Hi Geoff=0AIf you are measuring velocity not displacement there shouldn't b= e any =0Atemperature affects except maybe the electronics. There =A0was a p= ost awile back =0Awith a link to Ebay=A0for a coil winding gismo for <$20. = I'll see if=A0I can find =0Athe link.=A0=A0Regards=0ABarry=0Ahttp://www.sei= smicvault.com =0A=0A=0A=0A=0A________________________________=0AFrom: Geoff= rey=0ATo: psn-l@...................... Sun, July 18, = 2010 4:16:55 PM=0ASubject: Re: Velocity Sensor Question ?=0A=0AHere is the = preamp.=0AI was going to place it right at the geophone.=0AThe two exact co= ils will change in step=0Awith temperature to keep a stable DC=0Abaseline. = Minimal drift.=0A=0Ahttp://gmvoeth.home.mchsi.com/AMP001.jpg=0A=0AAny reaso= n this should not be right ?=0A=0AWill Larry sell only the coils ?=0AI migh= t get two to try my ideas.=0A=0AI looked into getting ten wound but the com= pany=0Awas outragious in its (retooling fees)=0AIt seems they cant simply d= o it even tho they=0Awind the things for a living.=0A=0AThanks for your res= ponse.=0A=0ABest Regards,=0Ageoff=0A=0APS: if PSN had a binary news server.= =0A=A0 =A0 we could post any kind of file=0A=A0 =A0 for people to have/look= at ?=0A=A0 =A0 Could someone create a [alt.binaries.seismic.psn]=0A=A0 =A0= news group, I understand there is a complex process=0A=A0 =A0 but the crea= tion is free and almost all ISP have=0A=A0 =A0 one as part of their service= .. I have tried to understand=0A=A0 =A0 the process but like Linux OS I cant= understand it.=0A=A0 =A0 I have tried Linux several times but cant make it= functional.=0A=A0 =A0 Fedora 10 installs OK but I just cant get it to be f= unctional.=0A=0A----- Original Message ----- From: "Brett Nordgren" =0ATo: =0ASent: Sunday, July 18, 201= 0 10:57 AM=0ASubject: Re: Velocity Sensor Question ?=0A=0A=0A> Hi Geoff,=0A= > =0A> At 07:30 AM 7/18/2010, you wrote:=0A>> Hello Mr. Nordgren;=0A>> =0A>= > The question I have is thus:=0A>> =0A>> Is that coil right for the magnet= s or,=0A>> Should it be rectangular in shape with the=0A>> two vertical sid= es of the rectangle outside the magnetic flux ?=0A> =0A> Ideally you want y= our sensor to be linear.=A0 If you move the coil at a constant =0A>speed ov= er its mechanical range you would like to see a relatively constant =0A>vol= tage out.=A0 You can achieve that in two ways.=A0 Have the magnet pole face= s =0A>large enough that all the coil wires stay well within the magnetic re= gion, or =0A>alternatively, make them small enough that all the magnetic li= nes stay within =0A>the region filled with coil wires.=A0 When you have the= edges of the magnetic =0A>field moving across the outside or inside edges = of the coil, the linearity =0A>suffers, though perhaps not enough to worry = about too much.=0A> =0A>> I figure I may need like 1206 feet of 36 AWG(B&S)= copper enameled wire=0A>> for a 2100 turns 500 ohm coil ?=0A>> =0A>> The 2= 100 turns are of enamled wire without a heavy coat of enamel.=0A>> =0A>> Is= 2100 turns enough ?=0A> =0A> I guess the question would have to be, enough= for what?=A0 It all depends on how =0A>sensitive you plan to make your sig= nal detection circuit--that is, how much =0A>amplifier gain do you plan to = have and if you are connecting to an A/D device, =0A>what is its sensitivit= y?=A0 In general, I would try to start with the smallest =0A>wire and the l= argest number of turns I could easily manage.=A0 Coil resistance of =0A>sev= eral K Ohms wouldn't be unreasonable.=A0 The coil Larry sells I believe has= =0A>10,000 turns and is 9,000 Ohms.=0A> =0A>> Would it be better if the co= il had a copper or iron core ?=0A> =0A> Definitely no.=A0 Iron would "suck = in" the magnetic lines, away from the wires =0A>where you want them to be.= =A0 Copper, unless it made a complete loop, wouldn't do =0A>much since it w= ouldn't be in the magnetic field, certainly nothing particularly =0A>helpfu= l.=0A> =0A>> This would mean a custom coil rectangular instead of circular.= =0A> =0A> Possibly you'd get slightly better linearity with a rectangular c= oil and =0A>rectangular magnet pole pieces, but either shape should work re= asonably well for =0A>what you are trying to do.=0A> =0A>> I think it may b= e possible to have two identical=0A>> coils center tapped in the middle wit= h a single=0A>> rare earth magnet in the middle between the two=0A>> coils = then you have the right setup for=0A>> a proper op amp differential circuit= ..