JP2015038428A - Temperature controller of furnace body for analyzer, and heat analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature controller of a furnace body for an analyzer that is based on PWM control and has high cost effectiveness.SOLUTION: The temperature controller of a furnace body controls the temperature of a furnace body 17. The temperature controller includes: a rectification circuit 31 connected to an AC power source 30; a PWM circuit 6 for modulating the pulse width of an output from the rectification circuit 31 in accordance with the duty ratio; and a heater 18 for receiving an output voltage from the PWM circuit 6, generating heat, and heating the furnace body 17. The rectification circuit 31 aligns the voltage of the AC power source 30 to one of positive voltage and negative voltage. An envelope of the rectified voltage as the output voltage of the rectification circuit 31 remains in the voltage supplied to the heater 18.

Description

  The present invention relates to a temperature control device for a furnace body for an analyzer that controls the temperature of the furnace body for the analyzer. The present invention also relates to a thermal analyzer using the temperature control device for the furnace for the analyzer.

  Said analyzer is an analyzer provided with the part which heat-processes using a furnace body. Examples of this type of analyzer include a thermal analyzer and an X-ray analyzer. The furnace used in this analyzer is used, for example, to increase the temperature of a sample that is a measurement target. This type of analyzer usually has a temperature control device. Many conventional temperature control devices perform temperature control based on a phase control (SCR control) method. (For example, refer to Patent Document 1, Patent Document 2, and Patent Document 3). In general, for example, as shown in FIG. 9A, the phase control method is such that a voltage E shown in FIG. This is a method of supplying waveform power to a heater or the like. The temperature control of the furnace body for the analyzer is different from the general temperature control of the furnace body, and the function of increasing the temperature at a constant rate of temperature increase is an important factor.

  In recent years, a PWM (Pulse Width Modulation) control method has become widespread (see, for example, Patent Document 4 and Patent Document 5). Many of the conventional PWM controls obtain a stable direct current (DC) voltage from an alternating current (AC) power supply. When the output voltage of this DC voltage is controlled by PWM control and the controlled voltage is applied to the load, the stabilized DC voltage is converted into an arbitrary voltage by an inverter, a DC-DC conversion circuit, etc. The temperature was automatically controlled by supplying to (for example, a heater).

JP-A-2004-259160 JP2013-068803A JP2013-097691A JP 2000-175453 A JP2010-259298A

The temperature control device using the phase control method has the following problems.
(1) In FIG. 10, (a) shows the power supply voltage waveform at the normal time, and (b) shows the phase control voltage waveform at the normal time. At a site where a heater as a heat source is installed, voltage fluctuations and waveform distortions as shown in FIG. 10C may occur in the power supply voltage waveform due to the influence of various external factors. When these voltage fluctuations and waveform distortion occur, the amplitude and waveform of the phase control voltage waveform fluctuate as shown in FIG. 10D, and temperature control by the heater may not be performed accurately.

(2) In FIG. 11, (a) shows the power supply voltage waveform at the normal time, and (b) shows the phase control voltage waveform at the normal time. In the phase control method, the ON period is defined with reference to the zero cross point of the power supply voltage waveform, but noise may enter near the zero cross when the heater is actually operated. If such noise enters, a malfunction occurs at the ON timing, and the ON period in the phase control voltage waveform varies as shown in FIG. 11D, and the temperature control by the heater cannot be performed accurately. There is.

(3) In FIG. 12, (a) shows the power supply voltage waveform at the normal time, and (b) shows the phase control voltage waveform at the normal time. In the phase control method, control is performed such that a part of the AC power supply is turned on. However, in actual control, as shown in FIG. There is a risk that the problem will occur. High-frequency currents may adversely affect surrounding circuits and must be avoided.

  The present inventors conducted research in order to solve the above-mentioned problems found in the phase control method. As a result, it has been conceived that the above three problems can be solved by using the PWM control method instead of the phase control method.

  However, the present inventors have disclosed a general power control method based on the PWM control method in Patent Document 4 (Japanese Patent Laid-Open No. 2000-175453), and further uses a PWM control method to control the power supplied to the heater. It has been found that the use is disclosed in Patent Document 5 (Japanese Patent Application Laid-Open No. 2010-259298).

