1. Temperature
URVISH SONI

2. Brief Overview Types of Sensors and how they work Sensor Applications
Advantages and Disadvantages
Sensors that will work with project

3. How is heat transferred?
Conduction
Metal coffee cup
Convection
Radiation
003

4. Temperature scales

5. Types of Temperature Sensors
Bi Metallic
Thermocouples
Resistance Temperature Detectors (RTDs)
Thermistors
Infrared Sensors

6. Expansion thermometer
Solid Expansion Thermometer
Bimetallic thermometer
Spiral Bimetal element
Helix Bimetal element
Liquid Expansion Thermometer- Mercury in Glass type.

7. Thermal Expansion Co efficient
Bimetal thermometer
100
300
200
400
Two dissimilar metals, tightly bonded
Forces due to thermal expansion
Result
Thermal Expansion Co efficient
Of Metal
013

8. Spiral and Helical

9. Liquid thermometer Mercury Liquid-filled thermometer 100
Accurate over a small range
Accuracy & resolution= f(length)
Range limited by liquid
Fragile
Large thermal mass
Slow
Mercury
100
014

10. Class I-Liquid Filled Systems

11. Class II- Vapour Systems

12. Class III- Gas Filled Systems

14. Class V- Mercury Filled Systems

15. Seeback effect

16. Peltier
an effect whereby heat is given out or absorbed when an electric current passes across a junction between two materials.

17. Thomson effect
Thomson effect is related to the emf that develops between two parts of the single metal when they are at different temperature
Thus thomson effect is the absorption or evolution of heat along a conductor when current passes through it when one end of the conductor is hot and another is cold

22. Thermocouples Two wires of different metal alloys.
Converts thermal energy into electrical energy.
Requires a temperature difference between measuring junction and reference junction.
Easy to use and obtain.

23. Cold junction
Maintaining an ice water slurry and actual cold junction is rarely feasible. Typically, the cold junction is omitted, and the potential is measured directly across the two terminal ends of the thermocouple wires at ambient temperature.

24. electronic cold junction compensation
Simulate the potential effects that would result for a thermocouple wire pair between the terminals, at their measured temperature, and another junction at a reference temperature of 0 degrees. Measure the potential across the thermocouple wire pair in series with the simulated potential. Apply the linearizing curve to the sum, thus obtaining an estimated absolute temperature directly. This is known as cold junction compensation. Usually, the simulation is done electronically with specialized integrated circuit devices.
electronic cold junction compensation

25. Independently measure the temperature of the cold junction
Independently measure the temperature of the cold junction. Measure the thermocouple potential and apply conversion curves to determine the temperature difference across the thermocouple. Then add the known cold junction temperature to the measured temperature difference to determine the absolute temperature measurement.
independent cold junction measurement

26. Thermowell

27. Thermocouple extension wires

28. Thermocouples selection criteria

29. Thermocouple Applications
Plastic injection molding machinery
Food processing equipment
Deicing
Semiconductor processing
Heat treating
Medical equipment
Industrial heat treating
Packaging equipment

30. Thermocouples Advantages Disadvantages Simple, Rugged
High temperature operation
Low cost
No resistance lead wire problems
Point temperature sensing
Fastest response to temperature changes
Least stable, least repeatable
Low sensitivity to small temperature changes
Extension wire must be of the same thermocouple type
Wire may pick up radiated electrical noise if not shielded
Lowest accuracy

31. Common Thermocouples Seebeck Coeff: uV/C Type Metals J K T S E N
Fe-Con
Ni-Cr
Cu-Con
Pt/Rh-Pt
Ni/Cr-Con
Ni/Cr/Si-Ni/Si 50 40 38 10 59 39
Microvolt output is a tough measurement
Type "N" is fairly new.. more rugged and higher temp. than type K, but still cheap
037 Type J, K, T, E and N are all base-metal thermocouples. Notice their high output signals, compared to the signal from a type S (noble-metal) thermocouple.
Even though the output of the base-metal thermocouples is high compared with noble metal thermocouple, the magnitude of either is still quite small. The outputs are measured in microvolts per degrees C, which tends to create serious problems in a noisy factory environment.
The nicrosil/nisil thermocouple is only a few years old, but it has gained rapid acceptance in replacing type K, because it is more rugged yet still inexpensive.
037

33. Resistance Temperature Detectors (RTDs)
Wire wound and thin film devices.
Nearly linear over a wide range of temperatures.
Can be made small enough to have response times of a fraction of a second.
Require an electrical current to produce a voltage drop across the sensor

