[sdiy] How to explain how negative feedback lowers noise?

[Gordonjcp]

On Mon, Mar 22, 2021 at 06:40:52PM +0100, cheater cheater wrote:

> feedback and not some form of other regulation. What's a simple
> /physical/ negative feedback?

The throttle on your lawnmower.  The throttle cable has a spring that pulls the throttle butterfly in the carb open, and a wire link to a flappy thing beside the cooling fan.  The faster the engine goes, the more the cooling fan blows on the flappy thing, which pulls the throttle closed against the spring.

When you hit a big divot of couch grass with the blades the engine revs drop, the cooling fan doesn't blow as hard, and the flappy thing gets pulled in by the spring opening the throttle.  As the engine speeds up it blows the flappy thing back again and pulls the throttle shut until the revs settle, with the engine making more power.

Once the blades have chewed their way through the couch grass the engine will rev up freely, the flappy thing will get blown out further, the throttle will close, and the revs will stabilise again.

When you're done you push the throttle to idle relaxing the tension on the spring (your control input) and the flappy thing will blow further out again because the spring isn't holding it, and close the throttle.

-- 
Gordonjcp