Hello,

We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).

All propositions and comments are welcome.

Thanks.
--
Eric Meurville

Eric Meurville wrote:
Hello,

We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).

All propositions and comments are welcome.

Can you paint marks on it?

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Eric Meurville wrote:

We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).

What's the minimum speed at which you need to monitor the position?

Can you use a pickup coil to make an AC generator and watch the phase?

Are there fast enough hall effect devices, that you could use one or
several of and interpolate position under an assumption of no abrupt
changes in speed?

Eric Meurville wrote:
Hello,

We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).

All propositions and comments are welcome.

Thanks.
Use two sensors
a Hall effect sensor for angular data and use a photo sensor and a spot
of white paint to index reference the rotor.
I have seen Hall Sensors used to monitor Centrifuges to 36,000 RPM !

Yukio YANO

On Fri, 04 Nov 2005 16:17:43 +0100, Eric Meurville
wrote:

Hello,

We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).

---
1. Is the rotor spinning about its cylindical axis or radially,
somewhere along its length?

2. What is the strength of the rotor's magnetic field?

3. How closely can the sensor approach the spinning cylinder?

4. I don't understand the +/-45° requirement. Do you mean that if,
in one instance, the sensor is located +45° off axis and, in the
next it's located -45° off axis it should still report the
absolute position of the rotor with respect to some arbitrary
reference?

5. Assuming that you want to know the angular position of the rotor
relative to some reference, how accurately do you need that
position to be known?

--
John Fields
Professional Circuit Designer

"Eric Meurville" wrote in message
...
Hello,

We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).

All propositions and comments are welcome.

What's making it spin? Can you monitor that or do you expect some slip?

Modern brushless DC permanant magnet motor controllers monitor the position
of the rotor using unpowered windings as a sensor coil.

If it's in a motor, use the windings. If not, use a hall effect sensor.
Phase will tell you angle; intensity will tell you distance. If you
don't know distance in 2 dimensions, you can use a second hall sensor.
If you don't know alignment, you can use another hall sensor. A BASIC
stamp can do any math you need if you don't have a computer connected.

http://en.wikipedia.org/wiki/Hall_effect_sensor

Jerry Avins wrote:
Eric Meurville wrote:

Hello,

We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300
Hz. The solution must not be too sensitive to misalignment of rotor
and sensor (e.g. up to +/-45°).

All propositions and comments are welcome.


Can you paint marks on it?

Jerry
Hello Jerry,

No I can't as this rotor is a part of an implanted biosensor.

--
Eric Meurville

wrote:

Eric Meurville wrote:


We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).


What's the minimum speed at which you need to monitor the position?

Can you use a pickup coil to make an AC generator and watch the phase?

Are there fast enough hall effect devices, that you could use one or
several of and interpolate position under an assumption of no abrupt
changes in speed?


Typically, the measurement is performed between from 300 to 1 Hz.

--
Eric Meurville

John Fields wrote:

On Fri, 04 Nov 2005 16:17:43 +0100, Eric Meurville
wrote:


Hello,

We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).


---
1. Is the rotor spinning about its cylindical axis or radially,
somewhere along its length?
The rotor spins around its cylindrical axis.

2. What is the strength of the rotor's magnetic field?
The rotor is made of SmCo and the typical energy product is around 200
kJ/m3.

3. How closely can the sensor approach the spinning cylinder?
10 mm.

4. I don't understand the +/-45° requirement. Do you mean that if,
in one instance, the sensor is located +45° off axis and, in the
next it's located -45° off axis it should still report the
absolute position of the rotor with respect to some arbitrary
reference?
No, the capsule enclosing the rotor is implanted and after implnattion
in the body, it is not supposed to move. The question is the tolerance
of the position sensor to a misalignment between the rotor and the sensor.

5. Assuming that you want to know the angular position of the rotor
relative to some reference, how accurately do you need that
position to be known?

It would be great if the position sensor output could toggle every
360/2^N°, with e.g. N=6 (that means every 5.625°). More would be better.

--
Eric Meurville

CWatters wrote:

"Eric Meurville" wrote in message
...

Hello,

We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).

All propositions and comments are welcome.


What's making it spin? Can you monitor that or do you expect some slip?

Modern brushless DC permanant magnet motor controllers monitor the position
of the rotor using unpowered windings as a sensor coil.




The rotor is excited by an external rotating magnetic field generator
composed of a 3-Phi coil and 3 PWM generators.

--
Eric Meurville

Eric Meurville wrote:
Jerry Avins wrote:

...

