JPS588730B2 - Method of obtaining fixed point in low temperature region and fixed point cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for easily obtaining a temperature fixed point necessary for calibrating a thermometer used in a low temperature region, and a fixed point cell used in the method.

Generally, a thermometer that measures the temperature in a low-temperature region is configured to determine an electrical resistance value through a detection element such as germanium or platinum, and then determine the temperature based on a predetermined reference resistance value.

In this case, it is desired that there be no error in the electrical resistance value detected by the detection element, but in reality there is variation due to non-uniformity of the germanium or platinum component.

Therefore, in order to obtain accurate temperature measurements, it is necessary to calibrate each thermometer used to determine the accurate resistance value. Conventionally, this work is extremely complicated and requires a high level of skill. Ta.

To calibrate a low-temperature thermometer, this is generally done using several fixed temperature points within the operating temperature range, and the boiling point, freezing point, triple point, etc. of a pure substance whose physical properties are well known are used as these fixed points. , this is because it is difficult to obtain these fixed points.

For example, the conventional method for obtaining these fixed points is to first store pure gas such as hydrogen, nitrogen, oxygen, or argon that has been purified through a gas purification device in a gas reservoir at approximately atmospheric pressure, and then to store it in a sealed cryostat. It is common to realize a fixed point by introducing it into a fixed point cell, but it requires precise pressure and pressure measurement work.

In addition, a pressure-resistant fixed point cell is required to measure the triple point.
Moreover, these fixed point devices are stationary in structure, so if the thermometer to be calibrated is used at a different location, it must be transported, and in some cases, the indicator must also be transported at the same time, resulting in inconveniences. .

Furthermore, when calibrating a large number of thermometers, the above-mentioned complicated operations, including purification of Ganu, are required each time, which requires a lot of manpower and time, and it is difficult to obtain sufficient accuracy. Ta.

The present invention solves such conventional drawbacks, and the high-purity Ganu is sealed, and a metal fixed-point cell with a pressure-resistant structure is cooled and then heated appropriately, so that the three of the sealed Ganu are sealed. The present invention relates to a method for obtaining a temperature fixed point, characterized in that the key temperature is realized on the outer surface of the fixed point cell, and a portable fixed point cell that can be used in the method, and will be described in detail below.

FIG. 1 is a partially cutaway sectional view showing an embodiment of a fixed point cell according to the present invention, in which 1 is an outer cylinder, and 2 is an inner cylinder, which is made of a material with excellent thermal conductivity, such as copper, nutenrene, etc. be done.

Next, numeral 3 is a gas reservoir, and 4 is a fixed point part where the enclosed GANU is liquefied and further solidified.

A short pipe 5 for sealing is inserted into the canine reservoir part 3 through the upper wall of the inner cylinder 2.
The short tube 5 is connected to the cannula supply tube, and the sample gas is filled under pressure into the gas reservoir section 3 and the fixed point section 4.

Reference numeral 6 denotes a hollow portion into which the thermometer to be calibrated is inserted, and the hollow portion 6 may be the entire middle portion or only the portion into which the thermometer to be calibrated is inserted, which is arbitrary.

To manufacture this fixed point cell, the steps shown in FIG. 2 are carried out.

That is, the short pipe 5 penetrating through the earthen wall of the T-shaped inner pipe 2 is fixed by means such as argon welding.

Next, the inner surface of the outer tube 1 and the outer surface of the inner tube 2 are washed and dried to clean the inner wall surface of the apparatus, but this treatment is especially carried out sufficiently on the outer surface of the inner tube 2.

After performing such preliminary treatment, the inner cylinder 2 is inserted into the outer cylinder 1, and the inner and outer cylinders 1 and 2 are fixed by argon welding at the bottom end of the soil, respectively, to form a T-shaped hollow double cylinder. Configure.

At this time, it is preferable to perform sufficient shielding with argon gas during welding so that the internal surface is not oxidized.

Next, the outside is washed and then dried. After thoroughly evacuating the inside of the canine reservoir and fixed point part of the fixed point cell thus obtained through the short tube 5, a desired sample canine whose physical properties are well known is introduced.

After a few minutes, the introduced sample tube was purged, evacuated, and the sample tube was introduced again.

By repeating this operation two or three times, the inside of the apparatus is sufficiently replaced with the sample gas, and then the sample gas is filled to a predetermined pressure and the short tube 5 is sealed off.

In this case, sealing off under high pressure will cause the filled gas to leak easily and it will be difficult to completely fill the gas, so the internal pressure will be lowered and the sealing process will be carried out.

That is, the fixed point part 4 is immersed in a low-temperature liquefied gas such as liquid argon or liquid nitrogen, and after confirming that the introduced sample gas has liquefied or solidified and the internal pressure has decreased, a part of the short tube 5 is pressed. Crush it.

