High speed rotation detector
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Posts: 46,084
I was wondering if there is another way to accurately detect the RPM of a
high-speed plastic gear? The gear may spin up to 20,000 RPM and I figured I
could use an separately mounted disk and an interrupter for that. Problem is,
because of limited space, I may not be able to mount a disk to read.
Is there some other non-contact device I could use in place of an interrupter?
Magnetic may work but I am not sure it would work at that high of a speed.
Hank
high-speed plastic gear? The gear may spin up to 20,000 RPM and I figured I
could use an separately mounted disk and an interrupter for that. Problem is,
because of limited space, I may not be able to mount a disk to read.
Is there some other non-contact device I could use in place of an interrupter?
Magnetic may work but I am not sure it would work at that high of a speed.
Hank
Comments
would need it a small hole in it
Original Message
From: "rcvehicles" <rcvehicles@y...>
To: <basicstamps@yahoogroups.com>
Sent: January 07, 2002 1:31 PM
Subject: [noparse][[/noparse]basicstamps] High speed rotation detector
| I was wondering if there is another way to accurately detect the RPM of a
high-speed plastic gear? The gear may spin up to 20,000 RPM and I figured I
could use an separately mounted disk and an interrupter for that. Problem
is, because of limited space, I may not be able to mount a disk to read.
|
| Is there some other non-contact device I could use in place of an
interrupter? Magnetic may work but I am not sure it would work at that high
of a speed.
|
|
| Hank
|
|
|
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purpose, and they may be smaller. Or you could use an LED for that matter
; you'd probably need a phototransistor on the back end.
On Mon, 7 Jan 2002, Larry Gaminde wrote:
> There are many IR sensors in TX/RX pairs that would do the job all the gear
> would need it a small hole in it
>
Original Message
> From: "rcvehicles" <rcvehicles@y...>
> To: <basicstamps@yahoogroups.com>
> Sent: January 07, 2002 1:31 PM
> Subject: [noparse][[/noparse]basicstamps] High speed rotation detector
>
>
> | I was wondering if there is another way to accurately detect the RPM of a
> high-speed plastic gear? The gear may spin up to 20,000 RPM and I figured I
> could use an separately mounted disk and an interrupter for that. Problem
> is, because of limited space, I may not be able to mount a disk to read.
> |
> | Is there some other non-contact device I could use in place of an
> interrupter? Magnetic may work but I am not sure it would work at that high
> of a speed.
> |
> |
> | Hank
> |
> |
> |
> | To UNSUBSCRIBE, just send mail to:
> | basicstamps-unsubscribe@yahoogroups.com
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> Body of the message will be ignored.
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> |
>
>
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>
Sean T. Lamont, CTO / Chief NetNerd, Abstract Software, Inc. (ServNet)
Seattle - Bellingham - Vancouver - Portland - Everett - Tacoma - Bremerton
email: lamont@a... WWW: http://www.serv.net
"...There's no moral, it's just a lot of stuff that happens". - H. Simpson
doesn't require a though hole or interruption.
Hank
Original Message
From: "Larry Gaminde" <lgaminde@t...>
To: <basicstamps@yahoogroups.com>
Sent: Monday, January 07, 2002 5:33 PM
Subject: Re: [noparse][[/noparse]basicstamps] High speed rotation detector
> There are many IR sensors in TX/RX pairs that would do the job all the gear
> would need it a small hole in it
something on the voltage input to the motor using an adc?
Original Message
From: "rcvehicles" <rcvehicles@y...>
To: <basicstamps@yahoogroups.com>
Sent: January 07, 2002 2:50 PM
Subject: Re: [noparse][[/noparse]basicstamps] High speed rotation detector
| Yes, I know. I was hoping to find a non optical solution. Or at least one
that doesn't require a though hole or interruption.
|
| Hank
|
|
|
Original Message
| From: "Larry Gaminde" <lgaminde@t...>
| To: <basicstamps@yahoogroups.com>
| Sent: Monday, January 07, 2002 5:33 PM
| Subject: Re: [noparse][[/noparse]basicstamps] High speed rotation detector
|
|
| > There are many IR sensors in TX/RX pairs that would do the job all the
gear
| > would need it a small hole in it
|
|
|
| To UNSUBSCRIBE, just send mail to:
| basicstamps-unsubscribe@yahoogroups.com
| from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
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|
the emitter, and count pulses that way.