Can you paint marks on it?

...

No I can't as this rotor is a part of an implanted biosensor.

Implanted, magnetically driven rotor! Implanted into what? Wow!

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Eric Meurville wrote:
CWatters wrote:

"Eric Meurville" wrote in message
...

Hello,

We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).

All propositions and comments are welcome.



What's making it spin? Can you monitor that or do you expect some slip?

Modern brushless DC permanant magnet motor controllers monitor the
position
of the rotor using unpowered windings as a sensor coil.




The rotor is excited by an external rotating magnetic field generator
composed of a 3-Phi coil and 3 PWM generators.

It seems that you can know the position of the magnetic field by
measuring the coil currents. A knowledge of the viscosity on the medium
that embeds the rotor and the velocity of the field should allow you to
calculate the power angle between the field and the magnet. If
accelerations are small enough, a static calculation will do. Otherwise,
the rotor's inertia will need to be accounted for.

What you have is essentially a synchronous motor. It must either spin at
the same rate as the magnetic field or stall. When spinning, the angle
between magnet and field must be less than 90 degrees.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

On Mon, 07 Nov 2005 10:50:15 -0500, Jerry Avins wrote:

Eric Meurville wrote:

The rotor is excited by an external rotating magnetic field generator
composed of a 3-Phi coil and 3 PWM generators.

It seems that you can know the position of the magnetic field by
measuring the coil currents. A knowledge of the viscosity on the medium
that embeds the rotor and the velocity of the field should allow you to
calculate the power angle between the field and the magnet. If
accelerations are small enough, a static calculation will do. Otherwise,
the rotor's inertia will need to be accounted for.

What you have is essentially a synchronous motor. It must either spin at
the same rate as the magnetic field or stall. When spinning, the angle
between magnet and field must be less than 90 degrees.

Jerry

I think Jerry's on to a good idea. If you're using external coils to
excite it then you should have everything you need to measure it as
well. Whether there are other objects within the fields which may
interfere with the measurements may be an issue, but you may be able
to calibrate or sense those and work around them.

Depending on the amount of power involved I think this may preclude
the use of a Hall effect sensor, anyway, which I think was the next
best idea. If this thing is small, though, and you can't get closer
than 10mm a Hall effect device may not have worked, anyway.


Eric Jacobsen
Minister of Algorithms, Intel Corp.
My opinions may not be Intel's opinions.
http://www.ericjacobsen.org

"Eric Meurville" wrote in message
...
It would be great if the position sensor output could toggle every
360/2^N°, with e.g. N=6 (that means every 5.625°). More would be better.

If the rotor is a two pole magnet, perhaps you could surround the rotor with
say 64 hall effect sensors. Scan and convert the analog value of each sensor
many times a second and "plot" a graph. Do averaging to improve S/N ratio
and curve fitting to look for the maximium and minimium flux positions
(indicating where the north and south poles are).

However I think I would investigate using something else in the rotor -
perhaps a directional antenna/coil that's externally excited? It's usually
better to start with an AC signal rather than a DC signal if you think you
are going to have S/N ratio problems.

"CWatters" wrote in message
...

"Eric Meurville" wrote in message
...
It would be great if the position sensor output could toggle every
360/2^N°, with e.g. N=6 (that means every 5.625°). More would be better.

If the rotor is a two pole magnet, perhaps you could surround the rotor
with
say 64 hall effect sensors. Scan and convert the analog value of each
sensor
many times a second and "plot" a graph. Do averaging to improve S/N ratio
and curve fitting to look for the maximium and minimium flux positions
(indicating where the north and south poles are).

However I think I would investigate using something else in the rotor -
perhaps a directional antenna/coil that's externally excited? It's usually
better to start with an AC signal rather than a DC signal if you think you
are going to have S/N ratio problems.

I forgot to add...

You will need to deal with noise produced by whatever is spinning the rotor.
Hope you don't have an electric motor too close to it.

On Mon, 07 Nov 2005 18:38:33 GMT, "CWatters"
wrote:


"CWatters" wrote in message
...

"Eric Meurville" wrote in message
...
It would be great if the position sensor output could toggle every
360/2^N°, with e.g. N=6 (that means every 5.625°). More would be better.

If the rotor is a two pole magnet, perhaps you could surround the rotor
with
say 64 hall effect sensors. Scan and convert the analog value of each
sensor
many times a second and "plot" a graph. Do averaging to improve S/N ratio
and curve fitting to look for the maximium and minimium flux positions
(indicating where the north and south poles are).

