Magnetic Problem

[KM]

Hi,
I'm having a problem using a minature magnetic reed switch to detect
when it has passed over a magnet. The application is for automotive and the
magnet is laid across the asphalt of a race track. It serves the purpose of
being a control line to identify to the driver when he has finished a lap.
I've mounted the magnetic reed switch in a slim line case under the kart.
The ride height of the kart is approximately 0.05 +/- 0.01 m. As for the
maximum speed it is approximately 90 km/hr.
When I fitted the device and it was taken for a test it seemed to
trigger randomly or not at all. But when I removed it from the kart and
physically waved it over the control line (magnet) it worked perfectly
(which it also did on the test bench). Although, I was moving it closer to
the asphalt than it is mounted on the kart. Which means, that the
sensitivity of the magnetic reed switch isn't enough.
Does anyone know of a way around this problem? I have been reading up on
Hall Effect sensors but from my understanding they only detect fields at 90
degrees. Any advice or links on the web would be greatly appreciated.

KM

 

[Mark Little]

Are you sure that the vibration of the cart is not causing the reed relay to
bounce closed? Have you also checked that the metal of the kart is not
putting your sensor in a "magnetic shadow"?

Are you sure the kart always goes directly over the magnet? Is it a strip
magnet of some kind that spans the whole track?

I can't imagine the orientation of a Hall Effect sensor is an issue, since
you just mount it so that it is sensitive in the required direction.

Mark



"KM" <kmeng@optusnet.com.au> wrote in message
news:40f27127$0$18195$afc38c87@news.optusnet.com.au...

Hi,
I'm having a problem using a minature magnetic reed switch to detect
when it has passed over a magnet. The application is for automotive and
the
magnet is laid across the asphalt of a race track. It serves the purpose
of
being a control line to identify to the driver when he has finished a lap.
I've mounted the magnetic reed switch in a slim line case under the kart.
The ride height of the kart is approximately 0.05 +/- 0.01 m. As for the
maximum speed it is approximately 90 km/hr.
When I fitted the device and it was taken for a test it seemed to
trigger randomly or not at all. But when I removed it from the kart and
physically waved it over the control line (magnet) it worked perfectly
(which it also did on the test bench). Although, I was moving it closer to
the asphalt than it is mounted on the kart. Which means, that the
sensitivity of the magnetic reed switch isn't enough.
Does anyone know of a way around this problem? I have been reading up
on
Hall Effect sensors but from my understanding they only detect fields at
90
degrees. Any advice or links on the web would be greatly appreciated.

KM

 

[KM]

The vibration of the kart isn't closing the magnetic reed switch as my lap
counter isn't incrementing.

The magnetic reed switch is under the "under tray" of the kart, so it is
faced directly towards the track surface with nothing in between.

The magnetic strip or control line spans the whole width of the track, the
usual length of a 2 lane road, with the strip being itself approximately
0.01 m wide.

I not sure of the orientation of the magnetic field on the magnetic strip
itself. Whether the magnetic poles are vertical with respect to the
horizontal or horizontal. So the Hall Effect sensor would have to be placed
in different ways to find out if it works. (Hey, thanks for helping...)

KM
Mark Little <mark@au.id.little> wrote in message
news:40f27404@duster.adelaide.on.net...

Are you sure that the vibration of the cart is not causing the reed relay
to
bounce closed? Have you also checked that the metal of the kart is not
putting your sensor in a "magnetic shadow"?

Are you sure the kart always goes directly over the magnet? Is it a strip
magnet of some kind that spans the whole track?

I can't imagine the orientation of a Hall Effect sensor is an issue, since
you just mount it so that it is sensitive in the required direction.

