I've been trying to get my head around as much of the physics of magnetism and how to measure it. This is quite a wide area, and so much background knowledge is required - at least for the level of my enquiries. Anyway, hoping someone else can help me out here, I'll tell you what I need:
I want to be able to measure the magnetic field intensity of permanent magnet from different positions. I would like the sensor to produce a voltage proportional to the distance (i.e. not a switch sensor). My source for a permanent magnetic might be something like a 6 inch speaker, or whatever strong magnets I can find.
My confusion is which type of sensor would be the best to get, taking into consideration the application, the range required, the cost. I have read but understood so little of all the different types of sensors and their various units of measurement etc. Any help would be greatly appreciated!
As far as I know, there are only two possibilities: hall or magnetometer.
Some hall sensors are switches (on or off), but some hall sensors have a linear analog output according to the magnetic field strength. They are called ratiometric hall sensors. You can buy them in different sensitivities. Connect it to the Arduino and you have a Gaussmeter
A magnetometer measures the earth magnetism. They will measure a strong magnet a few meters away. But because they are so sensitive, they easily clip to the maximum with a strong magnet.
I would like the sensor to produce a voltage proportional to the distance (i.e. not a switch sensor).
It is very difficult to get a distance measurement from a magnetic field strength measurement, unless you have a setup where the relative orientation of the magnet and sensor is fixed and only the distance changes. Furthermore, the field strength drops off in a highly nonlinear fashion as the distance changes, so the entire setup would need to be very carefully calibrated.
Yes, I was concerned about how much the orientation of the sensor would affect the sensor readings. For the most part, if the reading on the linear sensors gave me a rough idea of the distance, (not necessarily exact down to the centimeter readings) that would be good enough for the application I think.
I downloaded an app for my phone to read magnetic fields, and checked it when close to a speaker or far away. It works up to about a foot before hitting a floor value of around 48µT no matter how far away it is (is this reading coming from the earths field by the way?), and yes if I turn it, the reading changes, but the figures still stay in the general ballpark. If the hall sensor will work in the same way, then I think this will be OK for me.
Actually, the only question I have left is which would be the right hall sensor to get that will have an appropriate sensitivity and range to work with about a 2 foot distance of a speakers magnetic field. I've read the specs on many of them, but they don't seem to tell me the information I want. For example, the pdf:
Am I right in understanding from reading the specs on theSS49E sensor:
0 Gauss = 2.5 Voltage output,
Output voltage increases by 1.4V per Gauss
therefore giving me a range of 1.78 Gauss?
But then it says underneath that the magnetic range is +/-650Gauss
...I'm so confused...
I can't wait to get stuck in the even sticker schematics of this when I have all the parts!!
It detects possitive and negative Gauss. So the output is normally in the middle at 2.5V.
The sensitivity is 1.4 mV/Gauss, that is 1.4 milliVolt per Gauss.
I suppose that your phone has an electronic compass in it...
For reference, the Earth's magnetic field ranges in magnitude from about 25 to 65 microTesla, or 250 to 650 milliGauss. Although we are accustomed to thinking that a compass needle will point north, in 3D the magnetic field vector points in wildly different directions depending on where you on the Earth. In North America, it makes an angle of roughly 60 degrees down from the horizontal plane.