On Mon, 7 Jan 2002, rcvehicles wrote:
> Yes, I know. I was hoping to find a non optical solution. Or at least one that
doesn't require a though hole or interruption.
>
> Hank
>
>
>
Original Message
> From: "Larry Gaminde" <lgaminde@t...>
> To: <basicstamps@yahoogroups.com>
> Sent: Monday, January 07, 2002 5:33 PM
> Subject: Re: [noparse][[/noparse]basicstamps] High speed rotation detector
>
>
> > There are many IR sensors in TX/RX pairs that would do the job all the gear
> > would need it a small hole in it
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and Body
of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
Sean T. Lamont, CTO / Chief NetNerd, Abstract Software, Inc. (ServNet)
Seattle - Bellingham - Vancouver - Portland - Everett - Tacoma - Bremerton
email: lamont@a... WWW: http://www.serv.net
"...There's no moral, it's just a lot of stuff that happens". - H. Simpson
motor speed.
http://www.ezy.net.au/~fastvid/encoder.htm
Original Message
> Well how about checking the motor rpm vs voltage and maybe you can plot
> something on the voltage input to the motor using an adc?
> | Yes, I know. I was hoping to find a non optical solution. Or at least
one
> that doesn't require a though hole or interruption.
> | > There are many IR sensors in TX/RX pairs that would do the job all the
> gear
> | > would need it a small hole in it
many factors (voltage, load, etc.).
Hank
Original Message
From: "Larry Gaminde" <lgaminde@t...>
To: <basicstamps@yahoogroups.com>
Sent: Monday, January 07, 2002 5:55 PM
Subject: Re: [noparse][[/noparse]basicstamps] High speed rotation detector
> Well how about checking the motor rpm vs voltage and maybe you can plot
> something on the voltage input to the motor using an adc?
>
Original Message
> From: "rcvehicles" <rcvehicles@y...>
> To: <basicstamps@yahoogroups.com>
> Sent: January 07, 2002 2:50 PM
> Subject: Re: [noparse][[/noparse]basicstamps] High speed rotation detector
>
>
> | Yes, I know. I was hoping to find a non optical solution. Or at least one
> that doesn't require a though hole or interruption.
> |
> | Hank
Mount a piece of optics which will bounce back a light source towards its
sender. This is pretty similar to IR transmission/reception, and it's
available from most laser supply places (meredith instruments, etc.) Get a
little laser diode, CD-player style, which emits light towards the
rotating wheel. Your phototransistor will pulse each time the reflector
passes by as it's being reflected directly towards the beam.
Sean T. Lamont, CTO / Chief NetNerd, Abstract Software, Inc. (ServNet)
Seattle - Bellingham - Vancouver - Portland - Everett - Tacoma - Bremerton
email: lamont@a... WWW: http://www.serv.net
"...There's no moral, it's just a lot of stuff that happens". - H. Simpson
Use a Hall Effect sensor.
I've not used one for several years, but there are sensors out there with 5v
interfacing.
Regards,
Tony Wells
Original Message
From: "rcvehicles" <rcvehicles@y...>
To: <basicstamps@yahoogroups.com>
Sent: Monday, January 07, 2002 9:31 PM
Subject: [noparse][[/noparse]basicstamps] High speed rotation detector
> I was wondering if there is another way to accurately detect the RPM of a
high-speed plastic gear? The gear may spin up to 20,000 RPM and I figured I
could use an separately mounted disk and an interrupter for that. Problem
is, because of limited space, I may not be able to mount a disk to read.
>
> Is there some other non-contact device I could use in place of an
interrupter? Magnetic may work but I am not sure it would work at that high
of a speed.
>
>
> Hank
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
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Body of the message will be ignored.