Mark



"KM" <kmeng@optusnet.com.au> wrote in message
news:40f27127$0$18195$afc38c87@news.optusnet.com.au...
Hi,
I'm having a problem using a minature magnetic reed switch to detect
when it has passed over a magnet. The application is for automotive and
the
magnet is laid across the asphalt of a race track. It serves the purpose
of
being a control line to identify to the driver when he has finished a
lap.
I've mounted the magnetic reed switch in a slim line case under the
kart.
The ride height of the kart is approximately 0.05 +/- 0.01 m. As for the
maximum speed it is approximately 90 km/hr.
When I fitted the device and it was taken for a test it seemed to
trigger randomly or not at all. But when I removed it from the kart and
physically waved it over the control line (magnet) it worked perfectly
(which it also did on the test bench). Although, I was moving it closer
to
the asphalt than it is mounted on the kart. Which means, that the
sensitivity of the magnetic reed switch isn't enough.
Does anyone know of a way around this problem? I have been reading
up
on
Hall Effect sensors but from my understanding they only detect fields at
90
degrees. Any advice or links on the web would be greatly appreciated.

KM

 

[David]

If I assume the magnetic strip is 25mm wide and the reed is 25 mm long and aligned to cross the magnet perpendicularly, then at 90 km/h the duration of the reed passing over the magnet is approx 2 ms. Even at 18 km/h the duration is only 10 ms or so. I don't think you will find an affordable reed relay (if any) that will operate reliably at these short durations.

I have successfully used the Honeywell 400SR series hall effect position sensor in a few diverse applications. Have a look at the Honeywell catalogue page here, you might something of interest:

http://catalog.sensing.honeywell.com/vsg_compare.asp?FAM=solidstateSG&P=&ITEMLIST=273184,273185,273186,273188,273189

Unless the kart is crossing the strip at an acute relataive angle it shouldn't be affected. If it was such an acute angle I guess the kart driver would be worried about other things than when the line was crossed.

--

++++++++++++++++++++++++++++++++++++++++++
Any email address associated with the sender of
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is valid but munged to help combat spam. To
email simply remove the obvious.
+++++++++++++++++++++++++++++++++++++



"KM" <kmeng@optusnet.com.au> wrote in message news:40f27127$0$18195$afc38c87@news.optusnet.com.au...

Hi,
I'm having a problem using a minature magnetic reed switch to detect
when it has passed over a magnet. The application is for automotive and the
magnet is laid across the asphalt of a race track. It serves the purpose of
being a control line to identify to the driver when he has finished a lap.
I've mounted the magnetic reed switch in a slim line case under the kart.
The ride height of the kart is approximately 0.05 +/- 0.01 m. As for the
maximum speed it is approximately 90 km/hr.
When I fitted the device and it was taken for a test it seemed to
trigger randomly or not at all. But when I removed it from the kart and
physically waved it over the control line (magnet) it worked perfectly
(which it also did on the test bench). Although, I was moving it closer to
the asphalt than it is mounted on the kart. Which means, that the
sensitivity of the magnetic reed switch isn't enough.
Does anyone know of a way around this problem? I have been reading up on
Hall Effect sensors but from my understanding they only detect fields at 90
degrees. Any advice or links on the web would be greatly appreciated.

KM

 

[David]

Maybe one of these, mounted on the cart to detect a steel strip...

http://www.ssec.honeywell.com/magnetic/mark_det.html



--

++++++++++++++++++++++++++++++++++++++++++
Any email address associated with the sender of
this message, either in the headers or body
is valid but munged to help combat spam. To
email simply remove the obvious.
+++++++++++++++++++++++++++++++++++++

"David" <dave_lstr@ya--hoo.com> wrote in message news:hSuIc.90905$sj4.89648@news-server.bigpond.net.au...

If I assume the magnetic strip is 25mm wide and the reed is 25 mm long and aligned to cross the magnet perpendicularly, then at 90 km/h the duration of the reed passing over the magnet is approx 2 ms. Even at 18 km/h the duration is only 10 ms or so. I don't think you will find an affordable reed relay (if any) that will operate reliably at these short durations.

