Introduction
Orifice plates are mainly used for flow measurements. The orifice consists of a flat plate with a hole drilled in it. When a fluid passesthrough an orifice, the discharge is often considerably less than the amount calculated on the assumption that the energy is conserved and that the flow through the orifice is uniform and parallel.There are different types of orifice plates used for different fluids/process.
This reduction in flow is normally due to a contraction of the stream which takes place through the restriction and continues for some distance downstream of it, rather than to any considerable energy loss.With the flow through apparatus, arrangements are made to measure the extent of the reduction in flow, contraction of the stream and energy loss, as water discharges into the atmosphere from a sharp-edged orifice in the base of a tank
Concentric:
The concentric orifice plate is used for ideal liquid as well as gases and steam service.This orifice plate beta ratio fall between of 0.15 to 0.75 for liquids and 0.20 to 0.70 for gases, and steam. Best results occur between value of 0.4 and 0.6. beta ratio means ratio of the orifice bore to the internal pipe diameters. (45º beveled edges are often used to minimize friction resistance to flowing fluid )
Eccentric:
The eccentric orifice plate has a hole eccentric. Use full for measuring containing solids, oil containing water and wet steam. Eccentric plates can use either flange or vena contracta taps, but the tap must be at 180º or 90º to the eccentric opening.
Eccentric orifices have the bore offset from center to minimize problems in services of solids-containing materials.
Segmental:
The segmental orifice place has the hole in the form segment of a circle. This is used for colloidal and slurry flow measurement. For best accuracy, the tap location should be 180º from the center of tangency.
Segmental orifices provide another version of plates useful for solids containing materials.
Quadrant Edge:
It common use in Europe and are particularly useful for pipe sizes less than 2 inch. Quadrant edge orifices produce a relatively constant coefficient of discharge for services with low
Calibration procedure of DPT transmitter
