Design and construction of microprocessor based remote speed measurement, monitoring and control of d. C motor

2.0 LITERATURE REVIEW
2.1 History of Digital Tachometer
According to the “Tachometer – Facts from Encyclopaedia”(Yahoo! Education” Educationyahoo.com. Retrieved 2012-06-05), the first mechanical tachometers were based on measuring the centrifugal force, similar to the operation of a centrifugal governor. The inventor is assumed to be the German engineer Dietrich Uhlhorn; he used it for measuring the speed of machines in 1817. Since 1840, it has been used to measure the speed of locomotives. In the early days of the industrial revolution till now, they are used in control of motors in industries/manufacturing replacing speed governors. Conveyors and plastic injection molding machines heavily rely on tachometers to measure and control the speed of operation. In conveyor systems, the tachometers measure the speed of motor shafts and motor drives central to effective production control. In molding machines, they calculate the screw shaft rotation speed that regulates the flow of plastic pulled into the injection barrel, which must be consistent to produce uniform parts. As time passed science advanced with the advent of electrical tachometers, it found applications in automobiles, trucks, tractors, and aircrafts. It also found applications in modern manufacturing. Tachometers or revolution counters on cars, and other vehicles show the rate of rotation of the engine's crankshaft, and typically have markings indicating a safe range of rotation speeds. This can assist the driver in selecting appropriate throttle and gear settings for the driving conditions. Aircraft tachometers have a green arc showing the engine's designed cruising speed range. It also finds its application in the early days of electronics (radio and cinema), analogue audio recording, and a tachometer is a device that measures the speed of audiotape as it passes across the head.
There are so many applications of tachometer in industry but these were the earliest application of tachometers which were all of mechanical/electromechanical design.