Abstract

In a compact thermal flowmeter unit of the type wherein a portion of the fluid in a main flow path is shunted through a laminar-flow sensor passageway, that section of the main flow path which the sensor bypasses is occupied by an appropriate range-governing cartridge selected from among a family of externally-similar tubular flow-regulating cartridges each having a different flow capacity as determined by the totals of cross-sectional areas of its plurality of linear flow channels each exhibiting an effective ratio of length to cross-section which promotes laminar flow but is nevertheless advantageously relatively short. Such tubular cartridges are conveniently inserted into and removed from threaded fastening within the unit by way of one end thereof where there is an accommodating removable end fitting; not only may changes in measurement ranges be effected readily by substituting different cartridges, but the cartridges may also be removed, easily purged clean of possible contaminants and obstructions, and replaced simply and with little effort, skill or delay. Although each intricate cartridge is essentially a precision element, its critical multiple laminar-flow channels are uniquely produced conveniently and economically with the aid of a few common uniform-diameter wires extending linearly in a special press-fit relationship between a tubular casing and a coaxial core member.