Download Lab 6 Temperature Measurement

Laboratory Module
Lab 6: Temperature Measurement
DNT 121
Instrumentation & Measurement
Semester 2 (2006/2007)
LECTURER
PLV
TECHNICIAN
: MR ZULKARNAY ZAKARIA
: MRS FARIDAH HASSAN
: MR BAZLI BAHADON
Student’s Particular
NAME:
MATRIX NO:
DATE:
SIGNATURE:
School of Mechatronic Engineering
Kolej Universiti Kejuruteraan Utara Malaysia
SEM 2:06/07
DNT 121 Instrumentation & Measurement
Lab 5: Pressure & Flow Measurements
PART A: Pressure Measurement
1.0
2.0
OBJECTIVES
1.1
To learn fundamental temperature measuring techniques using
i.
Mercury-glass thermometer
ii.
Thermocouple (type K)
iii.
Thermistor
iv.
Resistance Temperature Detector (RTD)
v.
Bi-metal thermometer
vi.
Wet and dry bulb Temperature (Hygrometer)
1.2
To compare the accuracy of the various temperature measurement devices.
PARTS AND EQUIPMENT
Figure 1: Temperature Measurement Bench
Equipment apparatus :
 Vacuum flask.
 Water heater jug
 Digital resistance /mV indicator
 Direct reading digital
temperature indicator for use
with thermocouple
 Thermistor
 Vapor pressure thermometer
 Wet and dry bulb thermometer
qty
1
1
1
1
1
1
1
Equipment apparatus :
qty
 Thermocouples Type K & lead
1
wires
 Mercury in glass thermomerters:1
5 to 105 Deg C
 Mercury in glass thermomerters:1
-5 to 360 Deg C
 Platinum resistance thermometer
1
 Bimetallic temperature indicator :
1
0-400 Deg C.
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3.0
INTRODUCTION AND THEORY
Temperature, measure of the relative warmness or coolness of an object.
Temperature is measured by means of a thermometer or other instrument having a scale
calibrated in units called degrees. The size of a degree depends on the particular
temperature scale being used. A temperature scale is determined by choosing two
reference temperatures and dividing the temperature difference between these two points
into a certain number of degrees. The two reference temperatures used for most common
scales are the melting point of ice and the boiling point of water. On the Celsius
temperature scale, or centigrade scale, the melting point is taken as 0°C and the boiling
point as 100°C, and the difference between them is divided into 100 degrees. On the
Fahrenheit temperature scale, the melting point is taken as 32°F and the boiling point as
212°F, with the difference between them equal to 180 degrees.
The temperature of a substance does not measure its heat content but rather the
average kinetic energy of its molecules resulting from their motions. A one-pound block
of iron and a two-pound block of iron at the same temperature do not have the same heat
content. Because they are at the same temperature the average kinetic energy of the
molecules is the same; however, the two-pound block has more molecules than the onepound block and thus has greater heat energy.
The scale we use to measure temperature is "degrees" (°). There are three
temperature scales that are used today.
i. The Kelvin (K) scale is used by scientists and for astronomical temperatures.
ii. The Celsius scale (°C) is used in most of the world to measure air temperatures.
iii. The Fahrenheit scale (°F) is used to measure temperatures at or near the surface.
All three temperature scales are related to each other through the "triple point of
water". The triple point of water is the temperature at which water vapor, liquid water,
and ice can coexist simultaneously. The triple point occurs at 0.01 °C (273.16 K or 32.02
°F). To convert from one temperature scale to another, we need to use the equations as
below:
i. Convert Celsius to Kelvin: K = °C + 273
ii. Convert Celsius to Fahrenheit: °F = 1.8(°C) + 32
3.1
Mercury in Glass Thermometer
The mercury in glass thermometer (figure 2) is a thermometer consisting of
mercury in
a glass tube. Calibrated marks on the tube allow the temperature to
be read by the height of the mercury column in the capillary tube which varies
according to the
temperature. Glass
thermometer is accurate, economical
instrument that measures
temperature of liquids or
gases. All of the
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DNT 121 Instrumentation &
Lab 5: Pressure & Flow Measurements
glass thermometers conform to the International Temperature Scale of 1990
(ITS-90). ASTM (American Society for
Testing and Materials) thermometers
vary from 5.5 mm to 8 mm in diameter;
most other thermometers
have a 6 mm to 7 mm diameter. Glass thermometer temperature
ranges
are
around -199.8°C until 499.5°C.
3.1.1
Types of Glass Thermometer
a) Partial Immersion
Partial immersion thermometer is immersed in the fluid to a specified
immersion depth. The remaining (emergent) portion of the stem is
exposed to the air.
b) Total Immersion
Total immersion thermometer need to be immersed up to the liquid
temperature mark on the thermometer. Since the thermometer column is
fully immersed, this thermometer is the most accurate.
