The speedo is a gauge that is used to indicate the velocity at which a motor vehicle is being driven and most modern speedos are electric. They operate by way of a sensor that is mounted in the vehicle’s transmission, which delivers electronic pulses to the car’s onboard computer. The computer is able to convert the pulse signals that it receives into speed, which is then shown on the speedometer clock, which may be either analogue or digital.
The sensor is normally made up of a collection of magnets or a metal disc with teeth. As the drive shaft turns, these magnets or teeth, according to the type of sensor, produce the pulse signals that are sent to the computer. In newer versions of the electric speedo system the pulses are sent from sensors within the vehicle’s anti-locking brake system. The modern electric speedo, unlike older versions, has the ability to display the speed at which the vehicle is being driven when it is in reverse gear.
The electric speedo provides the driver with an accurate reading of the vehicle’s speed. As speed control is essential to driving a vehicle safely (and within legal speed limits) if a fault arises within the electric speedo system the vehicle should be taken for immediate repair and any faulty parts replaced.