I've been looking into a specific piece of equipment called a 'present weather sensor' that uses a sensor looking at a sample in air to determine the visibility and current weather (i.e. rain, snow, etc.). From what my research, I've found a expired patent from a company that currently makes these sensors, Vaisala. This is the expired patent. I also found a new patent for what seems to be the same exact thing here. As I mentioned before, this company still makes these sensors. However, there are a few other companies making seemingly identical pieces of hardware, like Campbell Scientific, and Biral.

Could someone explain how these companies are able to produce and sell these without infringing on the patents of the original company?

  • 1
    Do you have any indication that they are not simply paying a license for their use of the patented technology?
    – tripleee
    Jan 4, 2022 at 8:06
  • @tripleee I hadn't considered that possibility. What advantage would licensing give either parties considering the parent company is already manufacturing them?
    – Zero
    Jan 4, 2022 at 8:10
  • That's the purpose of patents. If the licensee can make it cheaper, they will probably win over some customers. If they can add the technology as a new feature to an existing product, they can prevent customers from switching, and improve the utility to customers of that product. The benefit to the licensor should be obvious; they get a slice of the profit even when a competitor gets the sale.
    – tripleee
    Jan 4, 2022 at 8:13
  • It may be that the competition’s products only use technology from the expired patent.
    – George White
    Jan 5, 2022 at 4:11

1 Answer 1


The first patent cited is expired. Any company can now produce the invention as described in that patent. The second patent is for an apparently improved forward scatter sensor. If you carefully read the claims, you will see that they aren't exactly the same at all. Companies must either avoid infringing on the second patent or else obtain a license. Companies very often out-license technologies that they produce. The idea is that the licensing income more than makes up for the lost sales.

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