I have successfully used the Honeywell 400SR series hall effect position sensor in a few diverse applications. Have a look at the Honeywell catalogue page here, you might something of interest:

http://catalog.sensing.honeywell.com/vsg_compare.asp?FAM=solidstateSG&P=&ITEMLIST=273184,273185,273186,273188,273189

Unless the kart is crossing the strip at an acute relataive angle it shouldn't be affected. If it was such an acute angle I guess the kart driver would be worried about other things than when the line was crossed.

--

++++++++++++++++++++++++++++++++++++++++++
Any email address associated with the sender of
this message, either in the headers or body
is valid but munged to help combat spam. To
email simply remove the obvious.
+++++++++++++++++++++++++++++++++++++



"KM" <kmeng@optusnet.com.au> wrote in message news:40f27127$0$18195$afc38c87@news.optusnet.com.au...

Hi,
I'm having a problem using a minature magnetic reed switch to detect
when it has passed over a magnet. The application is for automotive and the
magnet is laid across the asphalt of a race track. It serves the purpose of
being a control line to identify to the driver when he has finished a lap.
I've mounted the magnetic reed switch in a slim line case under the kart.
The ride height of the kart is approximately 0.05 +/- 0.01 m. As for the
maximum speed it is approximately 90 km/hr.
When I fitted the device and it was taken for a test it seemed to
trigger randomly or not at all. But when I removed it from the kart and
physically waved it over the control line (magnet) it worked perfectly
(which it also did on the test bench). Although, I was moving it closer to
the asphalt than it is mounted on the kart. Which means, that the
sensitivity of the magnetic reed switch isn't enough.
Does anyone know of a way around this problem? I have been reading up on
Hall Effect sensors but from my understanding they only detect fields at 90
degrees. Any advice or links on the web would be greatly appreciated.

KM

 

[KM]

Yeah, that is exactly what I thought!

So in doing some research I had a look at those bicycle computers you can
buy in electronics shops and took one apart. It too used a magnetic reed
switch which is exactly the same as that which I'm using. And the
specifications on these computer are up to 100km/hr with obviously a far
higher frequency as the magnet has a small circumference to travel. Whereas
I pass over the magnet in the track once every 40 seconds. I have the
magnetic reed switch connected to the 16F84 microcontroller, so it debouces
the switch. So it should be able to do it.

I have tested it with different magnets though and found that say with a
speaker cone magnet of diameter 0.05 m the maximum height from activation
was approximately (0.04 +/- 0.05) m. So I think the distance the switch is
away from the strip is the problem. So hopefully the Hall Effect sensor is
more sensitive. Thanks for the links on the 400SR, I'll definitely check it
out.

Thanks David.

KM

David <dave_lstr@ya--hoo.com> wrote in message
news:hSuIc.90905$sj4.89648@news-server.bigpond.net.au...

If I assume the magnetic strip is 25mm wide and the reed is 25 mm long and
aligned to cross the magnet perpendicularly, then at 90 km/h the duration of
the reed passing over the magnet is approx 2 ms. Even at 18 km/h the
duration is only 10 ms or so. I don't think you will find an affordable
reed relay (if any) that will operate reliably at these short durations.

I have successfully used the Honeywell 400SR series hall effect position
sensor in a few diverse applications. Have a look at the Honeywell
catalogue page here, you might something of interest:

http://catalog.sensing.honeywell.com/vsg_compare.asp?FAM=solidstateSG&P=&ITE
MLIST=273184,273185,273186,273188,273189

Unless the kart is crossing the strip at an acute relataive angle it
shouldn't be affected. If it was such an acute angle I guess the kart
driver would be worried about other things than when the line was crossed.

--

++++++++++++++++++++++++++++++++++++++++++
Any email address associated with the sender of
this message, either in the headers or body
is valid but munged to help combat spam. To
email simply remove the obvious.
+++++++++++++++++++++++++++++++++++++



"KM" <kmeng@optusnet.com.au> wrote in message
news:40f27127$0$18195$afc38c87@news.optusnet.com.au...

