hall sensors to detect slideby position of a magnet

[mook johnson]

I'm using linear hall sensors to detect the position of a small SmCo magnet
about 0.75" away.
There will be several sensors in a line, spaced about .4" apart. The magnet
will be directly below these sensors about and travel along a parallel path.
According to my calculations, the magnet will produce about 75G at this
distance, which will product a signal strength of 375mV from a sensor when
the magnet is directly below it.

What I'd like to accomplish is to resolve the position of the magnet down to
no greater than 0.05". Also, I must take into account that the magnet
strength and hall sensitivity will not be constant through out the life of
the part, so the measurement should take into account varying field strength
measurement. In-situ calibration is a fallback but not desired.

Any hall sensor gurus out there?

 

[Wayne]

"mook johnson" <mook@mook.net> wrote in message
news:FZRdc.11110$Y45.9055@fe2.texas.rr.com...

I'm using linear hall sensors to detect the position of a small SmCo
magnet
about 0.75" away.
There will be several sensors in a line, spaced about .4" apart. The
magnet
will be directly below these sensors about and travel along a parallel
path.
According to my calculations, the magnet will produce about 75G at this
distance, which will product a signal strength of 375mV from a sensor
when
the magnet is directly below it.

What I'd like to accomplish is to resolve the position of the magnet down
to
no greater than 0.05". Also, I must take into account that the magnet
strength and hall sensitivity will not be constant through out the life of
the part, so the measurement should take into account varying field
strength
measurement. In-situ calibration is a fallback but not desired.

Any hall sensor gurus out there?

Try using two opposing magnets side by side. ie. NS and SN. This will
produce a neutral field between the two.


>

 

[mook johnson]

How do I resolve the location of the null spot down to .05" with the sensors
..4" apart?


"Wayne" <noprivatemailthanks@abc.com> wrote in message
news:VMTdc.3400$ED.2210@news-server.bigpond.net.au...

"mook johnson" <mook@mook.net> wrote in message
news:FZRdc.11110$Y45.9055@fe2.texas.rr.com...
I'm using linear hall sensors to detect the position of a small SmCo
magnet
about 0.75" away.
There will be several sensors in a line, spaced about .4" apart. The
magnet
will be directly below these sensors about and travel along a parallel
path.
According to my calculations, the magnet will produce about 75G at this
distance, which will product a signal strength of 375mV from a sensor
when
the magnet is directly below it.

What I'd like to accomplish is to resolve the position of the magnet
down
to
no greater than 0.05". Also, I must take into account that the magnet
strength and hall sensitivity will not be constant through out the life
of
the part, so the measurement should take into account varying field
strength
measurement. In-situ calibration is a fallback but not desired.

Any hall sensor gurus out there?



Try using two opposing magnets side by side. ie. NS and SN. This will
produce a neutral field between the two.

 

[Rich Grise]

"mook johnson" <mook@mook.net> wrote in message
news:K1Udc.11376$Y45.8404@fe2.texas.rr.com...

How do I resolve the location of the null spot down to .05" with the
sensors
.4" apart?

I'd think look at all the outputs simultaneously and fit a curve, and

find that curve's maximum. But, as you've mentioned those things change -
(I went nuts once trying to protect a hall device that was metering cathode
current of an ion gun at about 5 KV. The transient from an arc didn't
_destroy_ the device, but changed its transfer function (mostly offset)
unpredictably.) so I can't see a way to get around _some_ kind of
periodic calibration.

Good Luck!
Rich

 

[Joerg]

Does it have to be Hall? Or could it be optical or inductive? Just thinking
about how to make it low maintenance.

Regards, Joerg.