Figure 2: Glass Thermometer
3.2
Thermocouples
Thermocouple (figure 3) is a temperature measurement sensor that consists of
two dissimilar metals that joined together at one end (a junction) that produces a
small thermoelectric voltage when the junction is heated. Thermocouple
thermometers interpret the change in thermoelectric voltage as a change in
temperature.
Thermocouple is available in various types with different combinations of
dissimilar metals. The most common types are: Type J, K, T and E. For example,
Type K Thermocouple is ranged between -249.75°C to 1373.625°C and Type J
Thermocouple is ranged between -189.81 °C to 999°C.
Exposed junction thermocouple is fast responding but the thermocouple itself is
unprotected and subject to corrosion from the environment. Also, the smaller the
probe sheath diameter, the faster the response. Often the thermocouple is located
inside a metal or ceramic shield that protects it from a variety of environments.
Metal-sheathed thermocouple is also available with many types of outer coating,
such as polytetrafluoro ethylene for trouble-free use in corrosive mediums.
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Figure 3 : Thermocouple with probe
3.3
Thermistor
Thermistor (figure 4) is a thermally sensitive resistor and has, according to type, a
negative (NIC) or positive (PTC) resistance/temperature coefficient. Thermistor
thermometry is based on the principle that metal oxides change resistance with a
change in temperature. Resistance decreases as the temperature decreases. The
meter where it is converted and displayed as a temperature reading detects this
resistance change. Thermistor has excellent accuracy over biological or ambient
temperature ranges when compared to RTDs or Thermocouples. Response time is
generally faster than RTDs.
Figure 4 : Thermistor with probe
Thermistor is generally composed of semiconductor materials. Most thermistors
have negative temperature coefficient (TC) which means resistance decreases
with increasing temperature. The negative TC can be as large as several percents
per degree Celsius (%/°C), allowing the thermistor circuit to detect minute
changes in temperature, which could not be observed with an RTD, or
thermocouple circuit.
Thermistor has a semiconductor material which changes its electrical resistance as
a function of temperature. Extension wires used with thermistor can be plain
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Lab 5: Pressure & Flow Measurements
copper wire. Thermistor offers accuracy similar to RTD within narrow
temperature ranges near to ambient temperature. It is generally responses faster
comparatively. Since thermistor standards vary, care must be taken to match the
instrumentation to the sensor. The resistance-temperature relationship of a
thermistor is negative and highly nonlinear. Thermistor is usually designated in
accordance with it's resistance at 25°C.
3.4
Resistance Temperature Detector (RTD)
A typical RTD (figure 5) consists of a fine platinum wire wrapped around a
mandrel and covered with a protective coating. Usually, the mandrel and coating
is glass or ceramic. Depositing can also make the platinum as a film on a
substitute and then encapsulating it. RTD is wire wound and thin film device that
work on the physical principle of the temperature coefficient or electrical
resistance of metals.
Figure 5 : RTD with probe
The electrical resistance of the RTD changes as a function of temperature.
Circuitry similar to a Wheatstone bridge is built into control designed for use with
RTD. Constant current into the bridge produces an output voltage that varies with
temperature. Lead wire resistance can significantly affect the RTD measurement.
This is typically corrected using a third (compensating) lead wire.
RTD is nearly linear over a wide range of temperatures and can be made small
enough to have response times of a fraction of a second. The classical resistance
temperature detector (RTD) construction using platinum was proposed by
C.H.Meyers in 1932. This requires an electrical current to produce a voltage drop
across the sensor that can be then measured by a calibrated read-out device.
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3.5
The Bimetallic Thermometer
The bimetallic thermometer (figure 6) uses a bimetal, which is composed of two
types of metals with different thermal coefficients of expansion and they are
wound into a helical form, change according to temperature is transmitted to the
indicator. This thermometer is simple in construction and reasonably priced.
Figure 6 : Bimetallic Thermometer
3.6
Wet and dry bulb Temperature (Hygrometer)
A hygrometer (figure 7) is used to measure the level of humidity in air. The usual
type that can be obtained is typically made from a fiber (originally horse hair) that
changes length with changes in humidity. Because the fiber hygrometer can be
affected by many different conditions, it should be calibrated regularly. It is
especially quite inaccurate at very high or low humidity.
The accurate type instrument has two thermometers, one of which has a cloth
sock on the bulb, which is kept wet from the tube of water. The wet bulb
temperature will be lower than the dry bulb temperature. Knowing the difference
in temperatures, simply consult the psychometric chart or hygrometric table to
determine the relative humidity at the dry bulb temperature.
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Lab 5: Pressure & Flow Measurements
Figure 7 : Hygrometer
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4.0
DNT 121 Instrumentation & Measurement
Lab 5: Pressure & Flow Measurements
PROCEDURE
PART 1 : Ambient air temperature measurement
1.
