### infra

```Sensor Physics
Non contact temperature measurement
Dr. Seres István
SENSOR PHYSICS
Thermometers based on thermal
Electromagnetic
spectra
c = lf
Dr. Seres István
name
AC
Longvawe range (LW)
medium vawe range (MW)
short vawe range (KW)
Ultrashort range(URH)
Microvawes
Visible light
red
orange
yellow
green
blue
violet
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
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
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
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
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
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
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
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
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
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
Theory: gray body
Dr. Seres István
12
http://fft.szie.hu
SENSOR PHYSICS
Thermometers based on thermal
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
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