pH Electrode housing needed
for process measurement

pH electrode housing

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 disadvantages.

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:

  • pressurized or "non-pressurized" housing?
  • immersion or insertion housing?
        and if insertion housing;
  • stationary or retractable housings?

Pressurized or "non-pressurized" housing

If a pressurized or "non-pressurized" housing is needed, depend on the chosen pH electrode type and the process pressure.

Housing for liquid electrolyte pH electrodes - pressurized housing

pressurized housing

To 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.

Housing for gel-filled or solid polymer electrolyte pH electrodes - "non-pressurized" housing

pH sensor housing

The 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.

Immersion or insertion housing

Immersion 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.

Stationary or retractable pH electrode housing

retractable housing

pH 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.

Installation guidelines

A bit of thought when designing an online pH measurement system can save a lot of headaches later on.

process pH
  • Make sure your pH sensor and housing of choice will handle the prevailing process conditions such as pressure, temperature and the corrosive nature of the process fluid.
  • Choose a location where your pH electrode and transmitter are close to each other and where it can be easily accessed. This will reduce the effort required when you need to check and calibrate the system.
  • Ensure that the pH sensitive glass of the electrode is always immersed. A dry pH sensor will not work properly and give unstable readings.
  • Make sure your chosen pH sensor position gives a representative mixture of the media and no stagnation or layering.
  • Where abrasion or coating is a problem, choose a location that gives an optimal fluid velocity.
  • Install pH sensors with the bulb down, within 80° from vertical, to promote good reference electrode function.

electrode holders

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Download the new release ISO 14001:2015