PSN-L Email List Message

Subject: Re: Seismograph for school
From: "tchannel" tchannel@..............
Date: Tue, 3 Oct 2006 10:28:57 -0600


Hi Bob,  I have questions about your great Horz. sensor and the picture.

1. You used solder for the mass,  is the mass volume fixed or is there a =
wide range of weights, one could use.  I guess the mass is to overcome =
the friction of the hinge and stay stationary.  The reason I ask is I =
see a wide range of masses, but most around 5#.  What is yours? and what =
is your beam length?

2. Again the solder, is non magnetic is this important as I see many =
things use as mass including iron?

3.  I see you used a resistor as a damp, and not a external damper =
device.  I have read about doing this, but could not understand the =
values for the resistor.  You used 94k (in parallal?) acrossed the coil? =
 How did you arrive at that value?

4. You indicate to use a 100k in place of the 10k when using Larry's =
amp,  which I will be using.  Why is that?

5.  The placement of the sensor:  Could it be on other than a concrete =
floor, a normal wood floor?  Could it be on carpet?  I know that is not =
the best choice, but many schools have such floors.  Or should one not =
bother with any other surface but a concrete floor?

Thanks for your advise, and "well done!"   Ted
  ----- Original Message -----=20
  From: Bobhelenmcclure@..........
  To: psn-l@.................
  Sent: Sunday, October 01, 2006 7:21 PM
  Subject: Re: Seismograph for school


  Hi all,

    I agree with Chris Chapman on the design of magnets and coils for =
horizontal sensors. Those who have an interest in building their own =
sensors should take a look at mine on John Lahr's web site, especially =
page http://www.jclahr.com/science/psn/mcclure/horiz2.html

    I operate three sensors for Z, N, and E. They are adjusted to fairly =
short natural periods, ranging from 5 to 14 seconds. I extend their =
effective period to 24 seconds by a digital filter of my own design, =
with excellent results.

    The magnets I recommend are available for $5.50 each, 50mm x 18mm x =
6mm block magnet, from http://www.gaussboys.com  You will need four of =
them and two pieces of 1/4 inch flat steel, two inches by three inches, =
and four steel bolts to make a magnet assembly. You do not necessarily =
need separate damping magnets. Just shunt the pickup coil with the =
appropriate resistance.

  Bob McClure







Hi Bob,  I have questions about your great Horz. sensor and = the=20 picture.
 
1. You used solder for the mass,  is the mass volume fixed or = is there=20 a wide range of weights, one could use.  I guess the mass is to = overcome=20 the friction of the hinge and stay stationary.  The reason I ask is = I see a=20 wide range of masses, but most around 5#.  What is yours? and what = is your=20 beam length?
 
2. Again the solder, is non magnetic is this important as I see = many things=20 use as mass including iron?
 
3.  I see you used a resistor as a damp, and not a external = damper=20 device.  I have read about doing this, but could not understand the = values=20 for the resistor.  You used 94k (in parallal?) acrossed the = coil?  How=20 did you arrive at that value?
 
4. You indicate to use a 100k in place of the 10k when using = Larry's=20 amp,  which I will be using.  Why is that?
 
5.  The placement of the sensor:  Could it be on other = than a=20 concrete floor, a normal wood floor?  Could it be on carpet?  = I know=20 that is not the best choice, but many schools have such floors.  Or = should=20 one not bother with any other surface but a concrete floor?
 
Thanks for your advise, and "well done!"   Ted
----- Original Message -----
From:=20 Bobhelenmcclure@....... =
To: psn-l@..............
Sent: Sunday, October 01, 2006 = 7:21=20 PM
Subject: Re: Seismograph for = school

Hi all,
 
  I agree with Chris Chapman on the design of magnets and = coils for=20 horizontal sensors. Those who have an interest in building their own = sensors=20 should take a look at mine on John Lahr's web site, especially page http://www= ..jclahr.com/science/psn/mcclure/horiz2.html
 
  I operate three sensors for Z, N, and E. They are adjusted = to=20 fairly short natural periods, ranging from 5 to 14 seconds. I extend = their=20 effective period to 24 seconds by a digital filter of my own design, = with=20 excellent results.
 
  The magnets I recommend are available for $5.50 each, 50mm = x 18mm=20 x 6mm block magnet, from http://www.gaussboys.com  = You will=20 need four of them and two pieces of 1/4 inch flat steel, two inches by = three=20 inches, and four steel bolts to make a magnet assembly. You do not = necessarily=20 need separate damping magnets. Just shunt the pickup coil with the = appropriate=20 resistance.
 
Bob McClure
Locust Valley, NY

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