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Speed is nothing but the distance travelled by any object in a unit of time. It tells us how fast or slow the object is moving.
A speedometer is a device which we encounter daily and is present in all vehicles, telling us the speed at which the vehicle is moving. It is usually present in combination with the odometer. An odometer is a device that determines the distance travelled by any wheeled vehicle.
Charles Babbage was the first person who invented the earliest speedometer for locomotives (rail engines). Croatian Josip Belusic 1888 got the credit for inventing the first electric speedometer. The device is now globally present in all vehicles. It is also known by other names, such as the device for measuring the speed of boats is called ‘pit log,’ whereas the device that measures the speed of an aircraft is called ‘aircraft indicator.’
Let’s learn about the working and uses of the speedometer.
Types of Speedometers
Based on their mechanism and function, speedometers can be of the following two types:
- Analogue Speedometers
- Digital Speedometers
Analogue Speedometer
This type of speedometer shows the speed of the vehicle by pointing a needle on the dial. The needle remains connected to the gearbox and has many parts that work together.
Working of Analogue Speedometers
On turning over the engine, the wheels spin around due to the turning of the driveshaft. The driveshaft powers the cable of the speedometer. Therefore, it also turns on turning the driveshaft. This cable will then spin the magnet at the same speed within the speed cut, and thus, the magnet will start to rotate continuously in a single direction (counter-clockwise).
These magnets will be responsible for creating eddy currents (an electric current that is induced as a result of an alternating magnetic field) in the speed cup. This current will cause the speed cup to rotate in the same direction (counter-clockwise) to reach the magnet. A layer of air is always present between the magnet and the speed cup. The speed cup gets restrained due to the tightening of the hairspring. As a result, the cup will only be able to turn a little distance. On turning, the speed cup will lead to turning the pointer up the dial, which will indicate the speed of the vehicle (car).
Digital Speedometer
Speedometers in some modern vehicles are digital (without needles). Based on the working of chips and sensors, these speedometers only display the speed on the LCD screen. They measure the number of rotations by the wheel; hence, they can also display the readings of the odometer (distance travelled).
Parts of a Digital Speedometer: Magnet, magnetic sensors, LCD, and an electric circuit.
Working of Digital Speedometers
The magnets remain connected to the outer shaft through magnetic sensors on either side. An electric pulse generates within the circuit whenever the magnet crosses the sensors. The electric circuit is responsible for converting this pulse into speed. As a result, it displays the speed on the LED display.
Calibration of a Speedometer
Calibration of speedometers is necessary to make sure that torque due to the magnetic field correctly shows the car’s speed. Calibration adjusts several variances. For instance, a car having a tire of a larger diameter will cover more distance than that of a smaller diameter. The manufacturer of the vehicle does the calibration by setting up this device to stay in tune with the tire size, factory-installed ring, and pinion ratio.
If your vehicle has fallen out of factory specifications, then you need to calibrate it. You can calibrate it either by manipulating the permanent magnet or by hairspring, or both. You can easily change the strength of the magnetic field by using a powerful electromagnet. This electromagnet will adjust the strength of the magnet of the speedometer (until the input from the rotating drive cable and the needle match).
However, you must know that none of these speedometers show 100 per cent accuracy. Therefore, it is necessary to calibrate them if there is any modification in the cars.
Conclusion
An instrument or a device that measures the speed of any vehicle is called a speedometer. It usually comes in combination with an odometer which evaluates the distance travelled by the vehicle.
Charles Babbage was the first person to invent the earliest speedometer for locomotives (rail engines). However, Josip Belusic invented the first electric speedometer in 1888. Based on their mechanism and function, speedometers can either be analogue or digital.
Analogue speedometers consist of needles that point to the speed of the vehicle. On the other hand, a digital speedometer only shows the speed on the LED display. Calibration of the speedometers is necessary to make sure that torque due to the magnetic field shows the car’s speed correctly.
