JP3597954B2 - Sample temperature control method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a sample temperature control method for raising or lowering the temperature of a sample according to a predetermined temperature program, such as a sample of a thermal analyzer, and more particularly to a sample for cooling a sample with a low-temperature gas obtained by evaporating a refrigerant. It relates to a temperature control method.
[0002]
[Prior art]
As a method of cooling the sample to a temperature lower than room temperature, there is a method of cooling the sample with a low-temperature gas in which liquid nitrogen is vaporized. In this case, it is possible to adjust the amount of vaporization by heating the heater provided in the liquid nitrogen container to adjust the flow rate of the low-temperature gas, and thereby adjust the sample cooling capacity. FIG. 8 shows such a “temperature change curve in the sample cooling method” (hereinafter, referred to as a cooling curve). For example, when cooling the sample from 50 ° C., supplying a large power W3 to the liquid nitrogen heater rapidly lowers the sample temperature, and supplying a smaller power W2 lowers the sample temperature slowly. The sample temperature becomes more moderate.
[0003]
In the case of cooling a sample in a thermal analyzer, it is normal to cool the sample at a constant temperature decreasing rate as shown in a temperature program curve 10, but in the case of cooling with a low-temperature gas from liquid nitrogen, such precise control is performed. Is impossible. Therefore, feedback control by the sample heater is used in addition to cooling by the low-temperature gas.
[0004]
By the way, when the sample temperature is controlled along the temperature program curve 10 by using the low-temperature gas and the sample heater together, the power supply to the liquid nitrogen heater is increased to some extent to ensure sufficient sample cooling capacity. Must. This will be described below. In FIG. 8, when cooling the sample from 50 ° C. to −100 ° C., if the power of the liquid nitrogen heater is set to W1, the cooling capacity becomes insufficient. When the power is set to W2, initially, the slope of the cooling curve based on the power W2 is larger than the slope of the temperature program curve 10, and has a sufficient cooling capacity. However, as the temperature decreases, the slope of the cooling curve due to the power W2 decreases, and when the sample temperature decreases to around Tc, the slope of the cooling curve due to the power W2 becomes equal to the slope of the temperature program curve 10. When the sample temperature is lower than Tc, the cooling capacity becomes insufficient. If the power is set to W3, the slope of the cooling curve due to the power W3 becomes larger than the slope of the temperature program curve 10 up to −100 ° C., so that a sufficient sample cooling capacity is provided. In this case, the temperature control along the temperature program curve 10 can be performed by using the sample heater in combination.
[0005]
Therefore, the electric power supplied to the liquid nitrogen heater needs to be sufficiently large. However, if this power is too large, the power supplied to the sample heater must be increased in order to perform feedback control along the temperature program curve 10, and the power supplied to the liquid nitrogen heater and the sample heater must be increased. Are both large, and power is wasted. Furthermore, the consumption of liquid nitrogen is wasted.
[0006]
Therefore, as a method for setting the electric power of the liquid nitrogen heater to an appropriate value, there is known a temperature control method disclosed in Japanese Patent Application Laid-Open No. Hei 2-105046 (hereinafter referred to as a prior art document). In this prior art document, in a method of cooling a sample by using a low-temperature gas in which liquid nitrogen is vaporized and a sample heater in combination, a preliminary experiment is used to determine the power to be supplied to the liquid nitrogen heater. That is, a constant power is supplied to the liquid nitrogen heater to measure the temperature attained by the sample after a predetermined time, and the relationship between the power and the temperature attained by the sample is experimentally obtained in advance for a plurality of powers. If such a preliminary experiment is performed, when a target temperature lower than room temperature is set as a temperature program signal, the supply power corresponding to the target temperature can be obtained from the result of the preliminary experiment. What is necessary is just to supply to a heater. Then, after a predetermined time, the sample temperature falls to the target temperature.
[0007]
[Problems to be solved by the invention]
In the sample temperature control method of the above-mentioned prior art document, when a target temperature lower than room temperature is determined, only one supply power of the liquid nitrogen heater corresponding thereto is determined, and the liquid nitrogen heater is heated by this supply power. Cold gas is being introduced into the sample chamber. However, this method has the following disadvantages.