  When power control is performed by PWM control, switching such as IGBT (Insulated Gate Bipolar Transistor) is generally used when controlling from AC (alternating current) to DC (direct current) or from AC to AC. A plurality of elements had to be used, and a complicated circuit had to be prepared as a circuit for controlling those switching elements. Making such a device for realizing PWM control was not easy and the price was very expensive.

  The inventors consider a heater for heating a furnace body for an analyzer such as a thermal analyzer. The inventor of the present invention has found that since the furnace body for an analysis apparatus has a large heat capacity (heat capacity), complete and strict power control that does not allow any errors in supplying power to the heater is not necessarily required. More specifically, the output voltage waveform obtained by the PWM control method (that is, the waveform in which the envelope of the rectified voltage remains in the main component of the output voltage waveform) can also be used as the voltage waveform supplied to the heater as it is. Found out.

  The present invention has been made in view of the above-described problems, and is a furnace body temperature control device based on PWM control, which is excellent in cost effectiveness (that is, inexpensive but excellent effect) It is an object of the present invention to provide a device capable of achieving the above.

  A furnace body temperature control apparatus according to the present invention is a furnace body temperature control apparatus for controlling the temperature of a furnace body for an analysis apparatus, comprising: a rectifier circuit connected to an AC power source; and A PWM circuit that modulates the pulse width according to a duty ratio; and a heater that heats the furnace body by receiving an output voltage of the PWM circuit, and the voltage supplied to the heater includes the rectifier The envelope of the rectified voltage that is the output voltage of the circuit remains. The effects of the present invention are described in the following [Effects of the invention] column.

  The envelope is an envelope. The rectifier circuit is a circuit that aligns the voltage of the AC power source with one of a positive voltage and a negative voltage.

  In the temperature control device for a furnace body for an analyzer according to the present invention, a pulse width modulation waveform may remain in the voltage supplied to the heater. Since the furnace for an analysis apparatus has a large heat capacity, temperature control is not disturbed even if a pulse width modulation waveform remains in the voltage supplied to the heater.

  The temperature control device for a furnace body for an analyzer according to the present invention is based on a detection result of the heater temperature detection means, a furnace body temperature detection means for detecting the temperature of the furnace body, and a control amount for power supplied to the heater. And a duty ratio calculation means for determining the duty ratio by calculation based on a control amount determined by the temperature control unit.

  In the temperature control device for a furnace body for an analyzer according to the present invention, the duty ratio calculation means determines the duty ratio of the power supply voltage entering the rectifier circuit in addition to the control amount determined by the temperature control unit. It can be a judgment factor.

  In the temperature control device for a furnace for an analyzer according to the present invention, the duty ratio calculation means can use the peak value of the power supply voltage entering the rectifier circuit as the determination factor.

  The temperature control device for a furnace for an analyzer according to the present invention can include a capacitor for removing harmonic components contained in the output voltage of the PWM circuit and having a capacity of 100 μF or less.

  In the temperature control device for a furnace body for an analyzer according to the present invention, the rectifier circuit can full-wave rectify the voltage of the AC power supply.

  In the temperature control device for a furnace body for an analyzer according to the present invention, the temperature control unit can determine the control amount based on PID control.

  Next, a thermal analysis apparatus according to the present invention includes a furnace body that heats a sample, a heater that heats the furnace body, and a temperature control device for a furnace body for an analysis apparatus that controls the temperature of the furnace body. In the analyzer, the temperature controller for the furnace body for an analyzer is the above-described temperature controller for a furnace body.

(1) In the present invention, pulse width modulation is applied to the rectified waveform voltage E2 (see FIG. 5B) after rectification (see FIG. 5C). Then, the pulse width modulation voltage E3 after the modulation or the voltage E4 (FIG. 5 (d)) obtained by smoothing the pulse width modulation voltage E3 is supplied to the heater. Therefore, even when the power supply voltage waveform fluctuates as shown in FIG. 6 (a), when power control is performed, as shown in FIGS. 6 (b), (c), and (d). Only by changing the duty ratio in each pulse, there is no change in the envelope (that is, envelope) of the voltage waveform, and therefore no fluctuation occurs in the secondary voltage output due to the fluctuation of the primary side power supply. It was.

