Rotational sensing - Analog Hall Sensor - Check me - RC Groups
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Dec 31, 2010, 03:52 PM
York Electronics
Gary Warner's Avatar
Discussion

Rotational sensing - Analog Hall Sensor - Check me


I 'know' about analog hall sensors, but I've never played with them. I'm reading the rotation angle of a shaft (+/- 30 deg.).

I'm using a ring magnet that's magnetized diametrically (not on it's axis) and slid onto the shaft. I'm placing the hall sensor on the side next to the magnet. Sensor setup in bipolar output.

Is this right? I'm not sure.

Hall Sensor:
http://www.analog.com/static/importe...ts/AD22151.pdf

Magnet:
http://www.kjmagnetics.com/proddetail.asp?prod=R424DIA
Last edited by Gary Warner; Dec 31, 2010 at 04:08 PM.
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Dec 31, 2010, 05:50 PM
Registered User
The chips have a "sense path", you have to supply lines of flux that are
aligned, or it won't see the magnet. Just hook one up to a dc source and
load R, and move the magnet by it different ways, to see what turns it on. Radial is more complicated.
Not sure.
Dec 31, 2010, 05:54 PM
Registered User
Sounds right.

in bipoler mode, the sensor output should go from Vcc/2 when neither pole is pointed at the magnet, to closer to Vcc when one pole is closer, and closer to zero when the other pole is closer.

To get an unambigous reading, the magnets travel should be limited between the poles..
, not from one side of a pole to the other side of the same pole....

HTH

SteveH
Jan 02, 2011, 08:58 PM
Registered User
Presumably you can only measure 0 to 180 degrees like this? So good for total rotations, but not absolute position.
Jan 02, 2011, 09:02 PM
York Electronics
Gary Warner's Avatar
Thanks guys for the feedback. The hardware will be here in a week and I'll report on how this configuration works. Even 2 EE's that are my friends can't agree on whether or not this configuration is what I want?

Anywho, I have the sensor vane made and all I need now is the Hall IC and magnet. Past that, a few thousand lines of code and I'm in business!
Jan 02, 2011, 09:24 PM
Registered User
You might try sim software, probably expensive.

http://www.google.com/images?hl=en&e...iw=790&bih=342
Jan 02, 2011, 10:14 PM
Registered User
I think you'll need two sensors to measure absolute orientation ..
Jan 03, 2011, 11:53 AM
Registered User
Maybe I misunderstood, can hte shaft freely rotate, or is the travel limited to +-30 degrees?

If limited to +- 30 degrees,
This seems to be the same application as in hobby servos like a falcon..
Only one sensor is need if you need to read +- 30 degress
if you orient the magnet correctly when the angle is zero..


SteveH
Jan 03, 2011, 12:05 PM
York Electronics
Gary Warner's Avatar
Yes Steve, it's an AoA sensor and the rotation will be limited, most likely from -20 degrees to +30 degrees.
Jan 03, 2011, 12:11 PM
Registered User
Dan Baldwin's Avatar
I did something very similar to what you are trying to do with a web unwind system. I needed to be able to sense the position of a "dancer" arm to about +- 30 deg. I used a hall effect sensor (mouser #785-ss495a1) and a cylindrical magnet that was magnetized on the end (McMaster Carr #5688k52 see picture below), and it worked, but I didn't have as much output as I wanted, so I ended up putting 2 magnets facing each other with the hall effect sensor in the 1/8" gap between them, and output was okay. The magnets were oriented with north pole of one facing the south pole of the other.

Dan


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