TR: push/pull dynamometer/Calibrated beam keyweight measure

[Bill Ballard]

At 2:33 PM +0200 5/10/03, Richard Brekne wrote:
>  >      Hey! Why not a calibrated beam on a pivot, on a
>>  stand, with sliding weights? As the weights were slid
>>  along the beam to the correct point, down and upweight
>>  measurements could be very easily and accurately
>>  taken. Anyone doing this?
>  >      Thump

Interesting idea. Yes, David Stanwood's been doing that for ten 
years. It's how he measures FW.

>I dont know, but I think I would sure like to get ahold of one of these
>things. And I like the idea of automatically being able to pump values
>into a puter. Nice idea for sure.

Not this puppy, if it's the same one I bought twenty years ago (and 
it appears to be). As far a reading DW/UW, one pushes again a live 
spring (instead of the force being a dead weight). That's fine when 
reading DW. You start at zero spring pressure at the key touch point 
and build up (pressing normal to the key), and at the point when the 
key starts to move the pointer's maximum position is recorded 
mechanically. Any further DW reading really has to start once again 
from dead zero as, once the key starts to move, the friction 
component of the DW is dynamic instead of static. Also if you decide 
to read DW after the key is moving, you must maintain a uniform speed 
with the dynamometer pressing on the key, or the key will 
decelerate/accelerate.

Reading UW is no less tricky. At the point prior to let-off, you 
start with a pressure leass than DW but greater than UW so that the 
key is stopped. You then move upwards slightly with the gauge, 
relieving spring pressure, until the spring pressure hits UW. As with 
DW, once the key is moving certain restrictions apply, the latest 
addition being that upwards motion has to be at a crawl.

It has spent the last twenty years in my shop desk drawer. I prefer a 
dead weight for DW/UW measurements. Far fewer variables affecting the 
reading, than with a live spring.

As far as a continuous stream of numbers into a computer, I'm sure 
state-of-the-art dynamometers exist which will do that. But not this 
one. It's purely mechanical. It lacks a means of translating 
mechanical readings into digital, and a USB port to export them.

Bill Ballard RPT
NH Chapter, P.T.G.

Reality is the first casualty of technology
     ...........NPR Commentator Daniel Schorr
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