(2) In the conventional phase control method, as shown in FIG. 12C, a harmonic current synchronized with the primary power source (ie, AC power source) may flow in response to the rise of the voltage waveform after phase control. was there. On the other hand, in the present invention, since a steep rise synchronized with the primary power supply does not occur, the generation of harmonic current is greatly reduced.

(3) In the present invention, pulse width modulation using a switching element such as a MOSFET or a transistor is not directly performed on an AC power supply, but is a voltage after rectification processing by a rectifier circuit (that is, a rectified waveform). Voltage). Here, the rectified waveform is not an AC waveform in which the voltage value changes alternately, and is not a DC waveform in which the voltage value is always constant, and the voltage value is changing, but the change range is positive or negative. The waveform is within a range of values (see FIG. 5B).

  In the present invention, the voltage with the rectified waveform envelope remaining (that is, not shaped into a clean DC waveform) is supplied to the heater. Since the furnace body for an analysis apparatus, which is the object of the temperature control apparatus according to the present invention, has a large heat capacity, it can be used without any problem even with a clean DC voltage but with a rectified waveform envelope remaining. For this reason, in the temperature control device of the present invention, it is not necessary to use a complicated switching control circuit or a large-capacitance capacitor for forming a clean DC voltage. Therefore, the temperature control device for the furnace body for an analyzer according to the present invention and the thermal analyzer using the same are very cost-effective.

It is a figure which shows one Embodiment of the temperature control apparatus and thermal analysis apparatus of the furnace body which concerns on this invention. It is a figure which shows one Embodiment of the PWM converter which is the principal part of FIG. It is a block diagram of PID control performed by the temperature control part which is the principal part of FIG. It is a figure which shows an example of the power supply waveform performed with the apparatus of FIG. It is a figure which shows an example of the rectification | straightening process and PWM process which are performed by the circuit of FIG. It is a figure which shows the other example of the PWM process performed with the circuit of FIG. It is a flowchart which shows an example of operation | movement of the thermal analyzer of FIG. It is a graph which shows the result of an example of the measurement performed using the thermal analyzer of FIG. It is a figure which shows the conventional phase control system typically. It is a figure which shows one problem in a phase control system. It is a figure which shows the other problem in a phase control system. It is a figure which shows the further another problem in a phase control system.

  Hereinafter, a control device for a furnace body according to the present invention will be described based on embodiments. Of course, the present invention is not limited to this embodiment. In addition, in the drawings attached to the present specification, components may be shown in different ratios from actual ones in order to show characteristic parts in an easy-to-understand manner.

  FIG. 1 is a diagram showing an embodiment of a furnace body temperature control device and a thermal analysis device according to the present invention. In the figure, a thermal analyzer 1 is a thermal analyzer that performs both thermogravimetry (TG) and differential thermal analysis (DTA) measurements. The thermal analysis device 1 includes a first balance device 2, a second balance device 3, an electric furnace 4, a control device 5, and a PWM control unit 6.

  The balance devices 2 and 3 include balance rods 12a and 12b that are swingably supported by fulcrums 11a and 11b, sample dishes 13a and 13b provided at one end of the balance rods 12a and 12b, and balance rods 12a and 12b, respectively. It has the fluctuation | variation detection parts 14a and 14b provided in the edge. The sample S to be measured is placed on the sample pan 13 a of the first balance device 2. The reference material R is placed on the sample pan 13b of the second balance device 3. The sample S is a substance whose characteristics with respect to temperature change are desired. The reference material R is a material whose characteristics do not change even when there is a temperature change. In the figure, the sample dish 13a and the sample dish 13b are shown apart from each other, but this is for easy understanding of both, and in reality, they are arranged as close as possible.

  One temperature measuring point 10a constituting the thermocouple 9 is fixed to the sample tray 13a. Another temperature measuring point 10b constituting the thermocouple 9 is fixed to the sample tray 13b. The fluctuation detection units 14a and 14b are portions that detect the swing angles of the balance rods 12a and 12b around the fulcrums 11a and 11b, respectively, and output them as electrical signals.