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>
>
>
being used? If it is a brushed DC motor you may be able to monitor the motor
supply and signal condition the commutation spikes to where they could be
used as a tachometer signal.
Tim
Original Message
From: "Larry Gaminde" <lgaminde@t...>
To: <basicstamps@yahoogroups.com>
Sent: Monday, January 07, 2002 4:55 PM
Subject: Re: [noparse][[/noparse]basicstamps] High speed rotation detector
> Well how about checking the motor rpm vs voltage and maybe you can plot
> something on the voltage input to the motor using an adc?
>
Original Message
> From: "rcvehicles" <rcvehicles@y...>
> To: <basicstamps@yahoogroups.com>
> Sent: January 07, 2002 2:50 PM
> Subject: Re: [noparse][[/noparse]basicstamps] High speed rotation detector
>
>
> | Yes, I know. I was hoping to find a non optical solution. Or at least
one
> that doesn't require a though hole or interruption.
It uses PWM for speed control an this may cause more problems then could easily
be solved.
Hank
Original Message
From: "Tim McDonough" <tim@m...>
To: <basicstamps@yahoogroups.com>
Sent: Monday, January 07, 2002 10:15 PM
Subject: Re: [noparse][[/noparse]basicstamps] High speed rotation detector
> I've lost track of the earlier parts of this thread. What type of motor is
> being used? If it is a brushed DC motor you may be able to monitor the motor
> supply and signal condition the commutation spikes to where they could be
> used as a tachometer signal.
>
> Tim
>
Emitter Sensor Pair? I looked on Digi-Key and Allied, even did a search on
Findchips and no one has spec sheets.
Hank
this subject, in the "Laser Insight" column. It uses a reflecting
dot on the shaft or wheel.
If you are looking at optical methods would you be better off using a
logic-level compatible slotted opto switch? There are loads of them around.
Fit the opto switch on the edge of the gear and use a divide by 100 counter
or more to reduce the rate of input pulses so the stamp can handle the speed
of the incoming stream.
Regards,
Tony Wells
Original Message
From: "rcvehicles" <rcvehicles@y...>
To: <basicstamps@yahoogroups.com>
Sent: Tuesday, January 08, 2002 3:30 AM
Subject: Re: [noparse][[/noparse]basicstamps] High speed rotation detector
> Does anyone know where I can find data or proper usage of the H23A1
Infrared Emitter Sensor Pair? I looked on Digi-Key and Allied, even did a
search on Findchips and no one has spec sheets.
>
> Hank
>
>
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>
near the gear. Across the diameter of the gear itself mount a strip
of metal that is easily attracted by the magnet so that it does not
interfere with the gear mesh and still maintains balance. As the
gear rotates the ends of the metal strip will momentarily distort the
magnetic field around the coil causing it to produce a pulse which
can be easily amplified and presented to the Stamp for counting. By
using a single supply opamp you will eliminate the need for a
negative supply voltage.
Hal
--- In basicstamps@y..., "rcvehicles" <rcvehicles@y...> wrote:
> I was wondering if there is another way to accurately detect the
RPM of a high-speed plastic gear? The gear may spin up to 20,000 RPM
and I figured I could use an separately mounted disk and an
interrupter for that. Problem is, because of limited space, I may not
be able to mount a disk to read.
>
> Is there some other non-contact device I could use in place of an
interrupter? Magnetic may work but I am not sure it would work at
that high of a speed.
>
>
> Hank
On Tue, 8 Jan 2002, halalbach wrote:
> Use a small coil with a small permanent magnet as its core mounted
> near the gear. Across the diameter of the gear itself mount a strip
> of metal that is easily attracted by the magnet so that it does not
> interfere with the gear mesh and still maintains balance. As the
> gear rotates the ends of the metal strip will momentarily distort the
> magnetic field around the coil causing it to produce a pulse which
> can be easily amplified and presented to the Stamp for counting. By
> using a single supply opamp you will eliminate the need for a
> negative supply voltage.