=0A> =0A> I may be wrong, but I am suspecting that you are wanting to conn= ect one output =0A>to each of the two inputs of an op amp.=A0 If that is wh= at you are thinking about, =0A>the problem will be too much gain.=A0 Typica= l op amps have voltage gains of 100's =0A>of thousands, or more often, mill= ions.=A0 Generally for approximate analyses =0A>designers assume that their= gain is infinite.=A0 That means that extremely tiny =0A>input signals (noi= se) would have the op amp output bouncing between its voltage =0A>limits--n= ot very useful.=0A> =0A> Usually op amps are connected up as single ended a= mplifiers using a =0A>two-resistor feedback circuit, which makes a very nic= e voltage amplifier.=0A> =0A> See: http://www.analog.com/static/imported-fi= les/tutorials/MT-032.pdf=A0 Figure =0A>3.=0A> =0A> If you do that, one coil= will work fine, and by changing the resistor values =0A>you can choose the= amplifier gain to complement your coil sensitivity.=A0 The only =0A>advant= age I can think of for some kind of differential coil setup is that it =0A>= might not be as sensitive to 60 Hz hum.=A0 Though it probably wouldn't be t= hat =0A>hard to connect a differential coil to a single-ended amplifier, so= rt of like a =0A>guitar "hum-bucking" pickup.=0A> =0A> An instrumentation a= mplifier *would* allow for independent connections to a =0A>pair of coils, = but they tend to be a lot more expensive and their gain usually =0A>can't b= e adjusted as precisely.=0A> =0A> See: http://www.analog.com/static/importe= d-files/tutorials/MT-032.pdf=A0 Figure =0A>2.=0A> =0A>> +COIL-=A0 NmagnetS = +COIL-=0A>> =0A>> THE left coil - is connected to right coil +=0A>> which i= s then the ground.=0A>> =0A>> Left Coil + goes to op amp +=0A>> and=0A>> Ri= ght coil - goes to op amp -=0A>> =0A>> The relative motion is magnet fixed = to ground=0A>> and coil fixed to device.=0A>> =0A>> Coil is stable and magn= et moves right and left=0A>> between the coils.=0A>> =0A>> Possibly +/- 2mm= of range of motion.=0A>> =0A>> Each coil having 1050 to 2100 turns=0A>> cu= stom wound to be exactly the same.=0A> =0A> Hope that's a start,=0A> Brett= =0A> =0A> =0A> =0A> _______________________________________________________= ___=0A> =0A> Public Seismic Network Mailing List (PSN-L)=0A> =0A> To leave = this list email PSN-L-REQUEST@.............. with the body of the =0A>messa= ge (first line only): unsubscribe=0A> See http://www.seismicnet.com/maillis= t.html for more information.=0A> =0A_______________________________________= ___________________=0A=0APublic Seismic Network Mailing List (PSN-L)=0A=0AT= o leave this list email PSN-L-REQUEST@.............. with the body of the = =0Amessage (first line only): unsubscribe=0ASee http://www.seismicnet.com/m= =0AHi Geoff=0AIf you are measuri= ng velocity not displacement there shouldn't be any temperature affects exc= ept maybe the electronics. There was a post awile back with a link to= Ebay for a coil winding gismo for <$20. I'll see if I can fin= d the link.Regards
Barry
http://www.seismicvault.com = =0A=0A=
=0A=0A
=0AFrom: Geoffrey &l= t;gmvoeth@...........>
To: psn-l@..............
Sent: Sun, July 18, 2010 4:16:55 PM
Subject: Re: Velocity Sensor Question ?
Here i= s the preamp.
I was going to place it right at the geophone.
The two = exact coils will change in step
with temperature to keep a stable DC
= baseline. Minimal drift.
http://gmvoeth.home.mchsi.com/AMP001.jpg
Any reason this should not be right ?
Will Larry sell only the = coils ?
I might get two to try my ideas.
I looked into getting te= n wound but the company
was outragious in its (retooling fees)
It see= ms they cant simply do it even tho they
wind the things for a living.
Thanks for your response.
Best Regards,
geoff
PS: if = PSN had a binary news server.
we could post any kind of file
&nb= sp; for people to have/look at ?
Could someone crea= te a [alt.binaries.seismic.psn]
news group, I understand t= here is a complex process
but the creation is free and alm= ost all ISP have
one as part of their service. I have trie= d to understand
the process but like Linux OS I cant under= stand it.
I have tried Linux several times but cant make i= t functional.
Fedora 10 installs OK but I just cant get it= to be functional.