  Inside the electric furnace 4, a furnace body 17 having a space inside, a heater 18 for heating the furnace body 17, and a temperature sensor 19 for detecting the temperature of the internal space of the furnace body 17 are provided. . The electric furnace 4 can reciprocate linearly as indicated by an arrow A-A ′. When the electric furnace 4 is in a predetermined position on the arrow A side (right side in the figure), the sample S and the reference material R are stored in the internal space of the furnace body 17. When the electric furnace 4 is in a predetermined position on the arrow A ′ side (left side in the figure), the sample S and the reference material R are out of the furnace body 17.

  In the present embodiment, the control device 5 is configured by a combination of a CPU (Central Processing Unit) and a memory. Inside the memory, software, a data table, a storage area, and the like are provided. The functions of the temperature control unit 22, the differential heat measurement unit 23, the weight measurement unit 24, and the duty ratio calculation unit 25 are realized by a combination of the CPU and software.

  The temperature control unit 22 performs known PID control. For example, as shown in FIG. 3, the PID control includes a P action (Proportional action) that makes the deviation close to zero in feedback control, an I action (Integral action) that makes the deviation completely zero, Is a combination of a D action (Derivative action) that quickly converges. In FIG. 3, Ve is a deviation input and V0 is a PID output. PID control is control for preventing overshoot from a target temperature curve and preventing hunting of a controlled temperature.

  The PID control unit 22 of FIG. 1 determines a control amount for performing feedback control so that the temperature of the furnace body 17 detected by the temperature sensor 19 becomes a target temperature. This control amount is sent to the duty ratio calculation unit 25.

  The thermocouple 9 is connected to the input terminal of the differential heat measuring unit 23. The differential heat measurement unit 23 achieves a function of measuring a temperature difference generated between the sample S and the reference material R as a function of temperature or time when the temperatures of the sample S and the reference material R are changed according to a predetermined program. Part.

  The output lines of the fluctuation detectors 14 a and 14 b are connected to the input terminal of the weight measuring unit 24. The weight measuring unit 24 functions to measure a difference in weight change generated between the sample S and the reference material R as a function of temperature or time when the temperatures of the sample S and the reference material R are changed according to a predetermined program. The achievement part.

  The PWM controller 6 has a PWM converter 28 and a PWM pulse generator 29. As shown in FIG. 2, the PWM converter 28 includes a rectifier circuit 31 connected to the AC power supply 30, a first capacitor 32 connected in parallel to the output terminal of the rectifier circuit 31, and one of the first capacitors 32. MOSFET 33 as a switching element having an input terminal connected to the terminal, a diode 34 having an anode connected to the output terminal of MOSFET 33, a coil 35 connected to the anode of diode 34, and a first element provided after coil 35. 2 capacitors 36. The AC power source 30 is a commercial power source, and is an AC voltage having a frequency of 50 Hz or 60 Hz and an amplitude of about 100 to 240V.

  The rectifier circuit 31 is formed by bridge-connecting four diodes 39 that are passive elements that allow current to flow only in one direction. By this rectifier circuit 31, the AC voltage E1 from the AC power source 30 is full-wave rectified as indicated by the symbol E2. That is, the AC voltage E1 is set to either a positive voltage (that is, a positive voltage) or a negative voltage (a negative voltage). In this embodiment, if the peak value of the input voltage is about 100V, a DC voltage of about 130V is formed as the peak value of the output voltage. Note that this DC voltage includes not pulsating current but completely smooth DC. In addition, as a mode of rectification, half-wave rectification can be used instead of full-wave rectification.

  The first capacitor 32 is used to remove the harmonic wave from the full-wave rectified voltage E2. In the conventional circuit of this type, an electrolytic capacitor having a large capacity for ensuring smoothness is used as the first capacitor 32. However, in this embodiment, since the object of control is the furnace body 17 having a large heat capacity, it is not necessary to obtain a complete DC voltage having no pulsating flow. For this reason, in this embodiment, a film capacitor having a relatively small capacity is used as the capacitor 32 mainly for the purpose of preventing harmonics. The capacitance of these capacitors is, for example, 100 μF or less.

