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7. Additional Information
7.1 Sensor Operating Principle
7.1.1 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 vapors 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 302°F (150°C) and
572°F (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 different gases, vapors and refrigerants. Electrical conductivity increases
significantly as soon as gas or vapor molecules come into contact with the sensor’s surface by diffusion.
When the molecules of the selected gas come into contact with the sensor’s surface, the conductivity of the
semiconductor material increases significantly in proportion to the concentration of gas. Consequently, the current
running through the sensor also varies. Water vapor, high ambient humidity, temperature fluctuations and low oxygen
levels can alter the readings, giving a higher concentration than the actual level.
By using this technology, CRLDS 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 specific device that detects that category of gas needs to be purchased, and
then the specific gas selected via app or Modbus.
The table in the next chapter shows the list of gases detected and the corresponding group.
7.1.2 Electrochemical Sensors
Electrochemical sensors measure the partial pressure of gases in atmospheric conditions. The monitored ambient air
diffuses through a membrane into a liquid electrolyte inside the sensor. Immersed in the electrolyte are a measuring
electrode, a counter 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 measurement and thus a current is generated that flows 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 amplified, digitized and corrected based on other control
parameters (for example, ambient temperature).
7.1.3 Pre-Calibrated Sensors and Devices
Pre-calibrated sensors and devices are supplied with the calibration certificate included in the packaging, in addition to
the instruction sheet.
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