[0008]
FIG. 9 illustrates an example of a sample temperature control method disclosed in the related art document. In a preliminary experiment, when the supply power of the liquid nitrogen heater is set to 100 W and the sample is cooled from room temperature (for example, 20 ° C.), the sample temperature becomes −90 ° C. after 30 minutes. The cooling curve 12 at that time is as shown in the figure. Then, a similar experiment is performed by changing the value of the electric power, and the relationship between the electric power and the attained sample temperature is obtained. In this preliminary experiment, the sample heater was not used. Next, in the actual thermal analysis measurement, when a constant value (eg, -90 ° C.) lower than room temperature is set as the temperature program signal Tp, the electric power (100 W) corresponding to the target value (−90 ° C.) is supplied to the liquid nitrogen heater. , It is cooled to the target sample temperature after 30 minutes.
[0009]
However, in a temperature program generally used in thermal analysis measurement, the sample temperature is raised or lowered at a constant speed. For example, in order to cool from room temperature (20 ° C.) to −90 ° C. in 30 minutes, it is usual to cool down along a temperature program curve 14 with a constant cooling rate such that the temperature decreases by about 3.7 ° C. per minute. It is. In order to cool the sample along the temperature program curve 14 at a constant rate of cooling, the sample is cooled with a low-temperature gas, and the sample is heated by a sample heater so that the sample temperature matches the temperature program curve 14. It is necessary to feedback-control the power of the sample heater. However, if 100 W of electric power is supplied to the liquid nitrogen heater according to the related art document, the cooling capacity falls short during cooling. For example, when the sample temperature is −70 ° C., the absolute value of the slope at the point A on the cooling curve 12 (that is, the cooling rate) when 100 W is supplied to the liquid nitrogen heater is the cooling rate of the temperature program curve 14. It becomes smaller than the absolute value of the speed. Therefore, even if the sample is cooled from the position of point B on the temperature program curve 14 while the liquid nitrogen heater power is kept at 100 W, the cooling curve 16 therefrom departs from the temperature program curve 14 and the cooling capacity is insufficient. It becomes.
[0010]
After all, in the method as disclosed in the prior art document, that is, in the method of determining one power based on the relationship between the power of the liquid nitrogen heater and the reached sample temperature after a predetermined time, the constant-speed cooling program It turns out that it is impossible to control the sample temperature along.
[0011]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method of controlling a sample temperature by cooling a sample with a low-temperature gas obtained by evaporating a liquefied refrigerant. An object of the present invention is to provide a sample temperature control method that optimizes electric power and minimizes electric power consumption and refrigerant consumption.
[0012]
[Means for Solving the Problems]
The inventors have found that the cooling rate when cooling the sample with the low-temperature gas that has vaporized the liquefied refrigerant not only depends on the power of the refrigerant heater, but also on the sample temperature at that time, It has been found that during cooling of the sample, the power of the refrigerant heater is optimized by changing the power of the refrigerant heater according to the sample temperature at that time. According to the present invention, the correspondence between the power of the refrigerant heater, the sample temperature, and the temperature change rate is determined in advance in a preliminary stage, and based on this, the optimal power of the refrigerant heater is determined every moment. Seeking. Moreover, in determining the electric power of the refrigerant heater, the electric power of the refrigerant heater is determined based on the above-mentioned correspondence based only on the data of the actually measured sample temperature and the actually measured temperature change rate without using information of the temperature program. It can be requested every moment. That is, the present invention provides a sample temperature control method in which a liquefied refrigerant is heated and vaporized by a refrigerant heater to generate a low-temperature gas, the sample is cooled by the low-temperature gas, and the sample temperature is feedback-controlled using the sample heater. After the following preliminary steps (a) to (c), the control steps (d) and (e) are performed. (A) A curve showing the relationship between the elapsed time and the sample temperature at that time by supplying a constant power to the refrigerant heater and cooling the sample with the low-temperature gas without heating the sample with the sample heater. (Hereinafter, referred to as a constant power cooling curve). (B) changing the value of the constant power to obtain a plurality of the constant power cooling curves; (C) determining a correspondence relationship between the power, the sample temperature, and the temperature change rate at the temperature in the plurality of constant power cooling curves. (D) Based on the actually measured sample temperature and the actually measured temperature change rate, a required refrigerant heater power is obtained from time to time based on the above-described correspondence, and the required power is supplied to the refrigerant heater. (E) feeding the electric power to the sample heater so that the sample temperature follows a predetermined temperature program while the required electric power is supplied to the refrigerant heater, and performing feedback control of the sample temperature.
