A Low Cost High Field Strength Hysteresigraph

A high field strength hysteresigraph deriving H directly from the mains is described. The coil is energised only during one and one-half cycles of the main frequency to produce the high field. The present unit is intended for testing several soft and fairly hard (e.g., magnetic tape) materials. The hysteresigraph consists of a zero cross over detector, a programmable timer, a high current switch and a magnetising coil. This novel design concept eliminates the use of the conventional and costly capacitor discharge system. In the present design a low cost triac has been used to switch peak current pulses of 200 amperes. A maximum pulsed field strength of 20,000 oersteds has been realised. However, the same design concept can be extended to realise much higher field strengths when a triac of higher current rating is used in the same circuit.