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 
trace 
> to move off to the right hand side of the screen.  It stays there until 
5:45 
> 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 
www.wardsci.com, 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?

    Regards,

    Chris Chapman
__________________________________________________________

Public Seismic Network Mailing List (PSN-L)