I think you mean the SIEMENS ULTRAMAT 6F instead of the SIEMENS ULTRAMET 6F


The ULTRAMAT 6 single-channel or dual-channel gas analyzers operate according to the NDIR two-beam alternating light principle and measure gases highly selectively whose absorption bands lie in the infrared wavelength range from 2 to 9 μm, such as CO, CO2, NO, SO2, NH3, H2O as well as CH4 and other hydrocarbons.

Looking at the description above, it uses an IR analyzer to determine the concentration of several gases.

The wiki has some more info on the working:

1. Getting the correct spelling of any device is critical in finding the documentation on that device.

2. General Observations about vendor documenation

Glossy brochures are designed to make managers who can sign off a purchase feel good. Brochures rarely contain useable information.

Spec or data sheets have information on what device does or features it has. Sometimes spec sheets include principles of operation. In answer to your question, read page 4 of the spec sheet that describes the analyzer's measuring principle at this link 6_en.pdf

Manuals sometimes include a principle of operation (they always did prior to 1980) but now usually are more oriented to providing some detail about the installation, configuration and operation of a device.