In a message dated 2006/10/18, tchannel@.............. writes:

> As a newcomer to these issues, I had no idea the importance of these 
> enclosures.   I did not realize that invisible air currents in the room, caused by 
> the different in floor vs. air temperature, would cause huge noise.

Hi Ted,
       
       With Larry's low noise amplifier and a Neo magnet sensor, your 
amplifier noise level is likely as a rough guess to be less than 20 nano metres. That 
is 20 millionths of 1 mm. My Lehman LVDT sensor has a noise level of about 7 
nano metres, but the environmental noise is well over 10x this. These sensors 
are extremely sensitive.

> Q 1. I understand that some people orient their sensor N/S others E/W,  Are 
> the sensors ever oriented at a 45 degree angle between the two?

       It is entirely up to you, but if you want to compare your results with 
others, or with USGS sites, you need the same orientation. Remember that if 
the axis of the Lehman is N/S, the detection sensitivity is E/W.

> Q 2. What are the expectations of a Lehman sensor? I know that depends on 
> many factors, and not the lease of which is the quality of the sensor, and its 
> environment, as well as the type and location of the events. But just in 
> general terms. The AS1, which is not a Lehman suggest one should be able to see 
> 6.0m from several thousand mile away, or something like that.  

       You should be able to get significantly better results than an AS-1, 
but what you see is likely to depend almost entirely on the local man made and 
natural environmental noise. With say a 25 to 30 sec period, good bearings and 
a rigid frame, I would expect you to be able to detect mag 6 quakes world 
wide. Mag 3 quakes from 200 to maybe 500 km. You need to learn how best to set 
your display filters. The professionals can get better results since they choose 
low noise sites and may also bury their seismometers ~100 m deep to reduce 
surface noise. 

       See http://jclahr.com/science/psn/magnitude.html Note the small 
control buttons at the bottom of the screen.

       Regards,

       Chris Chapman
In a me=
ssage dated 2006/10/18, tchannel@.............. writes:



As a newcomer to these issues,=20=
I had no idea the importance of these enclosures.   I did not real=
ize that invisible air currents in the room, caused by the different in floo=
r vs. air temperature, would cause huge noise.




Hi Ted,

       

       With Larry's low noise amplifier and a=20=
Neo magnet sensor, your amplifier noise level is likely as a rough guess to=20=
be less than 20 nano metres. That is 20 millionths of 1 mm. My Lehman LVDT s=
ensor has a noise level of about 7 nano metres, but the environmental noise=20=
is well over 10x this. These sensors are extremely sensitive.



Q 1. I understand that some pe=
ople orient their sensor N/S others E/W,  Are the sensors ever oriented=
 at a 45 degree angle between the two?




       It is entirely up to you, but if you w=
ant to compare your results with others, or with USGS sites, you need the sa=
me orientation. Remember that if the axis of the Lehman is N/S, the detectio=
n sensitivity is E/W.



Q 2. What are the expectations=
 of a Lehman sensor? I know that depends on many factors, and not the lease=20=
of which is the quality of the sensor, and its environment, as well as the t=
ype and location of the events. But just in general terms. The AS1, which is=
 not a Lehman suggest one should be able to see 6.0m from several thousand m=
ile away, or something like that.  




       You should be able to get significantly=
 better results than an AS-1, but what you see is likely to depend almost en=
tirely on the local man made and natural environmental noise. With say a 25=20=
to 30 sec period, good bearings and a rigid frame, I would expect you to be=20=
able to detect mag 6 quakes world wide. Mag 3 quakes from 200 to maybe 500 k=
m. You need to learn how best to set your display filters. The professionals=
 can get better results since they choose low noise sites and may also bury=20=
their seismometers ~100 m deep to reduce surface noise. 



       See http://jclahr.com/science/psn/magni=
tude.html Note the small control buttons at the bottom of the screen.



       Regards,



       Chris Chapman