Dashboard Lights and Gauges

How does a tachometer work?


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2014-06-11 15:23:01
2014-06-11 15:23:01

A magnet that magnetizes "teeth" of an iron gear located on the motor. In general... The magnet magnetizes the "teeth" as the approach then de-magnetizes as they move away.. which creates an electric field.. The wire attached to the magnet connects to the tachometer which displays the rpm,

There are multiple types out there. The modern, most exact, is to have a laser or infra red light with a receiver on the opposite side. When the wheel ( or shaft rotates) it has a mirror or a tab that obstructs the path of the light every time it revovles ... then there is simply a chip to count the number of obstructions per minute. This one is extremely accurate and can handle some of the highest speeds.

But there are a host of older versions ... many still in use.

One is quite the same as above except there is a magnet on the shaft and a sensor ( Google 'reed switch' for example ) nearby that detects the magnet passing.

Another way is a chip attached to a switch that is physically pushed or contacted by a cog on the shaft.

Still another is to have a generator attached to the shaft and the Tach is actually a voltage meter telling the reading off that generator.

Finalley ... saved this one for last ... chances are you looked up this question because you wanted to know how the oldest Tachs worked back when electrical gear wasn't commonly used in cars and such. How did they pull it off back then? Well here goes: The end of the shaft had 2+ arms attached to the side that are weighted and would swing outward further and further, the faster the shaft rotated. The weights had a collar attached below them that would rise upward, the faster the shaft ran. Still with me? Check out this graphic if you need http:/www.railway-technical.comgovernor.gif the wieghts are the round black objects and the rising collar is green. So now all that is left is to have a hook ( with wheel to reduce friction ) that is hooked in the path of the collar so that it will get pulled up with the collar. The hook is attached to a cable ... on the other end of that cable is ( drum roll ) the sneedle of the Tach ... tugging it against a spring, over more and more as the shaft spins faster and faster. No electricity and no chips involved! Obviously this is somthing of a percision device and only as accurate as its most recent callibration ... but it worked enough. There were even hand held versions, very precise instruments that machinist would press against the axels of gears and shafts to get RPM readings. Now they have little hand held laser devices that are pocket size and much more accurate.


Related Questions

The Mazda tachometer and the speedometer have separate cables. The tachometer cable probably does not work properly. Change the tachometer cable.

it sure would work.. behind the dashboard are plugs for each function. one for tachometer, one for speedometer, fuel, water temp. ect.. if your new dash doesn't have a tachometer it will not interfere with the speedomet aspect of it. but you will not have a tach obviously. that sucks kid

One possibility is that the tachometer connections to the circuit board of the cluster have become corroded. It is also possible that the tachometer has just become worn out and needs to be replaced.

There are several things that can cause your engine to misfire and the tachometer to not work properly. The most common cause is a malfunctioning vacuum hose.

If the tachometer only works a few times a year the VSS is malfunctioning. This can occur when oil is spilled on the unit and messes with the sensor. Cleaning the sensor will allow the tachometer to work properly.

A bad ignition coil can cause your 1987 Acura tachometer to quit working. A bad tachometer cable or ground wire can also cause it to quit working.

Remove the instrument panel cover. Remove the tachometer retaining screws. Remove the tachometer cable from the back of the tachometer. Reverse the process to install the new tachometer.

Usually. It can also pull the signal from a spark wire.

Replace the dash cluster that's what it sounds like to me since your tachometer and speedometer both don't work

Where is the tachometer on a 2004 chevy impala ss

Check VSS variable speed sensor that is mounted on transmission

I would say the mechanic didn't re-install the tachometer wire ,whereever it goes on this motor,which I don't know. I would say the mechanic didn't re-install the tachometer wire ,whereever it goes on this motor,which I don't know.

The tachometer cable may be faulty. The tachometer sensor, on the side of the engine might not be functioning properly.

wish i knew have the same prob on my 93 377 peterbilt

you dont need to cause it has a factory tachometer

You can perhaps buy a used portable tachometer by going on to www.amazon.com

Here's a site where you can buy a handheld tachometer: http://www.checkline.com/tachometers/

Like many engine and diagnostic parts of the 1990 Toyota Celica, the tachometer needs the assistance of a fuse to operate correctly. Check the fuse box for a blown fuse for this instrument.

it is a device that converts mechanical into electric measurements. it measures velocity. there are many types: electrical, mechanical, thermo-electrical... for example the mechanical tachometer converts the rotation motion into translation motion with the help of an axis so you can read it on the scale of the tachometer. sorry for not being so good at explaining this. hope somebody will be more documented.

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