However I think I would investigate using something else in the rotor -
perhaps a directional antenna/coil that's externally excited? It's usually
better to start with an AC signal rather than a DC signal if you think you
are going to have S/N ratio problems.

I forgot to add...

You will need to deal with noise produced by whatever is spinning the rotor.
Hope you don't have an electric motor too close to it.

---
LOL, go back and read the thread. It's _part_ of an electric
motor!


--
John Fields
Professional Circuit Designer

On Mon, 07 Nov 2005 13:51:46 +0100, Eric Meurville
wrote:
Jerry Avins wrote:
Eric Meurville wrote:
We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300
Hz. The solution must not be too sensitive to misalignment of rotor
and sensor (e.g. up to +/-45°).
All propositions and comments are welcome.

Questions:
- The position measurement is relative to what?
Displacement between the cylinder and it's container?

- Which axis do you want to measure displacement along,
the axis of rotation or either of the 2-axis at 90 deg to axis of
rotation? Or some angular displacement from the rotation axis
(i.e. precession).

- Is the container transparent (i.e. could you use a light pipe
combined with a light source and light sensor)?

- can you post a diagram online?

----------------------------
"Jerry Avins" wrote in message
...
Eric Meurville wrote:
CWatters wrote:

"Eric Meurville" wrote in message
...

Hello,

We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300
Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).

All propositions and comments are welcome.



What's making it spin? Can you monitor that or do you expect some slip?

Modern brushless DC permanant magnet motor controllers monitor the
position
of the rotor using unpowered windings as a sensor coil.




The rotor is excited by an external rotating magnetic field generator
composed of a 3-Phi coil and 3 PWM generators.

It seems that you can know the position of the magnetic field by measuring
the coil currents. A knowledge of the viscosity on the medium that embeds
the rotor and the velocity of the field should allow you to calculate the
power angle between the field and the magnet. If accelerations are small
enough, a static calculation will do. Otherwise, the rotor's inertia will
need to be accounted for.

What you have is essentially a synchronous motor. It must either spin at
the same rate as the magnetic field or stall. When spinning, the angle
between magnet and field must be less than 90 degrees.

Jerry
----------------------
I think you are on to the best bet so far.
However, the problem of the power angle is still there and there seems to be
a demand for a position reading in the order of 5 degrees. If the motor is
always lightly loaded then ignoring the power angle may be sufficient.
It does appear that the problem is still not well specified beyond 1-300Hz
and implanted as well as the type of drive. What is missing is the purpose
of the device, the location of the device, the necessity for accurate
position sensing and all in all the minimum satisfactory criteria.
Depending on these factors, this may well be something for a biomedical
engineering (assuming implantation is in a carbon based life form) grad
student to sink his/her teeth into. There are places which have good
biomedical engineering programs - the University of Alberta, Edmonton,
Alberta, Canada has (or at least had) such a program.
With due respect to this group, you need someone with the necessary skills
who can spend time and effort on this problem. Time and effort on the
definition of the problem is also required and this has, so far, been
minimal.
--

Don Kelly @shawcross.ca
remove the X to answer

Don Kelly wrote:
----------------------------
"Jerry Avins" wrote in message
...

Eric Meurville wrote:

CWatters wrote:


"Eric Meurville" wrote in message
...


Hello,

We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300
Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45�).

All propositions and comments are welcome.



What's making it spin? Can you monitor that or do you expect some slip?

Modern brushless DC permanant magnet motor controllers monitor the
position
of the rotor using unpowered windings as a sensor coil.





The rotor is excited by an external rotating magnetic field generator
composed of a 3-Phi coil and 3 PWM generators.

It seems that you can know the position of the magnetic field by measuring
the coil currents. A knowledge of the viscosity on the medium that embeds
the rotor and the velocity of the field should allow you to calculate the
power angle between the field and the magnet. If accelerations are small
enough, a static calculation will do. Otherwise, the rotor's inertia will
need to be accounted for.

What you have is essentially a synchronous motor. It must either spin at
the same rate as the magnetic field or stall. When spinning, the angle
between magnet and field must be less than 90 degrees.

