Apparatus for measuring the velocity of a fluid flowing in a conduit

A system for monitoring and controlling an arrangement in which a particulate material is transported through a conduit entrained in a fluid, the system comprising a first apparatus and a second apparatus,

• the first apparatus comprising a differential pressure generator including first and second bluff bodies which are positioned in the conduit to create a differential pressure that is a function of the velocity of the fluid, first and second pressure sampling apertures which are located downstream of the first and second bluff bodies respectively and a differential pressure sensor for providing an electrical signal which is a function of the difference between the pressures at the apertures, wherein the first and second bluff bodies are located in a substantially constant cross-section portion of the conduit with the first bluff body immediately upstream of and at least approximately in line with the second bluff body in a direction parallel to the axis of the conduit, and wherein the maximum cross-sectional area of the first bluff body taken on a plane perpendicular to the axis of the conduit is substantially less than the maximum cross-sectional area of the second bluff body, the first apparatus being positioned relative to the conduit such that the bluff bodies are located in a region of the conduit at least generally free of particulate material, and
• the second apparatus comprising means for producing a further electrical signal which is a function of the difference between the pressures at relatively widely spaced locations along the conduit,
• the system further including means for automatically controlling at least one flow parameter as a function of the first and further electrical signals.