AQ EXPERT Instruction & Operations Manual
Version 1.13
Page 18 of 63
E. Hydrogen Sulfide sensor. (H
2
S)
This is a 4-series three-electrode micro sensor with low methanol interference. It
measures the concentration of hydrogen sulfide, which is a highly toxic gas. Special
precautions must be taken during calibration.
F. Carbon Monoxide sensor (CO)
This is also a three electrode sensor that responds to carbon monoxide. It is equipped
with an inboard filter to remove any interference from other acidic gases.
The optional High Range CO sensor has four electrodes. One measures the
concentration of carbon monoxide gas and the other the concentration of any interfering
hydrogen gas (It is hydrogen compensated).
G. Ozone sensor (O
3
)
This is also a three electrode sensor that responds to ozone.
H. Formaldehyde Sensor (CH
2
O)
This is also a three electrode sensor that responds to formaldehyde. It is equipped with
an inboard filter to remove any interference from other acidic gases.
This sensor may have interference from H
2
S, H
2
, CO, and other reducing gases such as
alcohols. In applications where the user is measuring both H2S and Formaldehyde, the
Formaldehyde readings could be inaccurate as the levels of H2S increase. Relative
measurements could be appropriate in these situations.
2. NDIR (INFRARED) SENSOR (CO
2
)
A non-dispersive infrared (or NDIR) sensor is a simple spectroscopic device most
commonly used to measure CO
2
in indoor air quality applications. The main
components are an infrared source (lamp), a sample chamber or light tube, a
wavelength sample chamber, and the CO
2
gas concentration is measured electro-
optically by its absorption of a specific wavelength in the infrared (IR).
