| 摘要 |
PURPOSE:To make possible the measurement of the level of liquid helium with good accuracy by increasing (or decreasing) continuously and monotonously current from a specified value and determining resistance from the gradient of a straight line when the voltage change in this stage constitutes the straight line running zero. CONSTITUTION:A CPU12 increased (decreases) the output current of an electric power source 6 by power source control 7 via a digital I/O8 at a specified ratio. The current flows through a lead wire to a superconductor 2 when the conduction of electricity is started upon opening of switch 5. The voltage impressed to both terminals of control ler 7 increases nonlinearly and gradually when such current is passed at the specified sped. On the other hand, the voltage impressed to both terminals of the conductor 2 corresponding to the level of the liquid helium 1 is inputted from a lead wire 4 and is read through a differential amplifier 9 and an A/D converter 10 into a RAM11 by the measurement timing emitted by the CPU12. Whether the straight line passing the zero or not is then judged until the next sampling is executed when the specified number of the set of such current value and voltage value accumulates. The gradient is outputted as the resistance value to a display device 19 when the above-mentioned conditions are satisfied.
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