Recently, I asked a question about the speedometer, how it works and how accurate it is. But that got me thinking... how does the rest of the dash actually work?
I understand that the RPM measurement is a measure of the rotational speed of a mechanical component (the crankshaft) with respect to time (in minutes), partly thanks to this source from Wikipedia.
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)?
Note: Answers can exclude fancy dashboards such as the new Audi "cockpit" dashboard because that's clearly just a computer running bespoke software on an unusually shaped computer monitor. I want answers to explain information about the traditional, needle based tachometer found in the majority of cars (as far as I am aware).