Detect liquid on steel plate

What technique would you use to detect how large area of a steel plate is covered by ketchup or a similar liquid? Is capacitive sensor appropriate?

Some sort of photo-interpretation - on a PC, not an Arduino ?

…R

Ultrasound/piezo.

Glue a piezo-disk to the plate underside, set up an oscillator, and record the shift in amplitude/frequency when something is put on the plate.

// Per.

is the plate heated? if so to which temperature?

Is capacitive sensor appropriate?

No.

svecoldr: What technique would you use to detect how large area of a steel plate is covered by ketchup or a similar liquid? Is capacitive sensor appropriate?

If you know the temperature of the plate and the density, viscosity and surface tension of the liquid at that temperature, all you need to measure is the extra weight that's added to the plate by the liquid. You can then use the density to work out the volume of the liquid and the viscosity and surface tension to calculate its spread over time. All this assumes that the plate is dead level and that the liquid is applied to the plate in only one place.

Or you could just use a squeegee to spread the ketchup evenly over the plate for 100% coverage....

1- is the plate heated ? 2- dimensions ? 3-- reason for wanting to do this ? 4- budget ? 5- time frame ? (how soon do you need it )