Sensys Ltd

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Walchem pH/ ORP (REDOX) electrodes

Walchem’s WEL series electrodes are cost-effective differential pH and ORP electrodes for industrial applications. They are modular in design with a rugged CPVC housing that contains the electronics; pH and ORP cartridges can easily be connected or replaced in minutes without tools. The cartridges feature a unique threaded interlock connection and a double o-ring seal, ensuring a watertight fit and secure seating at all times. The optional differential preamplifier and temperature compensation element are in the housing, and are not thrown away when the electrode needs replacement. The electrode is powered by the controller it is connected to, so the signal is always preamplified and there are no batteries to go dead. A titanium solution ground rod integral to the housing enables the differential measuring technique. This results in prolonged electrode life and reliable measurement, resistance to stray voltages and currents or ground loop problems.

Summary of key benefits
• differential preamp
• universal mounting
• easily replaceable electrode cartridges
• electronics are not discarded with the electrode
• optional ATC
• easy to install
• cartridge Styles: flat surface, bulb/ rod & HF resistant
• resistant to electronic noise, ground loops

The differential preamplifier and optional automatic temperature compensation (ATC) element are built into the housing, resulting in signal amplification at the optimal location; right next to the sensor. Temperature response is fast, increasing accuracy of measurement. The titanium ground rod makes the differential measurement technique possible and it is resistant to aggressive chemistries. The electrode design enables a universal mounting style, a single housing and cartridge can be mounted in-line or submersed. This reduces inventory of parts and spares needed. The differential technology provides a longer electrode life, a signal that is more immune to electronic noise, high voltage potential in solution and ground loops. The preamp electronics are powered by the controller it is attached to: the signal is always pre-amplified, distance from the controller is not critical (less than 1000 ft. is recommended) and there is no concern about a battery going dead.

The electrode cartridge can be replaced without also having to replace the preamp or ATC element. Different styles are available to best fit your need: flat surface design resists fouling; low cost bulb version for less demanding applications; a fluoride resistant glass version for aggressive solutions. The cartridge has a unique threaded interlock connection which seats the electrode securely in the housing. Knurled machining of the casing at the surface end provides for a sure grip when removing or inserting a cartridge. The design of the electrode enables the unit to be used in immersion or in-line applications, reducing required inventory.

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Storage and shelf life
pH/ORP electrodes have limited lives, it is important to keep one or more spare electrodes. Electrodes supplied in soaker storage bottles have longer shelf lives than those supplied dry or with small vinyl caps.

The special solution in soaker bottles allows the electrode to be instantly ready for use as well as ensuring a long storage life without dehydration.

pH- single vs double junction
For many applications, a single junction reference electrode is satisfactory. However, if samples contain proteins, sulphides, heavy metals or any other material which interacts with silver ions, unwanted side reactions may occur.

These reactions can lead to erroneous reference signals or to precipitation at the reference junction leading to a short service life.

A double junction reference design affords a barrier of protection to combat the above interactions. When in doubt about the safest approach use the double junction design.

What is REDOX?
Oxidation reduction potential (ORP), also known as redox, is the measurement of a solution's oxidising and reducing activity.

When all of the oxidising and reducing materials have reacted, an equilibrium is reached and there is usually a surplus. It is this surplus material that creates the oxidation or reduction potential of a solution.