The Vaisala CARBOCAP® Sensor
The Vaisala CARBOCAP® is a silicon based Non-Dispersive Infra-Red (NDIR) sensor for the measurement of gaseous carbon dioxide. Its working principle is Single-Beam Dual-Wavelength NDIR, the same method that is commonly used in expensive high performance NDIR analyzers. However, in the Vaisala CARBOCAP® Sensor the traditional rotating filter wheel is replaced with a tiny electrically controlled Fabry-Perot Interferometer (FPI) made of silicon. A true Dual-Wavelength measurement can be provided in a very simple and practically solid state structure.
The operating principle
An infrared source at the end of the measurement chamber emits light into the gas chamber, where any carbon dioxide gas present absorbs part of the light at its characteristic wavelength. The FPI interference filter is electrically tuned so that its pass band coincides with the absorption wavelength of carbon dioxide. The detector measures the strength of the signal that gets through.
After this the pass band of the FPI is shifted to a wavelength where no absorption occurs. This provides the reference signal. The ratio of these two signals, one at the absorption wavelength and the other at the reference wavelength, indicates the degree of light absorption in the gas and thus the gas concentration. The reference signal compensates for the possible effects of sensor aging and contamination making the sensor very stable with time.
A groundbreaking concept
The Vaisala CARBOCAP® structure with the Fabry-Perot interferometer brings a new high performance solution to carbon dioxide measurements. The sensors have excellent stability both in terms of time and temperature. The sensor is accurate and durable and its small size enables the measurement system to be truly miniaturized. Yet the simplicity of the structure enables Vaisala to manufacture this high quality sensor at a price that provides the customer with a cost effective measurement. In particular Vaisala CARBOCAP® solutions will prove themselves economical over time: their stability will decrease maintenance costs significantly over the years.