Lambda Sensor 2 - Finger-type Sensor
As long as it concerns the exact adherence to a certain Lambda value and not the actual measurement itself, then the finger-type sensor is used. This was the first of it's kind in the motor vehicle sector, and in the beginning, it was still unheated. Although basically, it can be manufactured to measure other Lambda values, in this case however, is only responsible for the adherence to Lambda =1 (stoichiometric mixture).
For the main part, the Lambda sensor consists of a gas-impervious ceramic body made of Zirconium-oxide (brown part on the left), onto which, inside and outside, an electrically conductive, gas-permeable Platinum coating (in red) is vapour-deposited. One part is connected to the outer casing (earth) and the other, through a heat resistant tube, is connected to the control device. The outside of the ceramic body is exposed to the exhaust gas (grey), which swirls around it, while the inside is linked to the outside air (light blue). As a protection against impact stress, sudden temperature changes and combustion residue, in the exhaust pipe there is also a metal cover with a specially formed opening for the exhaust gas.
During operation, at 280 to 300°C, a difference in the oxygen content between the exhaust gas and the open air develops between the inner and the outer Platinum coating. Although the ceramic material is permeable for oxygen, it's electrons are kept out. Thus, the Lambda sensor tension is formed. The richer the mixture is, the lower the amount of oxygen there is in the exhaust gas.
In order to be able to reach the operational temperature as quickly as possible, even when mounted further away from the engine, most Lambda sensors are heated (in dark red), this is why they have two additional connections. If, when disconnected, the Ohmmeter for the heating shows approx. 2 - 15 Ohm at 20°C, then the heating is functional. In the event of fault indications concerning the Lambda sensor, the heating should always be examined. Should it's fuse blow noticeably often, then one shoud check to see what else is connected to this particular fuse as well. 01/14