On Thu, Aug 14, 2008 at 9:34 PM, JAMES ALLEN
<jcallen1@...........> wrote:
Meredith Lamb or any member using a Sprengnether 201 Long Period unit: There is an scale on the front of mine with the indicator pointer that is at the fourth line from the top, which is essentially at the top stop, and will normally oscillate to the 6th line from the top. Is this where it is supposed to be or should it be centered on the 20 unit scale which after a year of off and on fiddling seems impossible?
James Allen
Hmmm....either its my computer malfunctioned or ?, but here I see my response to Randall showing up below your message above???
James,
It "sounds" like you need to give some more slack to the top wire (top rear rotating knurled nut) ...just to allow the frame/mass to come
further down, which then allows the vertical seismometer boom/mass to get within the true center range of your
boom range/pointer mechanism. It normally should be able to range over the entire pointer scale of course. My wild guess is that the previous
owner/s had the same (which IS entirely solvable) problem also; but didn't do the necessary adjustment/s.
Remove the coil and dampening coil wires before exploring the adjustment mechanisms. I don't know what you've done before; so, all
I can do is text the below.
At the rear top is a knurled round threaded wire adjustment which will raise/lower the wire (and which changes the period). Try rotating that
slowly over whatever reaction range first....in conjunction with varying the front set screw, which you'll need to do probably constantly. Its
entirely possible that even a slight partial rotation or more; will get you into a full range of its indicator pointer.
Another potential "indicator/answer" could lie in your front single set screw adjustment setting. Try rotating that over a reasonable range
and observe whether the boom/mass hits the stop at the top the majority of the time. If (the boom/pointer) hits the top stop limit and stays there the
majority of the set screw range change; then that reaction would might re-affirm you need for more wire slack as above.
Adjusting both the front set screw and the top back screw is critical for this "boom/mass balance/pointer range" or in short; just being able to
see its oscillation movement range. The whole thing is kind of a crude weight balance with the spring acting as kind of a varying pivot force.
IF.....you've done all this before (?), and it still tends to go to the upper range limit/stop....then you might actually have to unclamp the
compression wire fitting and feed abit more wire down. Thats a really nasty job, as you'll be physically fighting the strong spring tension
while trying to place the wire lower and also be ready to tighten the compression wire clamp. Its possible that the previous owner/s might
have cut off the exposed wire coming out of the wire adjustment at the top/back (?), there should normally be some wire coming out there?
If there isn't any wire....and you're at the limit of adjustments...you may have to rewire it to give more room/slack of course. We can get
into that if necessary.
I have a love-hate relationship with this coil/magnet vertical. I like its long mechanical period; but I hate its temperature sensitivity. All in all, its
worth fussing with....theres no real mechanical alternative of course; outside of electronic extension of lesser period gizmo's. Most
amateurs have no vertical whatsoever....
Take care, Meredith