Sensor technologies and measuring principles

Which sensor technology is right for your application depends on the gases you need to measure, their expected concentrations and other factors such as cross-sensitivities to other gases, ambient conditions and explosion protection. With our wide range of fixed transmitters, portable gas detection devices and various sensors, you are able to reliably monitor combustible and toxic gases, oxygen and volatile vapors.

Catalytic Combustion (CC)

Catalytic combustion, also called heat tone (HT), is a reliable measuring principle for detecting flammable gases and vapors to the lower explosion limit (LEL). Two sensors (detector and reference) are connected via a "Wheatstone Bridge" circuit. A combustible gas or gas mixture burns on contact with the catalytic detector sensor and oxygen. The heat generated during this process increases the electrical resistance. This produces a measurable current flow that is proportional to the concentration of the combustible gas.

  • Sum measurement of combustible gases and vapors
  • 0 - 100 % LEL
  • High measuring accuracy
  • Linear display behavior

Thermal Conductivity (TC)

With thermal conductivity (TC), toxic and flammable gases can be measured in high concentrations of up to 100% by volume. The functional principle is similar to that of catalytic combustion, including the "Wheatstone's bridge" circuit. The difference between the two is in the measured element: Thermal conductivity does not measure flammability, and consequently does not rely on oxygen being present. A second gas with a different thermal conductivity level, suich as air, is therefore required as a reference.

  • Toxic and flammable gases
  • Wide measuring range (up to 100 vol.%)
  • Suitable for a variety of applications

Photoionization Detector (PID)

In a photoionisation detector (PID), air is absorbed and exposed to ultraviolet light in the sensor. The photons in the UV light cause certain molecules to decompose into positively charged ions and electrons. A measurable current flow is created between the electrodes in the measuring chamber, which the detector then converts into a measured value proportional to the gas concentration. Target gases of photoionisation are volatile organic compounds (VOCs) such as solvents and petrol, diesel, heating oil or paraffin vapors. They can be dangerous even in very low concentrations. Photoinonisation detectors can monitor over 300 of these substances in groups or individually - many even in concentrations of below 1 ppm.

  • Volatile organic compounds
  • Short response times
  • Very high sensitivity
  • Many measuring gases

Zirconium Dioxide (ZD)

This measuring principle with an electrochemical oxygen pump cell made of zirconium dioxide is used for oxygen measurement. At high temperatures (> 650 °C), zirconium dioxide behaves like an electrolyte for oxygen, which transports oxygen ions and generates measurable current in case of a partial pressure difference between the two sides of the membrane. This measuring principle is not susceptible to environmental influences and its results can be indicated in percentages as well as in the trace range (ppm).

  • Selective for oxygen
  • Very short response time
  • Not susceptible to ambient conditions
  • Long lifetime

Infrared (IR)

The infrared measuring method uses the property of certain gases to absorb light in particular wavelength ranges (bands), which the main natural components of air (nitrogen, oxygen and argon) cannot do. Two infrared beams of different wavelengths (measuring and reference beam) are guided into the measuring chamber where they hit two detectors (measuring and reference detector). If the measuring beam is weakened by the absorption of a gas present, the reduced intensity corresponds to the gas concentration. Gases that can be detected by infrared include all heteroatomic gases such as carbon dioxide and hydrocarbon compounds.

  • Combustible gases and CO2
  • Low cross-sensitivity
  • High accuracy
  • Long lifetime

Electrochemical (EC)

An electrochemical measuring cell is similar to a battery in the way it functions. The gas you need to measure diffuses through a membrane into the sensor, which consists of three electrodes (working, reference and counter electrode) and a conductive electrolyte. The individual components are adapted to the relevant gas. The reaction with the working electrode creates a flow of ions to the counter electrode. The measured current corresponds to the concentration of the monitored gas. The electrochemical measuring method is suitable for selective measurement of a specific gas.

  • Toxic gases, O2 and H2
  • Linear display behavior
  • Very energy efficient
  • High sensitivity

Chemisorption (CS)

In chemisorption, the sensor element consists of a metal oxide semiconductor (e.g. tin dioxide) located in a measuring chamber with a flame arrester. The oxidation of the monitored gas at the sensor element increases the electrical conductivity. The current flow is converted into an output signal corresponding to the gas concentration. The temperature of the sensor element is adjusted according to the gas being monitored. Chemisorption is suitable for detecting a wide range of combustible and toxic gases and is characterized by long-life sensors and low cost.

  • Flammable and toxic gases
  • Cost-effective
  • Different measuring ranges (vol.-%, LEL, ppm)
  • Long lifetime
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