Talk:Tachometer

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As the inventor of the 'Tachometer', Dietrich Uhlhorn, was indeed German and as his objective was to measure the speed of a moving object, not the rotation, the entire article is misleading or at least incomplete. The rotation of a wheel is used to show the speed on a scale. This scale however, does not show the actual number of rotations but its translation into distance/time. This can be confirmed by using the link for 'Deutsch': it will show the definition of a 'Drehzahlmesser' (or RPM Meter). The explanation of 'Tachometer' on the German site will explain the principle of a speedometer. (SunnyNM)

If we start with the premise that a 'tacho meter' is a speed meter, the 'Drezahlmesser' and English 'Tachometer' are the same thing. They measure the speed (frequency) of rotation of the engine. If we start with the premise that a 'tacho meter' is a speed meter, then the German 'Tachometer' and English 'speedometer' are also the same thing. They measure the speed (frequency) of rotation of a tire. The scale is variable because of the circumference of the wheel. Shifting gears obviously changes the ratio of the 'Drehzahlmesser' to the 'Speedometer'. The type of machine it was invented for did not have gears to change, did it? The ultimate question then is really what was it called first, chicken or egg. I believe it was indeed both, and therefore aptly described as a tachometer. So when we started attaching one to measure wheel speed, and the other engine speed, they were both still tachometers. The 'scale' show on the modern speedometer is either calculated by a computer (showing vehicle velocity) or in older vehicles in a Wirbelstromtachometer, which is a tachometer that indicates speed, called a Geschwindikeitsmesser. Both of these are 'scaled' tachometers.

Who is right or wrong? Nobody. Is that the name of the original part stuck in German driving lingo, and a new name was attached in English, that represents ultimately the same thing in a German drivers mind as the English drivers mind. — Preceding unsigned comment added by 50.252.17.166 (talk) 10:10, 11 November 2014 (UTC)

Anyone know how a diesel tacho works? --219.88.29.108 06:18, 24 April 2006 (UTC)
 * Diesel engines do not have a spark ignition system that could provide a signal for a tachometer. Diesel-engined automobiles have alternators which generate ac power at frequency proportional to engine rpm, and this can drive a tachometer. (cuddlyable3)84.210.139.189 00:07, 15 December 2006 (UTC)

Has the section "History" been vandalised? Now it says only "The first were mechanical" without a stop. I think stuff has been removed here! (cuddlyable3)84.210.139.189 00:07, 15 December 2006 (UTC)

Is it worth mentioning that the word "tachometer" is used in some other languages (e.g. German) to refer to a car's "speedometer"? Might be a "false friend".--Millard73 22:29, 21 July 2006 (UTC)


 * You are right, that is a problem for English speakers when in Greman speaking countries. And probably the reverse for a German speaker when in an English speaking country.--TGC55 (talk) 13:43, 21 January 2010 (UTC)


 * Beside German certainly also in French, Italian, Spanish, Russian, Polish, Swedish and Portuguese. 194.174.73.80 (talk) 13:29, 24 March 2017 (UTC) Marco Pagliero Berlin

This seems a bit opinionated for my tastes: ''that the driving conditions call for; or, perhaps more frequently, allow automotive enthusiasts to admire how fast they are 'revving' the engine. ''

24.69.25.201 09:41, 21 December 2006 (UTC) colin

Yellowline?
In the current photo, it shows and explains that the redline is from 6000-7000 rpm. but what are those yellow markings for from 5500-6000 rpm? does that "yellowline" indicate an engien speed that can damage the engine as well, or is that just some kind of warning? —Preceding unsigned comment added by Vandalism destroyer (talk • contribs) 01:31, 2 May 2008 (UTC)


 * Typically the "yellow line" is a warning that the engine is being operated very near its safe limit (the redline). The exact relevance depends on the engine and what it is powering.  It's common in reciprocating aircraft engines to set a time limit on running the engine at the yellow line, e.g., during takeoff and climb-out.  In automotive usage, the yellow line is usually an RPM range with a short time restriction due to cooling, lubrication or other issues that may substantially shorten engine life.  In theory, engine failure resulting from running in the yellow on a regular basis should not occur.  That's the theory... :-)

Bigdumbdinosaur (talk) 22:32, 21 July 2008 (UTC)

Measure rate not speed
All the tachometers described measure repetition rates, usually rotation speed (except the obscure haematachometer?). The rotation speed may or may not be linked to a vehicle speed or flow of tape or a fluid depending on the application, but I suggest it is misleading to define the tachometer as essentially an instrument to measure speed.

While the Greek root "tachos" can mean speed, the earliest use of the word tachometer seems to be in 1810. This indicates to me that tachometers are an offspring of the Industrial Revolution that brought us reciprocating machines. The first of these machines were steam engines that stayed in the place they were built.