>
> Hal
>
>
> --- In basicstamps@y..., "rcvehicles" <rcvehicles@y...> wrote:
> > I was wondering if there is another way to accurately detect the
> RPM of a high-speed plastic gear? The gear may spin up to 20,000 RPM
> and I figured I could use an separately mounted disk and an
> interrupter for that. Problem is, because of limited space, I may not
> be able to mount a disk to read.
> >
> > Is there some other non-contact device I could use in place of an
> interrupter? Magnetic may work but I am not sure it would work at
> that high of a speed.
> >
> >
> > Hank
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and Body
of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
Sean T. Lamont, CTO / Chief NetNerd, Abstract Software, Inc. (ServNet)
Seattle - Bellingham - Vancouver - Portland - Everett - Tacoma - Bremerton
email: lamont@a... WWW: http://www.serv.net
"...There's no moral, it's just a lot of stuff that happens". - H. Simpson
concerned this is a relatively slow reaction speed.
20,000rpm / 60 = 333.3333 revolutions per second
...and if you place a metal strip across the diameter
(for balancing) you will receive 2 pulses for every rotation.
or 666.6667 Hz going into the Stamp.
>Is this going to work at 20K rpm?
>
>On Tue, 8 Jan 2002, halalbach wrote:
>
> > Use a small coil with a small permanent magnet as its core mounted
> > near the gear. Across the diameter of the gear itself mount a strip
> > of metal that is easily attracted by the magnet so that it does not
> > interfere with the gear mesh and still maintains balance. As the
> > gear rotates the ends of the metal strip will momentarily distort the
> > magnetic field around the coil causing it to produce a pulse which
> > can be easily amplified and presented to the Stamp for counting. By
> > using a single supply opamp you will eliminate the need for a
> > negative supply voltage.
> >
> > Hal
Beau Schwabe Mask Designer IV - ATL
National Semiconductor Wired Communications Division
500 Pinnacle Court, Suite 525 Mail Stop GA1 Norcross, GA 30071
what sensor to use?
Hank
Original Message
From: "Beau Schwabe" <bschwabe@a...>
To: <basicstamps@yahoogroups.com>
Sent: Tuesday, January 08, 2002 3:27 PM
Subject: Re: [noparse][[/noparse]basicstamps] Re: High speed rotation detector
> Hal's solution should be fine. As far as the coil is
> concerned this is a relatively slow reaction speed.
>
> 20,000rpm / 60 = 333.3333 revolutions per second
>
> ...and if you place a metal strip across the diameter
> (for balancing) you will receive 2 pulses for every rotation.
> or 666.6667 Hz going into the Stamp.
>
This implies that you build it! ... Otherwise Hal was
describing a simple gear-tooth sensor, only this approach has
only two teeth; made by a piece of metal across the diameter of
anything rotating.
see this for a nice visual example:
http://www.melexis.com/site/products/apps/app_gts.htm
>OK, this would be a great solution then. Now, does anyone have a
>suggestion on what sensor to use?
>
>Hank
>
>
>
Original Message
>From: "Beau Schwabe" <bschwabe@a...>
>To: <basicstamps@yahoogroups.com>
>Sent: Tuesday, January 08, 2002 3:27 PM
>Subject: Re: [noparse][[/noparse]basicstamps] Re: High speed rotation detector
>
>
> > Hal's solution should be fine. As far as the coil is
> > concerned this is a relatively slow reaction speed.
> >
> > 20,000rpm / 60 = 333.3333 revolutions per second
> >
> > ...and if you place a metal strip across the diameter
> > (for balancing) you will receive 2 pulses for every rotation.
> > or 666.6667 Hz going into the Stamp.
> >
>
>
>
>To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
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>Body of the message will be ignored.
>
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>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
Beau Schwabe Mask Designer IV - ATL
National Semiconductor Wired Communications Division
500 Pinnacle Court, Suite 525 Mail Stop GA1 Norcross, GA 30071
filter to get rid of the PWM.
Original Message
> Yes, it is a brush type motor but I don't think this method would be
possible. It uses PWM for speed control an this may cause more problems then
could easily be solved.
> > I've lost track of the earlier parts of this thread. What type of motor
is
> > being used? If it is a brushed DC motor you may be able to monitor the
motor
> > supply and signal condition the commutation spikes to where they could
be
> > used as a tachometer signal.
