JP2000146878A - Sample temperature controlling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly precisely follow a sample temperature for any temperature programming curve including isothermal control, by inventing voltage control for the first heater in a sample temperature controlling method wherein a liquefied refrigerant is vaporized by the first heater to generate low temperature gas, the low temperature gas is introduced into a sample chamber, and wherein a second heater provided in an electric furnace of the sample chamber is heated to feedback-control the temperature of the sample chamber. SOLUTION: A voltage command is output to a second heater power source in a control system for a second heater to make zero a deviation ΔT between a target temperature Tr and an electric furnce temperature Tf. A predicted voltage command Ea based on a sample temperature Ts is output in a prediction controller in a control system for a first heater, and a voltage command Eb is output in a PID controller 42 to make the deviation ΔT zero. The Eb is added to the Ea in an adder 44. That is, the predicted voltage Ea predicted in the prediction controller is increased or decreased by the voltage command Eb based on the deviation ΔT.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a temperature of a sample when the temperature of the sample is raised or lowered according to a predetermined temperature program curve, such as a sample of a thermal analyzer.
In particular, the present invention relates to a sample temperature control method using a low-temperature gas obtained by evaporating a liquefied refrigerant as a means for cooling a sample.

[0002]

2. Description of the Related Art As a method of cooling a sample to a temperature lower than room temperature, there is a method of cooling a sample with a low-temperature gas obtained by vaporizing liquid nitrogen. 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. When a large electric power is supplied to the liquid nitrogen heater, vaporization is promoted and the sample temperature drops rapidly. When a smaller electric power is applied, the sample temperature gradually decreases.

When cooling a sample in a thermal analyzer, the sample is cooled, for example, at a constant cooling rate according to a predetermined temperature program curve. However, such precise control is not possible with cooling from liquid nitrogen with low-temperature gas, so feedback control using heating by an electric furnace heater in the sample chamber is used in addition to cooling with low-temperature gas. .

Japanese Patent Laid-Open No. 2-105046 discloses a conventional example of controlling the temperature of a sample by using both cooling of the sample by power control of a liquid nitrogen heater and heating of the sample by power control of an electric furnace heater. The technology described in the official gazette (hereinafter referred to as a first conventional technology) is known. In the first prior art, 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 temperature lower than room temperature is set as the temperature program signal, the supply power corresponding to the temperature can be obtained from the result of the preliminary experiment. This power may be supplied to the liquid nitrogen heater. Then, after a predetermined time, the sample temperature falls to the ultimate temperature.

In the first prior art, when an ultimate temperature lower than room temperature is set, only one power supply to the liquid nitrogen heater corresponding thereto is determined. When the sample is cooled by evaporating the liquid nitrogen with the supply power determined as described above, and the temperature of the sample is feedback-controlled using the electric furnace heater, it is possible to control the temperature of the sample according to a predetermined temperature program curve. . However, when trying to cool the sample to the above-mentioned reached temperature at a “constant cooling rate” using this method, the cooling capacity becomes insufficient during the cooling.

As a method for solving the insufficient cooling capacity of the first prior art, a prior art (hereinafter referred to as a second prior art) disclosed in Japanese Patent Application Laid-Open No. 9-196871 has been developed. In the second prior art, the power of the liquid nitrogen heater is changed to a necessary and sufficient value at any time based on the sample temperature at each time and the temperature decreasing rate, thereby solving the cooling capacity shortage. Also, wasteful power consumption is prevented.

[0007]

The second prior art described above works very effectively when the sample is cooled at a constant temperature lowering rate, but the control to keep the sample at a constant temperature is performed. (Hereinafter referred to as isothermal holding control), it was found that the temperature stability was inferior. For example, when there is an isothermal control region at the beginning of the temperature program curve, there is a problem that the holding temperature fluctuates. The cause of the fluctuation was that the power of the liquid nitrogen heater was determined depending on the temperature change rate (differential value of the temperature) at each time.

