Ozone Sensor SM-X

The SM-X ozone sensor was a replacement sensor for the OS-4, OS-6, and A-22.  However, the SM-X is no longer in production and is now obsolete.

SM-X Replacement Sensor

The SM-6 also used the SM-X as a replacement sensor and also no longer available for purchase.

SM-6 with SM-X

The replacement ozone sensor SM-X (also known as the SM-X-20 or SM-X-2) was paired with EcoSensors OS-4 Ozone Switch, OS-6 Ozone Controller, and A-22 Ozone Monitor. The following options are now available instead:

A-22 Ozone Monitor

A-22 Ozone Monitor

The A-22 is obsolete and there is no replacement sensor option available.  We recommend the following as comparable ozone monitor options to replace your A-22:
D-16 with Ozone 0-20 ppm – https://www.oxidationtech.com/d-16-gas-detector.html
S-300 with EOZ 0-10 ppm – https://www.oxidationtech.com/aeroqual-series-300.html

OS-4 Ozone Switch & OS-6 Ozone Controller

OS-4 Ozone Switch
OS-6 Ozone Controller

The OS-4 and OS-6 Ozone Detectors can be upgraded to use the SM-7/SM-EC electrochemical sensor as an ozone replacement sensor to the SM-6/SM-X.  The new SM-7 will need to be connected to the OS-4 and OS-6 via the wired cable.

SM-7/SM-EC Ozone Sensor

There are two range options for the new SM-7/SM-EC sensor: 0-20ppm or 1-50ppm.  Both range options can be used with the OS-6, but only the 0-20ppm can be used with the OS-4. After you have upgraded to the SM-7/SM-EC then only replacing the SM-EC sensor that’s inside of the SM-7 needs to be done for future sensor replacement.

SM-EC sensor module

The SM-7/SM-EC ozone sensors should be replaced annually as the sensor calibration is good for up to 1 year.

Feel free to contact us with any questions that you have about the SM-X ozone sensor being discontinued.

Measure ozone in water with ORP

Oxidation Reduction Potential (ORP) is a method to measure oxidation in water.  ORP is a common measurement of water quality in a wide variety of water treatment applications.  So, what is ORP and how does it work?

Fundamentals of ORP Measurement in water

ORP stands for oxidation-reduction potential, this is a measure, in millivolts of the tendency of water to oxidize or reduce substances within that water or that the water comes in contact with.

ORP sensor technology
Diagram of an ORP sensor

Oxidation is the loss of electrons, or an increase in oxidation state by a molecule, atom or ion. When a substance has been oxidized it’s oxidation state increases. Greater ORP values in water equate to create potentials for oxidation by that water. Any compounds within the water that increase the ORP of the water will be indicated by the ORP meter. In an ozone system, an elevated ORP value can be primarily attributed to the increase of ozone in water along with the resulting ozone by-products, oxygen, hydrogen peroxide, hydroxyl radical, etc.


An ORP sensor in water will measure very small voltages generated by the construction of that probe placed in water. The ORP sensor consists of an ORP electrode and a reference electrode. The principle behind the ORP measurement is the use of an inert metal electrode (commonly platinum) which, due to its low resistance, will give up electrons to an oxidant or accept electrons from a reductant. The ORP electrode will continue to accept or give up electrons until it develops a potential, due to the build-up of charge, which is equal to the ORP of the solution.

ORP sensors will, over time, become less accurate, or cease to provide any voltage changes or usable ORP values. Contamination in the water can coat the ORP sensor probes and cause less accurate ORP readings and slower reactions to changes in ORP values in water. The electrode used in the ORP sensor will also age, due to normal wear of the platinum electrode due to water flowing past the electrode. Due to normal aging and coating of the sensor an ORP sensor should be replaced annually, or as needed to provide accurate ORP readings in water.

Measure ozone in water with ORP

To use the ORP measurement to measure ozone in water a correlation must be made.  ORP is a mV signal while ozone is a PPM signal.  If the only oxidant added to the water is ozone, a safe assumption can be made that any changes to ORP (mV) are changes in ozone in water.  The ozone level in the water can be measured with a manual ozone test kit or meter.  This ppm level can be correlated to the mV reading to provide an accurate ozone reading with ORP.

K-7404 dissolved ozone meter, manual test kitI-2022 dissolved ozone test kit

As ORP levels go up the ORP sensor is less and less responsive.  To measure ozone in water at levels above 1.0 ppm the ORP sensor will not be suitable.

Why use ORP to measure ozone?

Any time the water is discolored or dirty a dissolved ozone meter will not accurately measure ozone in water.  In these cases, ORP is your only option.  Also, in most of these applications, dissolved ozone levels are very low, therefore ORP is a valuable method of measuring ozone in water.

Today in history – Christian Friedrich Schönbein

Christian Friedrich Schönbein

The 19th-century chemist discovered ozone.

Christian Friedrich Schonbein discovered ozone
Christian Friedrich Schonbein

Born on 18 October 1799 in Metzingen, Germany, Christian Friedrich Schönbein was a chemist best known for the discovery of ozone and the invention of guncotton. He attended primary school until age 13, when he was apprenticed to a chemical and pharmaceutical factory in Böblingen. At age 21, he took and passed an exam verifying his scientific and practical knowledge of chemistry. After pursuing further chemistry studies at the Universities of Erlangen and Tübingen and teaching at schools in England, France, and Germany, he accepted a position in 1828 at the University of Basel, Switzerland, where he would remain for the rest of his career. Schönbein’s ozone discovery occurred in the late 1830s, while he was doing experiments on the electrolysis of water. He noticed a distinctive odor, similar to the smell following a bolt of lightning. In 1839 he succeeded in isolating the new chemical substance and named it from the Greek word “ozein,” meaning “to smell.” Another of his discoveries, guncotton, came about by accident: In 1845, while using his wife’s cotton apron to clean up a chemical spill containing nitric and sulfuric acids, then rinsing it out and hanging it to dry, Schönbein saw it spontaneously ignite. Nitrocellulose, the highly flammable compound that was created, found many practical uses, among them in munitions and flexible films. When dissolved in ether, nitrocellulose forms collodion, which was used in medical dressings and early wet-plate photography. Schönbein is also credited with making the first observation of the fuel-cell effect in 1838; it was his friend William Robert Grove who would create the first prototype fuel cell in 1845. Over his professional life, Schönbein wrote more than 364 scientific papers. He died in 1868 at age 68.