The automobile tachometer familiar today is not intended to display vehicle speed, for which another instrument the speedometer is required by road laws.


 * The measure of revolutions per minute of an engine, electric motor etc. is usually called the speed of rotation or just engine speed, motor speed etc. It is not usually called a rate. The repetition rates are usually expressed as pulses per minute, beats per minute etc. However, the actual unit of measurement is 1/time in either case. --C J Cowie 00:42, 1 September 2006 (UTC)


 * The concept "speed" signifies general movement without implying repetitive movement. Introducing a distance unit (and a time unit) allows speed to be expressed as a (repetition) rate, such as miles per hour or feet per second, but that is an arbitrary introduction not inherent in "speed". A tachometer is essentially restricted to sensing a rate, and a rate must have the dimension of 1/time. That fact is being neglected if we call the tachometer a device to measure speed.
 * C. J. Cowie finds this to be unusual use of the word "rate" and seems to prefer to use "speed + a modifier" such as "speed of rotation". I have no objection to that.
 * I suggest deleting the vagueness of "used for measuring the speed of a moving body or substance" and instead defining like this:
 * A tachometer measures the speed of rotation of a shaft or disk (from Greek: tachos = speed, metron = measure), as in a motor or other machine. The device often displays the rate of revolutions per minute on a calibrated analog dial, but digital displays are increasingly common.
 * I think it is good to lead with the most common definition, but also good to make some reference to the medical and audio recording usages. --C J Cowie 00:36, 10 September 2006 (UTC)

Relevance?
I'm of the opinion (gee, don't we all have one?) that the section In trains and light rail vehicles is out of place in this article. It is confusing a tachometer with tachometry, which is the process of generating an analog output that varies as a function of a periodic rate input, e.g., frequency, shaft RPM, repeated hammer blows, etc.

For example, a speedometer displays a motor vehicle's road speed using tachometry. The mechanism may be similar to that of a tachometer but the meaning of the instrument is completely different. In fact, most racing tachometers are mechanically driven from some point on the engine and use a mechanism that is essentially the same as that of a speedometer. The only real difference is the latter produces a miles/kilometers per hour display and the tachometer produces an RPM display.

In another example, the input section of a frequency-to-voltage converter applies tachometry so an output voltage that varies linearly with frequency input is produced. The exact use to which the output voltage would be put would determine what the overall function would be. If the input frequency is produced by a magnetic reluctance pickup near a gear driven from an engine's crankshaft and the output of the F-to-V converter was arranged to drive an indicator calibrated in RPM, the result would be a tachometer. Relocate the magnetic reluctance pickup to a wheel and tire assembly and calibrate the indicator in MPH, and you have a speedometer.

Bigdumbdinosaur (talk) 22:56, 21 July 2008 (UTC)

Red Line Superfluous?
I disagree with the line The red zone is superfluous on most modern cars, since their engines typically have a rev limiter which electronically limits engine speed to prevent damage - repeatedly running an engine into the limiter is bad for the engine, most cars have the redline set a few hundred RPM before the limiter in order to prevent hitting it. Jellyfish dave (talk) 01:12, 22 July 2008 (UTC)

Handheld devices / tools - not a word!
There's not a word here about the handheld electronic devices people use for checking RPM. There's a lot to be explored here, with both contact and non-contact (photo/laser) tachometers. Someone who has some knowledge about these should add a section about these to the article. - Blueguy 65.0.200.209 (talk) 17:24, 8 July 2009 (UTC)

I agree, I came to this page looking for info on handheld versions and there is nothing. I've seen both physical and optical versions, and it seems to me like they're at least fairly common, at least in engineering applications. More information would certainly be appreciated. - Geoff — Preceding unsigned comment added by 98.102.244.254 (talk) 15:50, 11 October 2011 (UTC)

Angular velocity measurement
Since I'm not allowed to edit, I'll just say... There is a need for more technical information on angular velocity measurement. Seemingly simple, but quite complex when one considers noise, sampling latency, slow update of low-speed rotations, displayed signal filtering, integer calculation roundoff, requirement for immediate update upon sensor detection, need to be able to query algorithm at any time for a "best estimate" rate, calculation of acceleration, etc.

The fact that sensors may be magnetic, optical, capacitive (not even mentioned), inductive (also not mentioned), or otherwise is not particularly germane to the article. What DOES need to be said is that there are accelerometer-based methods (an accelerometer on the edge of a disk) which measure the centripetal force, and time-based methods which measure the rotational rate. They may be analog (i.e. measure voltage of sine wave generated by pickup coil) or digital (generate pulse on revolution). Of the later methods, they may generate one or more pulses per revolution, and they may measure period or frequency or a combination of both.

It should be pointed out that sometimes frequency, sometimes phase, sometimes both, and sometimes phase-locking are needed. 108.213.76.24 (talk) 21:55, 4 July 2014 (UTC)

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