At this time, in order to seal the ganu more completely, insert two short tubes.
It is desirable to crush it into steps, cut the crushed portion at the tip, and then weld the cut portion with argon.

After the thermometer to be calibrated is inserted into the hollow part of the fixed point section 4 in the sealed fixed point cell of the sample tube, it is cooled with the fixed point section facing downward.

This cooling is performed using a shielded cryonutat or the like containing liquefied gas having a boiling point lower than the solidification temperature of the sealed sample gas, which liquefies the sample gas and then solidifies it.

In this way, the periphery of the thermometer to be calibrated, which has been brought into thermal contact within the fixed point part, is substantially surrounded by the fixed point part containing the solid material.

Next, while gradually melting the solid using a heater or the like, the temperature of the thermometer to be calibrated is measured, a melting curve is drawn, and the triple point temperature is calibrated.

As an example of implementation, a case will be described in which pure argon is sealed as a sample in a fixed point apparatus as shown in FIG.

The specifications of the fixed point part are outer diameter 1611φ x inner diameter 13Uφ x depth 2
511, the volume of liquid to be collected (later solidified) is 0.88nl, and the specifications of the gas reservoir are 34mmφ.
If the diameter is 13 mm x 18 mm, the volume will be 14 ml.

Therefore, argon gas is sealed at a pressure of 48 kg/cm3G at room temperature (300K).

In this way, a fixed-point cell filled with argon gas as a sample was cooled in a shielded cryostat using liquid nitrogen as a cryogen to liquefy and solidify the argon gas, and then gradually heated to obtain a melting curve. The following measurement results for the triple point were obtained.

Triple point: 83.7952K Accuracy: 0.0001K The generally known triple point of argon is:
83.7948K (measured by Nagisa Flubacher et al.), 8
There are 3.7974K (Sideshore Kcmp et al.).

As mentioned above, in order to obtain the fixed point necessary for calibrating a low-temperature thermometer, a stationary fixed point device was conventionally used, which required complicated operations such as Ganu purification each time it was used. .

In contrast, according to the present invention, a desired high-purity GANU can be easily obtained by adjusting the external temperature of a fixed-point cell in which a desired high-purity GANU is sealed in advance under pressure.

Moreover, since it is only necessary to cool the L-shaped and portable fixed point cell alone, if appropriate cooling means are available, it is possible to realize a fixed point at a necessary location and calibrate the thermometer.

Therefore, for example, when calibrating a thermometer element attached to a low-temperature plant, it was conventionally necessary to remove it (and in some cases, the measuring instrument) and transport it to a location where a calibration device including a fixed point device is located. It can also be carried out on the machine side of the plant.

Further, according to the conventional method, it was difficult to calibrate a large number of thermometers at the same time, but with the present invention, it is easier to calibrate a desired number of fixed point cells, and the fixed point cells can be used repeatedly. It has characteristics.

In this case, it was confirmed that if the inner wall of the fixed-point cell was sufficiently cleaned, accuracy of ±0.001K could be maintained for an extremely long period of time.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway sectional view of a fixed point cell according to the present invention, and FIG.
The figure is a sectional view showing the manufacturing process of a fixed point cell. 1... Outer cylinder, 2... Inner cylinder, 3...
...Ganu reservoir part, 4...Fixed point part, 5...
Short pipe, 6...Hollow part.

Claims (1)

[Claims] 1. A method for obtaining a fixed point in a low-temperature region by cooling and heating a sample when calibrating a low-temperature thermometer, which includes an insertion part for a thermometer to be calibrated. and a fixed point in a low temperature region, characterized in that a desired fixed point is realized around the insertion part of the thermometer by adjusting the external temperature of a fixed point cell in which the sample is sealed in advance under pressure. How to get it. 2. A pressurized container made of a material with excellent thermal conductivity and having a hollow double cylindrical shape has an upper part between the inner and outer cylinders as a waste reservoir and a lower part as a fixed point part, and a gas reservoir for introducing sample waste into the gas reservoir. A fixed point cell for calibrating a low-temperature thermometer, characterized in that a short tube is provided, and after a desired sample gas is pressurized and filled, the short tube is sealed and sealed. 3. A patent claim characterized in that the volume of the Ganu reservoir section in the fixed point cell is configured to be larger than that of the fixed point section, and the pressurized sealed examination gas is liquefied and solidified in the fixed point section by cooling. A fixed point cell for calibrating a low-temperature thermometer according to item 2. 4. Claim 2, characterized in that the hollow part of the fixed point cell serves as an insertion part for a thermometer to be calibrated.
Fixed point selection 0 for low temperature thermometer calibration described in section 3