36. Measuring an RTD: 2-wire method
Rlead Rx
100 + d V
Rlead
I ref= 5 mA Pt -
R= Iref*(Rx + 2* Rlead)
Error= 2 /.385= more than 5 degrees C for 1 ohm Rlead! d
Self-heating:
For 0.5 V signal, I= 5mA; P=.5*.005=2.5 mwatts
@ 1 mW/deg C, Error = 2.5 deg C!
018 Since the RTD has a low resistance, we need to look very carefully at how we are going to measure it. Let's take a simple two-wire ohms measurement with 5 mA reference current being pumped through the unknown RTD. In the two-wire measurement, the lead resistance becomes part of the unknown. In the case of the 100 ohm platinum RTD, a total of two ohms lead resistance can result in more than five degrees C error!
Let's also look at the error due to self heating. For a 5 milliamp signal, the power in this device is about 2.5 milliwatts. At 1 milliwatt per degree C, that is an error of 2.5 degrees C.
The lesson that we can learn from this is to always use a 4-wire measurement, not a 2-wire measurement. If you must use a 2-wire measurement, be sure to null out the lead resistance and minimize the measurement source current. Now let's take a look at the 4-wire technique.
Moral: Minimize Iref; Use 4-wire method
If you must use 2-wire, NULL out the lead resistance
018

37. 3-Wire bridge d d V 3-Wire PRTD d d Keeps bridge away from heat source
1000
100 d d
Rlead 1 V
3-Wire PRTD
Sense wire
1000 d
Rlead 2
100 d
Keeps bridge away from heat source
Break DMM lead (dashed line); connect to RTD through 3rd "sense" wire
If Rlead 1= Rlead 2, sense wire makes error small
Series resistance of sense wire causes no error
021 You can move the RTD a good distance away from the bridge and add a third sense wire directly connected to the voltmeter. This has the advantage of keeping the bridge away from the heat source and it also has the advantage of having the lead resistances compensate for each other. However, any mismatch in lead resistances will cause an error. While this method of measurement does save one wire, it is typically not quite as accurate as a 4-wire technique.
022

38. d d The 4-Wire technique Rx + 100 V Rlead=1 I ref= 5 mA - R= Iref * Rx
Error not a function of R in source or sense leads
No error due to changes in lead R
Twice as much wire
Twice as many scanner channels
Usually slower than 2-wire
019 With the 4-wire technique, the voltage is sensed not at the voltmeter input terminals, but at the terminals of the RTD. That means that error is no longer a function of the lead resistance. It also means that there is no error due to changes in lead resistance, as there would be in the 2-wire measurement.
The disadvantage of the 4-wire technique is that is requires twice as much wire and twice as many scanner channels. It is also typically slower than a 2-wire method.
019

39. Bridge method
100 d
1000 d V
100 d
1000 d
High resolution (DMM stays on most sensitive range)
Nonlinear output
Bridge resistors too close to heat source
021 You could also use a bridge to measure an RTD. The advantage of the bridge is that the voltmeter always stays on its most sensitive range. The disadvantage shown here is that the bridge resistors are too close to the heat source, and hence we will get an incorrect reading due to the temperature coefficient of the bridge resistor. This can be solved by moving the RTD away from the bridge with an extra wire.
021

40. RTDs Advantages Disadvantages Most stable over time Most accurate
Most repeatable temperature measurement
Very resistant to contamination/
corrosion of the RTD element
High cost
Slowest response time
Low sensitivity to small temperature changes
Sensitive to vibration (strains the platinum element wire)
Decalibration if used beyond sensor’s temperature ratings
Somewhat fragile

41. Thermistors A semiconductor used as a temperature sensor.
Mixture of metal oxides pressed into a bead, wafer or other shape.
Beads can be very small, less than 1 mm in some cases.
The resistance decreases as temperature increases, negative temperature coefficient (NTC) thermistor.

42. Thermistors Most are seen in medical equipment markets.
Thermistors are also used are for engine coolant, oil, and air temperature measurement in the transportation industry.

43. Thermistors High sensitivity to small temperature changes
Advantages Disadvantages
High sensitivity to small temperature changes
Temperature measurements become more stable with use
Copper or nickel extension wires can be used
Limited temperature range
Fragile
Some initial accuracy “drift”
Decalibration if used beyond the sensor’s temperature ratings
Lack of standards for replacement

45. emissivity
The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation.
Thermal radiation is electromagnetic radiation and it may include both visible radiation (light) and infrared radiation,

47. Stefan–Boltzmann law
Stefan–Boltzmann law, statement that the total radiant heat energy emitted from a surface is proportional to the fourth power of its absolute temperature.
5.6704 × 10−8 watt per metre2∙K4
E = σT4

48. Black body
A black body is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence.
A white body is one with a rough surface [that] reflects all incident rays completely and uniformly in all directions

49. List sources of error in Non-contact type thermometry
Radiation pyrometer
Optical pyrometer
Optical Fiber Thermometry
Ultrasonic thermometry
Laser thermometry

51. Optical pyrometer

52. Optical Fibre Thermometry

53. Ultrasonic thermometry

55. Temperature switches

56. Thermostats

57. Actual Image