Fluid meters are divided into two functional groups -

One measures quantity (Positive Displacement); the other measures rate of flow (Inferential.)

All fluid meters, however, consist of two distinct parts, each of which has different functions to perform.

The first is the primary element, which is in contact with the fluid, resulting in some form of interaction.

This interaction may be that of imparting motion to the primary element; the fluid may be accelerated etc.

The second or secondary element translates the interaction between fluid and primary element into a

signal that can be converted into volume, weights or rates of flow and indicates or records the results.

For example, a weigher uses weighing tanks as its primary element and a counter for recording

the number of fillings and dumpings as its secondary element. In an orifice meter, the orifice together with

the adjacent part of the pipe and the pressure connections, constitute the primary element, while the

secondary element consists of a differential pressure device together with some sort of mechanism for

translating a pressure difference into a rate of flow and indicating the result, in some cases also recording

it graphically and integrating with respect to the time. This same combination of primary and secondary

elements will be observed in almost all other types of meters.

Positive Displacement (Quantity Meters) - Some of the more common positive displacement

meters are: Weighers, Reciprocating Piston, Rotating Piston, Nutating Disk, Sliding and Rotating Vanes,

Gear and Lobed Impeller, and the meter most commonly used to sell small quantities of gas at relatively

low flow rates, the Bellows meter.

Inferential (Rate Meters) - (a) Orifice Plates - The most commonly used rate or inferential meter

is the thin-plate, concentric orifice; a detailed discussion is covered in later paragraphs.

(b) Flow Nozzles & Venturi Tubes - Flow Nozzles and Venturi Tubes are primary rate devices

which will handle about 60% more flow than an orifice plate for the same bore under the same conditions,

and can therefore handle higher velocity flows. If a differential limit is chosen, then a smaller bore nozzle

or Venturi may be used to measure the same flow. They are more expensive to install and do not lend

themselves to as easy size change or inspection as orifice plates.

(c) Pitot Tubes - A Pitot or impact tube makes use of the difference between the static and kinetic

pressures at a single point. A similar device which is in effect a multiple pitot tube, averages the flow

profile.

(d) Turbine Meters - A Turbine meter is one in which the primary element is kept in rotation by the

linear velocity of the stream in which it is immersed. The number of revolutions the device makes is

proportional to the rate of flow.

(e) Swirlmeters, Vortex Shedding Meters, Rotometers, Mass Flow Meters, etc. - These are

devices that have applications in flow measurement. The manufacturers should be contacted for detailed

information

What is an Orifice Meter?

How does it work?

Orifice Flow Measurement – History

Fundamental Gas Laws

Orifice Plate Coefficient of Discharge – Cd

Critical Flow

Compressibility at Base Conditions (Pb Tb)

Major Advantage of Orifice Meter Measurement

Reliability (uncertainty/accuracy

Rangeability

METER TAP LOCATION

The Senior® Orifice Fitting

The Junior Orifice Fitting

The Simplex® Orifice Plate Holder

DANIEL SENIOR® ORIFICE FITTINGS

DANIEL JUNIOR ORIFICE FITTINGS

DANIEL SIMPLEX® ORIFICE PLATE HOLDERS

DANIEL ORIFICE METER TUBES

Pressure correction

Temperature correction...

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