Division 9.3.1.1 Probe design and construction

A probe is the first fitting in a sampling system. It protrudes into a raw or diluted exhaust gas stream to extract a sample, such that it's inside and outside surfaces are in contact with the exhaust gas. A sample is transported out of a probe into a transfer line.

Sample probes shall be made with inside surfaces of stainless steel or, for raw exhaust gas sampling, with any non-reactive material capable of withstanding raw exhaust gas temperatures. Sample probes shall be located where constituents are mixed to their mean sample concentration and where interference with other probes is minimised. It is recommended that all probes remain free from influences of boundary layers, wakes, and eddies — especially near the outlet of a raw-exhaust meter tailpipe where unintended dilution might occur. Purging or back-flushing of a probe shall not influence another probe during testing. A single probe to extract a sample of more than one constituent may be used as long as the probe meets all the specifications for each constituent.