PSN-L Email List Message

Subject: Re: Velocity Sensor Designed Specifiically for diff input
From: "Geoffrey" gmvoeth@...........
Date: Mon, 15 Feb 2010 21:20:38 -0700

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

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 ?


----- Original Message ----- 
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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