what does the tachometer measure

• 2022-02-25

Equipment tachometer is one of the necessary instruments in the equipment ministry assiduity. The tachometer can be used to measure the speed, direct speed and frequence of equipment auto. The speed of equipment can reflect the performance of equipment driving. It's a veritably important part of equipment. Tachometer is one of the necessary instruments of equipment, which can be used to measure the speed or direct speed of equipment motor. It's generally used in the addict of equipment equipment. Speed is the rate of gyration times and time of equipment corridor, which is suitable for describing the important parameters of equipment object gyration. Movable tachometer is generally used in equipment, and the unit of tachometer is revolution per nanosecond, The value marked on the tachometer can reflect whether the vehicle speed is normal or not, and can also check whether the service state of the vehicle addict is normal.

Generally speaking, the engine speed is determined by measuring the speed of the crankshaft, which is usually measured by the signal panel installed on the crankshaft. The following figure shows the signal panel and speed sensor installed on the crankshaft of Nissan hr16 engine:

There are generally three measurement methods:
1 Electromagnetic pulse type;
2. Hall effect formula;
3. Photoelectric type.

The principle of measuring rotational speed of electromagnetic pulse sensor is:

When the signal disk rotates, the disk teeth cut the magnetic field formed by the magnetic core of the sensor, resulting in magnetic induction, causing the coil in the sensor to generate alternating voltage and output pulse signal. The frequency of the pulse signal is directly proportional to the speed of the signal panel. The speed of the engine can be obtained by calculating the frequency of the pulse signal and the number of teeth of the signal panel.

The principle of measuring rotational speed by Hall sensor is:

When the hall element is placed in the magnetic field, a current perpendicular to the magnetic field is connected to both sides of the hall element (such as the upper and lower sides), and a Hall voltage will be generated on the other two sides (left and right sides). When the signal panel rotates, the impeller of the signal panel will cut off the magnetic field, the Hall voltage will disappear, and the sensor will output a rectangular pulse signal. For each revolution of the signal wheel, the number of sensor output signals is equal to the number of notches (or blades) on the signal wheel, so as to calculate the engine speed.

The principle of photoelectric sensor is:

When the photosensitive element is illuminated, the working characteristics will change from open circuit to path (inaccurate, let's understand it). Light transmission holes are processed on the signal panel, and light-emitting diodes and photosensitive elements are installed at the front and rear of the signal panel respectively. As the signal panel rotates, when the light emitted by the LED is blocked by the signal panel, the photosensitive element outputs low voltage; When the light emitted by the light-emitting diode shines on the photosensitive element through the light transmission hole, the photosensitive element outputs high voltage. Through this change, the sensor can output a rectangular wave and calculate the speed according to the frequency of the wave.