Oil condition sensor based on corrosiveness

The proposed oil condition sensor is used to measure the corrosiveness of lubricants. For this purpose, a metal film acting as sacrificial layer is exposed to the lubricant. Due to the corrosive attack by the oil, a material loss of the metal film occurs which can be monitored by electrical means.

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Fig. 1. Schematic setup of the proposed oil condition sensor for corrosiveness using capacitively coupled electrodes

Previous concepts measured the electrical resistance of a metal film (Agoston et al., 2005a; Agoston et al., 2007). This assembly requires a resistive connection between metal film and electronic measuring equipment. Experiments with this type of sensor setups clearly showed that corrosion occurred preferably at these contact points of the sacrificial layer. Furthermore, corrosion of the sacrificial layer was observed as even loss of material or as blotch type corrosion. In the latter case, the position of the blotches or spots on the sacrificial layer showed an influence on the sensor signal. (Agoston et al., 2006)

In order to overcome these shortcomings, a novel readout method was presented (Dorr et al., 2009) which is based on corrosion measurement without the need of an electrical contact using capacitively coupled planar electrodes. As shown in Figure 1, the novel sensor consists of an inert nonconductive substrate with a metal film as sacrificial layer on one side which is directly exposed to the corrosive medium. The material loss due to corrosion is monitored by measuring the capacitive coupling between the sacrificial layer and the readout electrodes on the backside of the substrate.

Using this setup, no resistive contact between the sacrificial layer and the electronic measurement equipment exists and hence no contact points with the danger of undesired corrosive attack exist, too.

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