11. Calibration and Use of Pressure and Temperature Measuring Instruments

8/13/2019 11. Calibration and Use of Pressure and Temperature Measuring Instruments

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1. OBJECTIVES a. To calibrate and adjust and to know the internal

mechanism of a Bourdon Dead Weight Gage Tester.

b. To familiarize oneself with the different types ofpressure and temperature measuring devices. ( Optical

and Radiation Pyrometers)

c. To calibrate thermometers with the known melting

and boiling points.

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2. THEORY / HYPOTHESIS Many of the instruments used to monitor systems or

processes in a plant measure pressure. In order to

understand how these instruments operate, instrument

technicians must understand:

a. the concept of pressure

b. the ways in which solids, liquids, and gases exert

pressure c. the standards established for measurement.

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2. THEORY / HYPOTHESIS (cont..) The definition for pressure, that is, the force applied per

unit of area, can be expressed in terms of a mathematical

formula:

P = F / A

where :

P = pressure

F = force

A = area

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2. THEORY / HYPOTHESIS (cont..) In metric system, the common unit of pressure is the

PASCAL. However, the PASCALS represent such a small

quantity that pressure is generally expressed in kilo-

Pascals.

The metric unit for force is Newton, and the metric unit

for area is the square meter.

Matter is considered a solid if it retains a definite shapeand volume.

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2. THEORY / HYPOTHESIS (cont..) Liquids unlike solids, do not have a definite shape.

However, liquids do have a definite measurable weight

and volume.

The pressure exerted by liquids can be divided into two

groups: hydraulic pressures and static pressures.

Hydraulic pressures are the pressures exerted by liquids

in motion, such as the pressures created by a mechanicalpump.

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2. THEORY / HYPOTHESIS (cont..) Hydrostatic pressures are pressure exerted by liquids at

rest, that is, liquids that are not in motion.

Hydrostatic pressure is determined by the height of a

fluid, not by its volume.

Hydrostatic pressures increase with depth, due to the

weight of the liquid pushing down from above.

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2. THEORY / HYPOTHESIS (cont..) Gases differ from solids and liquids in that they have

neither a definite shape nor a definite volume.

Gases do have weight, however due to the force of

gravity, so gases do exert pressure.

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2. THEORY / HYPOTHESIS (cont..) Atmospheric pressure is factor that must be considered

whenever pressure measurements are taken, because the

earth is always subjected to some atmospheric pressure,

with the amount being dependent on altitude and

weather conditions.

Consequently, the scales that have been established as a

basis for pressure measurement reference atmospheric

pressure, although in different ways.

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2. THEORY / HYPOTHESIS (cont..) The two scales most commonly used in pressure

measurements both reference atmospheric pressure:

the absolute scale references the absence of atmospheric

pressure,

while the gage scale reference the presence of

atmospheric pressure

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2. THEORY / HYPOTHESIS (cont..) It is possible to convert pressure measurements back and

forth from the absolute scale to the gauge scale because

the basic unit of measurement for both scales is pounds

per square inch (psi).

Absolute pressure equals gauge pressure plus

atmospheric pressure.

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2. THEORY / HYPOTHESIS (cont..) Conversely, gauge pressure equals absolute pressure minus

atmospheric pressure can be expressed in the followingequation

Pabs= Pgauge + Patm Pgauge= Pabs- Patm wherein :

Pabs= absolute pressure

Pgauge= gauge pressure Patm= atmospheric pressure

Vacuum pressure is any pressure below the atmosphericpressure.

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2. THEORY / HYPOTHESIS (cont..) Bourdon tube pressure elements are commonly used to

measure a wide range of pressures. They are made of

many materials, including bronze, brass, and stainless

steel. The type of material used to make a particular

Bourdon tube is generally determined by:

a. the type of process it is designed to measure.

b. The range of pressures it measures.

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2. THEORY / HYPOTHESIS (cont..) For most part, Bourdon tubes are made of strong, rugged

materials, that is designed to handle pressure ranging

from 5 psi to thousand of psi.

However, Bourdon tubes are sometimes designed and

constructed to measure very small pressure and vacuum.

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2. THEORY / HYPOTHESIS (cont..) The tube is made of oval thin-walled metal. One end of

the tube is open; the other end, called the tip is closed.

