News — Calibration

All infrared (NDIR) CO2 sensors have a dependence on pressure. This is because of the physics principle used to measure CO2 concentration. The NDIR type of sensor measures the IR radiation absorbed by CO2 molecules, which corresponds to the mole concentration. When pressure increases, the number of molecules in a given volume also increases linearly. Conversely, when pressure decreases (higher altitudes, for example) the number of molecules decrease. This app note includes both general information about Senseair sensors and pressure, as well as the equation for computing true CO2 level readings at various pressures useful for any NDIR CO2 sensor....

A customer recently wrote us and asked, "I am testing a SenseAir K-30 CO2 Sensor next to a desktop CO2 meter. The K-30 is reading 778ppm, while the desktop meter shows 846ppm. Which one is correct?" The simple answer is that they are both correct! Yes, they are different, but both sensors are working within their rated accuracy. What does that mean? How is accuracy defined? The accuracy of a CO2 sensor is defined as how close the measurement is to a reference gas, expressed as either a ± (plus-minus) value in parts-per-million (ppm) or as a percentage (%) of...

Recently we had a client ask if he could use SODASORB® as an alternative to compressed nitrogen for calibrating a CO2 sensor. SODASORB® absorbent is intended for use in anesthesia circle systems and respiratory therapy equipment for the purpose of removing exhaled carbon dioxide. SODASORB® makes it possible for intended in-line gases to be rebreathed by the patient. As it absorbs carbon dioxide, a dye added during manufacture changes color so you can tell when it must be replaced. We have had customers put SODASORB® in a condenser tube and push or pull air through it with a small pump to...

SenseAir K33 ELG, BLG or ICB CO2 sensors are pre-calibrated at the factory. During normal use, they are self calibrating using the ABC algorithm. If after rough transport or handling or for statistical purposes you want to re-calibrate these sensors, this document explains how using CO2 Meter's legacy DAS software as well as how to configure sensors, view data in real-time, or manage stored logs on sensors with internal memory. Note that you are encouraged to upgrade to the newer GasLab software which currently supports all K33 sensors. Download K33 Calibration Instructions (pdf).

Automatic Background Calibration algorithm (ABC) allows the CO2 sensor to dynamically shift its CO2 reading by a constant. It works via storing the lowest CO2 sample taken over the ABC Period and assuming that this low value is equal to a known value (the target value). It then adjusts the output of the CO2 reading by the delta between these values. This algorithm does not affect the linearization of the output signal. For example, by default ABC is enabled with an ABC Period of 180 hours, a target value of 400ppm, and a maximum delta of 30ppm. This operates under...