The present invention has been made to solve the above-mentioned problems of the second prior art, and an object of the present invention is to heat and vaporize a liquefied refrigerant by a first heater to generate a low-temperature gas. In a sample temperature control method in which a gas is introduced into the sample chamber and a temperature of the sample chamber is feedback-controlled by heating a second heater provided in an electric furnace of the sample chamber, the voltage control of the first heater is devised. It is an object of the present invention to provide a sample temperature control method capable of causing a sample temperature to follow any temperature program curve with high accuracy, including isothermal holding control.

[0009]

According to the present invention, a liquefied refrigerant is heated and vaporized by a first heater to generate a low-temperature gas, and the low-temperature gas is introduced into a sample chamber, and a low-temperature gas is provided in an electric furnace of the sample chamber. (2) In the sample temperature control method in which the temperature of the sample chamber is feedback-controlled by heating the two heaters, after the following preliminary steps (a) to (d), (e) to (g)
Are simultaneously performed.
(A) A constant voltage is supplied to the first heater without heating the second heater to introduce the low-temperature gas into the sample chamber, and shows the relationship between the elapsed time at that time and the temperature of the sample chamber. Measuring a curve (hereinafter referred to as a constant voltage cooling curve). (B) changing the value of the constant voltage to obtain a plurality of the constant voltage cooling curves. (C) measuring the temperature of the sample chamber (hereinafter, referred to as an intermediate attainment temperature) when the slope of each of the plurality of constant voltage cooling curves reaches a predetermined set value. (D) determining a combination of a voltage and the intermediate attainment temperature for a plurality of the constant voltage cooling curves, and determining a correspondence between the voltage and the temperature based on the combination; (E) determining the voltage of the first heater (hereinafter referred to as a predicted voltage) by applying the temperature of the sample chamber at each time to the correspondence. (F) increasing or decreasing the predicted voltage based on a deviation between the temperature of the sample chamber at each time and the target temperature at each time. (G) controlling the voltage of the second heater based on the deviation between the temperature of the sample chamber at each time and the target temperature at each time.

In the above control step (e), when determining the voltage of the first heater, the voltage is first predicted and controlled based on the temperature of the sample chamber at each time. Since this control does not depend on the deviation between the target temperature (the temperature on the temperature program curve) at each time and the temperature of the sample chamber, the control method is an open control. In this advance prediction control, regardless of the difference between the target temperature and the temperature of the sample chamber at each time, the voltage of the first heater suitable for the temperature of the sample chamber at that time is set in advance. Will be.

In the above control step (f), a voltage increase or decrease by feedback control of the first heater system is added to the predicted voltage obtained in the control step (e). The control step (f) is a feedback control as a control method, and is a follow-up control based on a deviation from a target temperature.
By adding the feedback control of (f) to the advance prediction control of (e), the advance control and the follow-up control are used together. There is a defect in which the steady-state error cannot be removed only by the preceding prediction control, and there is a defect by the follow-up correction control in the feedback control alone. Therefore, the optimum voltage of the first heater is determined by combining the disadvantages of both controls so as to complement each other.

By the way, in the advance prediction control of (e), the target temperature at each time may be used instead of the temperature of the sample chamber at each time. In the preceding prediction control, the temperature dependency of the prediction voltage to be used is not so large, and there is no significant difference in the control ability using either the temperature of the sample chamber or the target temperature.

The control steps (e) and (f) are the voltage control of the first heater, whereas the control step (g) is the voltage control of the second heater. By finally feedback-controlling the temperature of the sample chamber using the second heater (heater of the electric furnace), the sample temperature can be made to follow the target temperature with high accuracy.

The "temperature of the sample chamber" used in each of the above steps (a), (c), (e), (f) and (g) is a temperature sensor (for example, a thermocouple) arranged as close as possible to the sample. (This will be called the sample temperature.)
Or a temperature detected by a temperature sensor (for example, a thermocouple) disposed on the wall of the electric furnace (this will be referred to as an electric furnace temperature). However, the use of the predicted voltage is related to each other (a) (c)
In the three stages (e), it is necessary to unify either the sample temperature or the electric furnace temperature as the “sample chamber temperature”. In general, when the temperature of the sample chamber is feedback-controlled using the second heater (heater of the electric furnace), the temperature control is smoother using the electric furnace temperature. Preferably, furnace temperature is used. In the control of the first heater (liquefied refrigerant heating heater) system, it is considered that there is no great difference in using either the sample temperature or the electric furnace temperature.

