Ozone alarm in use, audible and visual

Remote Audible Alarm Panel (RAP-1) is Activated by OS-6 Monitor Relay when Ozone is above 0.1 PPM

RAP-1 Audible and Visual Alarm Activates when Ozone Levels are above 0.1 PPM

In this video the RAP-1, which is a remote audible / visual alarm, is wired to the safety relay switch in the OS-6 Ozone Monitor, which is set to trigger above a 0.1 ppm ozone level. According to OSHA, the exposure limit for workers is 0.1 ppm for 8 hours per day. This relay is permanently programmed to always activate above 0.1 ppm ozone levels.

The decibel levels on the RAP-1 range from 92-103 dBA. The volume can be adjusted by turning the little black dial on the RAP-1 (shown in the video). The RAP-1 light and audible alarm are activated the entire time the OS-6 reads above 0.1 ppm ozone. As the ozone levels drop, the readings drop and result in the flashing light and audible alarm stopping after the reading goes below 0.1 ppm ozone.

Both devices can be purchased through our website. Each product is linked to below:

The RAP-1 Remote Audible Alarm Panel can be purchased here:

The OS-6 Ozone Monitor can be purchased here:

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The A-22 is obsolete and there is no replacement sensor option available.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.

B12 Ozone Sensor is cost effective solution

The B12 ozone sensor was recently added to our website with options for an ozone sensor or oxygen sensor for ambient oxygen levels.  The B12 is a basic sensor offering a display, 4-20 mA output, XP rating, and remote sensor options.

B12 with a display
B12 Ozone Sensor with display

Starting at only $600, the B12 is a very cost effective option for basic ozone monitoring.  The reliability of ATI at a price point of much lower cost options!

Dimensions of B12 ozone gas sensor
B12 Ozone Sensor dimensions

For more ozone gas detection options check our our full list of ozone monitors HERE.

Ozone Sensor Calibration Information


Ozone Sensor Calibration Information

All Ozone Sensors will require periodic calibration to ensure your gas measurements are accurate and correct.  Different gasses, and sensor manufacturers will have differing requirements and methods for calibration.  This page will serve to provide general calibration information and links to specific calibration procedures from the sensor manufacturers we represent.

Should you have any questions about sensor calibration, or would like us to help you with your calibrations please contact us.


Most sensor manufacturers will recommend calibration annually.  This would be the longest interval Ozone Services would recommend for ozone sensor calibration.

The frequency of calibration will be depending upon the gasses measured, sensor type, and purpose of the ozone sensor.

Our general recommendation would be to perform a bump-test of the sensor at least monthly.  Perform a field or factory calibration or sensor check every 6-months, and a factory calibration or sensor replacement every 12-months.



Have you ever wondered who ensured 1 pound is exactly 1 pound?  and 1 meter is precisely 1 meter? The NIST is the answer.  this is the governing board that will hold the standard of measurement.

Every gas measurement calibration standard must be directly traceable to the NIST to ensure your sensors calibration is accurate.  When you are reviewing your calibration certificate it must be clearly stated that the calibration standard used to calibrate your sensor is NIST traceable.  If necessary, you can, and should request the proper documentation to validate that traceability.

Calibration gasses can also be NIST traceable The NIST has set-up specific protocols for manufacturers of calibration gasses to follow to ensure your cal gas can be provided with NIST traceability.



Calibration gasses are used to calibrate many gas sensors.  Known quantities of gas can be mixed with air to provide a span calibration gas to be used for calibration.  For example. if you are calibrating a chlorine sensor and would like to perform a span gas calibration at 5 ppm, you would purchase a cylinder of air mixed with exactly 5 ppm of chlorine.  This gas can be used according to the manufacturers specifications to perform a span gas calibration.

Ozone is a gas that must be produced on site in known quantities to perform calibration.  The only option for precise ozone gas sensor calibration is sending your sensor to a facility that has a specially build calibration chamber.


