PSN-L Email List Message
Subject: Re: gain for lehman type sensor ?
From: ChrisAtUpw@.......
Date: Sun, 20 May 2007 08:55:36 EDT
In a message dated 2007/05/20, jonfr@......... writes:
> Hi all
> What is the best gain for Lehman type sensor? I am going to use coils
> and magnet from Larry. The gain on the board is set on 1000.
> J=F3n Fr=EDmann
Hi Jon,
The 'best' gain is determined by the instrument period, the strength=20
of the magnet and the coil shape, area and turns. In practice you set the=20
Lehman to give a period of maybe 25 seconds and select the gain to give coun=
ts of=20
say 200. The signal will be mostly background microseisms, which you have to=
=20
filter out, leaving the quake signals.
Can you not get any NdFeB square magnets? I use four off 1" square x=20
1/8" thick ones on two 6mm mild steel backing plates and wind my own=20
rectangular coils to suit, made from old glass circuit board. See 'Sensor Co=
il / Magnet=20
System' at the bottom of=20
http://jclahr.com/science/psn/chapman/lehman/index.html
This allows about +/-12 mm tilt drift to still give the same output=20
sensitivity. You should be able to buy 0.125 mm dia insulated copper wire re=
f.=20
YN92A from your Maplins agent in Iceland. It will give a much higher output=
=20
than the Alnico U magnets.
Regards,
Chris Chapman =20
In a me=
ssage dated 2007/05/20, jonfr@......... writes:
Hi all
What is the best gain for Lehman type sensor? I am going to use coils
and magnet from Larry. The gain on the board is set on 1000.
J=F3n Fr=EDmann
Hi Jon,
The 'best' gain is determined by the in=
strument period, the strength of the magnet and the coil shape, area and tur=
ns. In practice you set the Lehman to give a period of maybe 25 seconds and=20=
select the gain to give counts of say 200. The signal will be mostly backgro=
und microseisms, which you have to filter out, leaving the quake signals.
Can you not get any NdFeB square magnet=
s? I use four off 1" square x 1/8" thick ones on two 6mm mild steel backing=20=
plates and wind my own rectangular coils to suit, made from old glass circui=
t board. See 'Sensor Coil / Magnet System' at the bottom of http://jclahr.co=
m/science/psn/chapman/lehman/index.html
This allows about +/-12 mm tilt drift t=
o still give the same output sensitivity. You should be able to buy 0.125 mm=
dia insulated copper wire ref. YN92A from your Maplins agent in Icela=
nd. It will give a much higher output than the Alnico U magnets.
Regards,
Chris Chapman
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