In the above-mentioned step (e), instead of "applying the temperature of the sample chamber at each time to the correspondence,""applying the target temperature at each time to the correspondence". Good.

In the above step (c), the meaning of the intermediate temperature is as follows. When a constant voltage is supplied to the first heater to cool the sample with a low-temperature gas and a constant voltage cooling curve at that time is measured, if a long time elapses,
The slope of the curve approaches zero as much as possible, and the temperature of the sample chamber is settled to a substantially constant value (hereinafter, referred to as the ultimate temperature). This final temperature depends on the voltage applied to the first heater. If the correspondence between the final temperature and the voltage is obtained in advance, the voltage of the first heater appropriate to the temperature of the sample chamber at that time during the actual temperature control of the sample can be obtained from the above-described correspondence. it can. However, using such a correspondence, the "just right"
The voltage will be determined. In this case, the voltage used for the advance prediction control is insufficient. This is because the voltage supplied to the first heater is slightly increased, and the sample temperature tends to be slightly lower than the target temperature, and the feedback control is made effective by supplementing the tendency with the sample heating by the second heater. This is because it is important to make them function. Therefore, it is appropriate to use the intermediate attainment temperature instead of using the above-mentioned final attainment temperature. This intermediate temperature can be defined as the temperature of the sample chamber when the slope of the constant voltage cooling curve reaches a predetermined set value. The actual problem is how to set the slope. According to the study of the inventors, the set value is set to a value within the range of minus 0.1 ° C./min to minus 3 ° C./min. It is appropriate that

When the "power control" of the first heater and the second heater is actually performed, the "applied voltage" is controlled as a control amount in the control circuit. Therefore, in the present invention, the expression in each control stage is voltage control. Ultimately, the power supplied to the heater is controlled.

[0018]

FIG. 1 is a block diagram showing an example of a thermal analyzer for implementing a sample temperature control method according to the present invention. This thermal analyzer is an example of a differential scanning calorimeter, in which a cylindrical electric furnace 12 is disposed inside a cylindrical sample chamber 10. The internal space of the sample chamber 10 is partitioned by a cylindrical partition 14, and a low-temperature gas is introduced into an annular space 16 between the partition 14 and the inner wall surface of the sample chamber 10. The outer peripheral surface of the electric furnace 12 is in close contact with the inner wall surface at the center in the height direction of the partition wall 14. A sample container and a reference container are mounted on a heat equalizing plate fixed to the inner wall of the electric furnace 12. A second heater 18 is embedded in the electric furnace 12. The second heater 18 is connected to a second heater power supply 19. The sample temperature is measured with a thermocouple 20 adhered to a soaking plate. The temperature of the electric furnace 12 is measured by a thermocouple 22 embedded in the furnace body. The second heater power supply 19 and the thermocouples 20 and 22 are connected to a temperature control device 24.

A liquid nitrogen container 28 contains liquid nitrogen 28.
Is housed. A first heater 30 is disposed inside the liquid nitrogen container 26. This first heater 30
When a voltage is applied from the first heater power supply 32 to the
0 is heated, the vaporization of the liquid nitrogen 28 is promoted, and the amount of low-temperature gas generated increases. Above the liquid nitrogen container 26, a low-temperature gas pipe 34 is connected.
4 is connected to the annular space 16 of the sample chamber 10. The low-temperature gas that has entered the annular space 16 of the sample chamber 10 from the low-temperature gas pipe 34 fills the annular space 16, cools the partition wall 14 and the electric furnace 12, and exits through the outlet 36.