----- Original Message ----- From: "Brett Nordgre= n" <brett3nt@.............>
To: <psn-l@webtro= nics.com>
Sent: Sunday, July 18, 2010 10:57 AM
Subject: Re: Velocity Sensor Question ?
> Hi Geoff,
>
> At 0= 7:30 AM 7/18/2010, you wrote:
>> Hello Mr. Nordgren;
>> <= BR>>> The question I have is thus:
>>
>> Is that c= oil right for the magnets or,
>> Should it be rectangular in shape= with the
>> two vertical sides of the rectangle outside the magne= tic flux ?
>
> Ideally you want your sensor to be linear. = ; If you move the coil at a constant speed over its mechanical range you wo= uld like to see a relatively constant voltage out. You can achieve th= at in two ways. Have the magnet pole faces large enough that all the = coil wires stay well within the magnetic region, or alternatively, make the= m small enough that all the magnetic lines stay within the region filled wi= th coil wires. When you have the edges of the magnetic field moving a= cross the outside or inside edges of the coil, the linearity suffers, though perhaps not enough to worry about too much.
>
&g= t;> I figure I may need like 1206 feet of 36 AWG(B&S) copper enamele= d wire
>> for a 2100 turns 500 ohm coil ?
>>
>>= The 2100 turns are of enamled wire without a heavy coat of enamel.
>= >
>> Is 2100 turns enough ?
>
> I guess the quest= ion would have to be, enough for what? It all depends on how sensitiv= e you plan to make your signal detection circuit--that is, how much amplifi= er gain do you plan to have and if you are connecting to an A/D device, wha= t is its sensitivity? In general, I would try to start with the small= est wire and the largest number of turns I could easily manage. Coil = resistance of several K Ohms wouldn't be unreasonable. The coil Larry= sells I believe has 10,000 turns and is 9,000 Ohms.
>
>> W= ould it be better if the coil had a copper or iron core ?
>
> Definitely no. Iron would "suck in" the magnetic lines, awa= y from the wires where you want them to be. Copper, unless it made a = complete loop, wouldn't do much since it wouldn't be in the magnetic field,= certainly nothing particularly helpful.
>
>> This would me= an a custom coil rectangular instead of circular.
>
> Possibly= you'd get slightly better linearity with a rectangular coil and rectangula= r magnet pole pieces, but either shape should work reasonably well for what= you are trying to do.
>
>> I think it may be possible to h= ave two identical
>> coils center tapped in the middle with a sing= le
>> rare earth magnet in the middle between the two
>> = coils then you have the right setup for
>> a proper op amp differe= ntial circuit.
>
> I may be wrong, but I am suspecting that yo= u are wanting to connect one output to each of the two inputs of an op amp. If that is what you are thinking about, the problem will be = too much gain. Typical op amps have voltage gains of 100's of thousan= ds, or more often, millions. Generally for approximate analyses desig= ners assume that their gain is infinite. That means that extremely ti= ny input signals (noise) would have the op amp output bouncing between its = voltage limits--not very useful.
>
> Usually op amps are conne= cted up as single ended amplifiers using a two-resistor feedback circuit, w= hich makes a very nice voltage amplifier.
>
> See: http://www.= analog.com/static/imported-files/tutorials/MT-032.pdf Figure 3.
&g= t;
> If you do that, one coil will work fine, and by changing the re= sistor values you can choose the amplifier gain to complement your coil sen= sitivity. The only advantage I can think of for some kind of differen= tial coil setup is that it might not be as sensitive to 60 Hz hum. Though it probably wouldn't be that hard to connect a different= ial coil to a single-ended amplifier, sort of like a guitar "hum-bucking" p= ickup.
>
> An instrumentation amplifier *would* allow for inde= pendent connections to a pair of coils, but they tend to be a lot more expe= nsive and their gain usually can't be adjusted as precisely.
>
&g= t; See: http://www.analog.com/static/imported-files/tutor= ials/MT-032.pdf Figure 2.
>
>> +COIL- Nmagn= etS +COIL-
>>
>> THE left coil - is connected to right c= oil +
>> which is then the ground.
>>
>> Left C= oil + goes to op amp +
>> and
>> Right coil - goes to op = amp -
>>
>> The relative motion is magnet fixed to groun= d
>> and coil fixed to device.
>>
>> Coil is stable and magnet moves right and left
>> between the coils.
&= gt;>
>> Possibly +/- 2mm of range of motion.
>>
&= gt;> Each coil having 1050 to 2100 turns
>> custom wound to be = exactly the same.
>
> Hope that's a start,
> Brett
&g= t;
>
>
> _____________________________________________= _____________
>
> Public Seismic Network Mailing List (PSN-L)<= BR>>
> To leave this list email PSN-L-REQUES= T@.............. with the body of the message (first line only): unsubs= cribe
> See http://www.seismicnet.com/maillist.html for more informat= ion.
>
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