How does a vehicle’s speedometer tell how fast it’s moving?

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How does a vehicle’s speedometer tell how fast it’s moving?

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2 Answers

Anonymous 0 Comments

There is a little gear in the end of the transmission that spins at the same speed as the wheels (depending on the design) if we know how big the gear is and how big the wheels are then we can do a little math and figure out how fast the car is going.

Anonymous 0 Comments

There are several designs for modern electronic speed sensors. For example shine a light through a rotating plate and detect the amount of light comming through. When the plate rotates different slots cut into it will produce signals at different rates. By counting these signals you can get a speed reading. Similarly you can record the reflected light and either holes in the plate or different paints on the plate will produce the signals. Another possability is to use different magnetic sensors like reed switches or hall effect sensors to detect the changing geometry of some metal. The on board computer will count the signals and convert them to a speed for display. Older cars with manual instruments would have a mechanical system in the guage which pushed the guage a bit up for every revolution of the wheels (either using an electric cable with the signal or using a rotating wire to the instrument panel). A dampened spring would pull the guage down to zero. The faster the wheels spun the higher the guage were pushed.