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Delphi's fluid sensor "could replace existing devices"

Delphi has a new sensor for measuring the fluid levels in automotive applications that it believes could replace almost all existing devices. It also has the potential to simplify manufacturing processes, Delphi says.

Fluid measurement is an important area for many processes in the automotive industry; but the most widely used fuel level sensor – a floating arm with contact resistance wipe – suffers when exposed to flex fuels with high ethanol content which can attack metal and cause corrosion.

Delphi’s “self-compensating capacitive fluid level sensor” is a “non-contact, non-moving part fluid level sensor” that works by having two receiver electrodes in its narrow tube design. The sensor has two raw signals and integrates the sine and cosine functions with the level changes, allowing the true level can be determined mathematically.

With this, it is possible to cancel the dielectric constant of the measurement, so that Delphi’s sensor does not need to be configured for use in different liquids, so the exact same sensor can be used for oil, transmission and brake fluid, petrol, diesel and ethanol flex fuels.

There are other technologies that are non-contact, such as ultrasonics, but the issue there is that you have to know the properties of the fluid to be able to measure it, and configure the sensor for each different fluid.

The drawback is that the sensor cannot be used in liquids with too high a conductivity such as water. But in these instances, says Delphi, you don’t need a dynamic sensor – just a switch that can tell you if you have enough water or too little.

Floating arm sensors usually comprise a ceramic PC board with silver palladium that is used to create a resistance. The floating arm is moving on top of those parts, changing the resistance value, so you can calculate the level of the liquid. The problem is that with ethanol fuels, it will attack the silver, causing wearing and degrading.

One solution is to use gold plated parts, but the cost can be prohibitive. Also, fuel tanks come in varying shapes and sizes, and if the arm does not fit correctly, it can cause accuracy problems. One area where Delphi is hoping to see success for the sensor is with motorcycles, where the shapes of the tanks make it hard to assemble floating devices.

The company believes the most benefit will be seen is where manufacturers are making different fuel systems for the same vehicle. Tanks for petrol, diesel and bio-ethanol versions of a car could potentially come with the sensor already installed without the need for configuration, simplifying manufacturing and parts supply for the aftermarket.

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