DE2929019C2 - Method and device for measuring temperatures in the temperature range of superconductors - Google Patents

Description

3. Device according to claim 2, characterized by the following features,

a) the ferromagnetic core (4) is cup-shaped as a ferrite core and is used to produce a Radial field suitable,

b) the core (4) is covered with an insulating film (9) designed as a thermal insulating layer,

c) on the insulating film (9) is a film-shaped variable magnetic resistance (3) arranged, which consists of a superconductor,

d) on the variable magnetic reluctance (3) is another film made of one Ferromagnetic as an anchor (6) arranged with the test object (8) and with the changeable magnetic resistance (3) is in thermal contact.

4. Device according to claim 2, characterized by the following features,

a) the ferromagnetic core (14) is designed so that its contacting the measurement object (8) Area is as small as possible,

b) the area of the core (14) in contact with the test object (8) has an air gap (16) on,

c) the ends of the legs of the core (14) delimiting the air gap (16) are through a magnetic shielding can be shielded from one another,

d) the magnetic shielding consists of a sudden change in temperature variable magnetic resistance (19),

e) the variable magnetic resistance (19) consists of a T-shaped superconductor, whose flat leg (20) rests on the measurement object (8) and its web (21) through the Air gap (16) is performed.

a) the coil (5, 18) generating the magnetic field has a ferromagnetic core (4, 14) with the relative permeability \ ι _κ ι ^ 1, which together with a variable magnetic resistance (3, 19) essentially forms the magnetic circuit the coil (5,18) forms,

b) the changeable magnetic widen, ind (3, 19) consists of a superconductor that conducts heat well at the point (7) of the temperature measurement Contact with a measurement object (8) is arranged,

c) a constant current generator (27) supplies the coil (5, 18) with a predetermined constant current / independent of the variable inductance L of the coil (5, 18),

The invention relates to a method according to the preamble of claim 1 and a device for Perform the procedure.

The increasing use of cryogenics and the constantly expanding technical use of Superconductors also requires a further development of suitable measurement methods that enable safe and reliable temperature measurements in the low temperature range, especially in the temperature range of Superconductors, i.e. in the range from 0 to 20 K, to be carried out.

It is known (VDIBildungswerk, BW 1944, page 7, right column), for temperature measurements of the mentioned Kind of using a carbon resistance thermometer

the one whose carbon resistor is in contact with the measuring point and from a constant current generator is fed with a current. The carbon resistance, which acts as a sensor, is caused by the current is heated up and thus falsifies the measured value small stream worked. However, this implies very small voltage changes, which is the one to be measured Map temperature inadequately, so that measuring amplifiers are necessary. The coal resistance must also be covered with an electrically insulating layer to short-circuit the resistor to be excluded when contacting the metallic measuring point. This insulating layer between the However, the surface of the object to be measured and the sensor delays the heat transfer «.

DEAS 10 75 862 discloses a measuring arrangement with a bolometer operating in the transition area between supra and normal conductivity, in which a thin superconductor wire absorbs the radiation to be measured and changes its electrical resistance as a result of the associated heating. The change in electrical resistance is a measure of the incident radiation energy. To improve the setting of the temperature and thus the working point of the bolometer to a predetermined point of the transition area, the bolometer is placed in a magnetic field, the field strength of which is regulated as a function of the output voltage of the bolometer so that the working point of the transition area is set by a coolant Bolometer temperature drops.

The invention is based on the object of a method and a device for measuring in To develop the temperature range of the superconductors at horizontal temperatures, which enables rapid To carry out temperature measurements, to keep the sensor free from influences which would falsify the measured values compared to known devices to generate several orders of magnitude larger measurement signal and at the same time significantly simplifying the measuring device and increasing its operational reliability.

This object is achieved in a method according to the preamble of claim 1 with the characteristics of the main claim specified features and with a proposed for performing the method Device with the features of the characterizing part of claim 2 solved.

The advantages of the invention are in particular that even with small temperature changes in the Measurement signal changes of the order of tenth of a degree Kelvin, i.e. voltage changes from the millivolt in the volt range can be achieved that compared to the carbon resistance with a significantly higher current, higher voltage and lower impedance is worked and therefore also the operational safety and the Measurement accuracy is significantly increased, and that good thermal contact with the measuring point is possible and however, contamination of the surface with adhesive is excluded.

The method and an embodiment of the device for performing the method with the Features of claims 1 to 4 is shown in the drawing and is described in more detail below. It shows

F i g. 1 Schematic HfT ^ diagram for lead and Niobium,

2 section of a temperature sensor for integral measurements,

Fig. 3 temperature sensor for point measurements,

F i g. 4 circuit diagram of the measuring device,

Fig. 5 Diagram of a temperature measurement with a carbon resistance sensor and with a superconductor sensor with rectifier diode.