  In general, electrolytic capacitors have a short life. This may shorten the life of the PWM converter 28, and hence the life of the furnace body temperature control device (19, 22, 25, 29, 28, 18), and consequently the life of the thermal analyzer 1. On the other hand, a capacitor having a small capacity such as a film capacitor has a long life, so that the life of the PWM converter 28 and the like can be extended. Further, by using a capacitor having a small capacity, generation of harmonic current and inrush current can be prevented.

  In FIG. 1, the PWM pulse generator 29 generates a pulse signal P <b> 1 having a frequency sufficiently higher than the power supply frequency of the AC power supply 30. Specifically, it generates a pulse signal P1 having a frequency that is 100 times the commercial power supply frequency of 50 Hz or 60 Hz and a frequency that is higher than the audible frequency. More specifically, a pulse signal P1 having a frequency of 24 kHz is generated. The reason for setting the frequency to 100 times or more of the commercial power supply frequency is to make it possible to stably form a secondary voltage that is not affected by voltage fluctuations of the primary power supply voltage. The reason why the frequency is higher than the audible frequency is to prevent the operator from feeling unnecessary sound during the temperature control based on the PWM control.

  The pulse signal P1 is input to the gate of the MOSFET 33 as a switching element in FIG. An IGBT, a bipolar transistor, or the like can be used instead of the MOSFET. The duty ratio D0 of the pulse signal P1 is determined by the duty ratio calculation unit 25 in FIG. In FIG. 1, a voltmeter 40 is connected to the output terminal of the AC power supply 30. The primary power supply voltage V 0, which is a voltage detected by the voltmeter 40, is sent to the duty ratio calculation unit 25. The duty ratio calculation unit 25 calculates the duty ratio D0 by calculation based on both the output value of the temperature control unit 22 (that is, the control amount that is a determination factor of feedback control) and the primary power supply voltage V0.

Specifically, for example
D0 = (100 / V0) × PID control amount (1)
To obtain the duty ratio D0. That is, in this embodiment, when determining the duty ratio of PWM control, the final duty ratio is obtained by taking the product of a coefficient inversely proportional to the AC power supply voltage with respect to the duty ratio obtained by PID control.

  In the above equation (1), the duty ratio is determined based on the PID control amount in order to realize feedback control by PWM control. The reason why the duty ratio is determined based on the primary power supply voltage V0 is to eliminate the influence of the fluctuation of the power supply voltage being reflected in the power control by the PWM control. This makes it difficult to be affected by fluctuations in the power supply voltage.

  By the way, since the output voltage of the AC power supply 30 is an AC voltage as shown in FIG. 10A, it is necessary to preliminarily determine which time point is set as the reference voltage V0. Further, since the output voltage of the AC power supply 30 may fluctuate as shown in FIG. 10C, it is necessary to preliminarily define which time point is set as the reference voltage V0 from this point.

  As a method of determining the reference voltage V0, for example, several methods such as a specific point from the zero cross point on the time axis, an effective voltage value, an average voltage value, a peak value of a voltage waveform, and the like can be considered. However, in this embodiment, it is determined that the peak value of the voltage waveform, for example, the peak value V1 shown in FIG. 4A, the peak value V2 shown in FIG. If the peak value of the voltage waveform is determined to be the reference voltage V0 in this way, the processing for determining the voltage value in the duty ratio calculation unit 25 of FIG. 1 can be speeded up. Further, in the present invention, the furnace body having a large heat capacity is targeted and the temperature is controlled by PID control. Therefore, it is not necessary to obtain a precise voltage value, and it is sufficient to obtain only the peak value of the voltage waveform.

  In addition, the duty ratio D0 based on the above equation (1) is determined by a method in which one duty ratio D0 is continuously used over a long period of time, or one duty ratio D0 is set for one measurement and each measurement is performed. A method of updating the duty ratio D0, a method of updating the duty ratio D0 at an appropriate timing during one measurement, and the like are conceivable.

  In the present embodiment, the duty ratio D0 is updated every half-wave period of the AC power supply 30 or every integral multiple of the half-wave period. By doing so, it is possible to perform temperature control that is not easily affected by fluctuations in the primary power supply voltage V0.

