## The Watt governor

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• I chose this system because it s interesting (to me), non-trivial, yet quite understandable. I hope I made this message these things as well. The centrifugal
Message 1 of 1 , Aug 2 9:16 AM
I chose this system because it's interesting (to me), non-trivial, yet
quite understandable.

I hope I made this message these things as well.

The centrifugal governor (or Watt governor):

http://en.wikipedia.org/wiki/Centrifugal_governor

is a mechanical dynamic system designed to achieve a point of
equilibrium in speed independent of the mass of the prime mover (for
example a steam engine ). Input to the governor might be provided from
belts which link the spinning of the wheels, to the spinning of the
governor. As the wheels of a train (for example) spin so does the
governor. The spinning of the governor results in a centrifugal force
causing the counter weights attached to the scissor arms to move up.
see the diagram:

http://en.wikipedia.org/wiki/Image:Centrifugal_governor.png

This upward motion of the counter weights causes the fulcrum arm on
the left side of the fulcrum pivot to move down and the right side of
the fulcrum to move up which closes a butter fly valve reducing the
working fluid delivered to the engine and reducing the speed of the
hypothetical train.

A train pulling a car full of cargo requires a greater opening at the
butter fly valve to achieve 50 mph than the same train at 50 mph when
the car is empty.

The centrifugal governor dynamically adjusts for this difference in
mass to maintain a constant 50 mph full or empty.

Question:

Is this system a "sensor"?

Well, this question is meaningless. It's meaningless for several
reasons (at least two anyway ;o)

#1 We have no working definition of "sensor".

#2 We have no idea of what it might be a "sensor" of. In other words,
it might be better to ask:

Is this system a sensor of "mass"?
Is this system a sensor of "speed"?
Is this system a sensor of "centrifugal force"?
Is this system a sensor of "working fluid flow rate"?

and even these "better questions" are still less than meaningful as
long as we lack a good working definition of sensor as stated in #1.
But, these "better questions" have already taken the first step
towards achieving a working definition of sensor.

And, if these questions are "better questions" then have we not
already ruled out any possibility that the Watt governor is a sensor?

Consider the list of question all being answered in the affirmative
(or all negatively):

Q. Is this system a sensor of "mass"?
A. yes!

Q. Is this system a sensor of "speed"?
A. yes!

Q. Is this system a sensor of "centrifugal force"?
A. yes!

Q. Is this system a sensor of "working fluid flow rate"?
A. yes!

In this case, certainly the list is no better than the original question:

"Is this system a "sensor""?

Any effort to classify the list as "better" than the original requires
both negative and positive responses, thereby including and excluding
what it is or is not a "sensor" of.

As far as I can tell, there is zero possibility of having both, the
list being "better questions" and a definition of sensor including
Watt governors. Further more, it surly seems to me that these are
"better questions" and therefore I must rule out Watt governors as
sensors.

John J. Gagne
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