GB1052821A - - Google Patents

Abstract

1,052,821. Automatic control of magnetic fields. VARIAN ASSOCIATES. Jan. 20, 1964 [Jan. 21, 1963], No. 2465/64. Heading G3R. [Also in Division G1] Apparatus for regulating the strength of a magnetic field comprises a Hall-effect sensor 1 having current leads 2, 3 connected over a variable resistor 12 to A. C. input terminals 4, 5; a Halleffect voltage proportional to the field strength appears at leads 6, 7 and is applied over an isolation transformer 9 to an output coil 10 which is connected in series opposition to an output coil 16 the voltage across which is derived, by way of an isolation transformer 15, from the resistor 12. When the Hall-effect voltage across the coil 10 is equal to the reference voltage across the coil 16, no signal appears at output terminals 17, 18. When the Hall-effect voltage differs from the reference voltage, an error signal is produced across the output terminals; this error signal may be amplified and used to control a servo-mechanism which may adjust the current level of an electromagnet, for example, so that the field strength detected by the Hall sensor 1 is maintained at a desired magnitude determined by the setting of resistor 12. Variations in supply voltage of terminals 4, 5 or in load across terminals 17, 18 have no effect on the error signal since resulting deviations are produced with equal magnitudes in series opposition across the coils 10 and 16. The Halleffect sensor 1 is compensated for temperaturedependent changes by the provision of a resistor 20, of suitable value, connected across the terminals 6, 7. A time-varying voltage may be superimposed on the stabilizing difference voltage, for producing a pre-determined continuous modulation of the steady state D. C. magnetic field Fig. 2, (not shown). The circuit for the electromagnet producing the field may include transistors controlled by the amplified error signal Fig. 4, (not shown).