Oxidation Reduction Potential (ORP) is a hallmark variable in the realm of liquid analytics. However, it doesn’t receive quite the same attention that other variables like pH and conductivity do, so we aren’t surprised when we hear the question, “WTF is an ORP sensor?” Let’s explore what ORP is, why we measure it, and how ORP sensors operate.

The Variable

ORP refers to the ability of a substance or system to undergo oxidation or reduction reactions. It quantifies a substance’s ability to gain or lose electrons in a chemical reaction, hence representing the ORP value in millivolts (mV). A positive ORP value indicates that a substance or system has a greater tendency to accept electrons and undergo reduction. A negative ORP value suggests a greater tendency to donate electrons and undergo oxidation. The more positive the ORP value, the more oxidizing the substance or system is, while the more negative the ORP value, the more reducing it is.

What’s the use?

Many predominantly associate ORP measurements with being a variable in water treatment applications. Values related to ORP act as a gauge for the cleanliness of water and its ability to naturally break down contaminants. Many people commonly use ORP sensors in private swimming pools, earning the nickname “a poor man’s chlorine analyzer” to some. While it’s true that ORP analysis is a crucial tool for water analysis, operators use ORP measurements in various unique applications, both industrially and privately.

For example, during the wine fermentation process, it is possible to prevent sulfur aromas by controlling the grape must’s ORP value. ORP measurement taken during fermentation is an indicator of yeast activity, which can lead to the formation of Hydrogen Sulfide, spoiling the aroma of the wine. The ability to accurately measure and control oxidation in a fermentation process can help ensure product quality throughout the Food & Beverage industry.

Sensor Anatomy

ORP sensors consist of several key components that work together to provide accurate ORP measurements. Listed below are the components of an ORP sensor that work in unison to obtain electrochemical ORP measurements.

Reference Electrode

The protective glass body of the sensor houses the reference electrode. It provides a stable reference potential against which the measurement is made. Additionally, a reference electrolyte solution usually fills or surrounds the electrode, establishing direct contact with the measured sample.

Measuring Electrode

The measuring electrode is the component responsible for detecting the ORP of the solution. Typically, manufacturers construct the electrode from a noble metal, like platinum or gold. The measuring electrode is in contact with the sample solution and undergoes an electrochemical reaction based on the oxidation or reduction potential of the solution.

Reference Electrolyte

The reference electrolyte is present in the reference electrode and helps maintain a stable reference potential. The specific composition of the electrolyte solution depends on the design and manufacturer of the ORP sensor.

Junction

The junction enables the exchange of ions between the reference electrode and the measured sample solution. It is a critical component that ensures proper electrical contact and ion flow, which is essential for accurate ORP measurements. The junction also acts as a barrier between the process fluid and the reference electrolyte. It is important to ensure these fluids do not come in direct contact to mitigate the poisoning of the electrolyte.

Discover Your Sensor

There are various forms of ORP sensors that are designed with certain applications in mind. It is important to ensure the anatomy of your ORP sensor is suitable for your application. Check out our ORP sensor options to learn more about what kind of sensor works best for your process.