  As described above, in the PWM converter 28 of FIG. 2, the power supply voltage E1 is rectified by the rectifier circuit 31 to become a rectified waveform voltage E2 having a pulsating current. When the pulse signal P1 is introduced to the gate of the MOSFET 33, a DC pulse voltage E3 in a state where the rectified waveform voltage E2 is turned on / off in a comb shape is applied to the output terminal of the MOSFET 33 as shown in FIG. can get. The pulse voltage E3 is smoothed by the coil 35 and the capacitor 36 of FIG. 2 and shaped into the output voltage E4 shown in FIG. 5 (d).

  The output voltage E4 is not a clean DC voltage with a constant voltage value, but a voltage having a voltage waveform similar to the envelope (ie, envelope) of the rectified waveform voltage E3. An output voltage E4 corresponding to the rectified waveform voltage E3 is supplied to the heater 18, the heater 18 is energized and generates heat, and the furnace body 17 is heated. By adjusting the duty ratio D0, that is, by adjusting the ON time of the pulse voltage, the output power of the PWM converter 28 (that is, the power supplied to the heater 18) can be adjusted.

  In FIG. 5D, the output voltage E4 having a smooth waveform is formed. Instead, the output voltage E5 in a state where the pulse width modulation waveform (see FIG. 5C) remains is obtained (FIG. 5). (E) may be formed.

  As understood from the above description, in this embodiment, the temperature control device for the furnace body includes the temperature sensor 19, the temperature control unit 22, the duty ratio calculation unit 25, the PWM control unit 6, and the heater 18 of FIG. 1. It is realized by a combination.

(Explanation of thermal analysis measurement)
Hereinafter, the operation of the thermal analyzer 1 of FIG. 1 will be briefly described. First, the electric furnace 4 is moved to the position on the arrow A ′ side, and the sample pan 13a of the first balance device 2 and the sample pan 13b of the second balance device 3 are opened to the outside. In this state, the sample S to be measured is placed on the first sample tray 13a, and the reference material R is placed on the second sample tray 13b. The sample S is a substance whose thermal characteristics are desired to be known, and the reference substance R is a stable substance that does not change even when there is a temperature change.

  Next, the electric furnace 4 is moved to the arrow A side, and the sample dish 13 a and the sample dish 13 b are stored in the furnace body 17. Next, the temperature control of the furnace body 17 is performed by operating the furnace body temperature control devices 19, 22, 25, 6 and 18 according to a predetermined program. FIG. 8 shows the results when the melting temperature of indium (In) as a sample is measured when the temperature of the electric furnace 4 is raised at a constant speed. The temperature of the sample S is as shown by a temperature curve T0 in FIG.

  While the temperature of the sample changes like the temperature curve T0, the characteristic of the reference material R does not change. On the other hand, the sample S melts at a predetermined temperature and changes its characteristics. For this reason, when the melting occurs, changes are observed in the TG curve Lt and the DTA curve Ld.

(Explanation of temperature control)
An example of temperature control will be described using the flowchart of FIG. First, in step S1, a temperature program stored in the memory in the control device 5 in FIG. 1 is read into a predetermined memory area for the CPU in the control device 5 so that the temperature control unit 22 can be executed. Next, in step S2, the temperature of the furnace body 17 is detected using the temperature sensor 19 of FIG.

  Next, in step S3, the temperature control unit 22 compares the temperature of the furnace body 17 detected as described above with a predetermined temperature program, and calculates a temperature difference between them. When this calculated value is positive (that is, the temperature program is higher), the temperature control unit 22 calculates a control amount in accordance with PID control in step S4, and further, in step S5, the control amount is calculated as a duty ratio calculation unit in FIG. Send to 25.

  The duty ratio calculation unit 25 receives the control amount sent from the temperature control unit 22 and detects the voltage of the AC power supply 30 in FIG. 1 (that is, the primary power supply voltage) using the voltmeter 40 in step S7 in FIG. The coefficient value is calculated in step S8 based on the detected voltage value. Next, the duty ratio calculation unit 25 multiplies the control amount for PID control sent from the temperature control unit 22 by a coefficient value in step S6 to determine the duty ratio D0.

