What is ORP Measurement and When Should You Use an ORP Sensor?
ORP stands for Oxidation-Reduction Potential (also known as redox potential). An ORP sensor measures the electrical potential that indicates the extent to which a liquid acts as an oxidising or reducing agent. This is relevant in applications where the presence of oxidising or reducing substances determines the process — such as chlorine control in swimming pools or cooling towers, monitoring of scrubbers, or semiconductor production. ORP measurement is often combined with pH measurement, as both parameters together provide a complete picture of the chemical state of a liquid.
What Types of pH Sensors Are Available?
There are three main types of pH sensors for industrial and process use, each suited to different conditions.
Combination pH sensors contain both a measuring and a reference electrode — and in the case of FIP and Georg Fischer, also an integrated temperature sensor — in a single housing. This makes them compact and easy to install. They are suitable for a wide range of process applications, from drinking water treatment and cooling water systems to swimming pools and reverse osmosis installations.
Differential pH sensors use an additional ground electrode alongside the measuring and reference electrodes. This design makes the measurement independent of electrical currents in the liquid and prevents contamination of the reference electrode by the process medium. Select this type when working with media that can attack the reference electrode of a standard combination sensor — such as wet air scrubbers, electroplating baths, wastewater streams containing metal ions, or strongly acidic and alkaline media.
Process pH sensors are built robustly with integrated process connections such as NPT threads or inline housings. They are suitable for continuous installation in a pipeline, submersion in a tank, or use in an insertion system. Select this type for continuous process monitoring under pressure or at elevated temperatures.
Selection Guide: Which pH or ORP Sensor Suits Your Application?
| Situation |
Recommended type |
| Drinking water, cooling water, swimming pool, reverse osmosis |
Combination pH sensor (standard) |
| Wastewater with metal ions, strongly acidic or alkaline medium |
Differential pH sensor |
| Continuous measurement in pipeline or tank under pressure |
Process pH sensor with inline or NPT connection |
| Media with particles, sticky or fouling substances |
Flat electrode — self-cleaning design |
| Clean liquid, high accuracy required |
Bulb electrode — larger contact surface |
| Chlorine or redox control (pool, cooling tower, chemical) |
ORP sensor, optionally combined with pH sensor |
Applications by Sector
pH measurement and ORP measurement are widely used across a range of industries:
- Water and wastewater treatment: effluent neutralisation, pH control for cooling towers and boilers, water pre-treatment for membrane filtration
- Food and beverage industry: quality control and food safety
- Pharmaceutical industry: monitoring during production and R&D
- Chemical industry and surface treatment: process control with aggressive media and metal processing applications
- Swimming pools and recreational water: continuous pH and ORP monitoring for water disinfection
- Pulp and paper industry: process monitoring at elevated temperatures and pressures
- Environmental monitoring and odour scrubbers: air scrubbers
For applications where ion concentration or water contamination also plays a role, pH measurement is often combined with
conductivity measurement. In processes where solid particles in a liquid need to be monitored,
turbidity sensors provide an additional measurement value.
What to Consider When Selecting a pH Sensor
When choosing a pH or ORP sensor, the following parameters are decisive:
- Process temperature and pressure: process pH sensors are available for higher pressure and temperature ranges; for temperatures above 60°C, select a version with heat-resistant glass
- Nature of the medium: for aggressive, contaminated or particle-containing media, choose a differential design or flat electrode
- Presence of metal ions: certain ions (such as bromide, cyanide, sulphide) can attack the reference electrode — in this case, choose a differential version
- Measuring range: standard pH sensors measure from 0 to 14 pH; for ORP, the range is expressed in millivolts
- Mounting type: inline (pipeline mounting), submersion in a tank, or insertion system
- Signal output: 4–20 mA or digital (Modbus, HART), depending on your controller or transmitter
Select your pH sensor based on pressure, temperature, medium and mounting method, or request a quote directly via the contact form.
Frequently Asked Questions
What is the difference between a pH sensor and an ORP sensor?
A pH sensor measures the acidity of a liquid on a scale from 0 to 14. An ORP sensor measures the oxidation-reduction potential in millivolts and indicates whether a liquid acts as an oxidising or reducing agent. Both sensors are electrochemical in nature and are often used together for process monitoring of water.
When should I choose a differential pH sensor instead of a combination sensor?
A differential pH sensor is the right choice when the process medium can contaminate or attack the reference electrode. This is the case with media containing metal ions such as bromide, cyanide or sulphide, with strongly acidic or alkaline liquids (pH below 2 or above 11), or in industrial processes such as electroplating baths, air scrubbers and heavily contaminated wastewater streams.
What is the difference between a bulb and a flat electrode?
A bulb electrode has a larger contact surface with the medium, resulting in faster response to temperature fluctuations and higher accuracy. A flat electrode has a self-cleaning design and is better suited for media with particles, sticky substances or fouling risk. FIP and Georg Fischer supply both versions for industrial process applications.
