How do you calibrate a D.P. transmitter?

The following steps are to be taken which calibrating:

1. Adjust zero of the Tx'r.
2. Static pressure test : Give equal pressure on both sides of the transmitter. Zero should not shift. If it is shifting carry out static alignment.
3. Vacuum test : Apply equal vacuum to both the sides. The zero should not shift.
4. Calibration Procedure: 
   1. Give 20 psi air or 24V dc supply to the transmitter.
   2. Vent the L.P. side to atmosphere.
   3. Connect output of the Instrument to a standard test gauge ot Multimeter and adjust zero.
   4. Apply required pressure to high pressure side of the transmitter and adjust the span.
   5. Adjust zero again if necessary.

How do you identify the H.P. side or inlet of an orifice plate in line?

The marking is always done H.P. side of the orifice tab which gives an indication of the H.P. side.

What is Bernoulli's theorem and where it is applicable?

Bernoulli's theorem states the "total energy of a liquid flowing from one point to other remains constant." It is applicable for non compressible liquids.

Why is the orifice tab provided?

The orifice tab is provided due to the following reasons.

1. Indication of an orifice plate in a line.
2. The orifice diameter is marked on it.
3. The materiel of the orifice plate.
4. The tagno. of the orifice plate.
5. The mark the inlet of an orifice.

How do you identify an orifice in the pipe line?

An orifice tab is welded on the orifice plate which extends outer of the line giving an indication of the orifice plate.

What are the different types of orifice plates and state their uses?

The different types of orifice plates are:

1. Concentric.
2. Segmental.
3. Eccentric.
4. Quadrant Edge.

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 liquid and 0.20 to 0.70 for gases, and steam. Best results occur between value of 0.4 and 0.6. Beta 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 be used either flange or vena contracts 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 plate 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 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 inches.

Quadrant edge orifices produce a relatively constant coefficient of discharge for services with low Reynolds numbers in the range from 100,000 down to 5,000.

What are the primary elements used for flow measurement?

The primary elements used for flow measurement are:

1. Orifice Plate.
2. Venturi tube.
3. Pitot tube.
4. Annubars.
5. Flow Nozzle.
6. Weir & Flumes.