Field calibration is just what it indicates.  Any calibration of a sensor performed in the field, or where the sensor is currently installed.  This can be performed with calibration gasses, or with devices designed to produce gasses that will react properly to ensure calibration is accurate on your sensor.

Field calibration is convenient for applications where many sensors are installed and would be challenging or inconvenient to send away for calibration.  Field calibration of your sensors can be performed by Gas Sensing, and many other service companies that will calibrate, and repair your sensors.



When you want to know if your sensor is responding a bump test is a great option.  This is simply a test that exposes the sensor to the specific gas it is intended to measure and ensure that the sensor does indeed respond.  While not a precise process, this does ensure that the sensor is indeed responding and can respond in a critical situation where human safety is critical.

ATI offers an Auto-Test generator for many of the sensors used on the D12 and F12 monitors.  This auto-test generator will produce a gas that causes the proper sensor to react.  A test is run on a pre-set schedule if the gas sensor does not respond as expected an alarm will come on indicating the sensor has failed.  This is a great option for gas sensing is critical applications.

Note: A bump-test is not an acceptable replacement for sensor calibration



Bump testing is a great method to ensure your sensor is responding to the gas it is intended to measure.  Bump testing is not a replacement for calibration.

Calibration verifies that the sensor is accurate and providing correct measurements.



Zero calibration ensured the sensor is reading an accurate 0, or pure air situation.  Most sensors have an easy way to reset the zero in the event that it drifts over time.



Span calibration is ensuring the actual measurement of gas is accurate.  The span should be done at a level of gas that would normally be measured.  Create a known amount of gas at a specific level and verify the sensor displays the same level of gas.



A calibration certificate is provided by the manufacturer when you purchase a sensor.  The calibration certificate provides you with the necessary information to prove that the sensor was calibrated to an NIST standard.  The Calibration Certificate will provide the date the sensor was calibrated, and the date calibration should be done again.

Click here to see a visual explanation of the contents of a typical calibration certificate.



Calibration information on ATI sensor

ATI Sensor Calibration Information



Aeroqual handheld sensors, and fixed mount sensor heads can be calibrated using the Series-300, or Series-500 base and R42 Calibrator.

Aeroqual Sensor Head Calibration Information



EcoSensors devices have a variety of options for calibration.  We provide necessary information at the link below:

EcoSensors Calibration Information

How to measure output of an ozone generator with an ozone sensor

Measuring Ozone Generator Output

Tech note from EcoSensors

We have sold many instruments for testing ozone generators either when they are manufactured or at the customer’s site. Most popular for this is our A-21ZX because of its 0-10 ppm range. Our new UV-100 ozone analyzer using the ultra violet absorption principle will measure over the 0-100 ppm which will be suitable for measuring the output of most smaller ozone generators. The UV-100 can log the data for playback and analysis at a later time, and it can send the data directly as it is sensed to a PC.


UV-100 ozone analyzer

It is key to realize that the output of ozone generators is almost always measured in grams per hour whereas ozone instruments measure concentrations in parts per million. To relate these two mathematically, you need to know the generator’s air flow rate in cubic meters per minute. The formula is:

Output (g/hr) = .128 X air flow(m3/min) X concentration(ppm).

= .00364 X cfm X ppm in cubic feet per minute units

For typical small generators, such as for room air “purification,” outputs of 1/10-1/2 gram/hour are used. For their air flow rates, our A-21ZX will reach its 10 ppm maximum reading at 1/2 gram per hour or a little less (from which we can deduce that the air flow rate is typically 3-4 m3/min which is indeed typical for equipment blowers). The easiest way to get the air flow rate is from the label on the blower.

The concentration of ozone declines rapidly as the measurement distance increases from the generator. Ozone that reads 10 ppm right at the output grill rarely exceeds .1 ppm 1 meter from the generator.