F i g. 1 shows the basic course of the critical magnetic field strength H as a function of the absolute temperature T in degrees Kelvin for the superconductors lead and niobium. The critical field strength H drops parabolically as the temperature T rises. In the area delimited by the HfO curve and the coordinates, there is superconductivity, above the H (T) K curve there is normal conduction. The transition from the superconducting area 1 to the normal line area 2 of the superconductor takes place at a constant temperature Γ by increasing the Feistickness H or at a constant Feistickness H by increasing the temperature T.

This transition from one area to the other takes place abruptly, analogous to a switching process. Switching to normal line area 2 is not only possible with an increase in the electrical power Resistance by several powers of ten is accompanied by a very strong one Reduction of the magnetic resistance linked. This physical property of the superconductor is used in the proposed method to abruptly change the inductance of a coil Iron core.

In the case of a temperature sensor for integral measurements, as shown in FIG. 2 shown in section, this effect is shown used by a variable magnetic resistance 3, which is arranged in a magnetic circuit and from a superconductor, such as. B. lead 0.1 mm thick.

The magnetic circuit consists of a ferromagnetic core 4, which is designed as a ferrite core 11 mm high and 42 mm diameter pot-shaped and a coil 5 with approx. 800 turns made of 0.18 mm ■ Cu wire to generate a magnetic field of field strength H. The ferromagnetic core 4 with the relative permeability μ _{Γ [} · / > 1 forms the magnetic circuit of the coil 5 with a ferromagnetic armature 6 of 42 mm diameter and 0.3 mm thickness.

The center of the ferromagnetic armature 6 is at the location 7 of the temperature measurement DUT 8 arranged. Measurement object 8 and armature 6 are in good thermal contact. This is also true for the variable magnetic resistance 3, which is arranged between armature 6 and core 4, with regard to the heat transfer to or from the armature 6. An insulating film 9 of 0.6 mm thickness and 42 mm diameter is used as thermal insulation between the core 4 of the coil 5 on the one hand and the variable magnetic resistance 3 made of superconductor material and the ferromagnetic armature 6 arranged on the other hand. As a result, the temperature of the measurement object 8 is indeed increased during the measurement process transferred via the armature 6 to the variable reluctance 3, but this remains of the ferromagnetic core 4 of the coil 5 thermally insulated.

A disk 10 is located on the side of the ferromagnetic armature 6 facing away from the measurement object 8 arranged in a recess 11 a helical spring f 2 'for pressing the armature 6 against the test object

8 receives and two soldering lugs 13 to ¹ η connecting the coil 5 carries.

In order to carry out point-like temperature measurements, a method shown in FIG. The embodiment of the temperature sensor shown in FIG. 3 has proven to be advantageous, the ferromagnetic core 14 has approximately the shape of a triangle, one tip 15 of which contacts the measurement object 8 on a very small surface, so that the temperature is measured almost point-like. The core 14 has at> a tip 15 an air gap 16 oriented perpendicular to the surface of the measurement object 8. The leg 17 of the core 14 opposite the air gap 16 carries a coil 18 for generating a magnetic field of predetermined magnetic field strength H. In the air gap 16 of the core 14 there is arranged a magnetic resistance 19 that can be suddenly changed by changing the temperature. The magnetic resistance 19 consists of a superconductor whose cross-section is T-shaped and whose flat leg 20 is in good thermal contact with the measurement object 8 and whose web 21 is easy through the air gap 16 to close to the surface of the coil 18. In the superconducting area 1 of the changeable m; Magnetic resistance 19, the magnetic resistance is very high, in the normal line area 2, however, very small, so that the magnetic resistance of the magnetic circuit formed from the ferromagnetic core 14 and the variable magnetic resistance 19 in the superconducting area is very large. Lead is used as the superconductor jo, the thickness of the leg 20 and the web 21 is 0.1 mm each.

In this arrangement, because of the relatively large distance between the coil IS and the measuring element, and because of The small mass of the core 14 does not require a thermal insulating layer. Because of the shape of the Core 14 and the arrangement of the air gap 16, a ferromagnetic armature is also superfluous. Of the flat legs 20 and the web 21 of the T-shaped superconductor are dimensioned so that a high proportion the scatter lines of the magnetic field is interrupted.

The function of the temperature measuring device is illustrated by the circuit shown in FIG. The coil 5, «8 with the ferromagnetic core 4.14 and the variable magnetic resistance 3.19 has a predetermined inductance L , the size of which can be changed abruptly with the aid of the variable magnetic resistance 3.19

The coil 5, 18 is supplied with power via a transformer 22, its high-voltage winding 23 is fed from the network with 220 volts AC voltage and a frequency of 50 Hz and its Low-voltage winding 24 delivers 36 volts at 50 Hz. In the line 25 between the low voltage winding and coil 5, 18 is a substantially determining load current / transformer 22 adjustable resistor 26 of 5 kOhms and 2 watts switched

The transformer 22 and the resistor 26 form a constant current generator 27 with which load currents bo / in the range from 20 to 100 mA and thus predetermined magnetic field strengths H at the coil 5, 18 can be set.

