Comparison of Technologies used in Measuring Magnet Characteristics
In comparing the different processes, one basic principle remains constant and that is in each case the magnet being tested is driven around part of, or all, of its hysteresis loop via an applied external field. A detail of each type of technique is given later.
PFM offers the highest of possible applied fields and a very rapid open circuit measurement cycle. Measurement cycles of 4 seconds are possible full loop measurements are made without the need for seperate magnetising equipment. Hirst F2F processes remove eddy current effects.
VSM offers an pen circuit measuremtn of, usually small samples. If the VSM uses an electromagnet, only 2nd quadrant of part of the rare earth magnets can be measured.
Super conducting magnets can achieve higher fields but usually at the cost of slower speeds and the need for Cryogenic gases.
Permeaters often called Permagraphs of Hysterisographs offer a closed magnetic circuit measurement, but are limited to lower applied magnetic fields, and 2nd quadrant measurements of many magnetic materials.
To avoid eddy currents in the electromagnet, measurement cycles are slow.
The power requirements of this process are higher than others such as the PFM. This can be important where electricity supply costs are high.