ORP FAQ – Sensorex, FAQ



The following are questions which are frequently asked of our Customer Service/Technical Support Department and these are their replies. Our Technical Support Department is available to help you regardless of which brand of electrodes you are using.

Q: Can I use a Sensorex ORP electrode with any meter or controller ?

A: Yes. The output signal of all ORP electrodes are compatible with virtually all meters and controllers. When ordering, please specify the type of connector, the length of cable, and the installation configuration (if installing in a tank, pipe tee, or insertion). You can read ORP output with most DVM’s (digital volt meter).

Q: What is the range of ORP (units of measure)?

A: ORP is expressed in millivolts (mV). A range of -1000 mV to 1000mV is common with most ORP instruments.

Q: What does ORP really measure?

A: ORP measures the total activity of a solution in mV or the total of reducing and oxidizing activities in a given solution. Practically speaking, ORP is useful for monitoring and controlling chemical addition of oxidizing or reducing agents. Oxidizing agents include chlorine, bromine, and ozone. Reducing agents include cyanide and sodium bisulfite and metabisulfite.

Q: How does an ORP electrode work?

A: An ORP electrode employs a nobel metal such as platinum to sense electron transfer in oxidizing and reducing reactions. ORP senses the total electron transfer, or more simply if a chemical mix has more oxidizers than reducers in it. Nobel metals such as platinum, silver, or gold are used because they can sense the electron transfer but are not consumed in the reactions.

 Q: What are some common ORP applications?


  • Control of chlorine addition in swimming pools
  • Fruit and Poultry washing (disinfection)
  • Cyanide destruction in plating
  • Hexavalent chromium reduction
  • Mining application,
  • Control/monitoring of ozone addition in swimming pools and aquariums or purification of water prior to bottling or use in sterile solutions.
  • Bromine addition for disinfection of pools and spas is also common.

Q: How is ORP calibrated?

A: ORP does not have to be “calibrated” but it can be tested if desired or required. Standard ORP Test Solutions with stable mV outputs are required. Two types of solutions are available. One type requires you to mix pH buffers 4 and 7 with quinhydrone. These offer two different stable values, but the shelf life is only several hours and they cannot be stored. Sensorex part number B125 is a complete kit with everything that you need to complete two-point testing. A second type of premixed solution is also available. Sensorex offers two of these for your analytical testing pleasure. B225 has a stable output of 230 mV while B425 has a stable output of 450 mV. Shelf life of these solutions is guaranteed for 12 months.