1. In The Name of Allah The Most Beneficent The Most Merciful

2. ECE 4550: Biomedical Instrumentation Lecture: Temperature Measurement
Engr. Ijlal Haider
University of Lahore, Lahore

3. Temperature Measurement
The human body temperature is a good indicator of the health and physiological performance of different parts of the human body.
Temperature indicates:
Shock by measuring the big-toe temperature
Infection by measuring skin temperature
Arthritis by measuring temperature at the joint
Body temperature during surgery
Infant body temperature inside incubators
Temperature sensors type
Thermocouples
Thermistors
Radiation and fiber-optic detectors
p-n junction semiconductor (2 mV/oC)

4. ROUTES TO MEASURE TEMPERATURE
Oral: By mouth
Rectally: By rectum
Axillary: Under the arm in the armpit
Tympanic: In the ear

5. Importance of Temperature
1st vital sign to any illness, system dysfunctionalities or fatalities
Fever associated to infection, severe trauma, allergies to medications & critical diseases
Hypothermia & Hyperthermia
Prevention of death & allow timely therapy for complications

6. Body Measurement Site

7. Body Measurement Site Best measurement site : Hypothalamus
Reflects the central or “Core” body heat
Base of the brain
Adjusting the temperature
Access is very inconvenient
Source:

8. Body Measurement Site Pulmonary artery (PA), Esophagus and Bladder
Involve invasive thermometry
Very impractical for routine use
Source:
Source:
Source:

9. Body Measurement Site Rectal Incapable of responding quickly
Source:
Rectal
Incapable of responding quickly
Higher measured temperature
Source:

10. Body Measurement Site The tympanic membrane (TM) i.e. Ear
Very near proximity to the hypothalamus
Reliable indicator
Infrared aural sensors are easily available
Source:
Source:

11. Advantages of IR Ear Thermometer
Rapid response rate (<5s)
Disposable plastic tips
Little or no contaminations
Pretty accurate & reliable
Safe
Easy to use
Thermopile sensors

12. TYPES OF THERMOMETERS
Digital Electronic: To be used for oral, rectal, and axillary
Thermoscan - Digital: To be used for tympanic
Mercury or glass: To be used for oral, rectal, and axillary

13. NORMS Orally: 97.6 - 99.6 degrees Fahrenheit
Rectally: degrees Fahrenheit
Tympanic - manufacturers say to measure as for rectal
Axillary: degrees Fahrenheit

14. WHAT THERMOMETER SHOULD BE USED?
Tympanic: Special device with plastic covers.
Electronic: All routes. Probes that are red in color for rectal temperatures; blue in color for oral and axillary.
Mercury: All routes. Red ends are rectal; blue ends oral and axillary.

15. DURATION FOR TAKING TEMPERATURES
Tympanic: As long as it takes to push a button
Electronic: Until the thermometer beeps
Mercury Oral: Three minutes
Mercury Rectal: Three minutes
Mercury Axillary: Ten minutes

16. BE CAREFUL ON RECTAL AND AXILLARY TEMPS
Always hold the thermometer in place while measuring both temperatures
Always use lubricant with rectal temperatures
Always remove clothing around axilla

17. READING THE THERMOMETER
Mercury Fahrenheit thermometers are read by degree and 0.2 of a degree
Long lines indicate degrees
Short lines indicate 0.2 of a degree
Four short lines between each long line (0.2, 0.4, 0.6, 0.8)

18. Thermocouple
Electromotive force (emf) exists across a junction of two dissimilar metals. Two independent effects cause this phenomena:
1- Contact of two unlike metals and the junction temperature (Peltier)
2- Temperature gradients along each single conductor (Lord Kelvin)
E = f (T T22)
T2  T1 T1
E = f(T1 –T2) A B
Advantages of Thermocouple
fast response (=1ms), small size (12 μm diameter), ease of fabrication and long-term stability
Disadvantages
Small output voltage, low sensitivity, need for a reference temperature

19. Thermocouple
Empirical calibration data are usually curve-fitted with a power series expansion that yield the Seebeck voltage.
T2  T1 T1
E = f(T1 –T2) A B
T: Temperature in Celsius
Reference junction is at 0 oC

20. Thermocouple Laws
1- Homogeneous Circuit law: A circuit composed of a single homogeneous metal, one cannot maintain an electric current by the application of heat alone. See Fig. 2.12b
2- Intermediate Metal Law: The net emf in a circuit consisting of an interconnection of a number of unlike metals, maintained at the same temperature, is zero. See Fig. 2.12c
Second law makes it possible for lead wire connections
3- Successive or Intermediate Temperatures Law: See Fig. 2.12d
The third law makes it possible for calibration curves derived for a given reference-junction temperature to be used to determine the calibration curves for another reference temperature. T1 T2 T3

22. Thermoelectric Sensitivity 
For small changes in temperature: T2 T1
E = f(T1 –T2) A B
Differentiate above equation to find , the Seebeck coefficient, or thermoelectric sensitivity. Generally in the range of V/oC at 20 oC.

