Intermittent Wipers

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How do the intermittent wipers work? Why is there is no timer setting...

The control unit is in the steering column.

The first "electronic" wiper to be used on a production car. (Citation needed)

On the intermittent setting, it "reads" the resistance between the wiper blade and the windscreen and adjusts the interval accordingly. It does this by passing the motor current through a small spiral of magnetic resistance wire next to a magnet. When the screen is wet, there is a low load on the motor and so the wire does not heat up and the circuit is left intact (so the wipers continue working nonstop). When the screen becomes dryer, the load on the wiper motor increases, requiring more current through the circuit and thus heating the wire past its Curie point. The wire moves away from the magnet which breaks the circuit via an attached contact point and stops the wipers until the wire cools down, re-magnetises, moves against the magnet and starts the wiper again. The drier the windscreen, the higher the load on the motor, and thus the frequency of cut-out increases.

See also