JPH0835875A - Level detection circuit in liquid helium container - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a level detection circuit in a liquid helium container that can always perform ideal energization regardless of the container type, etc. [Configuration] Liquid helium housed in a heat insulating container 1 The superconducting wire 3 whose lower end is grounded is vertically inserted into the. A heating resistor 4 is connected to the upper end of the superconducting wire 3, and a current is supplied from a power supply -VDD to a series circuit of the superconducting wire 3 and the resistor 4 via a switching transistor 5. The control circuit 8 monitors the detection signal -Ex from the detection circuit 6 sent through the A / D converter 9 and generates an end signal when the detection signal which has started to fluctuate from the start of measurement is stable and generates a transistor. 5 to stop the supply of current to the resistor 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid helium level detecting circuit in a liquid helium container.

[0002]

2. Description of the Related Art FIG. 1 shows an example of a detection circuit for detecting the remaining amount of liquid helium in a container used for a superconducting magnet or the like. In the figure, a superconducting wire 3 whose lower end is grounded is vertically inserted into liquid helium 2 housed in a heat insulating container 1. A heating resistor 4 is connected to the upper end of the superconducting wire 3, and a current is supplied to the series circuit of the superconducting wire 3 and the resistor 4 from a power source -VDD via a switching circuit 5. Reference numeral 6 is a detection circuit for detecting the potential of the connection portion A between the resistor 4 and the superconducting wire 3, and 7 is a pulse generation circuit for generating a pulse for turning on / off the switching circuit 5.

In the above structure, the superconducting wire 3 is immersed in liquid helium as well as the non-immersed part of the superconducting wire 3 by heat conduction from the part immersed in liquid helium to 4K.
Below, it is in a superconducting state.

In order to detect the level of liquid helium, a pulse is generated from the pulse generator 7 to turn on the switching circuit 5, and a current is passed through the resistor 4 and the superconducting wire 3. The superconducting wire 3 is warmed from the upper end portion by the heat generated from the resistor 4 by the electric current, and the portion not immersed in the liquid helium becomes a resistor. Since the electric potential Ex of the connection portion A changes due to the resistance change of the superconducting wire 3 according to the helium level, this electric potential is acquired as a signal representing the level of liquid helium. Such liquid level measurement is repeatedly performed at a desired cycle.

[0005]

In order to accurately detect the liquid helium level, current is passed through the resistor 4 so that all of the portion of the superconducting wire 3 extending from the liquid helium is in the normal conducting state. It is necessary to set the time and the value of the energizing current appropriately. If the energization time is too short, not all of the portion of the superconducting wire 3 that comes out of the liquid helium will be in the normal conduction state, and if it is too long, the liquid helium will be evaporated unnecessarily.

The energization time is conventionally determined by experiments, but it is always dependent on the type of the container due to the size of the container, variations in the characteristics of the superconducting wire 3 and the resistor 4, and differences in the hardware constituting the circuit. It was difficult to perform ideal energization.

The present invention has been made in view of the above points, and an object thereof is to provide a level detection circuit in a liquid helium container capable of always performing ideal energization regardless of the type of container. There is.

[0008]

To achieve this object, a level detection circuit in a liquid helium container according to the present invention is arranged in the liquid helium container such that the immersion length changes depending on the liquid helium level. A level detection circuit in a liquid helium container comprising a superconducting wire, a heating means for heating the superconducting wire from the upper end side, and a detecting means for detecting an electrical change caused by a resistance change of the superconducting wire. An end signal generating means for generating an end signal by detecting that the temporal change in the detection output of the electrical change detecting means after the heating by the heating means is started is below a reference value, The heating by the heating means is stopped based on the end signal.

[0009]

In the present invention, the end signal is generated by detecting that the temporal change of the detection output of the electrical change detecting means becomes equal to or less than the reference value after the heating by the heating means is started. Means is provided, and heating by the heating means is stopped based on the end signal.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 2 is a block diagram showing an embodiment of the present invention, in which the same components as those of the conventional example of FIG. In FIG. 2, reference numeral 8 is a control circuit, which sends a start signal instructing the start of measurement at a predetermined cycle to the pulse generation circuit 7, and further based on a detection signal sent via the AD converter 9. An end signal instructing the end of measurement is sent to the pulse generation circuit 7.

