PSN-L Email List Message

Subject: Re: strange jumps
From: ChrisAtUpw@.......
Date: Tue, 25 Jul 2000 20:35:56 EDT

In a message dated 25/07/00 03:40:20 GMT Daylight Time, 
John.Tacinelli@........ writes:

> I have one of the Ward's seismographs.  It is working pretty well. 
> My problem is that at 8:45 PM every night I get a sudden 
> increase (or decrease) in voltage through my amplifier that causes the 
> to move off to the right hand side of the screen.  It stays there until 
> every morning. Then it goes right back. The seismograph itself doesn't seem 
> to move. It is set up in the school where I teach....  Maintenance thought 
> it might be the outside lights turning on but that happens much earlier.  
> That timing happens to coincide with the setting and rising of the sun (
> pretty close) but I can't think of anything solar that could affect a 
> magnetic coil inside a building in a time span of about 2 seconds.

    I am not familiar with the sensor system on the Wards' instrument, or 
which type of instrument it is, but you do mention a coil. I found, but didn't find a seismometer. Is the coil shielded and what 
is it's resonant frequency?  Is any bit of connecting cable about the right 
length to form a resonant aerial? A couple of ferrite rings on the speaker 
leads stopped the 95 MHz VHF pickup on my Hi-Fi.....  Can you use a 'scope to 
look at the signal as it passes through the amplifier? Can you plug some 
headphones, or maybe a battery radio with a line input socket, into the 
output of the instrument?

    Is the instrument earthed and are you sure that the earth return is 
actually earthed? We had quite a lot of fun when maintenance replaced some 
copper water pipe with a length of plastic....

    Using Darrel's thoughts, do these times correspond to air conditioning 
fans being switched off? Could this flex the floor a bit?

    I rather liked:-
    When you hear the thunder of hooves, think horses, not zebras.
    But would,  
    When you hear the thunder of hooves, think kids, not horses.
    be as appropriate?


    Chris Chapman

Public Seismic Network Mailing List (PSN-L)

[ Top ] [ Back ] [ Home Page ]

Larry Cochrane <cochrane@..............>