[0013]
According to the present invention, during the feedback control of the sample temperature so as to follow the temperature program, optimal power is supplied to the refrigerant heater in accordance with the actually measured values of the sample temperature and the temperature change rate at that time. The electric power of the heater becomes necessary and sufficient. As a result, the electric power supplied to the refrigerant heater and the sample heater can be minimized. Also, the consumption of the liquefied refrigerant is minimized.
[0014]
By the way, in the actual temperature control, if the ideal power determined from the correspondence between the power in the constant power cooling curve, the sample temperature, and the temperature change rate is supplied to the refrigerant heater as it is, the feedback control by the sample heater may not function. There is. In other words, at ideal power, the sample temperature changes exactly along the temperature program curve without using the sample heater, so when the actual sample temperature becomes slightly higher than the temperature program curve, Feedback control by the sample heater becomes ineffective. Therefore, if a certain percentage (for example, about 5 to 20%) or a certain value (for example, 20 W) of electric power larger than the ideal electric power is supplied to the refrigerant heater, the temperature decrease rate by the low-temperature gas becomes the temperature decrease rate of the temperature program curve. , And the feedback control functions effectively in a state in which a small amount of power is always supplied to the sample heater.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a configuration diagram of an example of a thermal analyzer to which the sample temperature control method of the present invention is applied. This thermal analyzer is an example of a differential scanning calorimeter, in which a cylindrical furnace body 22 is disposed inside a cylindrical sample chamber 20. The internal space of the sample chamber 20 is partitioned by a cylindrical partition wall 24, and a low-temperature gas is introduced into an annular space 26 between the partition wall 24 and the inner wall surface of the sample chamber 20. The outer peripheral surface of the furnace body 22 is in close contact with the inner wall surface at the center in the height direction of the partition wall 24. A sample container and a reference container are mounted on a heat equalizing plate fixed to the inner wall of the furnace body 22. A sample heater 28 is embedded in the furnace body 22. The sample temperature is measured by the thermocouple 30. The output side of the thermocouple 30 is connected to a sample temperature controller 32 and a liquid nitrogen heating power supply 39. A heating command signal is output from the sample temperature control device 32 to the sample heating power supply 29, and based on this, power is supplied from the sample heating power supply 29 to the sample heating heater 28.
[0016]
On the other hand, the liquid nitrogen container 34 contains liquid nitrogen 36. A liquid nitrogen heater 38 is disposed inside the liquid nitrogen container 34. When electric power is supplied from the liquid nitrogen heating power supply 39 to the liquid nitrogen heating heater 38, the heater 38 is heated, the vaporization of the liquid nitrogen 36 is promoted, and the amount of low-temperature gas generated increases. A low-temperature gas pipe 40 is connected above the liquid nitrogen container 34, and the low-temperature gas pipe 40 is connected to the annular space 26 of the sample chamber 20. The low-temperature gas that has entered the annular space 26 of the sample chamber 20 from the low-temperature gas pipe 40 fills the annular space 26, cools the partition wall 24 and the furnace body 22, and exits through the outlet 42.
[0017]
The function of the sample temperature control device 32 will be described. The sample temperature control device 32 has a function of setting a desired temperature program, and measures a sample temperature based on the output of the thermocouple 30 to convert the sample temperature into a temperature program. A function of outputting a heating command to the sample heating power supply 29 so as to follow. Known PID control is used as feedback control for following the temperature program.
[0018]
Next, the function of the liquid nitrogen heating power supply 39 will be described. The liquid nitrogen heating power supply 39 has a function of storing the correspondence between the power of the liquid nitrogen heating heater 38, the sample temperature, and the temperature change speed, The function of measuring the sample temperature and the rate of temperature change (the sample temperature may be time-differentiated) based on the output of the thermocouple 30 and the above-described correspondence relationship based on the actually measured sample temperature and the temperature change rate. A function for determining the optimum electric power of the liquid nitrogen heater based on the above.
[0019]
In the embodiment shown in FIG. 1, the output of one thermocouple 30 is connected to the sample temperature control device 32 and the liquid nitrogen heating power supply 39, but the first thermocouple for the sample temperature control device 32 and the liquid A second thermocouple for the nitrogen heating power supply 39 may be arranged inside the sample chamber 20 separately.
