irreversibly damaged. For electrodes in
storage it is recommended that every three to four months the following procedure is carried out:
Remove the black storage boot or transit cover at the end of the electrode
Re-wet the fibre pack inside the storage boot with 3.8 Molar Potassium Chloride (KCl) saturated
solution or if this is not available use a quantity of 4pH buffer solution. Note do not use deionised
water.
Re-seal the storage boot or transit cover.
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