Parallel to the coil 5, 18, a capacitor 28 is connected, which forms with this for the frequency of *>"> measurement current a parallel resonance circuit, the resonance frequency can either be on the inductance L of the coil 5 may be set 18, which for the normal conducting state of the variable magnetic resistance 3, 19 results, or on the inductance occurring in the superconducting state of the same.

With a constant current / the voltage drop across the coil 5, 18 changes when the switchover point P ^ is reached. This voltage is measured with a voltmeter 29 which is connected to the coil 5, 18 via a non-linear rectifier 30.

Fig. 5 shows the diagram of a temperature measurement with a temperature sensor for integral measurements, as shown in FIG. 2 shown and explained. as A two-beam oscilloscope was used for the voltmeter 29, the upper first beam 31 of which is the measured value as a rectified 50 Hz signal and its lower second beam 32 shows a comparison measurement with a carbon resistor as a sensor. The first Beam 31 is the horizontal deflection 0.1 sec / cm and the vertical deflection 2 volts / cm with a measuring current of / = 30 mA.

In the case of the second beam 32, the vertical deflection is 5 mV / cm with the same horizontal deflection. This results in a voltage in the carbon resistance for a temperature increase from 4.2 K to 4.6 K. of approx. 8 mV. In the case of the proposed temperature sensor, however, the temperature rise is the same a voltage of 6 volts.

The peak in the lower part of the diagram is the calibration signal 33 generated with the carbon resistor.

List of reference symbols

Superconductivity area

Normal line area

changeable magnetic resistance

ferromagnetic core

Kitchen sink

6 ferromagnetic armature

7 Location of temperature measurement

8 test object

9 insulating film

10 disc

11 recess in 10

12 coil spring

13 soldering lug

14 ferromagnetic core

15 tip of 14

16 air gap in 14

17 legs of 14

18 spool on 17

19 variable magnetic resistance

shallow tavern! from 19

Bridge from 19

transformer

High voltage winding from 22

Low voltage winding of 22

Lead from 24 to 5.18

adjustable resistance

Constant current generator

capacitor

Tension meter

Rectifier

first ray of 29

second ray of 29th

Calibration signal

H magnetic field strength

T temperature in degrees Kelvin

L inductance J current of 27 H _c critical field strength T _c critical temperature Pc switchover point 1 - 2

For this purpose 2 sheets of drawings

Claims (2)

Patent claims: 1.Method of measuring temperatures in the temperature range of superconductors, at which the temperature-dependently changeable magnetic resistance of a superconductor, which is below a critical point P _c (switching point) _{determined in its coordinates by the critical temperature T c} - and the critical magnetic field strength H _c , i.e. in the superconductivity area (1), is very large and above the switching point P _a , i.e. in the normal line area (2), is very small, due to the instantaneous temperature at the location (7) of the temperature measurement from the superconductive area (1) to the normal line area ( 2) or vice versa and thereby changed abruptly and by setting a predetermined magnetic field strength H via the current to be absorbed by the field-exciting coil / the position of the switching point Pc on the H (T) curve of the superconductor used as a variable magnetic resistance (3, 19) and thus the size of the critical temperature T _{c is} determined by w ird, characterized in that a variable magnetic resistance (3, 19) which can be switched by changing the temperature T and / or the magnetic field strength H controls the magnetic resistance of the magnetic circuit of a coil (15, 18) and thus the inductance L of the coil (5, 18) changes abruptly as a function of the measuring temperature at the switching point P _c , and that an LC oscillating circuit (5, 18, 28) whose resonance frequency is used to increase the measuring signal generated by the abrupt change in the inductance L of the coil (5, 18) the superconducting or normal conducting state of the variable magnetic resistance (3.19) is set, and that when the H (T) curve forming the boundary between the superconducting area (1) and normal line area (2) is reached or exceeded, the LC oscillating circuit (5, 18, 28) is suddenly transferred from one of the two possible operating states (1, 2) to the other operating state (2, 1). 2. Device for performing the method according to claim 1 with a coil for generating a magnetic field of a predetermined field strength H, a generator for generating a predetermined current / in the field-exciting coil and a device for measuring the voltage on a measuring coil arranged in the magnetic field, characterized by the following features, d) a voltmeter (29) registers the voltage dropping across the coil (5, 18) during the sudden change in inductance L , which is a measure of the temperature of the measuring object (8) at the location (7) of the temperature measurement.