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But what was Gustave-Adolphe Hirn's pandynanometer? It does exist [1] Cutler 11:08, 7 March 2006 (UTC)

Eddy current?[edit]

What is an eddy current dynamometer? --Gbleem 04:22, 1 June 2006 (UTC)

See answer below by =Motorhead. I have added eddy current or electromagnetic brake to the article under heading: Types of absorption units. --C J Cowie 16:27, 1 June 2006 (UTC)

Why is it called brake horsepower?[edit]

Is there non-brake horsepower? --Gbleem 04:25, 1 June 2006 (UTC)

Brake horsepower refers to horsepower measured by braking the engine which is what dynomometers do as opposed to all the other possible horsepower designations such as friction horsepower, indicated horsepower, pumping horsepower etc.

An eddy current dynomometer is a type of electric dyno or "brake" which used magnetic/electrical currents induced in a spinning disk to provide the resistance. Similar in principal to some old mechanical speedometers.--=Motorhead 10:02, 1 June 2006 (UTC)

I think that brake horsepower generally refers to actual operating horsepower measured under specific operating conditions as opposed to rated horsepower or nominal horsepower. The term is often used to mean the actual horsepower that must be applied to the shaft of a pump to produce a specific flow at a specific head. Pumping horsepower may mean the power represented by the actual flow of water which would be the brake horsepower input at the pump shaft minus the energy losses dissipated as heat in the pump. --C J Cowie 16:27, 1 June 2006 (UTC)
In this case, by "pumping" I was referring to pumping horsepower as in "pumping mep", the horsepower required to pump gasses into and out of the engine, not to the workings of the brake itself.
Rated and nominal horsepower are artificial constructs by factories, insurance companies, governments etc. with a special interest and agenda. Totally non scientific and not considered at all in my comment. If you didn't measure the power on a dyno or "brake", you simply do not and cannot know the power output. All the other alternate terms I used are real measurable factors which happen to share the word "horsepower".
It would be good to point out in the article the differences between all those you mentioned though. So readers wont be fooled by some advertisers wet dream.--=Motorhead 00:39, 2 June 2006 (UTC)
I am not inclined to address the use or misuse of horsepower ratings in this article. Every product that contains an engine or motor is likely involved with some version of this problem. See: Talk:Electric motor#does horsepower really equal 750 watts?. The horsepower article also addresses some aspects of this problem. --C J Cowie 17:37, 2 June 2006 (UTC)

I'm surprised no one has mentioned that brake horsepower specifically refers to horsepower measured after mechanical losses, so yes, it has to be referenced as such. P Axford. —Preceding unsigned comment added by (talk) 20:42, 6 January 2010 (UTC)

Cont ... The alternative is "indicator horsepower" which is calculated from integrating cylinder pressure over the cycle, and therefore clearly does not account for mechanical losses. P Axford.

Inventor of the Dynamometer[edit]

I work at an engineering company and i am under the impression that William Froude invented the dynamometer. This article indicates it was Charles Babbage. Charles' page indicates he did a lot of work with computers, which were called 'engines' but nothing to do with dyno's. Could you confirm your source for this?  :o)

Gaspard de Prony invented the de Prony brake in 1821. The de Prony brake (or Prony brake) has been considered to be one of the earliest dynamometers, but I don't know if it is claimed to be the first. C J Cowie 14:15, 23 June 2006 (UTC)
Since William Froude was born in 1810, the invention of the Prony brake must have predated whatever type of dynamometer he invented.C J Cowie 14:27, 23 June 2006 (UTC)
According to, William Froude invented the hydraulic dynamometer in 1877 and Heenan & Froude was established and produced the first commercial dynamometers in 1881. C J Cowie 14:37, 23 June 2006 (UTC)
I have found a couple of references that indicate that, in about 1838, Charles Babbage built "what must have been the first example of a dynamometer car" for testing railroad engines. The information about Babbage needs to be moved to the dynamometer car article and the information about de Prony and Froude put in this article. C J Cowie 22:49, 23 June 2006 (UTC)
I have moved the Charles Babbage material to Dynamometer car and added a history section to this article with information on the de Prony brake and the invention of the hydraulic dynamometer by William Froude. --C J Cowie 00:40, 24 June 2006 (UTC)

Thanks for clearing that up :o), knew he invented some form of dyno.

I used to work at Froude in the early 80's. I think specifically he is credited with invented the hydraulic dynamometer for testing ship engines in-situ. The dyno was attached to the prop shaft in place of the prop and submerged, providing a convenient source of cold water. The torque reaction on the casing ("carcass")could be easily measured. P Axford. —Preceding unsigned comment added by (talk) 20:36, 6 January 2010 (UTC)

Another type of Dynamometer - Eddy Current[edit]

This type uses magnetic flux to apply load to the engine. I thought i'd let you add it though to maintain the flow of the article. It is 'Electric' in design but does not have the motoring capacity. —Preceding unsigned comment added by Arnie1066 (talkcontribs)

