In a message dated 16/11/2007, gpayton880@....... writes:

I am searching for wiring details for using  Aluminum Housed Wirewound Power 
Resistors used for thermal  control inside an insulated housing for the 
seismic sensors.  It has been  suggested wiring several such resistors in series to 
accomplish a 10-30 watts  from the 110v AC house supply source.  I'm a little 
leery about the house  current for safety reasons and possible AC hum.

 Hi Jerry,
 
    Put a sheet of Al inside the top of the box, bolt  the resistors to it 
and earth the sheet. There should be no problems. The Al  sheet spreads the heat 
over the top of the inside of the case and keeps the  resistors cool. What 
you definitely DON'T want is a very hot resistor  generating a heat plume which 
stirs up the rest of the air.
    You can buy a digital electronic thermometer with  two sensors for about 
$20 See Extech from Mouser. One sensor is on an extension  lead. You put this 
inside the top of the case / on the seismometer and leave the  thermometer 
case in the air outside. Radioshack also sell thermometers, but  don't get a 
radio one. They may not work all that well  from inside an Al screened box. 

In studying the Mouser Electronics catalog, I can find several possible  
configurations using one to several resistors in series.  The  resistors specify 
their wattage capability, but have different resistance  values to choose from.

    I would be inclined to use Arcol 10 W resistors in  parallel. 2.2K at 
110V = 5.5W, 1.5K at 110V = 8W You will certainly need at  least 5 W for a Lehman 
size case, probably quite a lot more.

    I recommend the use of an electronic Max/Min  thermometer. The conditions 
vary so much between locations that you need to  actually measure of what is 
happening inside your box. If you can't get adequate  regulation - there are 
still large temperature variations - try folding a  single large sheet of 
bubblewrap over the whole case with the bubbles on the  inside. You may need to put 
the extension sensor on the ground under the  seismometer to check the actual 
ground variations. You can also put  polystyrene sheet over the ground  for a 
foot or more outside the  seismometer case to reduce ground temperature 
variations - the  seismometer then follows the subsoil temperature more closely.  
 
    Regards,
 
    Chris Chapman



   





In a message dated 16/11/2007, gpayton880@....... writes:
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>
  
I am searching for wiring details for using=20
  Aluminum Housed Wirewound Power Resistors used for therma=
l=20
  control inside an insulated housing for the seismic sensors.  It has=20=
been=20
  suggested wiring several such resistors in series to accomplish a 10-30 wa=
tts=20
  from the 110v AC house supply source.  I'm a little leery about the h=
ouse=20
  current for safety reasons and possible AC hum.
 Hi Jerry,
 
    Put a sheet of Al inside the top of the box, bo=
lt=20
the resistors to it and earth the sheet. There should be no problems. The Al=
=20
sheet spreads the heat over the top of the inside of the case and keeps the=20
resistors cool. What you definitely DON'T want is a very hot resistor=20
generating a heat plume which stirs up the rest of the air.
    You can buy a digital electronic thermometer wi=
th=20
two sensors for about $20 See Extech from Mouser. One sensor is on an extens=
ion=20
lead. You put this inside the top of the case / on the seismometer and leave=
 the=20
thermometer case in the air outside. Radioshack also sell thermometers, but=20
don't get a radio one. They may not work all that well=20
from inside an Al screened box. 
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>
  
In studying the Mouser Electronics catalog, I can find several possib=
le=20
  configurations using one to several resistors in series.  The=20
  resistors specify their wattage capability, but have different resist=
ance=20
  values to choose from.
    I would be inclined to use Arcol 10 W resistors=
 in=20
parallel. 2.2K at 110V =3D 5.5W, 1.5K at 110V =3D 8W You will certainly need=
 at=20
least 5 W for a Lehman size case, probably quite a lot more.

    I recommend the use of an electronic Max/Min=20
thermometer. The conditions vary so much between locations that you need to=20
actually measure of what is happening inside your box. If you can't get adeq=
uate=20
regulation - there are still large temperature variations - try folding=
 a=20
single large sheet of bubblewrap over the whole case with the bubbles on the=
=20
inside. You may need to put the extension sensor on the ground under the=20
seismometer to check the actual ground variations. You can also put=20
polystyrene sheet over the ground  for a foot or more outside the=20
seismometer case to reduce ground temperature variations - the=20
seismometer then follows the subsoil temperature more closely.  
 
    Regards,
 
    Chris Chapman