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# Re: [femm] Speed Sensor

- To: femm@yahoogroups.com
- Subject: Re: [femm] Speed Sensor
- From: David Meeker <dmeeker@ieee.org>
- Date: Thu, 29 May 2003 10:19:58 -0400
- In-reply-to: <F3534F325314A243A60AF220E9A5377BFB6EC4@JAXCP01DATA.cp.ae.ge.com>
- References: <F3534F325314A243A60AF220E9A5377BFB6EC4@JAXCP01DATA.cp.ae.ge.com>
- User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.3.1; MultiZilla v1.4.0.3J) Gecko/20030425

`You are after some fairly detailed and specifc analysis. Since this is related to the analysis of your employer's product line, you may get the most mileage out of tracking down and picking the brains of whoever created the existing speed sensor designs. Otherwise, your company might consider hiring a consultant to model and optimize your device and/or to train you how to do it.`
`Dave.`
`Earanky, Vijay (GEAE, Unison-JAX) wrote:`

>     David,
>     Thanks for prompt advice. Like you suggested I want to develop the model.
>     Are there any tutorials or available models that can be modified for this
>     problem that I can get some guidance? I appreciate if you can help me
>     finding some working models to go about. Thanks.

> `Vijay`

>     -----Original Message-----
>     From: David Meeker [SMTP:dmeeker@ieee.org]
>     Sent: Wednesday, May 28, 2003 10:33 AM
>     To: femm@yahoogroups.com
>     Subject: Re: [femm] Speed Sensor

> `Earanky, Vijay (GEAE, Unison-JAX) wrote:`
> `> David,
> >
> > I want to simulate a speed sensor using FEMM. I am new to this program and
> > its capability. I will describe the problem briefly here. I have a permanent
> > magnet and attached to it is a core (1010 steel). There are 5000 turns of
> > wire on it. At the end of the core/coil assembly, there is a gear wheel of
> > ferrous material. As the wheel rotates it creates flux in the coil and
> > hence an emf generated of ac voltage. Now I want to develop a model to
> > see the relationship between no of turns, core material, the air gap
> > (between gear tooth and core) and magnet strength. The idea is to get
> > a linear curve between the speed and the induced voltage. Can the FEMM
> > model this and if so can someone show a direction. Thanks in advance.
> >
> > Vijay`
> `FEMM can model this sort of problem (as long as 2D is a good
> approximation of your geometry), but you'll get a lot more mileage as
> far as getting a feel for number of turns, core material, and air gap,
> by first making a relatively simple analytical model of your device--the
> effects of all of these parameters would be clearly in evidence in such
> a model.`
> `One interesting thing a simple model would show that if eddy currents
> (and possibly mechanical vibrations that would create "significant"
> variations in the nominal air gap or interacting pole area) are
> neglected, the induced voltage waveform ought to to have the same
> profile regardless of speed (just compressed over a shorter time), and
> the voltage amplitude ought to scale linearly with speed. This means
> that if you are seeing big nonlinearities in the output amplitude, I'd
> guess that you should be either looking at motion-induced eddy current
> effects in your assembly (FEMM can be used as /part/ of such an
> analysis, but not trivially--again, it would be best to start by
> including eddy current effects in the simple model as parasitic "shorted
> turns" around various parts of the teeth, core, and magnet), or
> artifacts of the way that you are measuring and/or filtering the output
> voltage. Then again, this could be the kind of situation where a little
> Horowitz and Hill would go a long way, e.g. make a circuit that looks
> for zero crossings in the induced voltage and ignore second-order
> effects in your sensor.`
> `Dave.`

``

    --
    David Meeker
    email: dmeeker@ieee.org
    www: http://femm.berlios.de/dmeeker

    --
    David Meeker
    email: dmeeker@ieee.org
    www: http://femm.berlios.de/dmeeker

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  - RE: [femm] Speed Sensor
    - From: "Earanky, Vijay (GEAE, Unison-JAX)" <Vijay.Earanky@unison.ae.ge.com>

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