Christopher said:
Hello Everyone,
Weak Magnetic Field Sensing
Before I begin to chase the madness into the evening, I would like to
know if using a magnetic sensor like the Hall Effect would allow me to
convert "a small magnetic rod's distance into resistance. " The few
circuits sensing magnetism I see seem to be more of a window
comparator behavior or 0/1 or a tripped on state.
Ideal: is a strong "hand held" magnet moving 8" to 1" from the sensor,
this would create a resistance change of 10k down to 1k or something
to that effect not necessarily that resistance change.
Question: Is this conversion possible or unreasonable?
Thank you for any input or humor,
Christopher
* * *
Christopher
Temecula CA.USA
http://www.oldtemecula.com
Christopher,
I can see what you are getting at.. maybe I am a different species?.
Yes this conversion is possible, but might require some cumbersome
electronics.
The true hall effect sensor you speak of outputs a voltage
proportional to both the applied field
and transverse bias current. In the 'easy' sense what you'd like to do is
unreasonable, but it can be acheived in effect,
approximately, with additional circuitry... with some likely requirement of
isolating the hall effect bias current voltage source from the rest of your
circuits. I think you can forget about using the hall device directly to
emulate some kind of resistor. However it's output voltage can be amplified
and sent through a transconductor of some kind which approximates a
resistor, or more readily an analog to digital converter driving a digital
potentiometer.. with some added resistors, or offset scheme to get your
range expressed in 64, 100, 256 ohmic range steps.
LakeShore has hall effect sensors of the type you are interested in. I
suspect Digikey or Allied also carries more than one proportional hall
effect device, and one that is easy to use... though most are as you say.
There are lots of way to skin a cat (no cats were harmed during testing)
.. Since hall devices are linear with respect to applied field and current,
the output will not vary linearly with distance, as the field strength of
the magnetic rod will not correspond linearly over that range (but will
appear close to linear over very very small incremental changes in distance
between rod and sensor).
There are magneto-resistive sensing elements out there, maybe there is
some way you could use a Honeywell device.. still I would wonder why you
couldnt use the changing voltage to effect whatever desired action somehow.
You could set up 10, 0/1 devices over the 8-inch range, each switching in a
new resistor with some clever way of latching the present state to hold
R-value in the dead-zones between sensors. It's crude, but sort of linear.
You can do this to some effect with a few components.. as you said, not
necessarily linear, but over some range.
I'm not sure how to set it up, but I've heard that if you shred the
constitution, torture people for corporate profits, and
(mile-long list truncated), resistance changes proportional to that... but I
think it usually means boycotting beer for an hour at best, which isn't
really resistance, or ohmically useful either.
Anna