Mech 215 Measuring Temperature Lab

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Mech 215Measuring Temperature Lab

• Lab TA Sharon Goldthorpe
• Professor M. Birk
• Email goldthorpe_at_me.queensu.ca

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Purpose of this lab

• To introduce you to some types of temperature
  measuring systems that may be required in
  industry
• To determine the sources of errors in temperature
  measurements
• To learn about the dynamic response of
  temperature measuring systems
• To learn why different measuring techniques work
  better for different systems

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Key Points in this Lab

• When mass is added to the sensor, the dynamic
  response will slow down
• When the heat transfer rate to the sensor is low,
  the sensor will take longer to reach thermal
  equilibrium
• While taking a temperature measurement, the
  details of the technique will determine the
  accuracy of the measurement

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Experiment

• This lab considers three temperature measurement
  devices
• Thermocouple
• Thermometer
• RTD (Resistance Temperature Detector)
• Infra red thermometer

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What is a Thermocouple

• Composed of two electrically conducting
  dissimilar metals which when joined generate a
  voltage which changes with temperature
• The two dissimilar metals are welded together to
  create a single junction
• Thermocouples used in this experiment are made of
  copper and constantan

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What is a Good Thermocouple

• Want to produce thermocouples that have a single,
  small junction.
• More than one junction or too large of a bead
  will introduce measurement errors. If the bead is
  too large then it will take longer to reach
  thermal equilibrium with the object you are
  measuring.
• The temperature reading will be taken from where
  the wires first make contact.

Good bead
Beads too large and wires are twisted before the
bead
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How to make a Thermocouple

• Twist the two wires on one end together
• Cut off excess wire at end
• Place thermocouple between the pliers
• Ensure that they are placed on bare metal and
  that the twisted part is outside of the pliers
• Set the welder to around 20
• Push in the button and hold it, then touch the
  end of the thermocouple to the carbon block
• Do not touch the pliers to the block, ensure only
  the thermocouple makes contact
• Need to make 4 thermocouples per group

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Thermocouple Welder
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ThermocouplesPart 1

• Produce a circuit similar to the circuit shown
  here using two thermocouples
• Place the reference junction in the hinged bricks
  which acts as the reference temperature (ice bath
  in the diagram)
• Turn on the soldering iron to the halfway setting
  and let it heat up for 10 minutes before using it
• Record the type of thermocouple (T-type
  thermocouple)

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How to Produce the Circuit

• Connect the already made thermocouples together
  by twisting similar wires together to create an
  electrical connection
• Ensure that you are connecting either two copper
  wires or two constantan wires together
• Connect the other end of both thermocouples to
  the board by placing each wire separately under
  the post connector and tightening it down to form
  an electrical connection
• When the measuring thermocouple is at the same
  temperature as the brick (room temperature) the
  voltage reading should be zero, if it is not zero
  then try reconnecting the wires to achieve a
  better electrical connection

Feb 2009
Mech 215 Temperature Measurement
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Thermocouples Part 1Measuring Temperature of a
Soldering iron

• Put a banana plug in the top of the two used post
  connectors and then attach one to the V-O port
  and the other to the COM port in the multi-meter
• This will measure the voltage between the
  reference junction and the measuring junction
• Record the temperature of the brick using
  the
  temperature measurement on the top
  
• Place the measuring junction against
  the tip of the
  soldering iron until it reaches a
  steady value, then measure the
  voltage
  using the multi-meter
• Record any uncertainties or fluctuations in
  the
  voltage reading

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Thermocouples Part 2Measuring Temperature of
Hot Water

• Place the measuring thermocouple against the
  outside of the cup of hot water and measure the
  voltage and any uncertainties in the value
• Is this an effective method of measuring the
  temperature of the water?
• Now put the thermocouple in the water and measure
  the voltage. Is this a better way to measure the
  water why?
• Discuss this in your lab write up

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Thermocouples Part 3 Thermopile

• Connect 4 thermocouples together to
  make a thermopile similar
  to the one shown in
  the Figure
• Place one thermocouple in the brick as a
  reference junction and record the temperature of
  the brick using the reading on the top of the
  brick
• Place the other 3 thermocouples in
  the
  measuring junction
• This method is used to get an average
  
  of the voltage readings and
  increase the
  accuracy
• Record the voltage of the hot water and then the
  soldering iron once the reading levels off using
  the thermopile

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Thermocouples Part 4 Using LabView

• Using the previous thermopile setup, connect the
  system to channel 1 on the data acquisition board
• Keep the multi-meter turned on and attached to
  the system so that the voltage measurements in
  LabView can be verified

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LabView

• Your LabView Program from the first lab session
  should resemble the diagram below

Write to Spreadsheet file VI
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Connecting to LabView

• Go to the wiring diagram in LabView by selecting
  Window Show Diagram
• Use the wiring tool to Create a Control on the
  format terminal of the Write to Spreadsheet file
  VI by right clicking and then selecting Create
  and then Control
• On the front panel, change .3f to f
• Change the values on the front panel under device
  and channels so that they are the same as those
  in the picture above
• Input limits will have to be used to get accurate
  values and the scale will also have to be changed
• Ensure to record the scan rate

