A pH electrode housing is designed to hold and protect the electrode
while attaching it to the process line. Various types of electrode
housings are available since process pH electrodes can be installed and
operated in several ways. Each type offers its own set of advantages and
There are basically six different types of pH electrode housings and to get the right type for your application you have to do three choices:
If a pressurized or "non-pressurized" housing is needed, depend on the chosen pH electrode type and the process pressure.
get proper and stable measurements, a liquid filled electrode has to be
subjected to an overpressure relative to the process pressure. This
internal overpressure ensures a gradual outflow of the reference
electrolyte through the diaphragm, preventing diaphragm fouling and poisoning of the reference system.
A manometer attached to the body of the housing makes sure it is easy
to monitor the pressure differential between the sensor and the process.
A large inspection window is also necessary to make it easy to monitor the electrolyte level. The level of electrolyte must be checked periodically and refilled, if necessary. Even liquid filled process pH electrodes in most cases are designed to handle a large electrolyte volume an option can be to have an external electrolyte reservoir connected to the sensor.
For optimum performance, experiment to find the appropriate pressure difference between the sensor and the process. A too high pressure difference will give an unnecessary high consumption of electrolyte, and frequent refill will be needed.
gel-filled pH electrode is pre-pressurized, and the polymer reference
system is pressure-resistant, which make it possible to use a simpler
electrode housing design than for the liquid filled electrode. This type
is more or less only an electrode holder with, in most cases, a screw
thread. You can also find on the market pH electrodes with polymer body
and designed for direct mounting into a vessel or pipe.
housings are used for measurements in reservoirs and tanks, and permit
measurements not only at the surface of the liquid, but also at various
deep inside it. The immersion housing is normally manufactured from
polypropylene (PP), and are supplied in various lengths.
Insertion housings are used when a pH sensor is to be inserted directly into a pipe, or through the side of a vessel.
electrodes need regular calibration and, in many applications, regular
cleaning. However, removing a pH electrode housing with screw-in
connections can be a problem. If an insertion housing is installed in,
for example, a process pipe the process might have to be shut down
before the sensor can be removed. In these situations, a retractable
housing can be the solution.
A retractable housing allows easy insertion and withdrawal of the pH electrode without interruption of the ongoing process. Retractable housings are available in a variety of models to suit specific process and user requirements. To avoid accidents, always follow the manufacturer's instructions for inserting and removing the pH electrode.
A bit of thought when designing an online pH measurement system can save a lot of headaches later on.