Some of the S/X still had physical rain sensors which are the correct solution to this problem, but Elon is maniacal about cost cutting and doesn't think deeply or listen to his engineers so there you go. Physical rain sensors work reliably so nobody complains if it goes on.
Sometimes if you clean the windscreen in front of the camera very well it can help with the problem, because it's trying to compensate by analyzing the front camera's images. It might help a little bit, but not reliably.
Since the focus of cameras (200m+) is not at the depth of the rain (0.5 cm), it can only try to detect rain by subtle features in the images like distortion or halos which may, or may not, be picked up my the machine learning classifier. Also the vision detection works better after it has seen moving images for a few seconds, so I've seen it freak out when first turned on then get better and slow down the wipe rate.
In Autopilot, you can hit the button on the left stalk and then manually turn the wipers to I (of IV), but not to off. That may make it less annoying.
PS: how physical rain sensors work: they emit an infrared light directly onto the glass and there is a close by photodetector. The normal dry case is set up to have total internal reflection from the outer edge of the glass but water drops on the windshield change this reflective behavior which can be picked up by the sensor. This works very reliably to detect stuff directly on the glass, and not be sensitive to anything else on the background.
There are many different techniques that automakers have experimented with to eliminate or substitute the wiper system. A rain sensor is a fairly recent addition to the windshield of a car. The technology has been around since the 50’s, however,…
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