Hi Chris, I agree 100% and I think that's exactly what I said below. I'll
try to state it clearer. Make sure the vertical upright is at zero degree
and then adjust the boom so that it is level. Next add 1-5 degree of tile in
the upper most point of the upright (not the boom). This will change centre
of the line between the two joins. Did anybody ever mention that by changing
the centre line in the uprights the boom will actually lower at the mass end
and the boom needs to be leveled again? Regards, Steve

 

From: psn-l-request@.............. [mailto:psn-l-request@............... On
Behalf Of ChrisAtUpw@.......
Sent: Saturday, May 09, 2009 8:44 PM
To: psn-l@..............
Subject: Re: Incresing the period of a lehmans seismomter ?

 

In a message dated 10/05/2009, shammon1@............. writes:

Try using a bubble level to know when the boom is level. Then tilt the end
of the boom down, never up. I normally start by using a level to make sure
the vertical upright is at zero degrees and then I level the boom. I then
add about 1-5 degree of tilt in the upper most point of the upright in the
direction of the boom. I have three level screws the base plate and a
machine screw in the end of the boom to make the adjustment. 
Regards, Stve Hammond 

Hi Steve,

 

    The period is not effected by the angle of the boom itself. It is the
angle between the local vertical and the line joining the two centres of
rotation which is critical for determining the period.

 

    In
http://jclahr.com/science/psn/chapman/2008%20lehman/lehman_prototype.jpg
this line joins the centre of the 1/2" ball bearing on the upright with the
fine wire at the top where it is clamped by the edges of the brass variable
rotating clamp washers. The horizontal arm is set up parallel to the base
bar just for convenience.

 

    Regards,

 

    Chris Chapman














Hi Chris, I agree 100% and I think that’s exactly =
what I
said below. I’ll try to state it clearer. Make sure the vertical =
upright
is at zero degree and then adjust the boom so that it is level. Next add =
1-5
degree of tile in the upper most point of the upright (not the boom). =
This will
change centre of the line between the two joins. Did anybody ever =
mention that
by changing the centre line in the uprights the boom will actually lower =
at the
mass end and the boom needs to be leveled again? Regards, =
Steve

 





From:=

psn-l-request@.............. [mailto:psn-l-request@............... On =
Behalf
Of ChrisAtUpw@.......

Sent: Saturday, May 09, 2009 8:44 PM

To: psn-l@..............

Subject: Re: Incresing the period of a lehmans seismomter =
?





 





In a message dated 10/05/2009, shammon1@............. =
writes:





Try using a bubble level to know when the boom is level. =
Then tilt
the end of the boom down, never up. I normally start by using a level to =
make
sure the vertical upright is at zero degrees and then I level the boom. =
I then
add about 1-5 degree of tilt in the upper most point of the upright =
in the
direction of the boom. I have three level screws the base plate and a =
machine
screw in the end of the boom to make the adjustment. 

Regards, Stve Hammond 







Hi Steve,





 





    The period is not effected by the =
angle of
the boom itself. It is the angle between the local vertical and the line
joining the two centres of rotation which is critical for determining =
the
period.





 





    In http://jclahr.com/science/psn/chapman/2008%20lehman/lehman_proto=
type.jpg this
line joins the centre of the 1/2" ball bearing on the upright =
with
the fine wire at the top where it is clamped by the edges of =
the
brass variable rotating clamp washers. The horizontal arm is set up =
parallel to
the base bar just for convenience.





 





    Regards,





 





    Chris Chapman