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ENG
Gas Leakage Detector +0300047IE rel 1.1 - 26.04.2023
Further information
5. FURTHER INFORMATION
5.1 Sensor operating principle
5.1.1 Semiconductor sensors
Semiconductor or metal-oxide-semiconductor (MOS) sensors are very versatile and can be used in a wide range of applications:
they can measure both gases and vapours at low ppm and combustible gases at higher concentrations. The sensor is made from
a blend of metal oxides. These are heated to a temperature between 150 °C and 300 °C, depending on the gas to be detected.
The operating temperature and composition of oxides determines the selectivity of the sensor with respect to dierent gases,
vapours and refrigerants. Electrical conductivity increases signicantly as soon as gas or vapour molecules come into contact
with the sensor’s surface by diusion.
When the molecules of the selected gas come into contact with the sensor’s surface, the conductivity of the semiconductor
material increases signicantly, in proportion to the concentration of gas. Consequently, the current running through the sensor
also varies. Water vapour, high ambient humidity, temperature uctuations and low oxygen levels can alter the readings, giving
a higher concentration than the actual level.
By using this technology, GLD Small allows the gas detected to be selected based on its category. Gases are divided into three
categories or groups. Group 1 includes R32 gases, group 2 those HFCs/HFOs and group 3 HCs.
Depending on the gas to be detected, the specic device that detects that category of gas needs to be purchased, and then the
specic gas selected via app or Modbus.
The table in the next chapter shows the list of gases detected and the corresponding group.
For example, if needing to detect R-410A, the required device needs to be purchased, described as “Group 1”. At the time of
installation, then, select R-410A via app or by setting the corresponding Modbus register.
The product can detect a wide spectrum of gases, setting the desired gas as described above; however the default gas must be
used to perform the calibration procedure, as described under “Calibration”.
IMPORTANT: Products with semiconductor technology may be aected by long-term exposure to high concentrations
of gas.
In this case, it is recommended to replace the pre-calibrated sensor only (available separately), to ensure correct gas detection.
5.1.2 Infrared sensors
Infrared technology detects certain types of gas using an electronic sensor that measures the infrared rays (IR) radiated at the
wavelength that the gas is sensitive to. This makes it possible to quantify the substance present in the surrounding air.
The NDIR detection method (non-dispersive infrared sensor) uses optical sensors.
The detector output is directly proportional to the absorption of infrared light at the specic wavelength.
5.1.3 Electrochemical sensors
Electrochemical sensors measure the partial pressure of gases in atmospheric conditions. The monitored ambient air diuses
through a membrane into a liquid electrolyte inside the sensor. Immersed in the electrolyte are a measuring electrode, a coun-
ter electrode and a reference electrode. An electronic circuit with a potentiometer supplies a constant voltage between the
measuring electrode and the reference electrode. The voltage, the electrolyte and the material used to make the electrodes are
selected according to the gas being measured, so that this is correctly transformed electrochemically on the electrode for meas-
urement and thus a current is generated that ows through the sensor. The current value is proportional to the concentration of
gas. At the same time, oxygen from the ambient air reacts with the counter electrode. At an electronics level, the current signal
is amplied, digitised and corrected based on other control parameters (e.g. ambient temperature).
5.1.4 Pre-calibrated sensors and devices
Pre-calibrated sensors and devices are supplied with the calibration certicate included in the packaging, in addition to the
instruction sheet.
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