FIG. 2 is a block diagram showing an example of a signal flow in the sample temperature control method of the present invention. A voltage command is output from the temperature control device 24 to the first heater power supply and the second heater power supply. The temperature control device 24 includes an electric furnace temperature Tf detected by the thermocouple 22 in FIG.
The sample temperature Ts detected by the thermocouple 20 in FIG. 1 is input. A desired temperature program curve can be set in the temperature program setter. During the temperature control, a target temperature (temperature on the temperature program curve) at each point in time is output from the temperature program setter.

First, the control system of the second heater will be described. In the comparator 38, the deviation ΔT between the target temperature Tr output from the temperature program setter and the electric furnace temperature Tf is ΔT = Tr−Tf.
Is calculated. This deviation ΔT is input to the PID controller 40 for the second heater. The PID controller 40 outputs a voltage command to the second heater power supply in a direction in which the deviation ΔT becomes zero. For example, if only the proportional control (P component) of the PID control is described as an example, if ΔT is positive (the electric furnace temperature Tf is lower than the target temperature Tr), the PID controller 40 determines the proportionality to ΔT. A voltage command is output to the second heater power supply. The voltage command increases as ΔT increases. Δ
When T becomes negative, the voltage command for the second heater power supply becomes zero. In this manner, the electric furnace temperature Tf becomes the target temperature Tr.
Is feedback-controlled so as to follow.

Next, the control system of the first heater will be described. In the prediction controller, a predicted voltage command Ea is calculated based on the sample temperature Ts.
Is output. The predicted voltage command Ea will be described later. On the other hand, the above-described deviation ΔT is input to the PID controller 42 for the first heater. Then, voltage command Eb is output to the first heater power supply in a direction in which deviation ΔT becomes zero. For example, if only the proportional component of the PID control is described, the absolute value of the PID controller 42 is Δ
A voltage command Eb of “opposite sign” is output in proportion to T. That is, when ΔT is positive, voltage command Eb is negative, and when ΔT is negative, voltage command Eb is positive. That is, Eb = −k · ΔT (where k is a positive proportional coefficient). Then, in the adder 44, the PID controller 42 for the first heater responds to the voltage command Ea from the prediction controller.
Is added. That is, the predicted voltage Ea predicted by the prediction controller is increased or decreased by the voltage command Eb based on the deviation ΔT. The voltage command Ec (= Ea + Eb) obtained in this way is input to the delay element. This delay element is a first-order delay filter (digital filter) connected in one to four stages, and a voltage command Ec
Is output with a delay. In this embodiment, the first-order lag filters are connected in four stages, and the time constant of the delay is set to about 3 seconds. The output of the delay element finally becomes the voltage command for the first heater.

In the present embodiment, the first heater PID controller 42 performs the following proportional control. During the period from the start of the temperature control of the sample to the first minute and a half (when the ejection of the vaporized gas starts), the above proportional coefficient k = 1.5 V / ° C., and thereafter, k = 1.5 V / ° C.
0.6 V / ° C.

In FIG. 2, there are two PID controllers 40 and 42. These PID controllers require all of the proportional component (P), the integral component (I) and the derivative component (D). is not. If necessary, one or two of these components may be employed for control. In particular,
The PID controller 42 for the first heater does not require as strict control as the PID controller 40 for the second heater (high-precision feedback control cannot be performed in the first place with temperature control using vaporized gas). Controller 4
In the case of 2, only the proportional control may be performed.

Next, the operation of the prediction controller will be described. FIG.
Is a graph of a constant voltage cooling curve, in which the horizontal axis represents time and the vertical axis represents sample temperature (or electric furnace temperature). The constant voltage cooling curve is obtained by measuring a time change when the sample temperature is lowered by supplying a constant voltage to the first heater after setting the sample temperature to 200 ° C. The voltage of the second heater is off. In this embodiment, constant voltage cooling curves are measured for five types of voltages, and each voltage is E1 =
20V, E2 = 40V, E3 = 60V, E4 = 80V,
E5 = 100V. When each voltage is applied to the first heater, 1A, 2A, 3A, 4A, 5A
When the current of A flows, each power supplied to the first heater is:
20W, 80W, 180W, 320W, 500W.

