Hi Folks,   In the past I have used 38ga copper wire for making standard 
magnet coils.   I have a friend who gave me a spool of 40ga copper magnet 
wire, approx 1lb.
This is not "paired" wire.  It is a single strand of coated, magnet wire.
This is very very fine wire.   I have not used it to wrap a coil, but I 
think I could if I was careful.  Obviously it can break easily.   I do 
believe this is was purchased at a Army Navy surplus store.

Happy to share this wire, I will never use it all.    I am not sure how 
share it, but I am open to suggestions.   One method would be to send me a 
empty spool, and instruct me as to how many wrap to apply to it?

On a different subject............for those interested.........The vertical, 
wall mounted sensor, I call the "Vertical Mount, Garden gate, Horizontal 
Seismic Sensor" VGHS,  which is mostly like a Lehman, but mounts to the 
wall, using a single vertical mechanism, is operating perfectly.   I have 
not adjusted it in several months, and it is recording very well.   I have 
it set to 22 seconds.
I have a .pdf file to share.

Cheers,
Ted




----- Original Message ----- 
From: "Geoffrey" 
To: 
Sent: Monday, February 15, 2010 9:20 PM
Subject: Re: Velocity Sensor Designed Specifiically for diff input


> Hello Chris,
>
> I have in the past ( like 1970s )
> seen wire that is "like" 40 guage paired
> magnet wire which was designed
> to be used with expendable
> bathythermograph probes.
> ( make a temp profile of the ocean waters )
>
> I have never seen such wire
> available to anything but
> government.
>
> have you ever seen such wire in any
> guage at all ?
>
> Maybe its not even copper
> If I know Govt it might be silver wire
> but i think it looked copper.
>
> Lets say twin 30 gauge copper wire
> which is enameled on a 1000 or more foot
> spool ?
>
> I would think this be the right kind of wire
> to make a center tapped sensor coil ?
>
> regards,
> geoff
>
> ----- Original Message ----- 
> From: 
> To: 
> Sent: Saturday, February 06, 2010 4:26 PM
> Subject: Re: Velocity Sensor Designed Specifiically for diff input
>
>
>> In a message dated 06/02/2010, gmvoeth@........... writes:
>>
>> What i  mean is a coil like a center tapped inductor
>>
>> +.......|
>> C
>> O
>> Gnd.....|
>> I
>> L
>> -.......|
>>
>> CO part  and the IL part have to be identical. I do not know if you can 
>> wind such a  thing all at once or need two identical yet seperate coil 
>> magnet  assemblies.
>> Hi Geoff,
>>
>>    You can wind it quite easily using two supply reels  winding on both 
>> wires at the same time.
>>
>> Forget  the amplifier part altogether, use what you want.
>>    The ordinary single opamp with four resistors will  allow you to wind 
>> a single coil and use an amplifier of that type.
>>
>> I have  never built such a singular thing and can only guess where to 
>> begin.
>>
>> I  do know that inital signal strength and signal to noise ratio is 
>> paramount for  any sensor at all and not just for areas of our own 
>> interest.
>>
>> Easiest  way to get a good signal to noise ratio seems to be to use a two 
>> ton (avd.)  mass instead of a two pound (avd.) one. The highest density 
>> material you can  afford.
>>    That is not neccessary or desirable.
>>
>> Superconducting wire sounds ideal yet none at room temp as far as I 
>> know.
>>    There is none and unlikely to be any in the  future.
>>
>> At the  moment i am thinking two of your coil/magnet ideas in additive 
>> fashion  connected to the same mass.
>> Two coils should double the signal right from  the start. Four would 
>> quadruple it.
>>
>>
>> You usually do better by doubling the number of  turns on a coil. A large 
>> increase in the output can be readily achieved by using  thicker NdFeB 
>> magnets, rather than by using more turns on the coil. The limit is  set 
>> by diamagnetic forces on the copper wire at the edges of the magnets. 
>> Copper  wire varies in it's magnetic properties.
>>    If you use a true differential amplifier like the  INA118 with a 
>> double wound coil, you can use finer wire since the coil  resistance is 
>> not so important. Calculate the kT noise voltage in the coil. Regards,
>>
>>    Chris  Chapman
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