Dennis
Original Message
From: rcvehicles [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=K27OomK38OrLnxpwLH9aQSGVJVgwpRaXDhVymz8RE5_qdKFfhDl5WVV1pD-f9C8mhGOW1OZ8gnUjvg]rcvehicles@y...[/url
Sent: Tuesday, January 08, 2002 12:56 PM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] Re: High speed rotation detector
OK, this would be a great solution then. Now, does anyone have a
suggestion on what sensor to use?
Hank
Original Message
From: "Beau Schwabe" <bschwabe@a...>
To: <basicstamps@yahoogroups.com>
Sent: Tuesday, January 08, 2002 3:27 PM
Subject: Re: [noparse][[/noparse]basicstamps] Re: High speed rotation detector
> Hal's solution should be fine. As far as the coil is concerned this
> is a relatively slow reaction speed.
>
> 20,000rpm / 60 = 333.3333 revolutions per second
>
> ...and if you place a metal strip across the diameter
> (for balancing) you will receive 2 pulses for every rotation. or
> 666.6667 Hz going into the Stamp.
>
To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
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http://www.allegromicro.com/
I used their 3133 with the Stamp because of its extreme sensitivity.
>I was wondering if there is another way to accurately detect the RPM of a
>high-speed plastic gear? The gear may spin up to 20,000 RPM and I figured
>I could use an separately mounted disk and an interrupter for that.
>Problem is, because of limited space, I may not be able to mount a disk to
>read.
>
>Is there some other non-contact device I could use in place of an
>interrupter? Magnetic may work but I am not sure it would work at that
>high of a speed.
>
>
>Hank
Hank,
Your solution should be optical, or magnetic. I would avoid the use
of op amps and inductive pick up coils entirely! keep the solution
completely digital. If you choose an optical solution it sounds
like your real estate might allow a reflective sensor. Pick one with
the correct focal length range, the distance between the gear surface
and the sensor. Drilling two holes 180 degrees apart(for balance)in
the drive gear will "defocus" or interrupt the beam reflection. You
may have to make your gear either more or less reflective. As long
as there's a high to low or low to high difference when you're over
the hole you're fine. If you choose a magnetic solution, hall
effects should be very easy to use. Strong rare earth magnets are
available in "disc" form. Match the thickness of the gear you're
using and choose one about 1/8 inch in diameter. Again drill two
holes 180 degrees apart and press (use super glue) the disk magnets
into the holes of the drive gear. This works with plastic gears too.
Using a narrow strip of magnetic material across the diameter of the
drive ( remember you've got to spin it too!) may not have enough Gauss
to trip the hall effect unless it's unusually sensitive so I prefer
the disk magnets. Each rotation of the drive gear will give you two
high periods and two low periods created by the holes or disk magnets.
The total high and low time for one rotation is the reciprocal of the
frequency in real time. Multiply the frequency by the gear ratio for
the motor frequency. Divide the motor frequency by 60 for RPM's.
PW = pulse width of one cycle = time high + time low
GR = Gear Ratio
Motor RPM = (GR(1 / 2(PW)))/60
Note that you will have to measure both the high and low periods.
A stamp is perfectly suited to handle this but I wouldn't expect
to measure each and every rotation of the gear!! Measuring both
periods at ten times a second seems a realistic goal. You may even
go faster depend on the type of stamp and of course, your code.
Also note that two holes in the drive gear may not be necessary
if aluminum, bronze or steel gears are used because the mass of
the disk magnet may closely match the mass removed by drilling,
depending how picky you are.
Sorry for the long post but it seemed such a good topic and stamp
application!!
Greg Hensley
Lawrence Livermore National Laboratory
Defense Sciences Engineering Division
7000 East Avenue Mail Stop L-369
Livermore, CA 94550
Phone: (925) 423-4850
Fax: (925) 422-2118
Email: hensley1@l...
the limited spaces that I will have.
But now I have another interesting question.
