PSN-L Email List Message

Subject: Re: What Do you think
From: ChrisAtUpw@.......
Date: Mon, 22 Jan 2001 22:36:41 EST

In a message dated 22/01/01, bgoss@.................. writes:

> Well I finally got my sight updated tell me what you all think.

    The results look OK, which is what counts.

    I see that you have used both magnetic and fluid damping. With the 
magnetic damping, you have used Al plate which is not nearly as effective as 
Cu and you have also used a very large magnetic gap. This suggests that your 
magnetic damping is a sort of 'add on' correction. The problem with fluid 
damping in general is the huge changes in fluid viscosity with temperature, 
particularly between summer and winter. If it works OK, don't 'fix' it. If 
you want to experiment at any time, I suggest you try a bit of 1/8" Copper 
plate, no fluid and reduce the magnet gap till you get ~critical damping. 
This will be independent of temperature. 

    You might want at some stage to fit a small underrun lamp (1/2 to 2/3 
rated voltage) inside the top of the box to give a stable temperature 
gradient to the internal air. A layer or two of bubble wrap with suitable 
viewing holes cut in it could provide additional insulation while still 
allowing light through. A layer of polythene damp proof sheeting under the 
whole apparatus could prevent any condensation problems from the flooring. If 
you get any problems with lightning where you are, you might consider 
mounting the amplifier on the baseplate and connecting the baseplates 
together with a common earth.

    For others still in the design stage, you can get threaded Brass and 
Stainless Steel rods, which are both non magnetic and so won't give problems 
with magnetic interactions. Another alternative is to get plain rod and have 
some thread put one end. Mounting the sensor system just inboard of the 
weight can give a more compact system. Socket cap screws can make levelling 
adjustments easier to perform and fine threads are available - it is a bit 
easier to get an extension rod into a hole than a flat screwdriver bit into a 

    What stable period did you manage to get?

    Good for you and Good Luck!


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Larry Cochrane <cochrane@..............>