Electrolux Appendix D - Lambda Probe, AOSQ OVENS - Service manual 593804600 - ENG

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AOS_Q OVENS – Service manual

(593804600 - ENG)

APPENDIX D – LAMBDA PROBE

In the lev. A ovens the lambda probe is used to measure the humidity. How does it work?

The lambda probe permits measurement of oxygen concentration through a solid electrolyte (ceramic element)

The ceramic part of the probe is in the form of a tube closed at one end. The inside and outside surfaces of the ceramic sensor have a microporous platinum layer (electrode). The platinum layer, which is in contact with the analyzed gas, is covered with a highly porous protective ceramic layer.

The ceramic sensor (ZrOB2 – solid electrolyte) is heated from inside by means of a ceramic heater so that the temperature of the sensor ceramic remains above 350 °C. Starting from 300°C, the ZrOB2B sensor becomes conductive for the oxygen ions so that if there is a different concentration of oxygen at the two sides of the sensors (one side is in contact with the analyzed gas, the other side is in contact with the external), a voltage is generated.

Since the Oxygen/Nitrogen ratio in the air is constant, a measurement of the concentration of oxygen enables the percentage of a third gas (in this case water vapor) to be determined. In fact the addition of a third gas to a sample of air has the effect of reducing in a proportional manner the presence of oxygen and nitrogen so that, as said, determining the relative concentration of oxygen allows the amount of the third introduced gas of the mixture to be determined (see the diagram).

1 2 3 4 5

100
90
80						water
70
60
50
40			nitrogen
30
20
10		oxygen
0
0	10	20	30	40	50	60	70	80	90	100
				water percentage

Connections on the lambda probe:

ƒPin 1: not used

ƒPin 2-3: connections to the main board (connector X23)

ƒPin 4-5: connections to the switching feeder

File: AOS ONE service manual (ENG).01.doc ©Copyright 2007 by Electrolux Professional P.24/31