NDIR

The NDIR gas sensor needs an infrared source for the excitation of the gas molecules. Thermal radiators such as Gilway's Visible/IR lamps are often employed for this task. Their operating temperature NDIR should be as high as possible to obtain a large output intensity and detector signal. Glass envelope lamps operate at higher filament temperatures when compared to other filament or ceramic heating elements. The envelope can be a gas-filled or a vacuum. However, the transmission of the glass envelope limits the useful spectral range, and constrains the types of gas molecules that can be measured by NDIR.

The transmission characteristics of a typical lamp glass NDIR are illustrated below together with the center wavelength of some common gas absorption bands. The intensity of the IR light decreases significantly above 4 mm with a cutoff wavelength located at 5 m.

A Visible/IR lamp is a very cost-effective component for an NDIR sensor, but NDIR has a limited IR range. For carbon dioxide (CO2) and hydrocarbon (HC) detection, it is an ideal technique.

The most desirable lamp characteristics of NDIR are:
` high IR output
` accurate filament position
` small size
` long lifetime
` low thermal time constant
The last characteristic of NDIR is important if the lamp power supply is to be modulated during operation to offset thermal background signals.

Gilway Visible/IR lamps feature thin glass envelopes that reduce infrared absorption and provide more output in the infrared. Double-coiled filaments operate at high temperatures, and are rugged and geometrically precise for applications requiring broad spectral emission and superior optical performance.

Gilway Visible/IR lamps are offered in T-1 and T-3/4 sizes with wire leads or bi-pin bases and operate at 5 volts. Several versions are available that operate from 45 mA to 150 mA with rated lifetimes from 5,000 to 100,000 hours. Gilway also offers a large line of reflector lamp assemblies with both fixed and adjustable focus options. Please contact the sales department at Gilway Technical Lamp to request a product catalog.