[0020]
FIG. 2 is a graph schematically showing a sample cooling curve (hereinafter, referred to as a constant power cooling curve) when a constant power is supplied to the liquid nitrogen heater. The horizontal axis is time, and the vertical axis is the sample temperature. No sample heater is used to measure this constant power cooling curve. In this graph, three types of power W1, W2, and W3 are supplied to the liquid nitrogen heater. The magnitude relationship of the powers is W1 <W2 <W3. When the initial temperature of the sample is set to a temperature TH higher than room temperature, when a large electric power W3 is supplied to the liquid nitrogen heater from this state and the sample is cooled, the sample temperature decreases as shown by a solid line and the saturation temperature TS Gradually approaching. If the slope of the constant power cooling curve is measured at each sample temperature, it is the rate of temperature decrease at that sample temperature. For example, in the cooling curve of the electric power W3, when the sample temperature is T1, the slope of the constant electric power cooling curve (which becomes a negative value and becomes the temperature decreasing rate) is V1. In this way, a correspondence relationship between “power W3, sample temperature T1, and cooling rate V1” is obtained. The lower the sample temperature, the smaller the absolute value of the slope of the constant power cooling curve.
[0021]
Next, when cooling is performed from the same initial temperature TH with power W2 smaller than W3, the constant power cooling curve becomes as shown by a broken line, and the absolute value of the cooling rate becomes smaller than that in the case of W3. The saturation temperature also increases. If the electric power W1 is made smaller, the absolute value of the cooling rate becomes smaller, and the saturation temperature becomes higher.
[0022]
Next, the initial temperature of the sample is set to a temperature TL considerably lower than room temperature (strictly, a temperature lower than the saturation temperature TS corresponding to the electric power of the liquid nitrogen heater), and the sample is cooled with a low-temperature gas. , The sample temperature rises so as to approach the saturation temperature TS. In the case of the large power W3, the saturation temperature TS is relatively low, and the constant power cooling curve from the low initial temperature TL has a low heating rate as shown by the solid line. For example, when the sample temperature is T2, the slope of the constant power cooling curve (which becomes a positive value and becomes the rate of temperature rise) is V2. Then, as the sample temperature increases, the absolute value of the slope of the constant power cooling curve decreases. When the power W2 is smaller than W3, the saturation temperature becomes higher, the constant power cooling curve from the initial temperature TL becomes as shown by the broken line, and the heating rate becomes higher. If the electric power W1 is made smaller, the heating rate becomes even higher. As described above, the constant power cooling curve from the low initial temperature TL indicates that the sample temperature rises because the ambient temperature is higher than the initial temperature TL despite the fact that the sample is cooled with the low-temperature gas. Will be. Even a curve in which the sample temperature rises in this way is referred to as a constant power "cooling" curve in the sense of a temperature curve when the sample is cooled with a low-temperature gas.
[0023]
FIG. 3 is a graph schematically showing the relationship between the sample temperature and the temperature change rate at that time in the constant power cooling curve of FIG. 2, using the power supplied to the liquid nitrogen heater as a parameter. In order to obtain this graph, for example, using a constant power cooling curve of the power W3 in FIG. 2, a temperature change speed V1 is obtained at the temperature T1, which is plotted on the coordinate axis in FIG. In this case, the temperature change rate V2 is obtained, which is plotted in the same manner, and the values of the temperature change rate are plotted at appropriate sample temperature intervals, and these may be connected. When the temperature change rate is negative, the temperature decreases, and when the temperature change rate is positive, the temperature increases. A graph of the correspondence between the sample temperature and the temperature change rate is similarly obtained for the powers W2 and W1. As can be seen from this graph, when the sample is cooled with the low-temperature gas, the temperature change rate of the sample depends on both the power supplied to the liquid nitrogen heater and the sample temperature. In addition, although the graph of FIG. 3 is drawn so that each electric power may become a straight line, it does not necessarily become a straight line in principle. Experimentally, it could only be approximated by a straight line. The graph of the correspondence between the sample temperature and the temperature change rate may be a curve.