Jerry

----------------------
I think you are on to the best bet so far.
However, the problem of the power angle is still there and there seems to be
a demand for a position reading in the order of 5 degrees. If the motor is
always lightly loaded then ignoring the power angle may be sufficient.
It does appear that the problem is still not well specified beyond 1-300Hz
and implanted as well as the type of drive. What is missing is the purpose
of the device, the location of the device, the necessity for accurate
position sensing and all in all the minimum satisfactory criteria.
Depending on these factors, this may well be something for a biomedical
engineering (assuming implantation is in a carbon based life form) grad
student to sink his/her teeth into. There are places which have good
biomedical engineering programs - the University of Alberta, Edmonton,
Alberta, Canada has (or at least had) such a program.
With due respect to this group, you need someone with the necessary skills
who can spend time and effort on this problem. Time and effort on the
definition of the problem is also required and this has, so far, been
minimal.

What's more, if the plane of the rotating cylinder is not normal to the
axis of the rotating field, it will lope like a canted Hooke coupling
(the standard -- not CV -- universal joint).

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

On Tue, 08 Nov 2005 00:26:56 -0500, Jerry Avins wrote:
Don Kelly wrote:
"Jerry Avins" wrote in message
Eric Meurville wrote:
CWatters wrote:
"Eric Meurville" wrote in message

Hello,

We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300
Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45[degrees]).

All propositions and comments are welcome.

What's making it spin? Can you monitor that or do you expect some slip?

Modern brushless DC permanant magnet motor controllers monitor the
position
of the rotor using unpowered windings as a sensor coil.

The rotor is excited by an external rotating magnetic field generator
composed of a 3-Phi coil and 3 PWM generators.

It seems that you can know the position of the magnetic field by measuring
the coil currents. A knowledge of the viscosity on the medium that embeds
the rotor and the velocity of the field should allow you to calculate the
power angle between the field and the magnet. If accelerations are small
enough, a static calculation will do. Otherwise, the rotor's inertia will
need to be accounted for.

What you have is essentially a synchronous motor. It must either spin at
the same rate as the magnetic field or stall. When spinning, the angle
between magnet and field must be less than 90 degrees.

I think you are on to the best bet so far.
However, the problem of the power angle is still there and there seems to be
a demand for a position reading in the order of 5 degrees. If the motor is
always lightly loaded then ignoring the power angle may be sufficient.
It does appear that the problem is still not well specified beyond 1-300Hz
and implanted as well as the type of drive. What is missing is the purpose
of the device, the location of the device, the necessity for accurate
position sensing and all in all the minimum satisfactory criteria.
Depending on these factors, this may well be something for a biomedical
engineering (assuming implantation is in a carbon based life form) grad
student to sink his/her teeth into. There are places which have good
biomedical engineering programs - the University of Alberta, Edmonton,
Alberta, Canada has (or at least had) such a program.
With due respect to this group, you need someone with the necessary skills
who can spend time and effort on this problem. Time and effort on the
definition of the problem is also required and this has, so far, been
minimal.

What's more, if the plane of the rotating cylinder is not normal to the
axis of the rotating field, it will lope like a canted Hooke coupling
(the standard -- not CV -- universal joint).

I wonder, is the guy constrained to magnetic sensing? My first thought,
on reading the OP, was, "Paint a white stripe on the shaft and use a
reflective sensor."

Thanks!
Rich

The device is implanted- I assume that optical means are not valid unless
the detection is also implanted.

--

Don Kelly @shawcross.ca
remove the X to answer
----------------------------
"Rich Grise" wrote in message
news
On Tue, 08 Nov 2005 00:26:56 -0500, Jerry Avins wrote:
Don Kelly wrote:
"Jerry Avins" wrote in message
Eric Meurville wrote:
CWatters wrote:
"Eric Meurville" wrote in message

Hello,

We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300
Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45[degrees]).

All propositions and comments are welcome.

What's making it spin? Can you monitor that or do you expect some
slip?

Modern brushless DC permanant magnet motor controllers monitor the
position
of the rotor using unpowered windings as a sensor coil.

The rotor is excited by an external rotating magnetic field generator
composed of a 3-Phi coil and 3 PWM generators.

It seems that you can know the position of the magnetic field by
measuring
the coil currents. A knowledge of the viscosity on the medium that
embeds
the rotor and the velocity of the field should allow you to calculate
the
power angle between the field and the magnet. If accelerations are small
enough, a static calculation will do. Otherwise, the rotor's inertia
will
need to be accounted for.

What you have is essentially a synchronous motor. It must either spin at
the same rate as the magnetic field or stall. When spinning, the angle
between magnet and field must be less than 90 degrees.

