Hi,
We don't know how your applicatio looks like, therefore we can only assume.
It's on you to provide good information, pictures, drawings....
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You said the water on the lens is the problem.....so IP67 (water inside the case) has nothing to do with the actual problem.
Otherwise you should give us related informations.
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Protecting tube:
I assume the water drops are moving in random direction.
And i assume the water can hit the lens from +/-90° horizontal direction and +/-90° vertical direction.
With a protecting tube you can narrow this angle, maybe to +/-3° or so, wich decreases the chance that water hits the lens to less than 1% than before..
Isn't this an improvement?
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Air burst:
Is there a solution that can avoid water between sensor lens and reflector?
I don't think so. So we have to live with that, but we can reduce the chance of an error. Not to zero.
I don't know how often actually there is the chance of an error...but I assume a short burst (100ms) every some seconds can reduce the chance of an error, or at least automatically removes the error without dusturbing the optics between sensor and reflector(in opposite to wiping clean the lense)
Klaus