Why is the Capnographic Waveform on a SprintIR Different from Other CO2 Sensors?

We received a question about our high-speed SprintIR CO2 sensor from a client via email:

"We want the sensor to work in a system for monitoring the concentration of human exhaled carbon dioxide. So we've checked the document "Capnographic Testing of GSS SprintIR CO2 Sensor" and we've noted that the waveform provided by the sensor in that case is close to a sine wave. In other hand, the capnogram from mechanical ventilators looks like a square wave. Do you have any idea about why this difference happens?"

Our engineers answered as follows:

"The difference in wave form that you see and what we demonstrate is due to the speed capability of measurement. The commercial capnographs that you are comparing do not have the SprintIR's measuring frequency or dynamic range of concentration measurement. They are more or less are integrations and therefore show a square wave of some duty cycle indicating the thresholds / saturation (flat tops) and hysteresis or depletions (base line). These will also be significantly phase shifted from real time. In the application notes, sampling pumps capable of moving sufficient volume from the mask and through the sensor to actually measure the rise and fall of the concentrations though the respiratory tide."

Here's the original capnographic speed test.

Posted by CO2 Meter on December 02, 2013.
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