Non-Dispersive Infrared (NDIR) Spectroscopy - Respiratory Gas Monitoring
04 Mar 2019
The ongoing technical advancements in the field of respiratory gas monitoring has seen the use of sensors that measure the amount of CO2, N2O, O2 and the five potent inhaled anaesthetic agents increase dramatically in operating rooms throughout the world. These gas sensors can alert the anaesthetist to several potentially adverse conditions such as inadvertent overdose.
Non-Dispersive Infrared (NDIR) spectroscopy is by far the most common gas detection method used today. Infra-red radiation generated by a broad band emitter is passed through the gas which is contained in a measurement cell. The detector uses an IR filter with an appropriate wavelength transmission band to measure the strength of the absorption of the target gas. The strong absorption allows relatively low concentrations of gas to be detected with small path lengths and inexpensive components.
LASER COMPONENTS manufactures a range of innovative pyroelectric detectors at our factory in Florida. These devices include multi-element current mode detectors with built in operational amplifiers providing a large output signal which means they can be used to directly drive post processing electronics.
The absorbance bands of the anaesthetic agents are in the 8-13 micron range and this requires the emitter to have an envelope that will transmit these wavelengths. From our office in the UK we can also supply broad band emitters for this application, the EF range is a pulsable device using a nichrome filament to achieve an operating temperature of 700K. The emitters are housed in a TO8 package sealed with a zinc selenide transmission window that transmits infra-red light out to 14 microns.