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CO2 Sensors

The COMET Non-Dispersive Infrared (NDIR) CO2 Sensor is a highly integrated analysis system for monitoring respiratory carbon dioxide concentration. The COMET Sensor includes a custom infrared source with power supply, infrared detector, barometric pressure transducer, temperature sensor, and EEPROM memory for storage of calibration coefficients. The analog outputs from the COMET are digitized and used in the calculation of CO2 partial pressure. This information can be used to additionally calculate respiration rate, end-tidal CO2, inspired CO2, inspiration and expiration times. There are two versions of the sensor available: the original low-power COMET and the new COMET II.

COMET II offers the following enhancements to the original COMET performance:

    • signal-to-noise improvement of 2.5 - 5X

      • less peak-peak noise on analog signal

      • better power supply rejection ratio (PSRR)

      • more accurate calibration and steady-state stability

    • significantly less drift due to temperature slew effects

    • less susceptible to ambient lighting conditions

COMET II can be used interchangeably with the original COMET in applications where minimum sensor current consumption is not critical (COMET II requires an additional 40 milliamps of current for its Vsrc power supply). The extra current translates into more infrared power for higher CO2 detector output. All sensor voltage ranges and the digital interface remain the same.

Interfacing to the CO2 Sensor is very simple. The COMET requires a +5V supply at less than 27mA maximum current (67mA for COMET II). The host reads the calibration coefficients from the EEPROM via serial communication lines and uses the coefficients during runtime to calculate the partial pressure of CO2. A four channel, 12-bit A/D converter is recommended for acquiring the analog signals from the COMET.

The COMET Sensor was designed to be easily connected to a circuit board and field-replaceable. It is held down by a 2-56 screw, mating to either a 2-56 nut or similar pem nut (such as the McMaster-Carr 94648A310). The flex circuit interfaces to a 16-pin, 1mm pitch flex connector such as the Hirose FH21-16S-1DSA.  The Sensor connects to the pneumatic circuit via 0.020 inch ID / 0.083 inch OD tubing.  Tygon™ tubing is recommended for its low CO2 gas retention properties.

COMET and COMET II are available for evaluation and product development by purchasing our CO2 Evaluation Kit.


Typical System Implementation of CO2 Sensor for Capnography Application




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