I was thinking of using the "count" command and count the times the magnet
passes the sensor in a given length of time. The advantages of this is it would
less sensitive to magnet placement. Disadvantage is that it does take a chunk of
processor time to do it.
Would the PW method offer any real advantage? What about placement on the gear?
Wouldn't the magnets have to be placed at the same diameter in every case to get
the same PW?
Hank
Original Message
From: "Greg Hensley" <hensley1@l...>
To: <basicstamps@yahoogroups.com>
Sent: Tuesday, January 08, 2002 11:32 PM
Subject: Re: [noparse][[/noparse]basicstamps] High speed rotation detector
> At 01:31 PM 1/7/2002 , you wrote:
> >I was wondering if there is another way to accurately detect the RPM of a
> >high-speed plastic gear? The gear may spin up to 20,000 RPM and I figured
> >I could use an separately mounted disk and an interrupter for that.
> >Problem is, because of limited space, I may not be able to mount a disk to
> >read.
> >
> >Is there some other non-contact device I could use in place of an
> >interrupter? Magnetic may work but I am not sure it would work at that
> >high of a speed.
> >
> >
> >Hank
>
>
> Hank,
> Your solution should be optical, or magnetic. I would avoid the use
> of op amps and inductive pick up coils entirely! keep the solution
> completely digital. If you choose an optical solution it sounds
> like your real estate might allow a reflective sensor. Pick one with
> the correct focal length range, the distance between the gear surface
> and the sensor. Drilling two holes 180 degrees apart(for balance)in
> the drive gear will "defocus" or interrupt the beam reflection. You
> may have to make your gear either more or less reflective. As long
> as there's a high to low or low to high difference when you're over
> the hole you're fine. If you choose a magnetic solution, hall
> effects should be very easy to use. Strong rare earth magnets are
> available in "disc" form. Match the thickness of the gear you're
> using and choose one about 1/8 inch in diameter. Again drill two
> holes 180 degrees apart and press (use super glue) the disk magnets
> into the holes of the drive gear. This works with plastic gears too.
> Using a narrow strip of magnetic material across the diameter of the
> drive ( remember you've got to spin it too!) may not have enough Gauss
> to trip the hall effect unless it's unusually sensitive so I prefer
> the disk magnets. Each rotation of the drive gear will give you two
> high periods and two low periods created by the holes or disk magnets.
> The total high and low time for one rotation is the reciprocal of the
> frequency in real time. Multiply the frequency by the gear ratio for
> the motor frequency. Divide the motor frequency by 60 for RPM's.
>
> PW = pulse width of one cycle = time high + time low
> GR = Gear Ratio
> Motor RPM = (GR(1 / 2(PW)))/60
>
> Note that you will have to measure both the high and low periods.
> A stamp is perfectly suited to handle this but I wouldn't expect
> to measure each and every rotation of the gear!! Measuring both
> periods at ten times a second seems a realistic goal. You may even
> go faster depend on the type of stamp and of course, your code.
>
> Also note that two holes in the drive gear may not be necessary
> if aluminum, bronze or steel gears are used because the mass of
> the disk magnet may closely match the mass removed by drilling,
> depending how picky you are.
>
> Sorry for the long post but it seemed such a good topic and stamp
> application!!
>
>
>
>
> Greg Hensley
> Lawrence Livermore National Laboratory
> Defense Sciences Engineering Division
> 7000 East Avenue Mail Stop L-369
> Livermore, CA 94550
> Phone: (925) 423-4850
> Fax: (925) 422-2118
> Email: hensley1@l...
>
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>OK, I've decided to go with a hall effect because it will be easier to
>mount in the limited spaces that I will have.
>
>But now I have another interesting question.
>
>I was thinking of using the "count" command and count the times the magnet
>passes the sensor in a given length of time. The advantages of this is it
>would less sensitive to magnet placement. Disadvantage is that it does
>take a chunk of processor time to do it.
>
>Would the PW method offer any real advantage? What about placement on the
>gear? Wouldn't the magnets have to be placed at the same diameter in every
>case to get the same PW?