Hi,
I'm having a problem using a minature magnetic reed switch to detect
when it has passed over a magnet. The application is for automotive and
the
magnet is laid across the asphalt of a race track. It serves the purpose
of
being a control line to identify to the driver when he has finished a lap.
I've mounted the magnetic reed switch in a slim line case under the kart.
The ride height of the kart is approximately 0.05 +/- 0.01 m. As for the
maximum speed it is approximately 90 km/hr.
When I fitted the device and it was taken for a test it seemed to
trigger randomly or not at all. But when I removed it from the kart and
physically waved it over the control line (magnet) it worked perfectly
(which it also did on the test bench). Although, I was moving it closer to
the asphalt than it is mounted on the kart. Which means, that the
sensitivity of the magnetic reed switch isn't enough.
Does anyone know of a way around this problem? I have been reading up
on
Hall Effect sensors but from my understanding they only detect fields at
90
degrees. Any advice or links on the web would be greatly appreciated.

KM

 

[Geoff C]

"KM" <kmeng@optusnet.com.au> wrote in
news:40f27127$0$18195$afc38c87@news.optusnet.com.au:

Hi,
I'm having a problem using a minature magnetic reed switch to
detect
when it has passed over a magnet. The application is for automotive
and the magnet is laid across the asphalt of a race track. It serves
the purpose of being a control line to identify to the driver when he
has finished a lap. I've mounted the magnetic reed switch in a slim
line case under the kart. The ride height of the kart is approximately
0.05 +/- 0.01 m. As for the maximum speed it is approximately 90
km/hr.
When I fitted the device and it was taken for a test it seemed to
trigger randomly or not at all. But when I removed it from the kart
and physically waved it over the control line (magnet) it worked
perfectly (which it also did on the test bench). Although, I was
moving it closer to the asphalt than it is mounted on the kart. Which
means, that the sensitivity of the magnetic reed switch isn't enough.
Does anyone know of a way around this problem? I have been reading
up on
Hall Effect sensors but from my understanding they only detect fields
at 90 degrees. Any advice or links on the web would be greatly
appreciated.

KM

Firstly, I think the magnetic system is very problematic. Read switches
may not respond fast enough, I have used Hall effect devices on several
non-related designs. Even the so-called high sensitivity ones only
operate at about 10mm with an approx. 0,2 tesla magnet. This may be
enough but I imagine aimingb the go kart is very difficult.

I built a system 2 years ago for a bicycle speed trial for recumbant
bikes. It used a rubber tube across the track, about 2 metres long. It
was 6mm O.D. One end was blocked, other end was connected to a pressure
switch, Farnell 731-912. Then I cleaned up the pulse with a monostable
and fed that into the switch of a $10 dick smith stopwatch (needed a p-
type FET though since the watch had postive common). Worked well, above
all it was relaiable and worked every time. Yes, $80 is a bit steep but I
found it flawlwss in operation and you don't have to think about it much
when driving.

 

[The Real Andy]

On Mon, 12 Jul 2004 22:07:21 +1000, "KM" <kmeng@optusnet.com.au>
wrote:

Yeah, that is exactly what I thought!

So in doing some research I had a look at those bicycle computers you can
buy in electronics shops and took one apart. It too used a magnetic reed
switch which is exactly the same as that which I'm using. And the
specifications on these computer are up to 100km/hr with obviously a far
higher frequency as the magnet has a small circumference to travel. Whereas

Its not how often you pass the magnet, its how quickly you pass over
it. The bike may use a more powerful magnet, and it may be closer to
the sensor.

I pass over the magnet in the track once every 40 seconds. I have the
magnetic reed switch connected to the 16F84 microcontroller, so it debouces
the switch. So it should be able to do it.

Not sure how you a looking at the switch with the pic, but perhaps you
should latch it with some high speed cmos. Me thinks the pic is not
real good when it comes to short duration pulses.