[0024]
FIG. 4 is a graph of an actual measurement example of the correspondence between the sample temperature and the temperature change rate. The horizontal axis is the sample temperature on the constant power cooling curve, and the vertical axis is the temperature change rate at that sample temperature. The power supplied to the liquid nitrogen heater is taken as a parameter. The power used in the experiment is six types: 0 W, 20 W, 80 W, 180 W, 320 W, and 500 W. As can be seen from this graph, in order to decrease the sample temperature by, for example, 5 ° C. per minute (that is, to decrease the temperature change rate to −5 ° C. per minute), when the sample temperature is around 0 ° C., the power of the liquid nitrogen heater is reduced. Must be between 20 W and 80 W, between 80 W and 180 W around -50 ° C., and between 180 W and 320 W near -100 ° C. Then, in order to obtain an ideal power at which the temperature falls at a rate of −5 ° C. per minute, an interpolation operation may be performed based on the graph of each power.
[0025]
FIG. 5 shows an example of a temperature program curve of a sample in the thermal analyzer. In this example, first, a start-up phase of “heating and holding the sample by 1 ° C. from the initial temperature (for example, 20 ° C.)” is performed, and then at a constant cooling rate of −5 ° C. per minute. The sample has been cooled to -100C. Thereafter, heating is performed to 100 ° C. at a constant heating rate of + 5 ° C. per minute.
[0026]
First, the starting stage will be described. FIG. 6 is a graph showing, in an enlarged manner, a change in the sample temperature in the starting stage. The initial temperature of the sample is assumed to be 20 ° C. When the start-up phase is started, 20 W of electric power is automatically supplied to the liquid nitrogen heater for 1 minute and 30 seconds. Thus, introduction of the low-temperature gas into the sample chamber is started. At the same time, the feedback control of the sample temperature is started at a temperature increase rate of + 5 ° C./min with a target temperature (21 ° C.) higher by 1 ° C. than the initial temperature. As a result, power supply to the sample heater starts, and the feedback control functions. Tens seconds after the start-up phase starts, the sample temperature reaches the target temperature and is maintained at that temperature. After 1 minute and 30 seconds, the power supply of 20 W to the liquid nitrogen heater ends, and thereafter, the power of the liquid nitrogen heater is obtained based on the sample temperature and the temperature change speed at that time. After this start-up phase has continued for a predetermined time (for example, 10 minutes), the original temperature program 50 (cooling at a temperature decreasing rate of −5 ° C. per minute) starts.
[0027]
At the stage of cooling the sample from near room temperature to −100 ° C. at a constant cooling rate of −5 ° C./min, the power of the liquid nitrogen heater changes as shown in the graph of FIG. In this graph, the step-like graph is an example in the case where one of the six types of power shown in FIG. 4 is selected to cool the sample. That is, at each sample temperature, the lowest power that can obtain the actually measured cooling rate at that time (substantially equal to -5 ° C. per minute) is selected from the above-described six types of power. For example, an electric power of 80 W is supplied to the liquid nitrogen heater until the sample temperature is around −40 ° C., and an electric power of 180 W is supplied until the sample temperature is around −80 ° C., and so on. On the other hand, a curve 44 is a graph in which an ideal electric power for obtaining an actually measured cooling rate (approximately −5 ° C. per minute) is obtained by an interpolation calculation. When the power of the liquid nitrogen heater is changed in accordance with the sample temperature based on the curve 44, the power continuously increases as the sample temperature decreases, and the sample temperature is almost equal to the target temperature decreasing rate. And will decrease. If the cooling rate of the temperature program is changed from the above-mentioned -5 ° C./min to another value, the power curve in FIG. 7 also becomes a graph corresponding to such another cooling rate.
[0028]
Curve 46 is a power curve that is 10% greater than ideal power curve 44. It is preferable to use this correction power curve 46 in actual sample temperature control. In order to cool the sample at a constant temperature lowering rate, it is necessary to perform feedback control of the sample temperature in combination with the sample heater, but in order to enable this feedback control, a cooling that is somewhat larger than the ideal power curve 44 is required. This is because it is necessary to have the ability. The corrected power may be power obtained by adding a fixed value (for example, 20 W) to the ideal power instead of increasing the power by a fixed ratio of the ideal power.
[0029]
In a preferred embodiment, the correspondence between the sample temperature, the temperature change rate, and the ideal power is finely determined in advance by interpolation based on the graph of FIG. 4, and the ideal power is further determined by a predetermined ratio (for example, 10%). The correction power that has been increased only by the calculation is calculated and stored in the liquid nitrogen heating power supply. Therefore, if the sample temperature and the temperature change speed are actually measured, the corresponding correction power is determined, and this correction power is supplied to the liquid nitrogen heater.
