PSN-L Email List Message

Subject: Re: Velocity Sensor Designed Specifiically for diff input
From: "Geoffrey" gmvoeth@...........
Date: Fri, 19 Feb 2010 06:56:16 -0700

Hello Mr. Channel,

Would you be willing to share your plans with
me for a 5 or 10 second device instead of a 22 second device ?

I am interested in possibly building
such a thing but do not have the
ability/monies to design it or test a prototype.

I may not be able to afford it but I need to
see it to know.

You can send me the plans
in an email at
gmvoeth at or
point me to a web
or ftp site or possibly post
on a common alt binary news group.
( Anarchist, Lunatics and, Terrorists :-/ )
{not kidding---That's what they call the alt news groups}
If you are willing to build and sell
only the sensor ( not the electronics )
I might be interested but first
I must understand this device.

I am no expert, yet , like to
build kits like the old Heath kit
stuff of the past.

It must be only vertical in its detection
of motion either displacement or velocity.

It must produce a signal level
being no less than
3Volts per inch per second.
at one hertz frequency into
,like ,  10K ohms of load.

It must have a magnetic damping system
separate from the sensor itself.

It must have a free period of 5 seconds with
a Q of 1/SQR(2) which might be slightly different
with minimum damping.

It must be relatively insensitive to
temperature changes.
I have tried playing with various sensors
like hall effect but have found them
too temperature sensitive.
Coil and magnet are just fine.

If I were like B. Gates Id hire
a real MIT physics major to design
a proper device and a real Mechanical engineer to build it.
But alas...I'm no such creature.

If the device had three fixed calibrated
settings one for 10 seconds and one for 5
seconds and one for 1Hz.
that's a nice feature also.

I have no need for more than 10 seconds
of free period at the sensor.
Since I am only interested in P and S

It would be required for me to build two
identical devices to use this in the
right way. Or there's no sense in
pursuing this further.

These specs are my own interests independent
of other people.
I have no interest in capitalizing on
this, its only a hobby for myself.

I figure if you have successfully built a 22 second
vertical device then what I want is easier to build.

If I could find a decent bathroom scale
Id simply set it up and put 5 gallons of water
on it and look at the output with
a 16 bit A/D converter.


----- Original Message ----- 
From: "Ted Channel" 
Sent: Tuesday, February 16, 2010 5:43 AM
Subject: Re: Velocity Sensor Designed Specifiically for diff input

> 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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