I have tested it with different magnets though and found that say with a
speaker cone magnet of diameter 0.05 m the maximum height from activation
was approximately (0.04 +/- 0.05) m. So I think the distance the switch is
away from the strip is the problem. So hopefully the Hall Effect sensor is
more sensitive. Thanks for the links on the 400SR, I'll definitely check it
out.

Perhaps a coil of wire may do the trick. What you really need to do is
look at the ouput of your sensor with a cro. Alternativly, if there is
a mag strip embedded in the ashphalt, then maybe some other people
make use of it. Try asking around.

Where is the track located?

 

[Brian Goldsmith]

"KM" <kmeng@optusnet.com.au> wrote in


I'm having a problem using a minature magnetic reed switch to detect
when it has passed over a magnet. The application is for automotive and the
magnet is laid across the asphalt of a race track.

***** Again?????????

Brian Goldsmith.

 

[KM]

No the bike magnet doesn't use a more powerful magnet. It's magnetic flux is
considerable smaller than the magnetic strip in the track.

The PIC is high speed CMOS.

Other people do use the control line with devices they have purchased. But
they are very expensive and I would like to design one more for my own
specification.


The Real Andy <.pearson@wayit_dot_com_dot_au_remove_the_obvious_to_reply>
wrote in message news:kc07f01avueh4ifpqufigc5mvqu81cr24m@4ax.com...

On Mon, 12 Jul 2004 22:07:21 +1000, "KM" <kmeng@optusnet.com.au
wrote:

Yeah, that is exactly what I thought!

So in doing some research I had a look at those bicycle computers you can
buy in electronics shops and took one apart. It too used a magnetic reed
switch which is exactly the same as that which I'm using. And the
specifications on these computer are up to 100km/hr with obviously a far
higher frequency as the magnet has a small circumference to travel.
Whereas

Its not how often you pass the magnet, its how quickly you pass over
it. The bike may use a more powerful magnet, and it may be closer to
the sensor.

I pass over the magnet in the track once every 40 seconds. I have the
magnetic reed switch connected to the 16F84 microcontroller, so it
debouces
the switch. So it should be able to do it.

Not sure how you a looking at the switch with the pic, but perhaps you
should latch it with some high speed cmos. Me thinks the pic is not
real good when it comes to short duration pulses.


I have tested it with different magnets though and found that say with a
speaker cone magnet of diameter 0.05 m the maximum height from activation
was approximately (0.04 +/- 0.05) m. So I think the distance the switch
is
away from the strip is the problem. So hopefully the Hall Effect sensor
is
more sensitive. Thanks for the links on the 400SR, I'll definitely check
it
out.

Perhaps a coil of wire may do the trick. What you really need to do is
look at the ouput of your sensor with a cro. Alternativly, if there is
a mag strip embedded in the ashphalt, then maybe some other people
make use of it. Try asking around.

Where is the track located?

 

[The Real Andy]

On Wed, 14 Jul 2004 00:37:07 +1000, "KM" <kmeng@optusnet.com.au>
wrote:

No the bike magnet doesn't use a more powerful magnet. It's magnetic flux is
considerable smaller than the magnetic strip in the track.

If that is the case, then it all comes down to timing. You need a cro
to find out what is happening.

The PIC is high speed CMOS.

Yeah, right. Slow speed inputs. Been there, done that. Aint that
flash. What pin are you using to catch the pulse and how are you
dealing with it in software?

Other people do use the control line with devices they have purchased. But
they are very expensive and I would like to design one more for my own
specification.

And what do the expensive devices use for detection?

The Real Andy <.pearson@wayit_dot_com_dot_au_remove_the_obvious_to_reply
wrote in message news:kc07f01avueh4ifpqufigc5mvqu81cr24m@4ax.com...
On Mon, 12 Jul 2004 22:07:21 +1000, "KM" <kmeng@optusnet.com.au
wrote:

Yeah, that is exactly what I thought!

