| 摘要 |
PURPOSE:To reduce the running cost by a method wherein a compensation signal generator means is provided to compensate for a drift in the magnetic field and a reference signal of a constant current amplifier is formed by adding up an existing reference signal and a compensation signal to obtain a stable magnetic field in a short time. CONSTITUTION:When the change in the output current I0 of a power amplifier 42 is represented by DELTAI0, a compensation signal Ec enough to cause the change DELTAI0 is added to a reference signal Erst to obtain another reference signal Erst as given by the formula with the compensation signal Ec added thereto. The compensation signal Ec is generated from a compensation signal generator 44, which is made up of a differentiation circuit. The amplitude and the generation timing of the generator 44 are determined by a signal from a delay timer 45 for outputting a unit step signal. The output current I0' following the compensation is as illustrated. As a result, a stable magnetic field can be obtained in a short time to reduce the running cost. |
