Sensor Physics
Non contact temperature measurement
Dr. Seres István
SENSOR PHYSICS
Thermometers based on thermal
radiation
Electromagnetic
spectra
c = lf
Dr. Seres István
name
AC
Radiovawes
Longvawe range (LW)
medium vawe range (MW)
short vawe range (KW)
Ultrashort range(URH)
Microvawes
Infrared radiation (IR)
Visible light
red
orange
yellow
green
blue
violet
Ultraviolet radiation (UV)
Röntgen radiation
Gamma-radiation
2
vawelength
> 3000 km
< 30 km
< 10 km
< 650 m
< 180 m
< 10 m
300 µm - 30 cm
< 1,0 mm
< 780 nm
640 - 780 nm
600 - 640 nm
570 - 600 nm
490 - 570 nm
430 - 490 nm
380 - 430 nm
< 380 nm
< 1 nm
< 10 pm
Frequency
< 100 Hz
> 10 kHz
> 30 kHz
> 650 kHz
> 1,7 MHz
> 30 MHz
1 GHz - 1 THz
> 300 GHz
> 384 THz
384 - 468 THz
468 - 500 THz
500 - 526 THz
526 - 612 THz
612 - 697 THz
697 - 789 THz
> 789 THz
> 300 PHz
> 30 EHz
http://fft.szie.hu
SENSOR PHYSICS
Thermometers based on thermal
radiation
Theory: black body
Definition: it absorbs all the EM radiation
Its model: hole in a wall
Dr. Seres István
3
http://fft.szie.hu
SENSOR PHYSICS
Thermometers based on thermal
radiation
Theory: Planck law for radiation
The power emitted by the unit surface of a
T temperature object :
J l , T  
Dr. Seres István
2 hc
l
5
2
1
hc
e l kT  1
4
http://fft.szie.hu
SENSOR PHYSICS
Thermometers based on thermal
radiation
Theory: Planck law for radiation
If
C2
e l T  1 ,
than the law can be written as:
J l , T d l  C 1 l e
5

C2
lT
dl
/the difference is < 1%, if lT < 3000mm∙K/
Dr. Seres István
5
http://fft.szie.hu
SENSOR PHYSICS
Thermometers based on thermal
radiation
Theory: Planck law for radiation
J l , T d l  C 1 l e
5

C2
lT
dl
Where (for what l) is the maximum value of
the function? /the derivetive there is zero/
d ( J l , T )
dl
Dr. Seres István
5

d ( C 1l e
dl
6

C2
lT
)
0
http://fft.szie.hu
SENSOR PHYSICS
Thermometers based on thermal
radiation
Theory: Wien law
Where (for what l) is the maximum value of
the function? /the derivetive there is zero/
d ( J l , T )
dl
5

d ( C 1l e

C2
lT
)
dl
6
C1  l e

C2
lT
C
C
 2
 2

C2
6
5
lT
lT

 C 1  5l e
l e
 2

l T

C2 

5
0
lT 

l T  C  2 ,898  10
Dr. Seres István

0


7
3
mK
http://fft.szie.hu
SENSOR PHYSICS
Thermometers based on thermal
radiation
Theory: Wien law
l T  5 C 2  2 ,8978  10
3
mK
• the color of the warming iron is changing
• the blue stars are hotter
Dr. Seres István
8
http://fft.szie.hu
SENSOR PHYSICS
Thermometers based on thermal
radiation
Theory: Stefan-Boltzmann law
J l , T d l  C 1 l e
5

C2
lT
dl
How much is the integral of the function
( 0< l <∞)? – /partial integration/
W  T
4
= 5,67∙10-8 W/m2K4St
Dr. Seres István
9
http://fft.szie.hu
SENSOR PHYSICS
Thermometers based on thermal
radiation
Theory: Stefan-Boltzmann law

W  K  T  Tk
4
4

= 5,67∙10-6 W/m2K
Tk the temperature of the environment,
K – depends on the surfaces and distances
Dr. Seres István
10
http://fft.szie.hu
SENSOR PHYSICS
Thermometers based on thermal
radiation
Theory: gray body
Kirchhoff law
E ( , T ) 
e( , T )
Independent from the material
a (  , T ) properties
Dr. Seres István
11
http://fft.szie.hu
SENSOR PHYSICS
Thermometers based on thermal
radiation
Theory: gray body
Dr. Seres István
12
http://fft.szie.hu
SENSOR PHYSICS
Thermometers based on thermal
radiation
Infra thermometer
The effect of the air, the transmission
coefficient of the air at different vawelengths
Dr. Seres István
13
http://fft.szie.hu
SENSOR PHYSICS
Thermometers based on thermal
radiation
Infra thermometer
Effektív vawelength
The calibration function of an
infra thermometer:
Where N is:
Dr. Seres István
14
http://fft.szie.hu
SENSOR PHYSICS
Thermometers based on thermal
radiation
Infra thermometer
Main parts:
• detector
termopile
(seriel connection of thermocouples,
photo-detektor –photovoltaic pyro-electric
• optical system
Dr. Seres István
15
http://fft.szie.hu