So in doing some research I had a look at those bicycle computers you can
buy in electronics shops and took one apart. It too used a magnetic reed
switch which is exactly the same as that which I'm using. And the
specifications on these computer are up to 100km/hr with obviously a far
higher frequency as the magnet has a small circumference to travel.
Whereas

Its not how often you pass the magnet, its how quickly you pass over
it. The bike may use a more powerful magnet, and it may be closer to
the sensor.

I pass over the magnet in the track once every 40 seconds. I have the
magnetic reed switch connected to the 16F84 microcontroller, so it
debouces
the switch. So it should be able to do it.

Not sure how you a looking at the switch with the pic, but perhaps you
should latch it with some high speed cmos. Me thinks the pic is not
real good when it comes to short duration pulses.


I have tested it with different magnets though and found that say with a
speaker cone magnet of diameter 0.05 m the maximum height from activation
was approximately (0.04 +/- 0.05) m. So I think the distance the switch
is
away from the strip is the problem. So hopefully the Hall Effect sensor
is
more sensitive. Thanks for the links on the 400SR, I'll definitely check
it
out.

Perhaps a coil of wire may do the trick. What you really need to do is
look at the ouput of your sensor with a cro. Alternativly, if there is
a mag strip embedded in the ashphalt, then maybe some other people
make use of it. Try asking around.

Where is the track located?

 

[KM]

CRO not needed.

Proximity to switch is too large.

Switch moved closer to track and operates.


The Real Andy <.pearson@wayit_dot_com_dot_au_remove_the_obvious_to_reply>
wrote in message news:3nm9f09obhqk60m0b280b2srasjh4gp92g@4ax.com...

On Wed, 14 Jul 2004 00:37:07 +1000, "KM" <kmeng@optusnet.com.au
wrote:

No the bike magnet doesn't use a more powerful magnet. It's magnetic flux
is
considerable smaller than the magnetic strip in the track.

If that is the case, then it all comes down to timing. You need a cro
to find out what is happening.


The PIC is high speed CMOS.

Yeah, right. Slow speed inputs. Been there, done that. Aint that
flash. What pin are you using to catch the pulse and how are you
dealing with it in software?


Other people do use the control line with devices they have purchased.
But
they are very expensive and I would like to design one more for my own
specification.

And what do the expensive devices use for detection?



The Real Andy <.pearson@wayit_dot_com_dot_au_remove_the_obvious_to_reply
wrote in message news:kc07f01avueh4ifpqufigc5mvqu81cr24m@4ax.com...
On Mon, 12 Jul 2004 22:07:21 +1000, "KM" <kmeng@optusnet.com.au
wrote:

Yeah, that is exactly what I thought!

So in doing some research I had a look at those bicycle computers you
can
buy in electronics shops and took one apart. It too used a magnetic
reed
switch which is exactly the same as that which I'm using. And the
specifications on these computer are up to 100km/hr with obviously a
far
higher frequency as the magnet has a small circumference to travel.
Whereas

Its not how often you pass the magnet, its how quickly you pass over
it. The bike may use a more powerful magnet, and it may be closer to
the sensor.

I pass over the magnet in the track once every 40 seconds. I have the
magnetic reed switch connected to the 16F84 microcontroller, so it
debouces
the switch. So it should be able to do it.

Not sure how you a looking at the switch with the pic, but perhaps you
should latch it with some high speed cmos. Me thinks the pic is not
real good when it comes to short duration pulses.


I have tested it with different magnets though and found that say with
a
speaker cone magnet of diameter 0.05 m the maximum height from
activation
was approximately (0.04 +/- 0.05) m. So I think the distance the
switch
is
away from the strip is the problem. So hopefully the Hall Effect
sensor
is
more sensitive. Thanks for the links on the 400SR, I'll definitely
check
it
out.

Perhaps a coil of wire may do the trick. What you really need to do is
look at the ouput of your sensor with a cro. Alternativly, if there is
a mag strip embedded in the ashphalt, then maybe some other people
make use of it. Try asking around.

Where is the track located?