>
>Hank
Hank,
I suggested the pulse width method because it's easy to implement
using the pulsin command. The gear size and the size of the magnet
will give a ratio of on to off periods. The hall effect on period may be
1 unit of time and the off period perhaps 10 periods or so. The maximum
pulse width of the pulsin command is 665 ms with 10 us resolution if
you're using a BS1, 131 ms with 2us resolution if you're using
a BS2, 49ms with .75us resolution if you're using a BS2p. Each will
cutoff at a slow speed where the pulsin command has reached its limit.
A stamp 1 will detect slower speeds. A stamp 2 will detect higher speeds
with better resolution etc. Fractions of an RPM are possible with pulsin.
Using the count command requires a BS2 or better but works just as well.
You have the freedom to specify the counting period up to 65 seconds for
a BS2 and up to 18 seconds for a BS2P. For this reason the count command
can detect lower RPM's than the pulsin command can. You wont get fractions
however, only integers. 2 RPM counts could be 2.999 RPMs but it is least
2 RPM and less than 3 RPM.
You could use both commands where you branch to a "slow speed" routine
at some setpoint and to a "high speed" routine at another setpoint. It
doesn't have to be an all or nothing decision!
As far as magnet placement, hall effects change state or they don't! There
are linear hall effects and you should avoid them for this application.
Most hall effects are pole sensitive. Other than that it is completely
non critical. Mount it 1 mm from the magnet and forget it! Also remember
that two magnets was chiefly for balance. You could use a steel slug in
one of the holes and balance equally well. If using two magnets, Yes, they
should be mounted an equal distance from the center of the hub and spaced
equally apart, 180 degrees in theory. Farther out is usually easier for
hall effect placement. You may have different pulse widths by a few counts
if your not exact, and who is?. If this is the case count both on periods
and both off periods and add them up. This is one rev in real time. Unless
you need atomic clock accuracies, just forget the difference because it will
probably be less than a few percent.
Greg
[noparse][[/noparse]Non-text portions of this message have been removed]
Thanks for the details and now I understand the thinking on the pulse width
idea. I think at this point I'll just use count and see how that works out.
Hank
> I suggested the pulse width method because it's easy to implement
> using the pulsin command. The gear size and the size of the magnet
> will give a ratio of on to off periods. The hall effect on period may be
> 1 unit of time and the off period perhaps 10 periods or so. The maximum
> pulse width of the pulsin command is 665 ms with 10 us resolution if
> you're using a BS1, 131 ms with 2us resolution if you're using
> a BS2, 49ms with .75us resolution if you're using a BS2p. Each will
> cutoff at a slow speed where the pulsin command has reached its limit.
> A stamp 1 will detect slower speeds. A stamp 2 will detect higher speeds
> with better resolution etc. Fractions of an RPM are possible with pulsin.
>
> Using the count command requires a BS2 or better but works just as well.
> You have the freedom to specify the counting period up to 65 seconds for
> a BS2 and up to 18 seconds for a BS2P. For this reason the count command
> can detect lower RPM's than the pulsin command can. You wont get fractions
> however, only integers. 2 RPM counts could be 2.999 RPMs but it is least
> 2 RPM and less than 3 RPM.
>
> You could use both commands where you branch to a "slow speed" routine
> at some setpoint and to a "high speed" routine at another setpoint. It
> doesn't have to be an all or nothing decision!
>
> As far as magnet placement, hall effects change state or they don't! There
> are linear hall effects and you should avoid them for this application.
> Most hall effects are pole sensitive. Other than that it is completely
> non critical. Mount it 1 mm from the magnet and forget it! Also remember
> that two magnets was chiefly for balance. You could use a steel slug in
> one of the holes and balance equally well. If using two magnets, Yes, they
> should be mounted an equal distance from the center of the hub and spaced
> equally apart, 180 degrees in theory. Farther out is usually easier for
> hall effect placement. You may have different pulse widths by a few counts
> if your not exact, and who is?. If this is the case count both on periods
> and both off periods and add them up. This is one rev in real time. Unless
> you need atomic clock accuracies, just forget the difference because it will
> probably be less than a few percent.
>
> Greg