In each curve, the temperature at which the slope reaches α (the temperature at a point in contact with the line segment of the slope α may be obtained, hereinafter referred to as an intermediate attained temperature) is obtained. For example, if α = −2 ° C./min, the voltage E1
In the curve, the intermediate temperature T1 = 20 ° C. With respect to the same slope α, when the intermediate attainment temperatures T2 to T5 are obtained for the constant voltage cooling curves of the other voltages E2 to E5, T2 = −
64 ° C., T3 = −109 ° C., T4 = −130 ° C., T5 =
-145 ° C. As a result, the intermediate temperatures T1 to T5 at the voltages E1 to E5 were obtained. In order to measure the constant voltage cooling curve, the sample temperature was raised to about 200 ° C. and then cooled. There is not much difference.

FIG. 4 is a graph obtained by plotting the correspondence between the voltage and the intermediate temperature in the constant voltage cooling curve of FIG. 3 on the coordinate axis of temperature on the horizontal axis and on the vertical axis on the coordinate axis of voltage. This is called a predicted voltage curve. The black circles on this graph are (E1, T1) to (E5, T5) described above.
5 are plotted. And these points are connected by a smooth curve. In this embodiment, the voltage E is connected by an approximate curve that becomes a cubic function of the temperature T. That is, this graph is expressed as E =
Expressed as f (T), the functional form of f is a cubic expression of temperature T. Strictly speaking, 4 of T is required to completely pass through 5 points.
Although the following equation is required, not so strictness is required, so that a curve approximation of a cubic equation is sufficient. Even if a larger number of combinations of (E, T) are measured and plotted, it is realistic to approximate with a curve of about the third order. Of course, a polygonal-line approximation (which is linear interpolation) may be used to obtain the predicted voltage curve, or an arbitrary multi-dimensional function of a quadratic function or more may be used.

Up to the point where this predicted voltage curve is formed is a preliminary stage. To perform actual sample temperature control, this predicted voltage curve created in advance is used. That is, the prediction controller of FIG. 2 stores the above-described predicted voltage curve, and can obtain the predicted voltage Ea from the sample temperature Ts at that time as shown in FIG. This predicted voltage E
a is the first necessary for obtaining the sample temperature Ts at that time.
The voltage is slightly higher than the heater voltage. That is, the value is a value slightly higher than the required voltage. The degree of addition is determined by the gradient α when the intermediate attainment temperature is obtained in FIG. Increasing the gradient α increases the additional voltage, and decreasing the gradient α decreases the additional voltage. In this embodiment, −2 ° C./min is adopted as α, but practically, −0.
It is sufficient to use any value within the range of about 1 ° C./min to about −3 ° C./min.

Next, the operation of the block diagram of FIG. 2 will be described with reference to specific numerical examples. In FIG. 2, at a certain time (one and a half minutes after the start of the temperature control, a certain time), the target temperature Tr on the temperature program curve is changed.
Is −120 ° C., and both the electric furnace temperature Tf and the sample temperature Ts are −109 ° C. In the predictive controller,
By applying the sample temperature Ts = −109 ° C. to the predicted voltage curve in FIG. 4, a voltage Ea = 60 V of the first heater is obtained. On the other hand, in the PID controller 42 for the first heater, the deviation ΔT =
Based on Tr−Ts = −11 ° C., Eb = −k · ΔT =
−0.6 × (−11) = 6.6 V is obtained. Therefore, in FIG. 2, Ec = Ea + Eb = 66.6V is obtained. This voltage is applied to the first heater power supply via the delay element. In the PID controller 40 for the second heater power supply, since the deviation ΔT = Tr−Ts = −11 ° C. is minus, the voltage command for the second heater power supply is zero.

FIG. 5 is a block diagram of a second embodiment of the present invention. FIG. 5 differs from FIG. 2 in that the electric furnace temperature is input to the predictive controller instead of the sample temperature.
FIG. 6 is a block diagram of a third embodiment of the present invention. FIG. 6 differs from FIG. 2 in that a target temperature is input to the predictive controller instead of the sample temperature. FIG. 7 is a block diagram of a fourth embodiment of the present invention. FIG. 7 differs from FIG. 2 in that the deviation between the target temperature Tr and the sample temperature Ts is input to the PID controller 42 for the first heater.

