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Gas sensors, cont.
1
Modulation of sensors working temperature
400 ppm NO2
1000 CO + 400 NO2
air
1000 ppm CO
Pulse power supply of the sensors
heater
2
Pellistor – type sensors
Pellistor wit a surface catalyst
(diam. ca.1 mm)
Pellistor fixed in an encapsulation
3
Thermoconductometric sensors
(catharometers)
T
G  2
d0 M 0
λG - heat conductivity of a gas
M0 – molecular weight
d0 - molecule diameter
SEM picture of the flow channel with
suspended Pt thermoresistor
(magnification 212 x)
μTAS with separation column and TCD detector for the
analysis of chemical composition of a gas mixture
4
Electrochemical sensors
E
RT
p
ln
n F pR
Lambda sensor characteristics at a
working temp. ca. 600oC.

A/ F
15
λ – air excess coefficient
A – quantity of air
F – quantity of a fuel
Oxygen Lambda sensor of
the finger type installed in
an exhaust pipe.
5
Electrochemical amperometric sensors
Oxygen sensor with
a current limit caused
by a slit.
Thin film amperometric sensor with a current
limit due to chemical reactions.
6
Optical sensors
Two-diode system for absorption
measurement in the NIR region
Methane absorption in a main
abs. band 3200 – 3400 nm;
1 – diode LED1,
2 - diode LED2,
3 - detector
7
Optical sensors
Integrated fluorescence sensor coupled
with a μTAS microchannel structure.
Absorption spectrum A
and fluorescence emission of DPB
compound in nitrogen atmosphere B
and oxygen atmosphere C .
8
Structues basd on the field effect
MISFET type transistor as gas
sensor.
Gate metal – mostly Pd
Change of the threshold
voltage of a FET transistor as
a consequence of interaction
with a gas atmosphere.
9
Structues basd on the field effect
Mechanism of detection of hydrogen molecules
and other hydrocarbons by a thick palladium
gate.
10
MOSFET arrays
Nordic Sensor
4 MOSFET-s with
cathalytic gate in a
micromachined structure:
1 – MOSFET
2 – Al
3 – PECVD nitride
4 – LPCVD nitride
Power consumption ca. 100 mW at 200oC.
11
Organic composites
Cyrano Sciences Sensor Technology
Thin layer of a composite : conducting carbon in a polimer matrix
12
Measurement with the help of sensor array
Gas
mixture
Sensor 1
Sensor 2
Calculation block
(microprocessor
with software)
Calculated
concentrations
Meter for measurements of CO and C3H8 concentrations
in a mixture.
13

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