[Land-speed] British Steam effort 139.843mph

Jon Wennerberg jonwennerberg at nancyandjon.org
Wed Sep 2 15:14:26 MDT 2009


On Sep 2, 2009, at 4:54 PM, Kirkwood wrote:

> I was very careful NOT to mention accuracy in my response to Malcolm.
> Accuracy is a completely different issue. You not only have the wire  
> to
> consider but the latency of the photo cell and the speed of light.  
> If the
> lights are 1000ft apart (across the track) you have a 1000NS delay for
> arrival to the photo cell. We also don't know the precision of the  
> surveyed
> mile. It was not my intent to open up another can or worms!  My  
> point was if
> you only have 0.001sec resolution you are introducing diminished  
> precision
> when rounding to mph.


The 1000NS sec delay would only b e in the instance that the vehicle  
crosses at maximum distance from the light-emitting beam, right?  If  
the vehicle was right by the receiver the delay would be much smaller,  
I think.  But realistic traps are narrower -- more like 100 feet,  
taking a full order of magnitude off that number.

The precision of the surveying has always been a question in my mind  
-- although today's high-end surveys are very accurate, I'm told by my  
surveyor friend.  But -- his new-end GPS surveys, which he reports are  
within a half-inch over ten miles -- are within the half-inch error  
when compared to old chain-type measuring.  How precise was that?

My proposed system would not be affected by speed of light (other than  
the delay in the photocell beam break) -- because each timing event  
would include clock information -- so delay in arriving at the  
computer is not of an issue.  And wouldn't many of the errors be  
consistent - and therefore subject to being tuned out of the system by  
measurement and then correction in all computations?

Jon


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