Working Principle of Tachometer: An Electric Tachometer works on the principle of relative motion between the magnetic field and shaft of the coupled device. Types of Tachometer: Contact type — This type of tachometer is usually fixed to the machine or electric motor. It works by bringing a freely spinning wheel in contact with a rotating shaft or disc. The shaft drives the wheel to generate the pulses.
These pulses are then read by a tachometer and measured in revolution per minute. It can also calculate the linear speed and distance. Non-contact type — It is also known as photo tachometer or non-touch tachometer.
It uses a laser, infrared light, or other light sources to take the measurements. The device sends out the beam of light. This beam reflects each time a tape makes a full rotation. The receiver needs to count these reflections during the process to measure the rotational speed in RPM.
This type of tachometer is efficient, durable, accurate, and compact. Electronic tachometer — It is made up of electronic components used to measure the engine speed. It measures the speed in revolution per minute. It is mainly used in the dashboard of the car to measure the driving speed. It uses a magnetic pickup placed near a rotating engine to generate electric pulses.
These pulses have frequency proportional to the engine speed. Fly weights and a vacuum advance control the timing in the distributor. Eventually instead of getting the pulses from the coil the signal came directly from the computer. Even to this day the basic structure and operation of the physical needle in the dash has remain effectively the same, the difference being only where the signal comes from and how the signal arrives at the dash board.
Since the engine computer knows the RPM digitally, in digital dashboards the engine computer sends the information to the dashboard over the network. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. How does the tachometer on my dashboard actually work? Ask Question. Asked 5 years, 9 months ago. Active 1 year, 7 months ago. Viewed 35k times.
How does the tachometer actually work? Is there some sort of sensor in the crankcase that can count each rotation? If so, how does that work? How does the data recorded from whatever it is that records the data get displayed on the dash? Electrical or mechanical signal? How is the tachometer needle calibrated to move the right amount and point to the correct number rather than just spin round in a circle or not move at all? Improve this question. Incidentally, electric tachometers are more accurate, making them far more useful.
An electric or electronic tach is simply a voltmeter. Instead of reading direct voltage from a wire, however, it reads from the ignition's circuitry. Since the voltage comes in pulse form from the ignition, the electric tach's needle only moves upward momentarily, following each pulse of current. The greater the number of pulses in a fixed period of time, the further the needle moves, because it is ultimately measuring average voltage. Properly calibrated, electric tachometers are extremely accurate.
If their internal circuitry is designed to limit voltage spikes and extraneous interference, such tachometers are very reliable and will last the life of the car.
The only possible downside of electric tach is that, since they are connected to the ignition system, a major short circuit in the tachometer can disable the ignition. The driver had to pull out of that portion of the race because he wasn't smart enough to disconnect the tachometer wire. Similar things happened frequently in races during the s until the instruments were designed to prevent ignition shorts. Oddly enough, nearly every vehicle sold in the U. SUVs, luxury cars, minivans and sports cars all have them, in spite of the fact that few are likely to be raced or even driven hard.
Even more significant is that fact that tach are no longer needed, even in racing situations!
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