Stabilisation and Calibration
Permanent magnets suffer extremely low loss except when driven beyond certain critical parameters at which point we say they have “irreversible loss.” If re-magnetisation restores all of the original magnetic output, then they have not suffered irrecoverable or structural loss. When only irreversible loss is present and it results in unacceptable differences between initial and subsequent operation, it is almost always possible to “precondition” the magnets so that little to no additional loss is observed in operation. (This assumes that the optimal material has been selected and extraordinary methods must be applied).
If the loss during use is expected to come from elevated temperature, then a Thermal Stabilisation is recommended. If the loss is due to demagnetising stress, then a Magnetic Stabilisation should be performed.
Variation in magnetic output (flux output) is unavoidable. Most applications can tolerate normal variations in flux output. For those that require extremely tight tolerances, magnets can be “calibrated” to a set output by partial knockdown. This is usually a magnetic calibration procedure, though occasionally thermal calibration is used – where uniformity at elevated temperature is essential.
Arnold has extensive experience in performing both thermal and magnetic procedures. For example, one consideration is that thermal conditioning can be performed either in open circuit or fixed load line.
For applications requiring stable output over a wide temperature range, many customers consider RECOMA® STAB , a grade of SmCo with less than 50 ppm change in output per ºC from -40 to 200 ºC.