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 a thermal analyzer other than the above, and can also be applied to 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]

According to the sample temperature control method of the present invention, the voltage to be applied to the first heater (the liquefied refrigerant heater) is obtained by using both the advance prediction control and the feedback control.
Highly accurate temperature control becomes possible. As a result, stable control can be realized not only in constant-speed temperature rise and constant-speed temperature decrease control but also in isothermal holding control.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an example of a thermal analyzer that implements a sample temperature control method of the present invention.

FIG. 2 is a block diagram showing an example of a signal flow in the sample temperature control method of the present invention.

FIG. 3 is a graph of a constant voltage cooling curve.

FIG. 4 is a graph of a predicted voltage curve in which a correspondence between a voltage and an intermediate attained temperature in a constant voltage cooling curve is plotted.

FIG. 5 is a block diagram of a second embodiment of the present invention.

FIG. 6 is a block diagram of a third embodiment of the present invention.

FIG. 7 is a block diagram of a fourth embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 sample chamber 12 electric furnace 18 second heater 19 second heater power supply 20 sample temperature thermocouple 22 electric furnace temperature thermocouple 24 temperature control device 26 liquid nitrogen container 28 liquid nitrogen 30 first heater 32 first heater power supply 38 comparison Container 44 Adder

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takashi Kanaya 3-9-1, Matsubara-cho, Akishima-shi, Tokyo F-term in Rigaku Electric Co., Ltd. (reference) 2G040 AB12 CA02 CB03 CB14 DA14 EA02 EA08 EB02 EC01 EC09 HA06

Claims (6)

[Claims] A liquefied refrigerant is heated and vaporized by a first heater to generate a low-temperature gas. The low-temperature gas is introduced into a sample chamber, and a second heater provided in an electric furnace of the sample chamber is heated to heat the sample. In the sample temperature control method for feedback-controlling the temperature of the chamber, the sample temperature is characterized by simultaneously performing the control steps (e) to (g) after the following preliminary steps (a) to (d). Control method. (A) A constant voltage is applied to the first heater without heating the second heater to introduce the low-temperature gas into the sample chamber, and shows the relationship between the elapsed time at that time and the temperature of the sample chamber. Measuring a curve (hereinafter referred to as a constant voltage cooling curve). (B) changing the value of the constant voltage to obtain a plurality of the constant voltage cooling curves. (C) For each of the plurality of constant voltage cooling curves,
A step of measuring the temperature of the sample chamber when the inclination reaches a predetermined set value (hereinafter, referred to as an intermediate temperature). (D) determining a combination of a voltage and the intermediate attainment temperature for a plurality of the constant voltage cooling curves, and determining a correspondence between the voltage and the temperature based on the combination; (E) The temperature of the sample chamber at each time is applied to the corresponding relationship to the voltage of the first heater (hereinafter, referred to as a predicted voltage).
Seeking stage. (F) increasing or decreasing the predicted voltage based on a deviation between the temperature of the sample chamber at each time and the target temperature at each time. (G) controlling the voltage of the second heater based on the deviation between the temperature of the sample chamber at each time and the target temperature at each time. 2. The method according to claim 1, wherein a sample temperature is used as the temperature of the sample chamber in the step (e), and an electric temperature is used as the temperature of the sample chamber in the steps (f) and (g). A method comprising using furnace temperature. 3. The method according to claim 1, wherein a sample temperature is used as the temperature of the sample chamber in the steps (e) and (f), and an electric temperature is used as the temperature of the sample chamber in the step (g). A method comprising using furnace temperature. 4. The method according to claim 1, wherein the voltage determined in the step (f) is supplied to the first heater via a delay element. how to. 5. The method according to claim 1, wherein the set value of the inclination in the step (c) is in a range of −0.1 ° C./min to −3 ° C./min. The method characterized by making it the numerical value in. 6. The method according to claim 1, wherein the “temperature of the sample chamber at each time” in the step (e).
Using a "target temperature at each time" instead of the target temperature.