روش های شناسایی گازها

اندازه گیری به روش کاتالیستی

Catalytic Measurement

The detector sensing element is made up of two platinum filaments electrically heated to around 400ÆC. One of them (1) is covered with an active catalytic layer which heats up strongly in the presence of a combustible gas. This temperature rise causes an increase in the resistance of the filament which is measured in the unit. The other filament (2), passive, serves as a thermal compensator.

اندازه گیری به روش الکتروشیمیایی

Electrochemical Measurement

The electrochemical cell is made up of a measurement electrode (1), a counter-electrode (2) and a reference electrode (3). These electrodes are bathed in an electrolyte inside the cell casing, which is itself fitted with a gas permeable membrane (4). The gas which is diffused inside the cell causes a chemical reaction on the measurement electrode and on the counter-electrode. The result is an electric current, proportionate to the concentration of the gas present, which circulates between these two electrodes.

This current is measured by the external circuit (5) to which the cell is connected.

اندازه گیری با استفاده از اشعه مادون قرمز

Infrared Measurement

The infrared cell functions according to the non-dispersive infrared (NDIR) principle. It is made up of a casing comprising:

• a diffusion membrane (1),
• a measurement chamber (2),
• an IR radiation source (3),
• an active sensor (4) and
• a reference sensor (4’).

The gas that reaches the measurement chamber absorbs – within a very precise range of wavelengths – a part of the radiation emitted by the IR source. The active sensor measures the remaining IR radiation and thereby determines the concentration of the gas present. The reference sensor measures the IR radiation within a range of wavelengths that is not influenced by the incoming gas. Its signal serves to compensate any variation in IR radiation which is not due to absorption caused by the targeted gas, such as a variation in temperature, humidity level, etc.

This enables us to obtain an accurate and reliable measurement in all conditions.

اندازه گیری با استفاده از نیمه هادی ها

Semi-Conductor Measurement

The cell is composed of a non-conductive element, for example silicon (1) to which a semiconductor metal oxide (2) is applied.
Two electrodes connected to a measuring device are connected to the semiconductor material (3).
In the absence of gas, oxygen is ionized onto the surface of the sensor, which then becomes a semiconductor.
When a gas enters the cell, its molecules take the place of the oxygen ions, resulting in a drop in resistance between the two electrodes. This variation is measured electrically (۴) and is proportional to the concentration of the gas present.

A heating element (5) allows the temperature in the sensor to be stabilized, which improves the measurement and reduces the effect of external temperature changes.