ORP Calibration Basics
ORP Sensor Design
Oxidation reduction potential or redox potential is a measure of the chemical exchange of electrons between multiple species in a solution. ORP sensors are based upon an electrochemical measuring principle similar to pH, and contain both measurement and reference half-cell electrodes. In place of a pH sensitive glass membrane, typical ORP probes contain a measurement electrode usually made from a noble metal such as platinum.
To offset electric potential of the sensor derived from individual components of the reference and measuring electrodes, a calibration is performed. In ORP, this is done by standardizing a sensor against a solution of known oxidation-reduction potential.
ORP Calibration and Temperature
A single point calibration is performed using ORP liquid buffer of a known value. Temperature is an important consideration when calibrating and measuring ORP, as temperature can influence the availability of free protons. Hamilton ORP buffers come with a standard table of ORP values at various temperatures. If an Arc ORP sensor is used, the ORP buffer value is automatically recognized within ArcAir software. Any correction due to temperature is compensated for with the built in RTD. With non-Arc ORP sensors, temperature should be compensated for manually at the transmitter.
Hamilton Redox (ORP) Buffer 475 ± 5 mV (Ref 238227)
Celsius | mV* | mV** | Celsius | mV* | mV** | Celsius | mV* | mV** |
---|---|---|---|---|---|---|---|---|
5 |
456 |
677 |
20 |
470 |
681 |
35 |
484 |
684 |
10 |
461 |
678 |
22 |
472 |
681 |
40 |
488 |
684 |
15 |
465 |
679 |
25 |
475 |
682 |
45 |
492 |
684 |
18 |
468 |
680 |
30 |
479 |
683 |
50 |
496 |
684 |
* E(Reference Potential based on Ag/AgCl element with 3M KCl electrolyte found in Hamilton sensors)
** E(Pt, Hydrogen)

Hamilton Duracal ORP Buffers come in 271 and 475 mV standards
Related Content
- Not sure when to specify an ORP sensor? See common applications where ORP sensors are used here.
- Go here to see Hamilton's DuraCal ORP liquid calibration solutions.
- Visit our Main pH / ORP Knowledge Base Article Page to see all articles on pH sensors.