Redox electrodes and redox instruments for measuring and controlling Redox / ORP in process environments

Redox (ORP) 

Redox is the measurement of a solutions potential for Reduction or Oxidation (the term Redox is derived from Reduction Oxidation). The same measurement is can also be referred to as ORP (Oxidation Reduction Potential).

Anecdotally in the UK we tend to refer to the Reduction Oxidation potential is Redox, and in America the preferred terminology is ORP. The important factor is that the two terms are interchangeable. As Automated Water & Effluent Ltd is based in the UK our preference is to use the term Redox.

Redox measurements can be explained in how they differ from pH measurements. Where pH is the absolute measurement of the acidity or alkalinity of a solution as defined by the hydrogen ion activity - an Acid is able to donate a hydrogen ion and an Alkali or Base is able to accept a hydrogen ion. With a Redox measurement it is an indicative measurement of the solutions reducing or oxidation potential as derived by its electron activity - an oxidising agent such as Bromine, Chlorine or Sodium Hypochlorite will accept an electron, a reducing agent such as Sodium metabisulphite will donate an electron. 

Where a pH measurement will measure a solutions relative state for donating or accepting hydrogen ions. A redox measurement is the measurement of a solutions relative state for donating or accepting electrons. 

A redox measurement can be stated as being indicative rather than absolute. Where a pH measurement measures a systems relative acidity or alkalinity specific to a hydrogen ion, a Redox measurement is influenced by all oxidising or reducing agents within a solution. 

When a Redox reaction occurs its worth noting that no Oxidisation can occur without a corresponding Reduction reaction happening, and a Reduction reaction cannot occur without a corresponding Oxidisation reaction. These corresponding reactions occur at the same time and is often the reason cited for a slower redox response time of a redox electrode when compared to a pH sensor.

Applications of Redox measurements 

There is a very strong correlation between the lifespan of bacteria in water and a solutions relative Redox measurement. Oxidising agents can be very powerful disinfectants. Our cooling tower controllers will incorporate redox control for delivery of an oxidising biocide like bromine or hydrogen peroxide to kill bacteria present in the water. 

Stand alone Redox controllers can also be used to monitor or control disinfectant agents in swimming pools and potable water applications. 

Redox control in conjunction with pH control is of vital importance the electroplating sector particularly when considering chrome plating treatment. 

Redox Value

Our instrumentation outputs the absolute Redox value in mV. 

Our range of instrumentation includes a portable Redox meter which is often used to corroborate a Redox reading from a permanently installed instrument.

A Redox transmitter is an installed piece of equipment which converts the Redox value to either a 0 - 20mA or a 4-20mA current signal for use with a PLC or chart recorder.

Our Redox controllers incorporate control relays as well as a (0) 4-20mA signal. Depending on which model of controller - these can be used to control a piece of control equipment such as a pump or solenoid valve. Often these pieces of control equipment can be controlled proportionally that is - causing the device to speed up, or dose faster / slower depending on how far from the desired Redox value the measured Redox value is.

We refer to our glass bodied laboratory style Redox sensors as Redox electrodes, and our industrial bodied Redox sensors as our Redox probes.

Due to the nature of the Redox measurement we don't offer temperature compensation for our Redox Sensors.

Redox Instruments & Redox Electrodes


Portable Redox Meter

Portable Redox Meter

A Redox meter is an instrument which is normally portable and can be taken out into the field.

Our portable redox meters are simple to use and are designed for use in commercial or industrial environments.

With a process connection we can use a full redox sensor cell for precision readings as well as test 'in process' redox electrodes.

Accurate readings are easily achievable in a number of applications including Redox measurement in process vessels, swimming pool water or in other biocide applications.

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Redox Transmitter

Redox Transmitter

The Redox Transmitter is an instrument for mounting near a Redox electrode system to provide a signal proportional to the Redox mV measurement.

The best redox transmitters have zero and span calibration controls and a local display so that the transmitter can be buffered or calibrated locally to the redox electrode to ensure the transmitted signal is as precise as possible.

The current output is an industry standard 4 – 20 mA output with the same two wires which power the 24 VDC transmitter carrying the current output.

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Redox Controller

Redox Controller

Redox Controllers are Redox (ORP) instruments which have the ability to operate a remote device to provide controls over a process.

Our range of Redox controllers include devices which offer standard on / off control, proportional control and even PID control of the Redox value.

In addition to the control options - Redox controllers include a 4-20mA output signal. In non-proportional systems this is normally linked back to a recorder or BMS system and with proportional control, the 4-20mA can be expanded to control a dosing pump or other piece of process equipment.

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Redox Electrode

Redox Electrode

Our Redox electrode range operate using a platinum band for unrivalled precision when making Redox measurements.

We carry a large range of redox electrodes to cover a number of applications including laboratory measurement, process control, water treatment, biocide dosing, hydroponics and wet leisure dosing control.

Compatible with our range of inline electrode holders and acrylic flow sensors our Redox electrodes offer precision and longevity across the board.

For our PVDF or PVC bodied Redox electrodes designed to be directly screwed into pipework please see our pH probe section.

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Redox Probe

Redox Probe

Our Redox probe range give precision Redox measurements in industrial environments and are all of combination, double junction variery to provide accurate and reliable Redox measurements in even the harshest environments.

The Redox probes are manufactured in either PVDF (Kynar) or PVC, with a number of reference options including annular ceramic, porous Teflon or PTFE junctions. All of our Redox probe range are threaded for screwing directly into a process either for inline mounting or for connecting to a riser tube for dip mounting into a tank or vessel.

For glass bodied pH probes or use in electrode holders or laboratory style applications please see our Redox electrode section.

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Redox Sensor Inline Holders

Redox Sensor Inline Holders

When continuous Redox (ORP) measurements inside a pipe or pipework are required we are able to offer our inline Redox electrode holders.

Within our range we have solutions for different diameters of pipework and each inline electrode holder is compatible with our standard Redox electrodes and Redox probes. Each features a simple quick release mechanism for removing the Redox probe or electrode for maintenance or calibration.

Our retractable inline Redox electrode systems allow Redox electrodes to be removed from pressurised pipework or vessels without having to halt the process being measured.

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Dip Redox Sensor Systems

Dip Redox Sensor Systems

When continuous Redox measurement inside an open vessel is required our dip Redox probe assemblies offer the perfect solution.

We offer a number of dip mounting Redox electrode assemblies each of which can be mounted into tanks, pits, sumps, lagoons or any other unpressurised vessel. 

Available in custom lengths up to 3 metres and with tuff tip, automatic temperature and auto-clean options - our dip Redox electrode systems are designed to provide accurate and reliable Redox measurements in tanks and processes.

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Redox Simulator

Redox Simulator

pH simulators precisely replicate the signal from a Redox electrode or pH electrode and are designed for testing and checking Redox and pH instruments.

Designed for water treatment and process engineers the Redox simulator is a robust battery operated unit which connects directly to a Redox instrument using a process connector.

As well as simulating Redox and pH signals the output resistance can be increased allowing the operator to test for connection problems and isolate errors in the field.

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Redox Calibration Standards

Redox Calibration Standards

Redox calibration standards are solutions of a known and stable Redox value supplied ready bottled and sealed.

These are used to calibrate a Redox sensor to an associated Redox instrument.

We offer a very wide range of Redox Calibration Standards which can be supplied with certification traceable to national standards if required and the values available include:-

  • 200mV
  • 220mV
  • 234mV
  • 300mV
  • 420mV
  • 468mV
  • 616mV

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