23. Thermistors
Thermistors are semiconductors made of ceramic materials whose resistance decreases as temperature increases.
Advantages
Small in size (0.5 mm in diameter)
Large sensitivity to temperature changes (-3 to -5% /oC)
Blood velocity
Temperature differences in the same organ
Excellent long-term stability characteristics (R=0.2% /year)
Disadvantages
-Nonlinear
-Self heating
-Limited range

24. Circuit Connections of Thermistors
Bridge Connection to measure voltage R1 R2 R3 Rt va vb V
Amplifier Connection to measure currents

25. Radiation Thermometry
The higher the temperature of a body the higher is the electromagnetic radiation (EM).
Electromagnetic Radiation Transducers - Convert energy in the form of EM radiation into an electrical current or potential, or modify an electrical current or potential.
Medical thermometry maps the surface temperature of a body with a sensitivity of a few tenths of a Kelvin.
Application
Breast cancer, determining location and extent of arthritic disturbances, measure the depth of tissue destruction from frostbite and burns, detecting various peripheral circulatory disorders (venous thrombosis, carotid artery occlusions)

27. Radiation Thermometry
Sources of EM radiation: Acceleration of charges can arise from thermal energy. Charges movement cause the radiation of EM waves.
The amount of energy in a photon is inversely related to the wavelength:
Thermal sources approximate ideal blackbody radiators:
Blackbody radiator: an object which absorbs all incident radiation, and emits the maximum possible thermal radiation (0.7 m to 1mm).

28. Thermal Detector Specifications1 10 50
100
Fused silica
Sapphire
Arsenic trisulfide
Thallium
bromide
iodine
Wavelength, mm
Infrared Instrument Lens Properties;
pass wavelength > 1 m
high sensitivity to the weak radiated signal
Short response
Respond to large bandwidth
Thermal Detectors
-Law sensitivity
Respond to all wavelength
Photon (Quantum) Detector
-higher sensitivity
-Respond to a limited wavelength
Fig. a 1 2 3
Wavelength, mm
Indium antimonide (InSb)
(photovoltaic)
Lead sulfide (PbS)
All thermal detectors 20 60
100 4 5 6 7 8
Fig. a) Spectral transmission for a number of optical materials. (b) Spectral sensitivity of photon and thermal detectors.
Fig. b

29. Figure 2.15 Stationary chopped-beam radiation thermometer
Radiation Thermometer System
Figure 2.15 Stationary chopped-beam radiation thermometer

30. Application of Radiation Thermometer
Measuring the core body temperature of the human by measuring the magnitude of infrared radiation emitted from the tympanic membrane and surrounding ear canal.
Response time is 0.1 second
Accuracy of 0.1 oC

31. Fiber-Optic Temperature Sensors
Small and compatible with biological implantation.
Nonmetallic sensor so it is suitable for temperature measurements in a strong electromagnetic heating field.
Gallium Arsenide (GaAs) semiconductor temperature probe. The amount of power absorbed increases with temperature

32. Advantages of IR Ear Thermometer
Rapid response rate (<5s)
Disposable plastic tips
Little or no contaminations
Pretty accurate & reliable
Safe
Easy to use
Thermopile sensors

33. IR Technologies All Bodies emit E-wave & IR radiation IR radiation:
Emitted from an object
Reflected off a surface
Source: IR
visible
microwave
Shorter λ
Higher f
Source:
Humans, at normal body temperature, radiate most strongly in the infrared, at a wavelength of about 10 microns
Source:

34. IR Technologies Wavelength emitted depends on Tempt.
Hot objects emit more of their light at short wavelengths
Cold objects emit more of their light at long wavelengths

35. IR Technologies Total energy radiated: P = energy radiated per second
IR wavelength = cm
IR frequency = 300 GHz THz
Total energy radiated:
P = σ A T4
P = energy radiated per second
σ = x 10-8 watts/m2 K4 Stefan-Boltzmann constant, A = surface area of the radiating object
T = temperature (Kelvin scale)
Hot objects = Higher Power
Cold objects = Lower Power

36. IR Technologies IR tempt. measurement is very competent Fast Dynamic
Non-contact
Precise
High sensitivity
Higher security
Low power requirements
Low circuitry costs
Simple circuitry
high resolution
reasonable fields of view
Wide area of applications

37. THANK YOU
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