Sensor Principle
Semiconductor Sensors
Semiconductor or metallic oxide sensors (MOSs) are among the most versatile of all broad-range sensors. They can be used to detect a variety of gases and vapors in low ppm or even combustible ranges. The sensor is made up of a mixture of metallic oxides. They are heated to a temperature between 150º and 300º C depending on the gas(es) to be detected. The temperature of operation as well as the “recipe” of mixed oxides determines the sensor selectivity to various toxic gases, vapors, and refrigerants. Electrical conductivity greatly increases as soon as a diffusion process allows the gas or vapor molecules to come in contact with the sensor surface. Water vapor, high ambient humidity, temperature fluctuations, and low oxygen levels can result in higher readings.
WARNING!
Certain substances in the environment to be monitored may impair the sensitivity of the sensors or influence readings:
| • | Materials containing silicone or silicone rubber/putty |
| • | Corrosive gases such as hydrogen sulfide, sulfur oxide, chlorine, hydrogen chloride, etc. |
| • | Alkaline metals, salt water spray. |
| • | Aerosols with propellant. |
| • | Cleaning agents and disinfectants. |
Failure to follow these warnings can result in serious personal injury or death.
Infrared Sensors
The infrared (IR) gas sensor is designed to measure the concentration of combustible gases and vapors in the ambient air. The sensor principle is based on the concentration-dependent absorption of infrared radiation in measured gases.
The monitored ambient air diffuses through a sintered metal material into the enclosure of an optical “bench”. The broadband light emitted by an IR source passes through the gas in the optical bench and is reflected by the walls from where it is directed towards a dual-element detector. One channel of the detector measures the gas-dependent light transmission, while the other channel is used as a reference. The ratio between measurement and reference signal is used to determine the gas concentration. Internal electronics and software calculate the concentration and produce an output signal.