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Thermometer Part 1Heating of a Thermometer in
Hot Water

• Fill cup up most of the way with boiling hot
  water
• Place thermometer in the full cup of hot water
• Record the initial temperature and start the stop
  watch
• Record the temperature of the water every 10
  seconds for 8 minutes

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Thermometer Part 2Cooling of a Thermometer in Air

• Remove the thermometer after being in the hot
  water for 8 minutes and dry it with a paper towel
• Prop the thermometer on the case so that the air
  contact on the thermometer has a larger surface
  area than if it was placed on the table
• Record the initial temperature and start the stop
  watch
• Record the temperature every 10 seconds for 8
  minutes

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Thermometer Part 3Heating of the Tip of a
Thermometer

• Put a small amount of fresh hot water in the cup
  so that only the tip of the thermometer will be
  in the water when put into the cup
• Record the initial temperature and start the stop
  watch
• Record the temperature every 10 seconds for 8
  minutes

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RTD Part 1Heating of an RTD with a Soldering Iron

• Ensure the soldering iron is still turned on and
  at the halfway setting
• Plug wires into ports 1 and 4, as shown in the
  diagram (Plug the wires in diagonally across from
  one another)
• Ensure the wires are pushed in all the way to
  produce a good electrical connection

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1
4
3
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RTD Part 1

• Plug the red wire into the V-O
  port and plug the black wire
  into the
  COM port
• Turn the multi-meter on, select DC, select kO and
  then select 200 O
• If the resistance values are fluctuating a great
  deal then double check the connection
• Measure and record the resistance of the RTD when
  exposed to room temperature air
• To do this hold it by the base and let the
  resistance reach a steady state with the air
  before recording the value

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RTD Part 1

• Remove the soldering iron and hold it against the
  tip of the RTD
• Comment on how long it takes the RTD to heat up
  compared to the other temperature measuring
  techniques
• Record the initial resistance and start the stop
  watch
• Record the resistance every 10 seconds for 8
  minutes

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RTD Part 2Cooling of an RTD in Room Temperature
Air

• Once the RTD has been exposed to the soldering
  iron for 8 minutes, remove it and record the
  initial RTD resistance
• Re-start the stop watch and record the resistance
  every 10 seconds for 8 minutes
• Turn the soldering iron down for the Wheatstone
  Bridge portion of the lab

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Wheatstone Bridge

• Use 4 resistors with the same resistance to
  produce the configuration shown in Fig 6.14 in
  Figliola
• Use a high enough internal resistance
• Resistor values in the 100 kO range should be
  used
• Record the resistance of the resistors
• Connect the negative and positive power supply
  across two of the nodes (either across CB or AD)
• Connect the multi-meter across the other two
  nodes so that the voltage across the circuit can
  be measured

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Wheatstone Bridge

• Your set up should resemble the picture below
• Ensure the Bread Board is turned on and the
  resistors are not touching one another
• Wires should be connected to the multi-meter so
  that the voltage across the circuit can be
  measured
• Measure the voltage across the
  circuit

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Wheatstone Bridge

• Use the hot soldering iron from the previous part
  of the lab to heat one of the 4 resistors
• Heat the resistor until a maximum voltage across
  the circuit is measured
• Note heat the resistor wire and not the actual
  resistor

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Wheatstone Bridge

• Record the maximum voltage across the circuit and
  then remove the soldering iron
• Start the stop watch and record the voltage
  across the circuit every 10 seconds until it
  levels off and is the same for a few readings
• Record which resistor was heated
• What happens if you heat one of the other
  resistors

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Infra Red Thermometer

• This technique can be used in industry to obtain
  temperature measurements in locations where a
  thermocouple or thermometer would be either
  difficult or impossible to use
• You can measure the surface temperature of an
  object without touching it
• Functions by measuring the thermal radiation
  emitted and reflected by an object
• It takes the average temperature measurement
  within the red circle
• When using this technique the radiation and
  reflective properties of the material need to be
  considered
• This is due to the probe seeing radiation from
  other parts of the room which can give a false
  reading

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Surface Emissivity

• Emissivity e describes how the surface emits and
  reflects thermal radiation
• If e 1 the surface only emits energy and
  reflects none
• If e 0 the surface only reflects and emits
  nothing
• Infra Red thermometer only works well for
  surfaces with e close to 1
• Most painted, oxidized, dirty surfaces have e
  larger than 0.8
• Polished metals are highly reflective and have
  low e

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Things to keep in mind while performing the
experiment

• Record all units for all measured values along
  with uncertainties
• Values with no units have little meaning
• The soldering irons are hot, so ensure you do not
  touch them or burn anything with them

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Lab Write Up

• Report should be brief but complete and concise
  (see web page for more report writing details).
• Answer discussion questions and discuss the
  methods and their pros and cons as they relate to
  the experiments you did
• Email me if you have any questions about the lab
  at goldthorpe_at_me.queensu.ca