On Tue, 07 Apr 2009 00:02:58 -0400, Joseph Gwinn
wrote:

In article ,
Don Foreman wrote:

On Sun, 05 Apr 2009 13:42:14 -0400, Joseph Gwinn
wrote:

In article ,
Spehro Pefhany wrote:

On Sat, 04 Apr 2009 19:50:29 -0400, the renowned Joseph Gwinn
wrote:


As for manufacture by a HSM, either approach is practical, but the Wyler
approach is far simpler mechanically. In either case, the electronics
part is dead simple by present-day standards, but was a big deal back in
the 1960s and 1970s.


Joe Gwinn

Have you considered the liquid type? They claim 5 arc second
repeatability.

Yes, I did consider electrolytric types (a bubble level vial with
electronic readout). The pendulum units are a factor of ten better in
resolution and repeatability, 0.1 or 0.2 arc seconds versus 5 arc
seconds. Long term drift is also an issue. It sure would be easier if
the electrolytic sensors were better than they are.

Joe Gwinn

Have a look at
http://www.spectronsensors.com/datas...S-105-2704.pdf

Not bad. The resolution is up there, but the repeatability is 0.0008
degrees, or 2.9 arc seconds, versus 0.1 arc seconds. Better than 5 arc
seconds, but still. This is why people bother with pendulum tiltmeters.

Joe Gwinn

I thought it was better but you are correct.

2.9 arc seconds is about 14 microinches per inch or .00014" in 10".
Will you post your pendulum design and results as time goes on,
please? Interesting project!