Post by Lake Shore Ryan on Jan 17, 2019 10:46:46 GMT -5
Would love to help with suggesting a solution.
Do you know what performance characteristics for these magnets will be? Is it a specific field value some distance from a point on the magnet? Direction of magnetization? Or if you're not sure exactly what metrics you want to test, what is the final intended purpose of the magnet?
Oh, there is another way you could look at this too: How does your supplier specify the magnet? You may want to implement a test that your supplier is already doing to make troubleshooting easier if you find magnets that don't meet your supplier's specifications.
Ryan Oliver Director of Product Management, Sensors and Instruments Lake Shore Cryotronics
Post by Lake Shore Ryan on Jan 30, 2019 16:02:16 GMT -5
Thanks for sending the test documents. I'll speak in general terms so I don't disclose details of your magnet. There are quite a few options for characterizing magnets, so I'll just let you know some options and hopefully you can determine which option would be best for your situation.
It looks like you have a very thick ring magnet and the supplier has provided you with a 2nd quadrant plot from a hysteresisgraph like the one shown below:
A hysteresisgaph is a fairly serious piece of equipment that would be quite time consuming to use for 100% incoming inspections, but it would allow you to make your own BH measurements.
So if you're looking for an easier way to test your magnets, I think you're left with two options:
1. Fluxmeter and Helmholtz Coil to measure magnetic moment
Combining knowledge of the magnet geometry and the measured magnetic moment will allow you to calculate these
2nd quadrant parameters, or back calculate what the magnetic moment should be based on their specified values. We have a document on our fluxmeter download page that may be helpful in making these calculations. I'm just not sure whether the volume should be the total volume of the cylinder, the volume of metal, or something in between.... Maybe you would be better off taking a magnet that you know meets requirements, measure the magnetic moment and use that as your reference. Information on how this measurement is made can be found in our FH-6 Helmholtz coil manual and shows the process of moving the magnet in and out of the Helmholtz coil to determine the magnetic moment.
In comparison to a hysteresisgraph, this method is much faster and very good at giving you an idea of the total magnetization of the magnet.
2. Teslameter/Gaussmeter and Hall probe to measure field at a point.
This method measures magnetic field (B) at some point away from the magnet. This is useful if you want to test the effect produced by the magnet and can be faster and less expensive than the fluxmeter approach. The biggest drawback of this solution is that the position of the magnet and Hall probe must be controlled very precisely if repeatable measurements are to be made. If you're measuring at a location where you know the direction of field, such as along the axis of the magnet, you could use a single-axis Hall probe and simplified gaussmeter like our Model 425. This is a very economical method of testing and would allow you to quickly measure a magnetic field and be given pass/fail indicators on the screen of the unit. More advanced measurements can be made with multi-axis (vector) field measurements. Our F71 teslameter is a good example of this, but will require a 3-axis probe, bring the cost very close to that of a fluxmeter. However, you would then be able to examine field strength and direction all around the magnet.