How does a speedometer work?

Question

And what exactly does a speedometer tell you? I would have thought it's only possible to know your speed over a certain time and distance, not in any single instance?

Furthermore how can it tell you how fast you are actually travelling as opposed to simply how fast your wheels are turning?

Answer 1

By knowing the RPM of your wheels and the circumference of the wheels you can then calibrate and extrapolate the MPH. It is very easy using electronics to do this and not too difficult using gears and flex extensions to mechanically drive a small generator that puts out a voltage based upon the RPMs of the Generator. The output of the small generator then is routed to an electromagnetic device at the Speedometer that then shows the MPH that the car is going.

Answer 2

Speedometer
A device for indicating the speed of a vehicle. There are three types of speedometers in general use: mechanical analog, quartz electric analog, and digital microprocessor.

The mechanical analog speedometer is driven by a cable housed in a casing and connected to a gear at the transmission. This gear is designed for the particular vehicle model, considering the vehicle's tire size and rear axle ratio. In most cases, the speedometer is designed to convert 1001 revolutions of the drive cable into registering 1 mi on the odometer, which records distance traveled by the vehicle. The speed-indicating portion of the speedometer operates on the magnetic principle. In the speedometer head, the drive cable attaches to a revolving permanent magnet that rotates at the same speed as the cable. Floating on bearings between the upper frame and the revolving permanent magnet is a nonmagnetic movable speed cup. The magnet revolves within the speed cup, producing a rotating magnetic field. The magnetic field is constant, and the amount of speed cup movement is at all times in proportion to the speed of the magnet rotation. A pointer, attached to the speed cup spindle, indicates the speed on the speedometer dial.

The quartz speedometer utilizes an accurate clock signal supplied by a quartz crystal, along with integrated electronic circuitry to process an electrical speed signal. This signal is generated by a permanent-magnet generator mounted in the transmission. This permanent-magnet generator, designed to be used with both quartz and digital speedometers, provides a sinusoidal speed signal that is proportional to vehicle speed at the rate of 4004 pulses per mile (2503 per kilometer).

In the digital microprocessor speedometer, the vehicle speed is monitored by the permanent speed sensor mounted in the transmission. The signal is transmitted to the microprocessor where the counter converts the speed signal to a digital signal and stores it in memory. The timing circuit has the capacity to handle the counter and memory storage in less than 0.25 s. Memory circuit signals are sent to the electronic display circuit, which selects the display numerals representing the vehicle's speed, according to the number of pulses received from the speed sensor. See also Automotive transmission; Electronic display.

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Answer 3

It is based on the pascal or lever principle.As you pull little bits of energy on the brake system,it will transfer through fluid to the wheel that can stop down the high speed car!It tell us about the speed.Since your car is travelling, the wheel surely will in the turning state, and therefore it will lenghten the needle of speedometer that result in your speed!

Answer 4

It used to be via a small gear on the side of a gearbox and transmitted up a cable to the speedo, now it's done by a small generator on the engine wired to an electronic speedo.
It's a matter of ratios that has been calculated by the designing engineers.
The speed of the wheels is immaterial because if you put larger or smaller tyres on, it affects the speed and fuel consumption.

Answer 5

Speed = Distance / (divided) by time!
It records the speed at which you are going which takes in to effect the simple calculation that you follow. A science theory from school

Answer 6

Yes. It measures how fast the wheels are turning and convert to mph. The conversion is done via calibration of the meter..

Answer 7

A spedometer is calbrated to accuracy during production. Speed is measured against resistance.

Answer 8

Firstly, you have answered your own question, if you know yr
speed over a definate distance, that should equte!!
Secondly, have you ever been to a Gym ? ? if not please
try, it will get you out and explain all !!