In a message dated 2006/10/27, jonfr500@......... writes:

> How does sensor failure appear in the 4.5Hz geophone ?
> 
Hi Jon,

       The most likely problem is the failure of a soldered joint giving an 
open circuit, a cable break giving an open circuit, or a melted cable 
insulation giving a short circuit.

       The L15B geophones that I bought from Larry were 380 Ohms. I needed to 
solder a 2.7 K Ohm resistors across them to give optimal damping.
       1/380 + 1/2700 = 1/R = 1/333, hence putting a resistance meter on the 
end of the cable should read about 333 Ohms.

       When you bought the geophones, were they wired up with connecting 
cable, or did you have to fit one? I seem to remember you were using CAT5 cable? 
The main reason why I don't use this for geophones is that the wires are solid 
copper which can simply break when bent repeatedly.
       I use screened multicore which may have 7 or more small wires twisted 
together as the conductor. I use six core with a braided copper screen 
enclosing the bundle of wires. 

       Were the damping resistors soldered across the geophone terminals in 
the plastic case, or did you have to do it? 

       Use the resistance range on your meter to measure the resistances 
where the cables connect to your amplifier board. What are the readings? Remember 
that the 380 Ohm geophones have +/-5% tolerence ---> 361 to 399 Ohms.

       Regards,

       Chris Chapman
In a me=
ssage dated 2006/10/27, jonfr500@......... writes:



How does sensor failure appear=20=
in the 4.5Hz geophone ?



Hi Jon,



       The most likely problem is the failure=20=
of a soldered joint giving an open circuit, a cable break giving an open cir=
cuit, or a melted cable insulation giving a short circuit.



       The L15B geophones that I bought from L=
arry were 380 Ohms. I needed to solder a 2.7 K Ohm resistors across them to=20=
give optimal damping.

       1/380 + 1/2700 =3D 1/R =3D 1/333, hence=
 putting a resistance meter on the end of the cable should read about 333 Oh=
ms.



       When you bought the geophones, were the=
y wired up with connecting cable, or did you have to fit one? I seem to reme=
mber you were using CAT5 cable? The main reason why I don't use this for geo=
phones is that the wires are solid copper which can simply break when bent r=
epeatedly.

       I use screened multicore which may have=
 7 or more small wires twisted together as the conductor. I use six core wit=
h a braided copper screen enclosing the bundle of wires. 



       Were the damping resistors soldered acr=
oss the geophone terminals in the plastic case, or did you have to do it? 


       Use the resistance range on your meter=20=
to measure the resistances where the cables connect to your amplifier board.=
 What are the readings? Remember that the 380 Ohm geophones have +/-5% toler=
ence ---> 361 to 399 Ohms.



       Regards,



       Chris Chapman