FIG. 3 is a waveform diagram for explaining the operation of the above configuration. Reference symbol a indicates a measurement start signal generated from the control circuit 8 at a predetermined cycle. Reference character b denotes a current supplied to the resistor 4 and the superconducting wire 3 via the switching circuit 5, and power supply is started based on the start signal. The superconducting wire 3, which has begun to be heated by the heat from the resistor 4 that has started to generate heat, gradually starts to enter the normal conducting state from the upper end portion. Therefore, the detection signal -Ex obtained from the detection circuit 6 gradually rises as shown in FIG. 3c, and eventually becomes stable at a constant value when all the portions not immersed in the liquid helium are in the normal conduction state.

The control circuit 8 monitors this detection signal -Ex sent via the A / D converter 9, and when the detection signal which has started to fluctuate from the start of the measurement becomes stable, the end signal (Fig. 3d). ) Is generated, the detection signal value at that time is held, and the liquid helium level is determined based on the held signal value. Based on the termination signal, the pulse generation circuit 7 stops the current supply to the resistor 4 as shown in FIG.
The measurement is completed. Then, such measurement is repeatedly performed at a predetermined cycle.

FIG. 4 is a flow chart showing a control flow in the control circuit 8. In FIG. 4, step 1
Then, the timer is started, and a measurement start signal is generated in step 2. In step 3, the initial value of the detection signal is read as Ex1. Until the timer runs out in step 4, the detection signal value is read as Ex2 at every predetermined period T determined in step 5 (step 6), and the difference from the previous measured value Ex1 (Ex2-Ex1) is the reference value X. It is determined whether or not (Ex2-Ex1≤X) (step 7). Steps 4 to 7 are repeated until this condition is satisfied, and when the condition is satisfied, the final detection signal value is read (step 8) and a measurement end signal is generated (step 9).

If the condition of step 7 is not satisfied even if the timer runs out of time, it is determined to be abnormal, a measurement end signal is immediately generated, and the current supply is stopped.

As described above, according to the present invention, the detection signal is constantly monitored, and when the detection signal becomes constant, the heating is stopped and the measurement is terminated. Without, the liquid helium level can be detected with the minimum evaporation amount of liquid helium.

The cycle of level measurement performed by the control circuit can be selected in two steps, long and short, and if the measurement interval is shortened when liquid helium is filled, it can be accurately determined whether liquid helium is normally filled. Can be monitored. At other times, the level change of liquid helium is slow, so that the consumption of liquid helium due to measurement can be minimized by increasing the measurement interval.

In order to prevent forgetting to return to the long measurement interval even after the filling is completed by selecting a short measurement interval at the time of filling,
If a short measurement interval is selected, a timer is operated, and after a lapse of a predetermined time, the measurement interval is forcibly returned to a long measurement interval, thereby preventing wasteful consumption of liquid helium due to forgetting to return.

The present invention is not limited to the above-mentioned embodiment and can be modified. For example, in the above-described embodiment, the heating resistor 4 and the superconducting wire 3 are connected in series to supply the current from one power source. However, the resistance of the power source and the superconducting wire that supplies the heating current to the heater that heats the superconducting wire from the upper end portion. It can also be applied to a level detection circuit in which a power supply for supplying a current to measure a change is separately provided.

[0019]

As described above in detail, according to the present invention, it is detected that the temporal change in the detection output of the electrical change detecting means becomes less than the reference value after the heating by the heating means is started, and the end signal is detected. The end signal generating means for generating is provided, and since the heating by the heating means is stopped based on the end signal, heating of the superconducting wire is insufficient, or
Appropriate heating can always be performed in any container without overheating.

[Brief description of drawings]

FIG. 1 is a diagram showing a conventional example of a detection circuit for detecting the remaining amount of liquid helium in a container used for a superconducting magnet or the like.

FIG. 2 is a diagram showing one embodiment of the present invention.

FIG. 3 is a waveform diagram for explaining the operation of the embodiment of FIG.

FIG. 4 is a flowchart showing a control flow in a control circuit.

[Explanation of symbols]

 1 Insulation container 2 Liquid helium 3 Superconducting wire 4 Heating resistor 5 Switching transistor 6 Detection circuit 8 Control circuit 9 A-D converter

Claims (1)

[Claims] 1. A superconducting wire arranged in a liquid helium container such that the immersion length changes depending on the liquid helium level, a heating means for heating the superconducting wire from the upper end side, and a superconducting wire of the superconducting wire. A level detection circuit in a liquid helium container having a detection means for detecting an electrical change caused by a resistance change, wherein the detection output of the electrical change detection means with respect to time after the heating by the heating means is started. A level detection circuit, comprising: an end signal generating means for detecting that the change is equal to or less than a reference value and generating an end signal, and stopping heating by the heating means based on the end signal.