ORP Sensor: What Is It And How Does It Work?

An ORP sensor (oxidation-reduction potential) is often used to evaluate if a liquid sample has an oxidation ability. It tells the possibility of pollution, particularly from industrial effluent. Moreover, this liquid sensor could be a useful quantification if the operator knows certain chemicals in the water sample that is the major reason for the effects. Excessive chlorine in liquid waste sewage, for example, will lead to the increase of ORP quantity, although the existence of hydrogen sulphide will lead to a decrease in ORP quantity.

Furthermore, ORP is calculated by detecting the possibility of a chemical stability sensor that is submerged in liquid. The detecting sensor’s potential is measured compared to the pH probe’s reference electrode, and the result is shown in millivolts (mV).

What Is an ORP Sensor?

An ORP sensor is composed of ORP equipment that contains an interface design, a metallic half-cell, and a reference cell for detecting ORP. Oxidation-reduction is a chemical process involving the development of electrons from different materials in this sensor. Moreover, the oxidising species releases electrons, whereas the decreased species obtains them. It also acts as an indicator of how much oxidation or reduction occurs under the given circumstances. The trade of electrons is referred to as a redox reaction. Because oxidation involves the loss of electrons, the liquid is more positive.

Furthermore, the reduction in the process of acquiring electrons results in a negative value. For the reaction to take place, both organisms should be existent. In addition, the interchange conductivity results from concentrations, the oxidation-reduction process, and the sensor are directly connected to the velocity of the ORP equipment. The speed decreases whenever the specimen ORP is comparable to the emitter ORP.

The limitations described above may be mitigated by cleaning the instrument’s electrodes prior to measurements and matching the systems by testing the reducer and oxidizer in a stable system using wet testing and detecting pH.

How Does The Orp Sensor Work?

When the monitoring sensor is subjected to oxidation or reduction chemicals, electrons are continually transported back and forth on its monitoring surfaces, resulting in minimal power. The liquid sensor measuring element comprises gold, graphite, or platinum. A seawater liquid is linked to the sensor, which has a half cell potential of 0.0mV. Since they offer robust and dependable functions, this sensor is constructed of saturated calomel or silver chloride.

The ORP sensor measures the power over a circuit created by two electrodes, and the test may be performed using a pH metre’s millivolt option. The singular power is the oxidation-reduction potential, and a positive voltage indicates that a liquid is collecting electrons. The ORP sensor can measure oxidation-reduction possibilities ranging from -450 to +1100 mV. In the positive part of this scale, these equipment’s scanners suggest a strong oxidizer, whereas values in the negative region indicate a reducing agent.

ORP Sensor Specifications

An ORP sensor is classified into three types based on their performance:

  • The ORP / redox range: Reaction creates a negative or positive ORP according to the kind and intensity of the response. The oxidation scale may range between -1000 and +1000. It is better to invest resources with a significant negative ORP.
  • Accuracy: The variations in measurements are influenced by the size of the sensor. A sensor with a more extensive detecting area is a superior detector. If the curves generated by the gathered information coincide, it is safe to believe that the reaction occurred when the electrodes were in balance.
  • Response time: For liquid sensors, responsiveness is often stated as a percentage in 10 secs.

Junction Type

When choosing ORP sensors, junction style is an essential physical parameter to examine. There are two fundamental kinds:

  1. Single junction– A singular electrolyte is used in a single junction reference. The electrolyte keeps the ion perceived by the irreversible reference element at a consistent level and produces a relatively low water connection with the liquid sample.
  1. Double junction– A second reference cell is placed next to the potassium chloride cells in the double junction reference. The material from potassium chloride reference is screened in this cell. Double junction cells often have a longer lifespan and better durability.

ORP Sensor Maintenance

Appropriate maintenance and care are essential for effective readings and a long lifespan. The OPR sensor should be prepped by eliminating air bubbles and processed by washing in a pre-treatment solution before beginning an ORP study. As a reduction therapy, quinhydrone is utilised, while as an oxidising medicine, sodium hypochlorite with 1 M hydrochloric acid or bleach is employed.

To avoid accumulation, it must be cleansed and washed after each usage. It must also be examined for scrapes or fissures, and the ground must be cleaned and polished until no residues of the cleaning agents remain. The sensor must be kept moist in a pH four buffer storage system and washed regularly. Keeping this liquid sensor in deionized or distilled water is not recommended.


ORP sensors assess the efficiency of oxidative disinfection induced by combining all oxidising agents in the liquid. ORP is measured with an ORP probe and analyser. Millivolts are the standard measurement for ORP (mV). Electrons are consumed by oxidisers, whereas oxidising agents give electrons. For example, when chlorine is constantly introduced to the pool, the disinfecting activity is mainly driven to chlorine chemicals, especially hypochlorous acid.

Furthermore, the liquid sensor assesses a disinfectant’s ability to execute its job of neutralising bacteria and oxidising organic compounds. The greater the millivolt measurement, the more effectively the pool water may oxidise and sterilise. Oxidizers raise the millivolt value, which increases disinfecting.