Testing Magnets - DIY Gauss Meter

[rkosiorek]

I don't do spring cleanups. instead i do pre-hibernation cleanups. this year i looked around my storage area and i found i have way too many dead and fried motors hanging around. time test whether some of these are just junk or if they can be rescued.

Specifically i need to figure out which of these motors need repairs to the magnet assembly. to do that i need to measure not only the polarity but also the strength of the magnets.

I Googled Gauss Meter and i found a couple of really simple designs using Hall Sensor chips. so i decided to try one.



This is an add on probe for a regular voltmeter. R2 is used to Zero or Null the meter. The "Branded" face of the hall sensor is the measuring side. (+) voltages will show on the voltmeter as the branded face is brought near to the "S" pole of a magnet. (-) voltages as the face is brought near the "N" pole.

the meter will also show field strength. it is not calibrated for accurate field strength readings but it will measure approximately +/- 2000 Gauss. the scale is 1mV/Gauss.

rick

 

[Bartimaeus]

Can you compare this against the smartphone Gauss meter apps that are out there?

 

[rkosiorek]

mostly the range of measurement.

the Gauss meter apps use the 2 or 3axis compass chip built into the smartphone. these are used to measure the earths extremely WEAK magnetic field. usually the maximum measurement is less than -/+ 10 Gauss (1000 uT). this sensitivity is achieved by using magneto-resistive elements in a wheatstone bridge measuring circuit in each axis. these are small resistors whose resistance value is changed by a magnetic field. this meter adapter reads STRONG magnetic fields of -/+ 2000 Gauss. strong vs weak field measurement is the biggest difference

it is also hard to tell where is exactly the measuring point of the phone app. what exact spot on your phone is the sensor chip located? it is easy to tell precisely where that tiny hall sensor chip is measuring. being smaller it is easier to fit the hall sensor into smaller spaces. I glued my sensor to the end of a BIC pen tube with a dab of epoxy to make it easy to handle.

Caution. the field strength of some large magnets can exceed 10K Gauss. some magneto resistive elements may be permanently damaged by exposure to such powerful magnetic fields. it's just a warning. i don't know if the chip inside your phone will be damaged by a strong magnetic field but it is a possibility. you could be taking a risk of permanent damage by sticking your phone inside of a large magnet ring. a risk i'm not willing to take seeing that the parts for the adapter are less than $10.00. and the hall sensors are almost impervious to damage even by magnetic fields stronger than any in a motor.

rick

 

[Bartimaeus]

Ah. Good to know, haven't done any messing about with my phone for that, was just curious.