I think you are on to the best bet so far.
However, the problem of the power angle is still there and there seems
to be
a demand for a position reading in the order of 5 degrees. If the motor
is
always lightly loaded then ignoring the power angle may be sufficient.
It does appear that the problem is still not well specified beyond
1-300Hz
and implanted as well as the type of drive. What is missing is the
purpose
of the device, the location of the device, the necessity for accurate
position sensing and all in all the minimum satisfactory criteria.
Depending on these factors, this may well be something for a biomedical
engineering (assuming implantation is in a carbon based life form) grad
student to sink his/her teeth into. There are places which have good
biomedical engineering programs - the University of Alberta, Edmonton,
Alberta, Canada has (or at least had) such a program.
With due respect to this group, you need someone with the necessary
skills
who can spend time and effort on this problem. Time and effort on the
definition of the problem is also required and this has, so far, been
minimal.

What's more, if the plane of the rotating cylinder is not normal to the
axis of the rotating field, it will lope like a canted Hooke coupling
(the standard -- not CV -- universal joint).

I wonder, is the guy constrained to magnetic sensing? My first thought,
on reading the OP, was, "Paint a white stripe on the shaft and use a
reflective sensor."

Thanks!
Rich

Rich Grise wrote:

...

I wonder, is the guy constrained to magnetic sensing? My first thought,
on reading the OP, was, "Paint a white stripe on the shaft and use a
reflective sensor."

Read my first message in this thread and the response to it.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Well, you *can* use optical means: bright infrared LEDs, infrared
markings, and an infrared-filtered CCD, for example. Magnetic sensing
is just better.

On 10 Nov 2005 14:40:39 -0800, "bhauth" wrote:

Well, you *can* use optical means: bright infrared LEDs, infrared
markings, and an infrared-filtered CCD, for example. Magnetic sensing
is just better.

---
Didn't you bother to read the thread?

It's _implanted_.


--
John Fields
Professional Circuit Designer

"John Fields" wrote in message
...
On 10 Nov 2005 14:40:39 -0800, "bhauth" wrote:

Well, you *can* use optical means: bright infrared LEDs, infrared
markings, and an infrared-filtered CCD, for example. Magnetic sensing
is just better.

---
Didn't you bother to read the thread?

It's _implanted_.

Only 10mm deep though. Try shining a torch through your hand. I'm sure I
read that someone was trying to use light to replace some hospital x-rays.
They were experimenting with using sensitive sensors similar to those used
by optical telescopes. Probably wouldn't work for this application but it
might not as daft as you imply.

CWatters wrote:

"John Fields" wrote in message

Didn't you bother to read the thread?

It's _implanted_.

Only 10mm deep though. Try shining a torch through your hand. I'm sure I
read that someone was trying to use light to replace some hospital x-rays.
They were experimenting with using sensitive sensors similar to those used
by optical telescopes. Probably wouldn't work for this application but it
might not as daft as you imply.

I'm with you. I've seen strange and subtle things happen with different
lighting conditions and different sensors... all in the optical or
near-optical range (i.e. not X-ray).

I'm not sure it WILL work, however I am certain it's worth
investigating.

Ciao,

Peter K.

["Followup-To:" header set to sci.electronics.misc.]
On 2005-11-07, Eric Meurville wrote:
Jerry Avins wrote:
Eric Meurville wrote:

Hello,

We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300
Hz. The solution must not be too sensitive to misalignment of rotor
and sensor (e.g. up to +/-45°).

All propositions and comments are welcome.


Can you paint marks on it?

Jerry
Hello Jerry,

No I can't as this rotor is a part of an implanted biosensor.


you say diametrically magnetised meaning north pole at 0 degrees and south
at 180 degrees and spinning so to that north and south swap places?

what's the minimum rate of spin?

will it spin backwards, if it does do you need to know it's going backwards?

do you need angle information?

In what environments must the sensor operate, hand-held or worn ....

are momentary failures acceptable? how often and for how long?


--

Bye.
Jasen

["Followup-To:" header set to sci.electronics.misc.]
On 2005-11-07, Eric Meurville wrote:
CWatters wrote:

"Eric Meurville" wrote in message
...

Hello,

We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).

All propositions and comments are welcome.


What's making it spin? Can you monitor that or do you expect some slip?

Modern brushless DC permanant magnet motor controllers monitor the position
of the rotor using unpowered windings as a sensor coil.





The rotor is excited by an external rotating magnetic field generator
composed of a 3-Phi coil and 3 PWM generators.

external to the implantee?

so you have to cancel that field out before you can read its position,
any nearby magnetic materials are going to muddy the water no matter how
finely you tune the sensor.

--

Bye.
Jasen