sighting tube

sighting tube

[′sīd·iŋ ‚tüb]
(engineering)
A tube, usually ceramic, inserted into a hot chamber whose temperature is to be measured; an optical pyrometer is sighted into the tube to observe the interior end of the tube to give a temperature reading.
References in periodicals archive ?
Ground cover and canopy cover were estimated using a sighting tube with crosshairs at one end (Winkworth and Goodall, 1962).
A crosswire sighting tube for point quadrat analysis.