Steinway Vertical Climate Control/Damppchaser humidistat longevity

[Frank Cahill]

Bdshull@AOL.COM wrote:
> 
> Jim, thanks for your note.   I need to put a system in my own Steinway upright
> (has the cast duplex bar) - Grandma brought it from Missouri to Pasadena in
> 1909, and now its in my house - I hate to tune it (my associate did for my
> birthday, first tuning in about 10 years), and a Damppchaser is the way to go.
> Great piano when in tune.
> 
>  About Damppchaser systems:  Now that the humidistats on some of these systems
> are getting along in years, are they showing signs of malfunction?  The pianos
> we have discussed have systems 15-20 years old and they are very stable, but I
> wonder if anyone has studied these older systems.  I have several old
> humidistats and think I will set up an older system in my old Steinway, set a
> Radio Shack or Damppchaser humidity gauge in it for a week and check its high
> and low readings.   Not real accurate but it should tell something.    Maybe
> the folks at Damppchaser have a pretty good idea of their longevity.  Should
> we begin replacing systems after a time?
> 
> Bill Shull
> University of Redlands, La Sierra University
> 25826 Davis Way
> Loma Linda, CA  92354
> (909) 796-4226



I suspect that there is not much to the humidistat.  In the early 80's I
was an engineer and did some work that required monitoring of humidity.

The device we used looked like a rear window defogger, only about 2" X
2". It had a fine wire in a zig-zag pattern that covered one side of the
device.  The electrical resistance of the wire was proportional to the
humidity.  If the humidity changed, so did the resistance of the wire. 
The resistance change was monitored by an electonic circuit that
controlled an analog meter to indicate humidity changes.

I bet the humidistat uses a similar arrangement.  At the two extremes of
the desired humidity window, a switch (it could be a relay or an
electronic switch)is activated to turn on the heater bar or the
humidifier.

I feel certain that very few of the humidistats are no longer
functional.  At worst, they may be a little out of calibration, but as
long as the humidity remains somewhat constant, you won't notice. 

If things seem ok....if the piano is holding its pitch....the system is
ok.  
-- 

Frank Cahill
Associate Member, Piano Technicians Guild
Northern Va