[0030]
Next, a case where the temperature of the sample is raised will be described. As shown in the graph of FIG. 4, it is necessary to supply the liquid nitrogen heater to the heating stage from the low temperature to the vicinity of the room temperature and at a gentle heating rate, as can be seen from the graph of FIG. is there. On the other hand, if a higher heating rate is required than the graph of the temperature change rate of “0 W” in FIG. 4, the sample is raised using only the sample heater without using the low-temperature gas. Just warm it. In the temperature program of FIG. 5, since heating is performed at a constant rate of + 5 ° C. per minute from -100 ° C. to + 100 ° C., according to FIG. 4, power supply to the liquid nitrogen heater is not required.
[0031]
The present invention is not limited to the above embodiment, and the following modifications are possible. (1) Although FIG. 1 shows an example of a differential scanning calorimeter, the present invention can be applied to a sample temperature control method in other thermal analyzers and to a temperature control of a sample other than thermal analysis. (2) Liquid nitrogen is optimal as the liquefied refrigerant, but other liquefied refrigerants may be used.
[0032]
【The invention's effect】
According to the sample temperature control method of the present invention, the power supplied to the refrigerant heater is changed every moment based on the actually measured sample temperature and the actually measured temperature change rate. The power supplied to the refrigerant heater and the sample heater can be minimized. Also, the consumption of the liquefied refrigerant is minimized.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an example of a thermal analyzer to which a sample temperature control method according to the present invention is applied.
FIG. 2 is a graph showing a constant power cooling curve when constant power is supplied to a liquid nitrogen heater.
FIG. 3 is a graph showing a correspondence relationship between a sample temperature and a temperature change rate in the constant power cooling curve of FIG. 2;
FIG. 4 is a graph of an actual measurement example of a correspondence relationship between a sample temperature and a temperature change rate.
FIG. 5 is a graph showing an example of a temperature program curve of a sample.
FIG. 6 is a graph showing, in an enlarged manner, a change in sample temperature in a starting stage.
FIG. 7 is a graph of liquid nitrogen heater power according to sample temperature.
FIG. 8 is a graph showing a constant power cooling curve and a temperature program curve.
FIG. 9 is a graph illustrating an example of a sample temperature control method disclosed in the related art document.
[Explanation of symbols]
Reference Signs List 20 sample chamber 22 furnace body 24 partition wall 26 annular space 28 sample heater 29 sample heating power supply 30 thermocouple 32 sample temperature controller 34 liquid nitrogen container 36 liquid nitrogen 38 liquid nitrogen heater 39 liquid nitrogen heating power supply 40 low temperature gas pipe 42 outlet

Claims (3)

A liquefied refrigerant is heated and vaporized by a refrigerant heater to generate a low-temperature gas, the sample is cooled by the low-temperature gas, and the sample temperature is feedback-controlled using the sample heater. A sample temperature control method characterized by performing the control steps (d) and (e) after the preliminary steps (c) to (c).
(A) A curve showing the relationship between the elapsed time and the sample temperature at that time by supplying a constant power to the refrigerant heater and cooling the sample with the low-temperature gas without heating the sample with the sample heater. (Hereinafter, referred to as a constant power cooling curve).
(B) changing the value of the constant power to obtain a plurality of the constant power cooling curves;
(C) determining a correspondence relationship between the power, the sample temperature, and the temperature change speed in the plurality of constant power cooling curves.
(D) Based on the actually measured sample temperature and the actually measured temperature change rate, a required refrigerant heater power is obtained from time to time based on the above-described correspondence, and the required power is supplied to the refrigerant heater.
(E) feeding the electric power to the sample heater so that the sample temperature follows a predetermined temperature program while the required electric power is supplied to the refrigerant heater, and performing feedback control of the sample temperature. 2. The sample temperature control method according to claim 1, wherein, in the step (d), the required power is increased by a fixed rate or a fixed value from a power determined based on the correspondence. Before starting the control step including the steps (d) and (e), a state in which the low-temperature gas is generated by supplying a constant initial power to the refrigerant heater for a predetermined time, 2. The sample temperature control method according to claim 1, wherein by setting a temperature higher than an initial sample temperature as a target temperature, power is supplied to the sample heater to perform feedback control.

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