| 摘要 |
PURPOSE:To obtain a stable magnetic field for a long time by providing a reference signal altering circuit for altering the reference signal of a reference signal source on the basis of the detection signal of a sensor. CONSTITUTION:A sensor 10 produces a control signal I/D for controlling to increase or decrease the value of a reference signal to a microprocessor 11 when the fact that the intensity B of a magnetic field generated from a normal conducting magnet 4 arrives at the value of a predetermined range with respect to a target value B0 is detected. Since the microprocessor 11 varies the reference signal according to the signal I/D, the value of a current I flowing to the magnet 4 is varied to alter the intensity B of the magnetic field. Thus, when the intensity B of the magnetic field generated from the magnet 4 is varied so that a deviation from the value B0 becomes sufficiently small, the sensor 10 produces a lock signal LKD to the microprocessor 11. Then, the microprocessor 11 alters and stores the value of the reference signal at that time according to the signal LKD in a memory 12.
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