Froude made a "regenerative" hydraulic motoring dynamometer in the early '80s that was installed at Ford Dunton, UK. The engine under test drove an off-the-shelf fixed displacement swash plate pump for which the casing torque reaction could be measured by a load cell. The hydraulic hoses were hooked to a similar but variable displacement swash plate pump drive by a synchronous AC motor of around 300 hp. Clearly by varying the variable pump's swash plate setting torque could be applied either way to the test engine, transferring power to and from the electric grid. — Preceding unsigned comment added by (talk) 00:22, 5 November 2011 (UTC)


Are there examples of dynos being used to measure the output of molecular motors or nanomotors? I've similarly never seen them used to measure pneumatic or hydraulic motors. Is the ambiguous reference to "motors", then, truly correct? -- Mikeblas 14:52, 12 August 2006 (UTC)

I would assume that molecular motors and nanomotors can be tested only by operating them as they are to be used. If the designers of pneumatic motors and hydraulic motors need to quantify motor performance, they would need to come up with some type of dynamometer test. When I was involved in marketing dynamometers, I viewed every designer of any kind of motor as a potential customer. C J Cowie 15:44, 12 August 2006 (UTC)
That's a healthy and ambitious view. What we document here would be actual applications, though. I think that the article would do better with a more specific link (or links) that reflect the actual applications of dynamometers. The article already references "prime mover" and "heat engine"; referencing "motor" in place of "electric motor" smacks of shotgunning and leaves only more questions. If dynamometers are not available for most of the motor type listed at "motors", why link to it instead of linking to individual and accurate topics? -- Mikeblas 17:13, 12 August 2006 (UTC)
From All Products Catalog Section 9 Positorq Absorber Brakes: “There are many applications where Positorq brake dynamometers can be used. A few typical applications are shown below. (A) Hydraulic Motor Testing is a way to test hydraulic motors after repair or for trouble shooting. Also full load torque and efficiency can be verified.”
Here is another dyno manufacturer that apparentyl believes that there are potential customers for dyno's to test pneumatic and hydraulic motors: C J Cowie 22:21, 12 August 2006 (UTC)

Another type of dyno[edit]

what about a reference to the dynamometers that are attached to the axle, removing the wheels to procede with the testing. Maybe someone can mention those. --Cirilobeto 22:51, 27 August 2006 (UTC)

I don't see any need to differentiate as to where you attach the dyno. — Preceding unsigned comment added by (talk) 00:12, 5 November 2011 (UTC)

prop dynamometer[edit]

What about dynamometers that use a prop or fan and air? --Gbleem 15:31, 5 October 2006 (UTC)

They are mentioned in the types section.--=Motorhead 14:25, 6 October 2006 (UTC)

Another usage of the word[edit]

"Dynamometer" is also the name of a device for testing a person's grip strength. I don't know enough about it to create a separate article, and I can't think of any good way to integrate it into this article. Keith Lynch 17:26, 15 October 2006 (UTC)

I'm not sure if this is the best place for this comment, but there is a discrepancy with some of the articles in other languages that it is linked to. For instance, the spanish article is clearly referring to spring scales. Newsspots5 (talk) 12:53, 18 April 2010 (UTC)newsspots5


for example:

-What does the peak represent? -Why are there fluctuations on the graph?

The introductory definition is blatantly incorrect[edit]

Time and again I encounter the claim that power cannot be measured directly on a dynamometer, which is simply rubbish. Now I find the same thing on Wikipedia, which is rapidly becoming the universal repository for disinformation. This article makes this claim:

"Only torque and speed can be measured Power must be calculated from the torque and speed figures according to the formula:"

This is rubbish. It categorically ignores inertial dynamometers as a class. With inertial dynamometers, rotational speed is repeatedly sampled in order to deduce angular acceleration, and power is deduced from angular acceleration and from the inertial moment of the drum. Moreover, it is not at all difficult to visualize a dynamometer that is equivalent in effect to a brake dynamometer, but would operate not by using a brake per se, but would accumulate energy in a form other than heat, and would do so in a manner in which the rate of increase of that more usable form of energy can be regulated and measured directly. For example, if the drum is replaced with spinning masses held in place using arms of variable, controllable length, the inertial moment can thus be regulated, with the effect being the same as a brake dynamometer in that the steady-state power output is measured, by multiplying together the steady-state angular velocity and the inertial moment.

It is thus demonstrably true that the statement that I quoted above, is patently false. Moreover, the introductory definition is patently false:

"A dynamometer ... is a machine used to measure torque and rotational speed (rpm) from which power produced by an engine, motor or other rotating prime mover can be calculated."

This definition contains arbitrary, unsupportable presumptions about the basic nature of how physical quantities are measured. It states outright that power is not measured directly, but is rather calculated from torque and the rotational speed. This is incorrect on multiple levels. If it is meaningful to distinuish between that which is measured directly and that which is measured indirectly, then neither torque nor rotational speed are measured directly. You measure distance and time in order to measure speed, and you measure distance and force in order to measure torque. The distinction between that which is measured directly, and that which is measured indirectly, is illusory and meaningless. And that is in addition to the fact that it is simply not true that it is necessary to first measure torque in order to measure power, not even in the case of brake dynamometers as a meaningful class. As such, the summary definition is absurdly incorrect. It should simply say that a dynamometer is an apparatus used to measure the instantaneous rate at which a system is performing usable work.