The open end of the tube is attached to a socket, or base,

which contains an inlet passage way to the inside of the

tube.

The pressure source is connected to the socket, so

pressure goes from the source through the inlet into the

tube.

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2. THEORY / HYPOTHESIS (cont..) When pressure is applied to a Bourdon tube, the tube

moves. Depending on the design of the element and the

type of pressure applied, Bourdon tube is either try to

straighten out or to coil.

However, the distance that the tip travels when pressure

is applied is relatively small. In most cases, it is around

1/4 to 3/8 of an inch.

The amount of tip travel is proportional to the amount of

applied pressure.

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2. THEORY / HYPOTHESIS (cont..) A pointer mechanism, connected to the tip by a

mechanical linkage, converts the small amount of tip

travel to a larger amount of the pointer travel that is

easier to read.

All thermometers are designed so that temperature are

indicated on one or more four scale: Fahrenheit, Celsius,

Rankine, and Kelvin.

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2. THEORY / HYPOTHESIS (cont..) In order to compare temperature readings from different

scales, it is necessary to convert temperature readings

from one scale to another.

The formula for converting from degrees Celsius to

degrees Fahrenheit is as follows:

oF = (1.8 x oC) + 32

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2. THEORY / HYPOTHESIS (cont..) This formula was derived by using the freezing and

boiling points of water as reference points. Since there

are 180 degrees between the freezing and boiling points

of water on the Fahrenheit scale and 100 degrees

between two points on the Celsius scale, the ratio of

degrees Fahrenheit to degrees Celsius is 180:100.

In other words, there are 1.8 times as many degrees

between freezing and boiling on the Fahrenheit scale as

there are on the Celsius scale (180/100 = 1.8).

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2. THEORY / HYPOTHESIS (cont..) Furthermore, because the freezing temperature of water

is 32 degrees higher for Fahrenheit than for Celsius, 32

must be added to (1.8 x oC) to make both sides accurate

and reliable temperature measuring instruments help

industrial facilities operate with maximum safety and

efficiency.

In industry, thermometers are used to monitor and in

some cases control the temperature of process system.

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2. THEORY / HYPOTHESIS (cont..) An understanding of how temperature measuring devices

operate depends on understanding the concept of

temperature and the ways in which solids, liquids, and

gases respond to temperature changes.

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2. THEORY / HYPOTHESIS (cont..) Temperature is the degree of hotness or coldness of a

substance, as measured on a definite scale. The relativehotness or coldness of a substance is often determined by

the sense of touch. Things feel hot if their temperature is higher than skin

temperature, or cold if their temperature is lower thanskin temperature.

However, the sense of touch is not enough to be aneffective and reliable method of temperaturemeasurement; instruments marked with definite scalesare needed.

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2. THEORY / HYPOTHESIS (cont..) A thermometer is a commonly used instrument that

measures and indicates temperature. But temperatures

of very hot surface body like the blast furnace, bed of

coal, fire tube type boilers and the like, optical and

radiation pyrometers are used.

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2. THEORY / HYPOTHESIS (cont..) To understand temperature completely, it is necessary to

distinguish between temperature and heat.

The terms heat and temperature are often used

interchangeably, but their meanings are not the same.

Heat is the thermal energy of a substance.

The addition or removal of heat is what causes

temperature to increase or decrease. Because heat is notthe same as temperature, heat is measured in units

rather than degrees.

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2. THEORY / HYPOTHESIS (cont..) Two units often used to measure heat are the British

Thermal Unit (BTU) and the calorie.

A BTU is the quantity of heat required to raise the

temperature of one pound of water one degree

Fahrenheit.

A calorie is the quantity of heat required to raise the

temperature of one gram of water one degree Celsius.

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3. LIST OF APPARATUS a. Bourdon Gage Tester

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3. LIST OF APPARATUS (cont..) b. Set of Standard Weights

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3. LIST OF APPARATUS (cont..) c. Thermometer

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3. LIST OF APPARATUS (cont..) d. Optical Pyrometer

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3. LIST OF APPARATUS (cont..) e. Radiation Pyrometer

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3. LIST OF APPARATUS (cont..) f. Beakers

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3. LIST OF APPARATUS (cont..) g. Bunsen Burner

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3. LIST OF APPARATUS (cont..) h. Steam Bath

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4. SET-UP OF APPARATUS:

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5. PROCEDURE: A. Calibration of Bourdon Gage By Dead Weight Gage

Tester

1. Open the handwheel fully and the valve of the oil

reservoir.

