Technical Information


General Considerations

  • Safe and economical access to the sampling points are required. A cherry picker or crane should be a last option
  • 240v power should be within 20 metres of the sampling area
Ideal Sampling Plane

Ideal sampling plane

  • A straight vertical section of the flue is preferred
  • Ports are 6-8 internal diameters upstream of the last obstruction or bend
  • Ports are at least 2 internal diameters downstream from any obstruction, bend or the top of the flue
  • The number of port holes is determined by the flue diameter
  • Diameter between 350 and 1500 mm requires a minimum of 2 port holes placed at 90° to each other, in the same plane

The real world

Always seek written approval from your licence administrator, before placing new ports in non ideal sampling planes

The longest possible straight (vertical) section of flue is chosen

Ports are positioned in an 8:2 ratio of the flue internal diameter

Port holes are placed as high on the flue as possible while still allowing suitable access

Diagram Illustrating the Principle of Isokinetic Sampling

Isokinetic Sampling

The velocity of the stack gas going into the sampling probe's nozzle is equal to the velocity of the moving stack gas at that point in the stack.

The air is disturbed as little as possible so that the same particles (no more and no less) go into the nozzle as would have passed the area of the nozzle had it not been there.