This article also misrepresents the most important distinction between classes of dynamometers. Dynamometers fall into two general classes: those which measure steady-state power, and which give results that are uninfluenced by the tendency for the system to absorb energy, and those which measure power dynamically, which give results that are influenced by the tendency for the system to absorb energy. Inertial dynamometers, which are not even mentioned in this article, give results that are influenced by the tendency for the engine under measurement to absorb energy in the form of internal kinetic energy, the amount of which depends on its aggregate inertial moment and its instantaneous rotational speed. --- Preceeding unsigned commentary by: Terrible barbarian 11:25, November 15, 2006

"With inertial dynamometers, rotational speed is repeatedly sampled in order to deduce angular acceleration, and power is deduced from angular acceleration and from the inertial moment of the drum." -- In other words, speed is measured repeatedly. Acceleration is calculated from successive values of speed data samples and the time interval between speed samples. Instantanious torque is calculated from acceleration and the inertial moment of the drum. Instantanious power is calculated from instantanious speed and torque. Power is not measured directly it is "deduced" AKA calculated. Speed and torque may not actually be measured directly, but there are transducers that convert such things as time and force measurements to speed and torque indications. -- C J Cowie 19:18, 15 November 2006 (UTC)
Although I don't believe the lead paragraphs of this article are "blatantly incorrect," I agree that the it is too focused on measurement of speed and torque. A more general statement might be better. "A dynamometer is a machine that is used to apply a load in a controlled way to a prime mover such as an engine for the purpose of evaluating the performance of the prime mover." -- C J Cowie 21:35, 15 November 2006 (UTC)

Its true in a nitpicking kind of way that no measurement is truly direct. All instruments involve some kind of transducing mechanism to make a force or other condition usable to us. But it still stands that you cannot buy a "horsepower meter" to hook up to your engine. I suppose you could get yourself a 33,000 pound weight and see how far the engine can lift it in a minute and that would be as close as you can get to measuring horsepower directly. No one does that. Why not? … the only other way is to measure related parameters and calculate horsepower.

Currently somewhat fashionable inertial dynos give only aparent horsepower for the particular dyno-engine-acceleration rate combination as the acceleration adds the rotating masses of the engine and other components, which are seldom (virtually never) known. The power figure is lower than the actual steady state output and they can function only under acceleration. It is useful as a RELATIVE comparison tool but does not give accurate horsepower or torque figures, which might be used for further calculations. Granted, its simulated real world data and speed of operation make it attractive in some instances but for real research it is lacking. Even a simple BMEP figure would be an estimate at best. For repeated rapid testing of the same engine where you only what to know the difference, nothing beats it.--=Motorhead 23:41, 15 November 2006 (UTC)

Re erroneous edit[edit]

Many types of AC and DC motors can function as either motors or generators. Permanent magnets are not required. —The preceding unsigned comment was added by C J Cowie (talkcontribs) 15:24, 7 December 2006 (UTC).

Accuracy and completeness[edit]

I wish the person who found this article rubbish would spend as much time replacing the article as criticizing it; then there would be real benefit and it would make Wikipedia less of a repository of misinformation, as the writer terms it. The comments in that notice strike me as sound and valuable observations--please share them publicly!

My own observation is that dynamometers have applications for testing forces in lots of contexts not mentioned in the article--springs spring to mind.

If I had better technical knowledge I would contribute, rather than adding my own ignorance to what appears, and I can only add these observations, which I hope can be constructive.

BLATANTLY INCORRECT —Preceding unsigned comment added by (talk) 15:39, 21 September 2007 (UTC) 18:32, 29 June 2007 (UTC)LINKBook The introductory statement is correct, and the "criticism" of that statement then goes on the confirm that it is correct. When you measure other parameters, and the calculate or "deduce" the parameter of interest, you are NOT measuring the parameter of interest. In this case, torque is measurable, and can be used to calculate power. "Heat" is another parameter that can't be measured directly, and there are many others. The ones that CAN be measured are very few, like length, and temperature, but those that can be measured are then used to "deduce" the ones that can't. —Preceding unsigned comment added by (talk) 15:37, 21 September 2007 (UTC)

Eddy Current Brake Composition[edit]

Can anyone explain what an 'exterequire' is? I am guessing that this is an artifact of a bad edit back in May 2008. I'd gladly correct it but I'm not too sure what the initial intent was. Assuming that this is the case, I will just go ahead and correct it. Cam Finnigan (talk) 20:53, 7 September 2008 (UTC)

Power calculations[edit]

To calculate power in kilowatts use:

\mathrm{kW} = {{\mathrm{Torque \times rpm}\over{9549}}}
Torque is in newton-metres (N·m)
Rotational speed is in revolutions per minute (rpm)

This does not seem right - where does the 9549 come from?

9549 = 60 000/(2 pi) (see below)

Power = Torque * rpm * 2Pi / (60 * 1000)

Power in kilowatts, torque in N·m.