2. Fill up the oil reservoir up to its desired level and

open the drain valve.

3. To eliminate or remove the air trapped inside the oilcylinder, tightened the handwheel slowly so that the oil

will spill out through the drain cock.

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5. PROCEDURE: (cont..) 4. Close the drain valve.

5. Twist the rotating plunger to minimize friction.

6. Close the handwheel slowly until the platform risesto approximately one cm. Record the pressure reading.

7. Add weights one after the other with an increment

stated on the data sheet and make 12 trials repeating

procedure no. 6.

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5. PROCEDURE: (cont..) 8. After all weights have been placed, get the difference

between the standard equivalent pressure and the gage

pressure readings.

9. Compute for the percentage of error.

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5. PROCEDURE: (cont..) A. Calibration by Reference the Known Melting and

Boiling Points

a. For Melting Point

1. Place the ice into the graduated cylinder.

2. Place the mercury thermometer into the cylinder

and lower the thermometer until the bulb is near the

bottom.

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5. PROCEDURE: (cont..) 3. Leaving the ice to melt, read the temperature on the

thermometer. There will come a point when the

temperature is stable. Record this temperature as the

melting point of the ice.

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5. PROCEDURE: (cont..) b. For Boiling Point

1. Place a fair amount of water on the steam bath.

2. Place the thermometer in the steam bath throughthe desired location.

3. Make a flame with the Bunsen burner place at the

bottom of the apparatus.

4. There will come a point when the water will begin toboil. Read the thermometer and record the result as the

boiling point reading of the thermometer.

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6. DATA AND RESULTS: A.

1. Increasing Weight

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6. DATA AND RESULTS: (cont..) 2. Decreasing Weights

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6. DATA AND RESULTS: (cont..) B. Calibration By Reference The Known Melting and

Boiling Points

Melting Point = ______________oC

Boiling Point = _______________oC

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7. SAMPLE COMPUTATION:

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8. QUESTIONS: 1. Convert 60F to degrees Celsius, to the nearest tenth

of a degree.

2. Encircle the correct answer. Mercury is commonly

used in fluid thermometers because

a. It is expensive.

b. It expands and contracts at a consistent rate.

c. It forms a convex meniscus. d. It forms a concave meniscus.

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8. QUESTIONS: (cont..) 3. If the temperature indicated on two thermometers

measuring the same process read differently, then it is

likely that

_______________________________________________

_______________________________________________

____________________________.

4. True or False

Ambient temperature changes have a little effect on

partial immersion thermometers.

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8. QUESTIONS: (cont..) 5. True or False

Mercury freezes at a lower temperature than a mercury-

thallium alloy.

6. An inclined tube manometer has an angle of 30

degrees and is calibrated to read directly in head of water

when a gauge liquid with a specific gravity of 0.832 is

used. The cross sectional area of the tank is 6 times that

of the tube and tube is 64.52 mm2. Determine the vertical

rise of liquid in the tank in terms of rise of liquid along the

inclined manometer.

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8. QUESTIONS: (cont..) 7. A mercury manometer is used to determine the

pressure of oil with a specific gravity of .91 in a cast iron

pipe. The interface level is 500 mm below the center line

of the cast iron pipe and the level in the open leg of themanometer is 175 mm above the interface level.

Determine the oil pressure in the pipe in kg/cm2.

8. An incline manometer has a sensitivity 10 times as

great as a vertical pipe. What must its angle be to provide

this sensitivity?

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8. QUESTIONS: (cont..) 9. In manometer readings, one often encounter

vacuum and gauge pressure readings. Why?

10. An incline water manometer is used to measure the

pressure of gas in a main. The open leg is included at

angle of 30 degrees from the horizontal and the reading

on the inclined leg is 150 mm using the vertical leg as

datum. What is the gas pressure in kpa, psi and bar?

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9. ANSWERS:

10. DISCUSSION:

11. CONCLUSION / RECOMMENDATION:

12. REFERENCES

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END

11. Calibration and Use of Pressure and Temperature Measuring Instruments

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