Here are the most frequently asked questions about our NDIR sensors.

Products & Function

For monitoring indoor air, e.g. for concentrations of refrigerants, smartGAS offers the TRANSMITTEREVO series.

Our TRANSMITTEREVO is designed as a pure measuring head, without alarm function. The signals of the TRANSMITTEREVO are passed on to a control center, which controls any alarms or downstream actions.

The TRANSMITTEREVO is not designed as a stand-alone device!

Basically, you can send us all inquiries via our contact form and we will answer the inquiry or forward it to our authorized sales partners.

The sensors of the BASICEVO and FLOWEVO series can also be read out via analog signals with the optional Connect Interface electronics:

  • (0)4 - 20 mA
  • 0 - 2 V DC
  • 0 - 5 V DC
  • 0 - 10 V DC

The TRANSMITTEREVO is already factory equipped with the Connect Interface, likewise sensors of the C4 series based on the BASICEVO series.




With sensors of the NDIR technology very many different gases can be measured like:

Take a look at the complete overview of the gases smartGAS offers.

No, basically the gases have a different absorption behavior in the infrared spectrum.

The gases SF6  and CO2  are strong absorbers and can be measured well in the ppm range.
On the other hand CO or C2H4  are weakly absorbing gases that are very difficult to measure.

In addition, there are interferences when different gases occur simultaneously in a mixture.


Oxygen (O2) is not measurable with the NDIR and the photoacoustic method, because it is not "IR-active". smartGAS can nevertheless offer solutions for O2 if required, but these are then based on other measurement methods.
Please do not hesitate to contact us.

Basically our sensors are not designed for the measurement of H2O. However, H2O is infrared active and can therefore interfere with the accurate measurement of the gases in various applications! Therefore, it is recommended to use accessories for gas drying, such as the gas cooler or absorber.


The diffusion sensors of the BASICEVO series are designed for monitoring and measuring room air. They are mounted stationary in a device and are surrounded by the measuring medium (usually the room air).

Therefore, use in a gas stream is not the application area for the BASICEVO sensors.

Here, sensors from the FLOWEVO- or SILAREX series should be used instead.

In many applications it is necessary to measure different gases. The sensors of the SILAREX-series are ideal for this purpose. They can detect up to 3 gases simultaneously and compensate the influences of the gases among each other equally.

With the sensors of the BASICEVO- and FLOWEVO-series, only one gas can be measured at a time, but they can be combined as desired. Due to the standardized digital interfaces, the implementation effort here is very low.


The sensors of the FLOWEVO- oder SILAREX-series are designed for a flow rate of 0.1...1.0 l/min. The operating mode can be described as cold-extractive, which means that the gas sample is extracted from the process via pumps and hoses and, after cleaning and drying, is fed to the sensor in the analyzer.
Direct connection to a gas stream, without filter and drying, is not recommended, as particles and moisture can interfere with the measurement and damage the sensor.
It is best to use the appropriate accessories from smartGAS for your measurement.


In gas measurement and analysis, a flow rate in the range between 0.5 - 1.0 l/min has become established as a good standard. Higher values can lead to back pressure and consequently to falsified measurements. At very low flow rates, the purging time for gas exchange in the sensor increases and the sensor operates more slowly.

The smartGAS sensors of the FLOWEVO- oder SILAREX-series are in almost all cases designed for a range between 0.1...1.0 l/min, for more details you can take a look into the data sheets.

The operating temperature depends on the sensor type:

For more detailed information, please refer to the respective data sheets for all products.

Gas treatment & Accessories

In gas analysis and process measurement technology, the gas samples must be prepared before measurement in order not to damage the sensors and to obtain meaningful measurement results without interfering influences.
The gas preparation should therefore always consist of the following components:

Depending on the application, smartGAS offers the appropriate accessories.

Support & Maintenance

For sensors of the FLOWEVO- or BASICEVO-series, a flashing of the red LED on the sensor indicates exceeding or falling below the calibrated measuring range. This condition is usually reversible by zero and end point calibration. For more information about the status LEDs, please refer to the respective product manual.

Die smartGAS Sensoren sind wartungsarm, erfordern jedoch wie alle Messwerkzeuge regelmäßige Überprüfung und ggf. Justage. Der Anwender kann hierfür das kostenlose nutzen, welches zum Download zur Verfügung steht.
The smartGAS sensors are low-maintenance, but like all measuring tools they require regular checking and, if necessary, adjustment. The user can use the free smartGAS Calibration Tool, which is available for download.

The calibration function of the sensors can already be taken into account during design-in. It can then either be completely automated or triggered by the user of the terminal device by pressing a button.

If the FlowEVO- or BasicEVO sensor is equipped with an additional Connect Interface, NP (zero point) and EP (end point) can be set via jumper. More detailed information on this is described in the manual.

The calibration interval cannot be determined across the board. In many applications for gas sensors, there are normative or legally prescribed inspection and calibration intervals. In addition, the quality of the gas processing (particle filtering / gas drying), for example, influences the function of the sensors.

We therefore recommend carrying out long-term tests under real conditions as part of the design-in and using the results to determine the service intervals.

In case of a digital integration of the sensors via Modbus, different values can be read out from the sensors as well as written back. The triggering of the calibration is e.g. thus possible, provided that the required test gases are also applied in the same process.

The NDIR dual-beam method we use is characterized by extreme long-term stability. Nevertheless, our sensors, like all other technologies on the market, are subject to drift. This is caused by changes in the optical emitters and detectors (so-called aging). Therefore, the sensors should be checked at time intervals in the zero and end point and recalibrated if necessary. This can be done directly via Modbus command or via our free Calibration Tool Software.

Replacing the radiation sources requires recalibration of the sensors in order to calibrate the entire system again. This can only be done by us as the manufacturer. We will be happy to submit an offer for this.

With the help of our smartGAS Calibration Tool, various settings can be made and sensors parameterized. This also includes resetting to factory settings. If a sensor does not function as expected or has been "wrong calibrated" during tests, a reset can be carried out with this tool.

Data communication & Interfaces

The measured concentration can be read out either via the analog interfaces as current or voltage, or digitally via the Modbus data bus. Alternatively, our free smartGAS Calibration Tool can be used for many smartGAS sensors to read out the sensors.

Our sensors use Modbus RTU/ASCII as data protocol. The register assignment in the sensor is described in the instructions, information about Modbus can be found at: