Transcript T - Engr. Ijlal Haider

1
In The Name of Allah
The Most Beneficent The Most Merciful
ECE 4550:
Biomedical
Instrumentation
Lecture:
Temperature
Measurement
Engr. Ijlal Haider
University of Lahore, Lahore
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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)
ROUTES TO MEASURE
TEMPERATURE
 Oral:
By mouth
 Rectally:
 Axillary:
By rectum
Under the arm in the armpit
 Tympanic:
In the ear
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
Body Measurement Site
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:
http://nl.wikipedia.org/wiki/Hypothalamus
Body Measurement Site
 Pulmonary
-
artery (PA), Esophagus and Bladder
Involve invasive thermometry
Very impractical for routine use
Source:
http://catalog.nucleusinc.com/generateex
hibit.php?ID=2639&ExhibitKeywordsRaw=&T
L=4294967295&A=2
Source: http://health.allrefer.com/picturesimages/esophagus.html
Source:
http://hon.nucleusinc.com/generateexhibit.php
?ID=4537&ExhibitKeywordsRaw=&TL=4294967295
&A=1027
Body Measurement Site
 Rectal
-
Incapable of responding quickly
Higher measured temperature
Source:http://www.patienthealthinternational.com/nc
mprintchapter.aspx?type=article&param=500830
Source:
http://www.amazon.com/exec/obidos/tg/detail//B0002AHVZU/103-6985049-8479059?v=glance
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:
http://www.emedicine.com/ent/images/1117ExtEar.jpg
Source:
http://www.actamed.co.uk/ProductDetails.asp?
CategoryID=2&ProductCategoryID=43&ProductI
D=206
Advantages
of
IR
Ear
Thermometer
 Rapid response rate (<5s)
 Disposable
 Little
plastic tips
or no contaminations
 Pretty
accurate & reliable
 Safe
 Easy
to use
 Thermopile
sensors
TYPES OF THERMOMETERS
 Digital
Electronic: To be used for oral,
rectal, and axillary
 Thermoscan
tympanic
 Mercury
- Digital: To be used for
or glass: To be used for oral,
rectal, and axillary
NORMS
 Orally:
97.6 - 99.6 degrees Fahrenheit
 Rectally:
99.6 - 100.6 degrees Fahrenheit
 Tympanic
rectal
 Axillary:
- manufacturers say to measure as for
96.6 - 98.6 degrees Fahrenheit
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.
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
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
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)
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)
T1
A
B
B
T2  T1
E = f(T1 –T2)
2- Temperature gradients along each single conductor (Lord Kelvin)
E = f (T12 - T22)
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
Thermocouple
Empirical calibration data are usually curve-fitted with a power series
expansion that yield the Seebeck voltage.
T1
A
B
B
T2  T1
E = f(T1 –T2)
1
E  aT  bT 2  ....
2
T: Temperature in Celsius
Reference junction is at 0 oC
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.
1
1
E23  E13  E12  a1T3  b1T3  a1T2  b1T2
2
2
T1
T2
T3
Thermoelectric Sensitivity 
E  T
For small changes in temperature:
T1
1 2
E  aT  bT    
2
A
B
T2
E = f(T1 –T2)
Differentiate above equation to find , the Seebeck coefficient, or
thermoelectric sensitivity. Generally in the range of 6.5 - 80 V/oC at 20 oC.
dE

 a  bT    
dT
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
Circuit Connections of Thermistors
Bridge Connection to measure voltage
R1
V
vb
va
R2
Amplifier Connection to measure currents
R3
Rt
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)
http://en.wikipedia.org/wiki/Blackbody_radiation
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:
E
1

1 eV  1.602 10
19
J
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).
Thermal Detector Specifications
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
Fused silica
100
Sapphire
Arsenic trisulfide
Thallium
bromide
iodine
50
10
0
1
10
Wavelength, m
100
Fig. a
All thermal detectors
100
Indium antimonide (InSb)
(photovoltaic)
60
Fig. a) Spectral transmission for a
number of optical materials. (b)
Spectral sensitivity of photon
and thermal detectors.
Lead sulfide (PbS)
20
0
1
2
3
4
Wavelength, m
5
6
7
8
Fig. b
Radiation Thermometer System
Figure 2.15 Stationary chopped-beam radiation thermometer
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
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
Advantages
of
IR
Ear
Thermometer
 Rapid response rate (<5s)
 Disposable
 Little
plastic tips
or no contaminations
 Pretty
accurate & reliable
 Safe
 Easy
to use
 Thermopile
sensors
IR Technologies


(a)
(b)
All Bodies emit E-wave & IR radiation
IR radiation:
Emitted from an object
Reflected off a surface
Shorter λ
visible
IR
microwave
Source: http://en.wikipedia.org/wiki/Infrared_radiation
Higher f
Humans, at normal body
temperature, radiate most
strongly in the infrared, at a
wavelength of about 10
microns
Source:
http://coolcosmos.ipac.caltech.
edu//cosmic_classroom/ir_tutori
al/what_is_ir.html
Source:http://imagers.gsfc.
nasa.gov/ems/infrared.html
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
IR Technologies
 IR
wavelength = 0.000075 - 0.1 cm
 IR frequency = 300 GHz - 400 THz
 Total
energy radiated:
P = σ A T4
P = energy radiated per second
σ = 5.6703 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
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
THANK YOU
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