Information obtained from EcoSensors Tech Support

New Dual Gas Sensor Head, O3, and NO2


Aeroqual Dual Gas Sensor, CO2, CO

The Dual Range Sensors from aeroqual can measure two gasses at one time to save you time and money.
The MS3 sensor can measure Ozone (O3) and Nitrogen Dioxide (NO2) simultanously using a fan based sensor for real-time measurement.

Aeroqual Dual Gas Sensor, CO2, CO

This Dual Gas sensor will measure Ozone (O3) and Nitrogen Dioxide (NO2) simultanously and real-time with only one sensor.

The new O3-NO2 dual sensor is designed specifically for outdoor and indoor air quality professionals who wish to measure these two criteria pollutants simultaneously. The dual sensor incorporates a proprietary algorithm which automatically corrects for ozone interference on the electrochemical NO2 sensor, resulting in true real-time measurements of both gases. Aeroqual has filed for a patent on this unique technology which we believe is a world first.

Carbon Dioxide Sensor uses GSE technolgoy to measure NO2 from 0-1 ppm, with a resolution of 0.001 ppm.  Accuracy of 10%, and a minimum detection limit of 0.005 ppm.

Ozone Sensor uses GSE technolgoy to measure O3 from 0-10 ppm, with a resolution of 0.01 ppm.  Accuracy of 7.5%, and a minimum detection limit of 0.01 ppm.

This sensor head will be a direct fit onto any Series-200, Series-300, or Series-500 Aeroqual ozone monitor.  This head can be purchased as an addition to your existing monitor, or with a new base unit.  To purchase with a base unit see our Aeroqual ozone monitor page.  If you currenty have an Aeroqual ozone monitor this sensor will be a direct fit for your current monitor.  The Series-200, Series-300, or Series-500 will automatically detect this as a dual gas head and react accordingly.

Series-500 with sensor
Aeroqual handheld with sensors


GAS Carbon Dioxide (CO2), Carbon Monoxide (CO), Dual – CO, CO2
RANGE 0-2,000 ppm CO2, 0-100 ppm CO
MAXIMUM EXPOSURE 2,000 ppm CO2, 100 ppm CO
ACCURACY < +/- 5% CO2, < +/- 10% CO,
RESOLUTION 1 ppm CO2, 0.1 ppm CO
RESPONSE TIME 120 seconds CO2, 30 seconds CO

Aeroqual Series-300 Ozone Monitor

We have updated the options and online ordering for our Series-300 Ozone MonitorAeroqual Series-300 with sensors

If you have not looked at the Aeroqual Handheld Monitor line it is time you do.  There are a variety of great updates to these monitors.

Aeroqual Series-300

Remember that The Series-300 can measure a variety of gasses.  This means one device can use multiple sensors to save you money.

Large carry case for Aeroqual handheld monitorsNew Large Heavy Duty Carry case


Replacement & Add-On Sensors:

Replacement (or additional) sensor heads are available for all of the gases listed above. You can find their details and pricing on our Replacement Sensors page!


The Series-300 includes all the features of the popular Series-200 handheld but adds features like, controls, alarms, calibration capabilities, and analog outputs.  The Series-300 is highly functional as it can be used as a handheld, but also as a safety monitor mounted to the wall, or even controlling your ozone system system.



Series 300 Product Spec Sheet

Series 300 Quick Guide

Series 300 Product Manual

Links to more info:

Calibration information

Tech info and Specivications on each available Gas Sensor

Measuring Ozone in an Occupied Room

Measuring Ozone in an Occupied Room
ozone concentrations can vary greatly at various locations, and the concentrations are often highest in unexpected places. Key points to consider are:
  • Ozone is much heavier than air and tends to sink to lower levels.
  • Ozone has a low vapor pressure and so it doesnot try to fill the room uniformly. It tends to stay where it is.
  • Ozone tends to cling to rough surfaces such as fabrics and breaks down (converts back to oxygen) when passing through restricted and obstructed passageways.
  • Ozone reverts back to oxygen with a “half life” (time to go to half of its original concentration) typically of 10-30 minutes.
  • Ozone can be confused by instrumentation with other oxidizing gases such as chlorine compounds, acid fumes, and oxides of nitrogen (NOx). Strong “reducing” gases, such as vapors of alcohol and  solvents, can reduce the apparent concentration of ozone.
  • Ozone has a sweet smell, but the odor threshold varies widely by the person and by ambiental conditions. Therefore “smell” is not a reliable test for the presence or concentration of ozone.
The important measurement is:
What is the ozone concentration at the breathing level where room occupants will be?
For ozone introduced via HVAC systems with good room air circulation, the alternate point of measurement is near the entrance to the return air duct.
Suggested ozone Monitors:

A-21ZX Ozone Sensor
A-21ZX Ozone Sensor

C-30ZX Ozone Monitor
C-30ZX Ozone Monitor

OS-6 Ozone Controller
OS-6 Ozone Controller

Aeroqual Ozone Monitor recognized by US EPA

US EPA Highlights Series 500 Leading Low Cost Air Sensors

EPA Ozone Air Sensor Guidebook

The United States Environmental Protection Agency (US EPA) has published a guide for those looking to invest in low cost air sensors for the purposes of measuring ambient air quality. The Series 500 is highlighted as leading the pack for measuring ozone, nitrogen dioxide, carbon monoxide.

Valuable guidance for low cost air monitoring

The US EPA has been surprised by the recent surge in demand for low cost air sensors from the public, community groups, researchers and air quality professionals. The Air Sensor Guidebook is their effort to offer guidance and support for those users so they can make the good decisions about what equipment to buy and how best to use it.

Aeroqual is fully supportive of the Guidebook and is recommending it to all current and prospective customers.

Leadership in ambient air pollution sensors

The Guidebook specifies the Aeroqual Series 500 sensors for the measurement of ozone (O3), nitrogen dioxide (NO2), and carbon monoxide (CO). Other leading manufacturers such as Met One Instruments and Dylos are highlighted for low cost particulate monitoring – PM10, PM2.5 and TSP.

The fact Aeroqual features so strongly (see pages 23 onwards) highlights the leading position we have in low cost sensors for ambient pollution monitoring.

Step 1 towards standards for next generation air quality monitors

The Guidebook shows the US EPA is going to take a more proactive role in defining the new market for low cost air sensors, and other regulators are likely to follow their lead.

In the 2013 Next Generation Air Monitoring Roadmap the US EPA acknowledged that: “Current sophisticated, expensive ambient air pollution monitoring technology is not economically sustainable as the sole approach and cannot keep up with current needs, specifically new monitoring networks and special purpose monitoring”.

As a result the US EPA is now accelerating plans to test and develop alternative air quality measurement devices such as the AQM 60 and Series 500 made by manufacturers like Aeroqual. In time appropriate standards for these monitors will follow.

Aeroqual S-500 Ozone Sensor
Aeroqual Series 500 Ozone Monitor

New ozone measurement technology

Characteristics of the MiCS-2610 Ozone Gas Sensor

Sponsored by SGX Sensortech

Table of Content

Operating Conditions
Measurement Circuit
Heating Resistor
Gas Sensitivity
About SGX Sensortech (IS)


The article discusses salient features and applications of the MiCS-2610 ozone gas sensor.

Basically the instrument can be used for determining the levels of ozone from an ozone-generating source within a building as well as for identifying dangerous concentrations of ozone in the air outside.

To prevent water and dust contamination of the sensing element, the sensor is placed inside a housing. By gas diffusion, ozone-containing air reaches the sensing element. When electric resistance is changed in the sensing layer, a voltage change occurs. The voltage change is utilized to determine an equivalent concentration of ozone with the aid of a microcontroller. The voltage can also be used to raise an alarm when the sensor’s voltage is compared with a pre-set threshold voltage (Figure 1).

