What does a car’s speedometer measure?

What does a car’s speedometer measure?

The speedometer in the car measures the speed of the car using the unit of kilometer per hour, or the unit of mile per hour, and it varies depending on the country the car is in.

  • Since the beginning of the era of cars, the presence of a speedometer in the car has increased the cost of the car, before the manufacture of the electronic speedometer, which was invented in 1935, and all car manufacturers worked at that time to integrate the speedometer. inside the car, and it is one of the devices that must be available inside the car.

The idea of ​​a speedometer in a car

The idea of ​​automobile speedometer is based on the connection between mechanical movement and magnetic field which generates electric current.When two strong magnets rotate fast and fast, a strong magnetic field is created which can generate energy if a metal rod is passed through this field. The intensity of this electric current increases as the intensity of the magnetic field increases due to the increase in the speed of rotation of the two magnets, and vice versa.

  • In the case of electronic speedometers, this type of new speedometer works in the process of measuring the speed of the car using a special sensor, so that the rotation that exists during the movement of the car generates a field magnetic and works to cause flashes that reach the computer inside the car.
  • The computer analyzes the number of signals coming to it from the sensor, so it measures the number of rotations of the car tires and the distance traveled by the car in general, and displays the result of this analysis on the screen in the front of the car in front of the driver of the car.
  • In this way, the meters measure the distances traveled by the car, and by using the coupling process that the meter performs to measure the distance traveled over time, it can thus measure the speed of the car.

How the speedometer works

The speedometer is basically to let the driver of the car know how fast he is going, so the driver may not feel how fast he is going and how dangerous it is sometimes, especially on highways, which makes the speedometer a simple and important indicator in controlling the speed of the car and informing the driver of the car how fast he is moving, so that he is not subject to legal liability, and accordingly , the car meter works in a simple way, and it is as follows .

  • Through the fuel combustion process that works to move the motion lists in the combustion chamber inside the car engine.
  • The driveshaft then transmits this motion from the engine to the wheels, spins those wheels, and moves the car.
  • And near one of the wheels, there’s a wire called a “speed cable.” The role of this cable is to rotate with the tire of the wheel, and it works to produce a magnetic field inside the cable, equal in speed to the speed of movement of the car tire, and equal to the direction in which he is moving.
  • Due to this magnetic field resulting from the rotational motion, the magnetic currents begin to cause an electric current, which increases as the speed of the car increases.
  • Thanks to the sensor located inside the meter for the intensity of the electric current, it analyzes it and displays the current speed at which the car is driving. When the speed of movement increases, the intensity of the magnetic field increases, therefore the electric current increases, and the indicator rises to higher numbers in the meter.

Inaccurate car speedometer

There may be errors that appear on the speedometer, with a maximum value of about 4% lower or higher than the current speed, and this usually occurs at low speeds, which means the car can go faster than what appears on the speedometer. , and the tires can also be the cause of this problem, because heavily inflated tires affect the speedometer reading, so the speed is measured based on the car’s factory tires.

The reasons for the failure of the car meter

There are many reasons for the odometer to malfunction, including the following.

  • Deviations occur in the speedometer when there are faults in the speedometer itself, whether due to problems with the speedometer cable connections or other miscellaneous faults.
  • If any of the valves or wires connected to the speedometer malfunction.
  • If a disturbance or malfunction occurs in the electronic control unit, which is the electronic brain of the car.
  • When the speed sensor is broken or injured.
  • Some of the roads the car travels on, especially those that are unpaved, or even poorly paved, negatively affect the car and can interrupt the speedometer, which is connected to the tires.
  • The climatic conditions in which the car is driven, the process of low or high temperatures can greatly affect the accuracy of the car odometer.

How to test speedometer accuracy

You can check the accuracy of your car’s speedometer using a small stopwatch, and in most phones it’s present as a companion app to its operating system, and it doesn’t have no need to be invited or searched, then you follow the following steps.

  • It starts counting when you pass the “kilometer or mile” sign while driving on the highway.
  • You stop the stopwatch immediately after reaching the next mark.
  • The second hand will indicate the size of the gear you are currently traveling at, so compare it with the speed displayed in front of you on the speedometer.

What are the other meters in the car?

Inside the car there are many gauges, among which are the following.

  • Fuel volume meter.
  • Oil pressure gauge.
  • Engine temperature gauge.
  • Tachometer

In the interior of modern cars, another set of meters is also available, including the following.

  • Car interior thermometer.
  • Pressure gauge located inside the tires.
  • Car engine torque meter.






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