  Thereafter, based on the determined duty ratio D0, PWM control is executed by the PWM control unit 6 of FIG. 1 in step S9. And the voltage after control is output from the PWM control part 6 in step S10. Thereby, the temperature of the furnace body 17 rises according to the temperature program.

(Effect of embodiment)
(1) When the conventional temperature control method of the phase control method is applied to the furnace body 17 in FIG. 1, when voltage fluctuation or waveform distortion occurs in the power supply voltage waveform as shown in FIG. As shown in FIG. 10D, the amplitude and waveform of the phase control voltage waveform vary, and the temperature control by the heater 18 cannot be performed accurately.

  Further, as shown in FIG. 11C, if noise enters near the zero cross, a malfunction occurs at the ON timing, and the ON period in the phase control voltage waveform varies as shown in FIG. 11D. And temperature control by the heater may not be performed accurately. Further, as shown in FIG. 12C, a high-frequency current periodically flows at the rise of the ON period, which may adversely affect the peripheral circuits.

  In the present embodiment shown in FIG. 2 for the phase control method as described above, the pulse signal P1 is sent to the MOSFET 33, so that the rectified waveform voltage E2 after rectification is shown in FIG. The output voltage E4 was formed by applying smooth pulse width modulation and further smoothing as shown in FIG. The output voltage E4 was supplied to the heater 17. Therefore, even when the power supply voltage waveform varies as shown in FIG. 6A, when performing power control, each pulse is shown as shown in (b), (c), and (d). No change in the overall shape of the voltage waveform is caused only by the change in the duty ratio at, and therefore no fluctuation occurs in the secondary side voltage output due to fluctuations in the power supply on the primary side.

(2) Further, in the present embodiment shown in FIG. 2, a small-capacitance capacitor is used as the capacitor 32 for preventing harmonics from being applied to the voltage after rectification by the rectifier circuit 31. According to conventional general methods, large-capacity electrolytic capacitors are often used instead of small-capacitance capacitors for the purpose of smoothing. However, the electrolytic capacitor has a short life under a high temperature environment, and thus the life of the PWM converter 28 has to be shortened.

  If it is a small capacity capacitor, a film capacitor can be used. Considering that the film capacitor has a long life, according to the present embodiment using a small-capacitance capacitor, it is possible to extend the life of the PWM converter 28 and thus the thermal analyzer 1. For example, according to the present embodiment, it is possible to easily obtain a life of 50,000 hours or more. In addition, the use of a small-capacitance capacitor can prevent the generation of harmonic currents and inrush currents that were generated when a large-capacity electrolytic capacitor was used.

(3) Further, in the conventional phase control method, as shown in FIG. 12C, there is a possibility that harmonic current flows in synchronization with the power supply voltage in response to the rise of the voltage waveform after phase control. . There are public regulations on harmonic currents. For example, according to the regulation of IEC61000-3-2, the maximum harmonic current that can be passed is regulated to be equal to or less than a predetermined regulation value. In the present embodiment based on the PWM control shown in FIG. 2, the sharp rise of the voltage waveform as seen in the phase control method does not occur, so the generation of harmonic current is greatly reduced. . Therefore, in the present embodiment, it is possible to easily cope with harmonic regulation (for example, IEC61000-3-2).

(4) Further, according to the PWM converter 28 of the present embodiment shown in FIG. 2, the pulse width modulation by the MOSFET 33 is not performed directly on the AC power supply 30, but after the rectification processing is performed by the rectification circuit 31. The DC voltage (in this embodiment, a full-wave rectified waveform voltage) is used. When directly performing pulse width modulation on the AC power supply 30, it is necessary to use a plurality of switching elements such as transistors, and a complicated control circuit must be prepared to control the operation of these switching elements. did not become. On the other hand, according to the present embodiment in which pulse width modulation is performed on a voltage waveform subjected to rectification processing, one transistor as a switching element is sufficient, and therefore the operation of the switching element is controlled. The circuit to do can be formed very easily. Therefore, the PWM converter 28 of the present embodiment and the furnace body temperature control apparatus (a combination of 19, 22, 25, 6 and 18 in FIG. 1) and the thermal analysis apparatus 1 using the PWM converter 28 of the present embodiment are cost-effective. Very good.

