LI-820 Description

Operating Principle

The LI-820 analyzer is a single beam, dual wavelength NDIR sensor. The CO₂ measurement is a function of the absorption of IR energy as it travels through the optical path.

The IR source emits radiation into the optical path, where CO₂ absorbs photons of a certain wavelength. The CO₂ sampling channel uses an optical filter centered at 4.26 micrometers, corresponding to the absorption band for CO₂. A filter with a center wavelength of 3.95 micrometers serves as a reference channel. The detector measures the strength of the signal that passes through the optical path; the ratio of the sample and reference signals indicates the amount of light absorption by CO₂, and thus, the gas concentration.

Interchangeable optical benches swap out easily by means of two source headers on the main circuit board; swapping the benches takes only a few minutes.

Optical benches (5 cm and 14 cm) can be easily swapped or cleaned.

Making Measurements

The LI-820 is a very simple gas analyzer to use.  A pump is used to connect to the inlet port so that air will pass through the optical path and exit through the outlet port.  You have a choice of Windows® software (included), a datalogger, such as the LI-1400 Datalogger, or the XML communication protocol to set up your measurement protocol and collect data.  Real time numeric or graphic data can be viewed using the Windows® software.  You can also use either the Windows® software or the XML communication protocol to zero and span the analyzer.

Sophisticated Measurement Technology

The LI-820 optical path is a thermostatically controlled IR detection system that provides excellent stability over both time and temperature, which extends the required interval for calibration. Integrated thermistors and a pressure transducer provide for high accuracy in the concentration calculation over the entire measurement range.