2.
3.
4.
5.
6.
Take out the mercury-glass thermometer, close inspection will reveal a column of
mercury protrude from the bulb. Temperature measurement is achieved by relating
the length of this column to an engraved scale on the glass. Read the temperature
indicated by the column at ambient air temperature.
Take out the bi-metal thermometer, close inspection will reveal a metal rod at the
end of the indicator. Temperature measurement is achieved by transferring heat to
the metal rod.
Take out a Type K thermocouple. Connect the blue and yellow plugs to the
corresponding sockets of the Type K thermocouple temperature indicator. Place
the thermocouple on the baseboard and allow the readings to stabilize at the
ambient air temperature. Read the temperature indicated on the temperature
indicator.
Take out a resistance temperature detector (RTD). Connect the RTD plugs to the
corresponding sockets of the RTD indicator. Place the RTD on the baseboard and
allow the readings to stabilize at the ambient air temperature. Read the temperature
indicated on the RTD temperature indicator.
Take out a thermistor. Connect the thermistor plugs to the corresponding sockets of
the thermistor indicator. Place the thermistor on the baseboard and allow the
readings to stabilize at the ambient air temperature. Read the temperature indicated
on the thermistor indicator.
Take out the vapor pressure thermometer. Place the vapor pressure thermometer on
the baseboard and allow the readings to stabilize at the ambient air temperature.
Read the temperature indicated on the indicator
PART 2 : Ice-point temperature measurement
1.
2.
3.
4.
5.
6.
Half fill the vacuum flask with a mixture of crushed ice and pure water
Insert the bulb of the thermometer into the water-ice mixture; stir gently to ensure
intimate contact with the mixture. Observe the reading on the thermometer.
Insert the metal rod of the bi-metal thermometer into the water-ice mixture; stir
gently to ensure intimate contact with the mixture. Observe the reading on the
bimetallic temperature indicator.
Insert the thermocouple probe into the water-ice mixture; stir gently to ensure
intimate contact with the mixture. Observe the reading on the thermocouple
temperature indicator
Insert the RTD probe into the water-ice mixture; stir gently to ensure intimate
contact with the mixture. Observe the reading on the RTD temperature indicator.
Insert the thermistor probe into the water-ice mixture; stir gently to ensure intimate
contact with the mixture. Observe the reading on the thermistor temperature
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DNT 121 Instrumentation & Measurement
Lab 5: Pressure & Flow Measurements
indicator.
Insert the metal rod of the vapor pressure indicator into the water- ice mixture; stir
gently to ensure intimate contact with the mixture. Observe the reading on the
indicator.
PART 3 : Boiling-point temperature measurement
1.
2.
3.
4.
5.
6.
7.
8.
Half fill the water heater jug with clean water and connect the power cord.
Switch ‘ON’ the water heater jug. Wait until water is boil .
Be careful to the hot water.
Insert the bulb of the thermometer into boiling water. Observe the reading on the
thermometer.
Insert the metal rod of the bimetalic indicator into boiling water. Observe the
reading on the bimetallic indicator.
Insert the thermocouple probe into boiling water. Observe the reading on the
temperature indicator.
Insert the RTD probe into boiling water. Observe the reading on the resistance
indicator.
Insert the thermistor probe into boiling water. Observe the reading on the
thermistor indicator.
Insert the metal rod of the vapor pressure indicator into boiling water. Observe the
reading on the thermometer.
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4.2
4.6
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4.0
DNT 121 Instrumentation & Measurement
Lab 5: Pressure & Flow Measurements
RESULT
PART 1: Ambient air temperature measurement
No.
1.
2.
3.
4.
5.
6.
Temperature device
Mercury-glass thermometer
Bi-metal thermometer
Thermocouple Probe (type K)
RTD probe
Thermistor probe
Vapor pressure indicator rod
ºC
PART 2: Ice-point temperature measurement
No.
1.
2.
3.
4.
5.
6.
Temperature device
Mercury-glass thermometer
Bi-metal thermometer
Thermocouple probe (type K)
RTD probe
Thermistor probe
Vapor pressure indicator rod
ºC
PART 3: Boiling-point temperature measurement
No.
1.
2.
3.
4.
5.
6.
5.0
Temperature device
Mercury-glass thermometer
Bi-metal thermometer
Thermocouple probe (type K)
RTD probe
Thermistor probe
Vapor pressure indicator rod
ºC
DISCUSSION
Hints: Important points to highlight:
i.
ii.
iii.
iv.
6.0
Include a discussion on the result noting trends in measured data.
Compare measurements with theoretical predictions when possible.
Include the physical interpretation of the results, the reasons on deviations of your findings from expected results.
Include your recommendations on further experimentation for verifying your results, and your findings.
CONCLUSION
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