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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 |
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.
