How do “smart” dishwashers know that the dishes are clean?

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Experts warn that pre-rinsing will confuse modern dishwashers because they will think the dishes are already washed … so how exactly do they know that dishes are / aren’t washed?

In: Technology

They do a pre-wash cycle that rinses the dishes with plain water to see how dirty the water gets (basically shine a light through it) during this cycle. It then works out how dirty they are likely to be.

That is also why you put the detergent in a closed receptacle in the door – it doesn’t drop into the water until after the pre-wash.

They don’t necessarily “know” that the dishes are clean. There are just time-based rotating jet sprays, bottle sprays and other sprays which “assume” the dishes are clean after that time.
Of course, this configuration varies machine to machine but basic functionality stays time-based.

They have a sensor that measures the opacity of the water. As more food gets washed off the dishes into the water, it becomes darker and lets less light through which is what the sensor measures. Its a pretty crude method that allows the machine to roughly estimate how heavy the load is and therefore how long the washer needs to give for the enzymes/chemicals in the tablet to break everything down.

Pre-rinsing is generally a waste of time. This removes the food particles from the water which are actually part of the scrubbing action – so no food particles = worse cleaning. Certain things like oatmeal/porridge might benefit from a quick blast under the tap to loosen any stuck on thick bits.

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