Hysteresis: was Soundboard springs ...

[Carl Meyer]

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David, hysteresis in electronics is sometimes referred to as dead band.  =
It may be desirable in certain applications.  An air compressor that =
turns off at 120 psi and then turns on again at 90 psi has 30 lbs. of =
hysteresis.  If it had no hysteresis then it would never know what to =
do.  Some is necessary.  Your thermostat is another good example of a =
device with lots of hysteresis.  I would say that even a single leaf =
spring would have a bit of hysteresis due to the small amount of =
friction at the contact.  A coil spring should have minimal hysteresis =
unless there were some friction present.

A feedback servo system whether electronic mechanical or hydraulic needs =
at least some hysteresis because without it they would be prone to =
become unstable and oscillate.  The dead band is the amount of error =
required to cause a correction from the system.  Weird, huh??

Carl Meyer  Assoc. PTG
Santa Clara, California
cmpiano@attbi.com =20


From: David Love=20
  To: pianotech@ptg.org=20
  Sent: Sunday, February 10, 2002 8:19 PM
  Subject: Hysteresis: was Soundboard springs ...


  Sorry Del, it was Ron Overs actually.  I'm still not sure what =
hysteresis is exactly and why a leaf spring might have a problem =
compared to a coil spring?  Ron, if you're listening?

  David Love
    ----- Original Message -----=20
    From: Delwin D Fandrich=20
    To: pianotech@ptg.org=20
    Sent: February 10, 2002 7:27 PM
    Subject: Re: Soundboard springs and hysterisis: question for Del F.


      ----- Original Message -----=20
      From: David Love=20
      To: Pianotech=20
      Sent: February 10, 2002 11:14 AM
      Subject: Soundboard springs and hysterisis: question for Del F.


      Del:

      Been reading the past posts on soundboard springs and have come to =
your comments that a leaf spring arrangement would be subject to =
"hysterisis" and would not be as effective.  Could you define what you =
mean by that term as it applies here?

      Thanks

      David love

    Did I say that? Surely not.=20

    Hysteresis would only be a problem if leaf springs of multiple =
layers were used. Then the breakaway friction between the various leaves =
might cause a response problem. (Bearing in mind that I've not actually =
tried this.) Otherwise, with a single leaf, I don't see the problem. And =
I can't think of any reason to use a multiple leaf spring arrangement =
for this application. Using a single leaf spring it should be relatively =
easy to figure out a virtually frictionless coupling between a leaf =
spring and the soundboard. Assuming, of course, that one really wanted =
to use a leaf spring.

    Del

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