1

Gas sensors, cont. 

2

Modulation of sensors working temperature

400 ppm NO2

1000 CO + 400 NO2

air

1000 ppm CO

Pulse power supply of the sensors heater

3

Pellistor – type sensors

Pellistor wit a surface catalyst(diam. ca.1 mm)

Pellistor fixed in an encapsulation

4

Thermoconductometric sensors(catharometers)

λG - heat conductivity of a gas

M0 – molecular weight

d0 - molecule diameter

μTAS with separation column and TCD detector for the analysis of chemical composition of a gas mixture

SEM picture of the flow channel with suspended Pt thermoresistor

(magnification 212 x)

020 Md

TG

5

Electrochemical sensors

Lambda sensor characteristics at a working temp. ca. 600oC. Oxygen Lambda sensor of

the finger type installed in an exhaust pipe.

/

15

A F λ – air excess coefficient A – quantity of air F – quantity of a fuel

lnR

RT pE

n F p

6

Oxygen sensor with a current limit causedby a slit.

Thin film amperometric sensor with a current limit due to chemical reactions.

Electrochemical amperometric sensors

7

Optical sensors

Two-diode system for absorptionmeasurement in the NIR region

Methane absorption in a main abs. band 3200 – 3400 nm;1 – diode LED1, 2 - diode LED2,3 - detector

8

Absorption spectrum A and fluorescence emission of DPB compound in nitrogen atmosphere B and oxygen atmosphere C .

Integrated fluorescence sensor coupled with a μTAS microchannel structure.

Optical sensors

9

Structues basd on the field effect

Change of the threshold voltage of a FET transistor as a consequence of interaction with a gas atmosphere.

MISFET type transistor as gas sensor.Gate metal – mostly Pd

10

Mechanism of detection of hydrogen molecules and other hydrocarbons by a thick palladium gate.

Structues basd on the field effect

11

MOSFET arrays

4 MOSFET-s with cathalytic gate in a micromachined structure:1 – MOSFET2 – Al3 – PECVD nitride4 – LPCVD nitride

Power consumption ca. 100 mW at 200oC.

Nordic Sensor

12

Organic composites

Cyrano Sciences Sensor Technology

Thin layer of a composite : conducting carbon in a polimer matrix

13

Measurement with the help of sensor array

Calculation block (microprocessor with software)

Sensor 1

Sensor 2

Meter for measurements of CO and C3H8

concentrations in a mixture.

Gasmixture

Calculatedconcentrations