ABSTRACT
The process industries by their very nature deal constantly with flowing fluids, and measurement of these flows is essential to the operation of the plant. These measurements are indicated, recorded, totalized, and used for control. Flow measurement is generally the most common measurement found in the process plant. The orifice plate is the most popular primary device found in most process plants. A conventional orifice plate consists of a thin circular plate containing a concentric hole. Occasionally a pipe elbow may be used as a primary device. Elbow taps have an advantage in that most piping configurations contain elbows that can be used. Secondary instruments measure the differential produced at the primary devices and convert it into a signal for transmission or into a motion for indication, recording, or totalization. The bellows or diaphragm secondary devices are popular when a direct indication or record is desired.
