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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