From: Brett Nordgren 

Sent: Fri, 16 Nov 2012 23:07
Subject: Re: Geophone Velocity Question


Geoff:
For wire resistance, see:  http://bnordgren.org/seismo/WireTempco.pdf
I assume that copper still acts the way it did in 1961 when the table=20
was printed.
Their formula apparently is RT2 =3D RT1*(1+(T1-T2)*0.00393)) which=20
should be a fairly decent approximation.
Regards.
Brett

> The geophone is HS10-1 1Hz and the
>resistance vary greatly over the year.
>In winter it can be near 400Ohms and in
>summer about 440 or 450.=20

****Hi Geoff,=20
    The resistivity temperature coefficient of Copper is about + 4.3x10^-3 =
per C Deg --> the resistance=20
of a copper coil INCREASES as the temperature increases. Assuming that you =
have a coil of resistance=20
4,000 Ohm at 0 C, you can expect about 690 ohms increase at 40 C and -690 O=
hms decrease at -40 C.=20
That should cover ALL your likely weather conditions !  Sounds like you cou=
ld have either a resistance=20
measuring problem or a dud geophone.     =20

>The single best way to get a proper response
>is with a 5 second geophone with like 3V/(in/sec)
>or better generator constant and vertical and small
>enough to bury in the ground.=20
>just need that 5 second geophone at a reasonable cost.
>I have seen no better geophone than the SPZ HS10-1.
>But it is horribly expensive as a new device.

****5 second geophones are NOT MADE - but you can extend the period range o=
f a geophone by about=20
x10 fairly easily !! You can sometimes get secondhand Willmore III sensors =
which cover this range.=20
    You can MAKE quite a cheap 5 sec. sensor from a 44mm OD piezo sounder d=
isk and a ~1 oz weight.=20

    Regards,=20

    Chris Chapman

=20
From: Brett Nordgren <br=
ett3nt@.............>


Sent: Fri, 16 Nov 2012 23:07=



Subject: Re: Geophone Velocity Question















Geoff:
For wire resistance, see:  http://bnordgren.org/seismo/WireTempco.pdf
I assume that copper still acts the way it did in 1961 when the table=20
was printed.
Their formula apparently is RT2 =3D RT1*(1+(T1-T2)*0.00393)) which=20
should be a fairly decent approximation.
Regards.
Brett

> The geophone is HS10-1 1Hz and the
>resistance vary greatly over the year.
>In winter it can be near 400Ohms and in
>summer about 440 or 450.=20


****Hi Geoff, 

    The resist=
ivity temperature coefficient of =
Copper is about + 4.3x10^-3 =
per C Deg --&g=
t; the resistance 

of a copper coil INCREASES as the=
 temperature increases. Assuming that=
 you have a coil of resistance 

4,000 Ohm at 0 C, you can expect =
about 690 ohms increase at 40 C and -690 Ohms decrease at -40 C. 

That should cover ALL your likely=
 weather conditions !  Sounds like you could have either=
 a resistance 

measuring problem or a dud geopho=
ne.      

>The single best way to get a proper response
>is with a 5 second geophone with like 3V/(in/sec)
>or better generator constant and vertical and small
>enough to bury in the ground.=20
>just need that 5 second geophone at a reasonable cost.
>I have seen no better geophone than the SPZ HS10-1.
>But it is horribly expensive as a new device.

****5 sec=
ond geophones are NOT MADE - but you can =
extend the period range of a geophone by about 

x10 fairly easily !! You can sometimes get secondhand Willmore III sensors =
which cover this range. 

    You can MAKE quite a cheap 5 sec. sensor from a=
 44mm OD piezo sounder disk and a ~1 oz weight. 



    Regards, 



    Chris Chapman