Dpt Principle

Differential Pressure Transmitter (DPT) using orifice plate.


The Orifice Plate is a device that houses, and accurately positions for measuring flow within a pipe or tube. The orifice meter consists of a flat orifice plate with a circular hole drilled in it. There is a pressure tap upstream from the orifice plate and another just downstream. There are in general three methods of placing the taps. The coefficient of the meter depends upon the position of taps. When placed, an orifice plate will produce a differential pressure by abruptly constricting the fluid flowing through it. The differential pressure is measured across the plate through taps precisely located on the orifice plate. An orifice plate installed in a line creates a pressure differential as the fluid flows through it. This differential pressure is measured via impulse lines by a differential pressure transmitter which converts it into an analogue or digital signal which can be processed to provide a display of the instantaneous rate of flow. The relationship between the rate of flow and the differential pressure produced is very well understood and is fully covered by comprehensive national standards. The relevant standards are BS 1042 and the equivalent ISO 5167. One of the principle advantages of orifice plates manufactured and installed following these standards is that they do not require calibration. This means that orifice plates are very cost effective on larger line sizes.

  b) Vortex Flow meter


An everyday example of a vortex shedding phenomenon is a flag waving in the breeze: the flag waves due to the vortices shed by air moving across the flagpole. Within the flow meter, as flowing liquid moves across the tiny strut or “bluff bar”, vortices are also shed but on a smaller scale. The meter transmits an ultrasonic beam through the vortex pattern downstream of the strut. As vortices are shed, the carrier wave of the ultrasonic signal is modified. This change...