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