Measurement of speed of rotation and torque（测量旋转的速度和扭矩）.pdfVIP

2. measurement Measurement of speed of rotation and torque 1. Aim of the measurement The aim of measurement is • to measure the losses of an electrical motor/generator and • to analyse the influence of load on the losses. 2. Introduction For rotating motion, power is the product of torque and angular velocity P = M ⋅ω = M ⋅ 2π ⋅ n Thus, to determine the power of the rotating motion the torque (M) and the revolution number (n) must be measured. Measurement of the revolution number From the point of view of the measuring concept the instruments measuring the revolution number can be divided into three groups • speed indicators measuring the average revolution number, • tachometers measuring the momentary revolution number and • stroboscopes working on the principle of comparison. a) Measurement of small revolution number can be performed simply with stopwatch and by counting revolutions with naked eye. When the mark on the rotating machine part gets to the marked position, we start the stopwatch and begin counting (with 0). Having measured the time (T) and the number of revolutions (N) the revolution number is simply n=N/T. b) For higher speed of rotation a special counting device must be used. One of the simplest of these is the so-called jumping-figure speed counter . The rotating shaft of this device turns gears. One of them completes one revolution while the other rotates only 1/10, and so on. Reading the numbers uniformly painted from