A speedometer is an instrument used to measure the speed of a shaft or disc. Pressure gauges usually display revolutions per minute on a calibrated analog dial. With the help of the OEM speedometer, the driver can evaluate the "engine speed" and change the gear ratio accordingly. Each speedometer indicates the maximum RPM of that particular engine. Exceeding this limit may cause engine damage or complete failure.
Common types of speedometers are as follows:
Analog speedometer-including pointer and dial type interface. They have no rules for storing readings, nor can they calculate detailed information such as averages and deviations. Here, the speed is converted into a voltage by using an external frequency-voltage converter. Then display the voltage through an analog voltmeter.
Digital Speedometer-Includes LCD or LED readings and memory for storage. They can perform statistical operations and are very suitable for accurate measurement and monitoring of any time type. Nowadays, digital speedometers are more common. They provide digital readings instead of using dials and pointers.
Contact and non-contact speedometers-the contact type are in contact with the rotating shaft. The non-contact type is ideal for mobile applications and using lasers or optical discs. In the contact type, an optical encoder or a magnetic sensor is used. Both types are data acquisition methods.
Time and frequency measurement speedometer-both are based on measurement methods. Time measuring equipment calculates speed by measuring the time interval between input pulses; frequency measuring device calculates speed by measuring the frequency of input pulses. Time measurement speedometer is ideal for low-speed measurement, frequency measurement speedometer is ideal for high-speed measurement.
Early models of speedometers relied on gear-driven rotating mechanical drives, which were taken from certain moving parts of the engine, such as flywheels, camshafts, fan pulleys, etc. The drive rotates the magnet, which induces eddy currents in the aluminum disc, like a speedometer, but the scale is marked in revolutions per minute. Modern speedometers are electronic and are driven by low-tension "on and off" distribution points.