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How Long Does My Lancom 4 Probe Need to Be?

Lancom 4 is a portable flue gas analyser that can be used to make spot checks of the combustion efficiency and air pollution emissions on a variety of combustion sources. 

It is a flexible and robust tool that has proven its worth in many hundreds of applications worldwide. It can be configured with between three and nine gas sensors as well as flow and pressure (draft) measurements.

A key question relates to the length of sample probe that needs to be specified. The standard probe, used for measurements in ducts with temperatures up to 600 °C (1112 °F), includes a thermocouple to measure the flue gas temperature and a sintered filter which protects the instrument from particulate matter in the flue gases. 

AMETEK Land offers this design in lengths ranging from 0.3 m (12”) to 3.0 m (120”). The ideal length balances the ability to obtain a representative sample of the gases within the duct with ease of use. A probe that is longer than necessary will be awkward to carry and may be difficult to insert into the flue if the measurement point is at all cramped.

The measurement point needs to be chosen to ensure the Lancom 4 will receive a representative sample of the gases in the process. This means the user must avoid bends where stratification can occur and joints where air leaks are likely, especially in negative-pressure ducts. The probe needs to be long enough to pass through any standpipe or other port and into the bulk flow of gas. 

For a small duct, the ideal measurement point is in the central part of the flow. For larger ducts, a position at least 0.5 m (20”) from the wall is usually enough. Therefore, a probe length of 1.0 m (40”) or 1.5 m (60”) is sufficient for the great majority of applications. A probe length of .3 m (12”) may work for the smallest ducts but it cannot always always penetrate far enough into the duct to reach the bulk flow. Longer probes up to 3 m (120”) in length allow for measurements at different points in the duct and may be useful where stratification cannot be avoided, but these probes are difficult to carry and store so they are only used in specialist applications.

In conclusion, a probe length of 1.0 m (40”) or 1.5 m (60”) works well for the great majority of flue gas measurements, striking a good balance between portability and effective penetration into the gas flow.

Learn more about the Lancom 4 here

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