(Other embodiments)
The present invention has been described with reference to the preferred embodiments. However, the present invention is not limited to the embodiments, and various modifications can be made within the scope of the invention described in the claims.

  For example, the present invention can be applied not only to a thermal analysis apparatus but also to a furnace body temperature control apparatus for an arbitrary apparatus other than the thermal analysis apparatus.

  In the above embodiment, as shown in FIG. 1, the present invention is applied to the temperature control device that performs PID control in the temperature control unit. However, the present invention is not limited to the temperature control unit based on any method other than PID control. It is also applicable to a device that uses

  In the above embodiment, the furnace body temperature control apparatus of the present invention is applied to the TG-DTA apparatus, but the present invention is applicable to any other thermal analysis apparatus. Examples of such a thermal analysis device include a TG device, a DTA device, a DSC (Differential Scanning Calorimetry) device, and the like.

  In the above embodiment, the present invention is applied to the thermal analysis apparatus. However, the furnace body temperature control apparatus according to the present invention is applied to a furnace body used in any apparatus other than the thermal analysis apparatus. It is possible.

  1. 1. Thermal analysis device 2. a first balance device; A second balance device; 4. Electric furnace, 5. Control device, 6. 8. PWM control unit, Thermocouple, 10a, 10b. Temperature measuring points, 11a, 11b. Fulcrum, 12a, 12b. Balance bar, 13a, 13b. Sample pan, 14a, 14b. 16. variation detector; Furnace body, 18. Heater, 19. Temperature sensor, 22. Temperature controller, 23. Differential heat measurement section, 24. Weight measuring section, 25. Duty ratio calculation unit, 28. PWM converter, 29. 30. PWM pulse generator, AC power supply 31. Rectifier circuit, 32. First capacitor, 33. MOSFET (switching element), 34. Diode, 35. Coil, 36. Second capacitor, 39. Diode, 40. Voltmeter, R. Reference substance, S. Measurement sample

Claims (9)

A temperature control device for a furnace body for controlling the temperature of the furnace body for an analyzer,
A rectifier circuit connected to an AC power source;
A PWM circuit for pulse-width modulating the output of the rectifier circuit according to a duty ratio;
A heater for receiving the output voltage of the PWM circuit and generating heat to heat the furnace body,
The temperature control device for a furnace body for an analyzer, wherein an envelope of a rectified voltage that is an output voltage of the rectifier circuit remains in the voltage supplied to the heater.   The temperature control device for a furnace for an analyzer according to claim 1, wherein a pulse width modulation waveform remains in the voltage supplied to the heater. Furnace body temperature detecting means for detecting the temperature of the furnace body;
A temperature control unit that determines a control amount for the power supplied to the heater based on a detection result of the heater temperature detection unit;
Duty ratio calculating means for determining the duty ratio by calculation based on a control amount determined by the temperature control unit;
The temperature control device for a furnace body for an analyzer according to claim 1 or 2, characterized by comprising:   4. The analysis according to claim 3, wherein the duty ratio calculation means uses a power supply voltage entering the rectifier circuit as a determination factor in determining the duty ratio in addition to the control amount determined by the temperature control unit. Equipment furnace temperature control device.   The temperature control device for a furnace body for an analyzer according to claim 4, wherein the duty ratio calculation means uses the peak value of the power supply voltage entering the rectifier circuit as the determination factor.   6. The capacitor according to claim 1, further comprising a capacitor for removing a harmonic component from the output voltage of the PWM circuit and having a capacitance of 100 μF or less. The temperature control apparatus of the furnace body for analyzers as described.   The temperature control device for a furnace body for an analyzer according to any one of claims 1 to 6, wherein the rectifier circuit performs full-wave rectification on the voltage of the AC power supply.   The temperature control device for a furnace for an analyzer according to claim 3, wherein the temperature control unit determines the control amount based on PID control. A furnace body for heating the sample;
A heater for heating the furnace body;
In the thermal analyzer having a furnace body temperature control device for controlling the temperature of the furnace body,
9. The thermal analysis apparatus according to claim 1, wherein the temperature control device for a furnace body for an analysis apparatus is the temperature control apparatus for a furnace body for an analysis apparatus according to any one of claims 1 to 8.

Images