Figure 1. Schematic of a portable ozone detection system with built-in alarm

Operating Conditions

The MiCS-2610 ozone gas sensor satisfies the specifications mentioned in Table below:

Parameter Symbol Typ Min Max Unit
Life time tl 5 5 year
Switch on/off cycles ncycle 100’000 100’000
Heating power PH 70 mW
Relative humidity range RH 50 5 95 %RH
Ambient operating temperature Tamb 20 -40 70 °C

Measurement Circuit

The sensor unit is provided with 5V power (Figure. 2). An 88Ω resistor Rserial is connected in series with a heating resistor Rheaterl so as to achieve a nominal heating power of 70mW.

RSl is calculated using the following formula:

     RSl = RL /(VCC – VS) # x VS

Figure 2. Electronic circuit to power the heating resistor and to measure the sensing resistor

The changes occurring in the Rheaterl cause heating power variations, which are compensated by the simple circuit as shown in Figure 3.

For heating resistor values between 60 and 120Ω, the relative heating power variation is ±2 %.

Figure 3. Ph as a function of Rh. Rserial = 88 Ω and VCC = 5 V

Heating Resistor

The sensing layer’s temperature is based upon both the ambient temperature and the heating power. It is ideal to maintain the sensing layer’s temperature within 350-400°C in order to gain quick response times and good sensitivity. When it goes below 350°C, sensitivity reduces thereby causing the sensor response to be much slower. Likewise when it goes above 475°C, the structure of the sensor can be damaged due to excess heat.

The graph (Figure 4) shows ΔT as a function of Ph where ΔT is the temperature increase and Ph is the applied heating power.

While in operation mode, the heating resistor gradually increases (Figure 5). However when a constant heater voltage is used, heating power decreases. If the power compensation circuit is constructed as per figure 2, loss of power can be limited. Around 40% of Rh increases after the 10,000h of operation, thereby resulting in less than 2% of heating power.

Figure 4. ΔT as a function of Ph

Figure 5. Relative increase of Rh as a function of power-on time at ambient temperature

Gas Sensitivity

The graph (Figure 6) displays the sensitivity of the MiCS-2610 to CO, H2, ethanol (VOC), and CH4 (HC). Many interfering gases are known to be reducing gases that make the resistance to decrease; however ozone, which is an oxidizing gas, makes the sensing resistance to increase. The sensor’s resistance value varies with respect to humidity and temperature.

The gaseous form of water is humidity and reacts with the sensing layer similar to a reducing gas. When it is increased, there is a decrease in the sensing resistance. Similarly, temperature also behaves in the same manner as humidity. The negative temperature coefficient is because of the semiconductor properties found in the sensing layer material.

Figure 6. Sensitivity to CO, H2, CH4, and C2H5OH at 25°C and 50% Rh

Figure 7. Temperature dependence of baseline resistance Rair for 20%, 50%, 70% and 90% Rh

About SGX Sensortech (IS)

SGX Sensortech is a market leader in innovative sensor and detector devices that offer unrivalled performance, robustness and cost- effectiveness.

SGX have been designing and manufacturing gas sensors for use in industrial applications for over 50 years, offering excellent applications support for an extensive range of gas sensors and the expert capability for custom design or own label.

As an independent OEM supplier of gas sensors, we pride ourselves on providing customers with unrivalled product reliability and personal product support via specialist engineers.

SGX gas sensors are built to the highest standards with all pellistor and infrared gas sensors achieving ATEX and IECEx certification, SGX gas sensors are also UL and CSA approved.

Our product portfolio has continued to expand in technology and detectable gases used in a wide range of applications including:-

  • Mining
  • Oil and gas
  • Confined space entry
  • Indoor air quality
  • Industrial area protection
  • Leak detection

This information has been sourced, reviewed and adapted from materials provided by SGX Sensortech (IS) Ltd.