JPH09287881A - Temperature control method of heating furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature control method of a heating furnace capable of raising the temperature of a furnace by eliminating the cycling of the temperature, and maximizing the charged heat input without operating an alarm setting device to shut off the energization to an electric heat generating body as much as possible to rapidly and smoothly change the temperature as much as possible. SOLUTION: When the temperature of an electric heating furnace 3 of relatively low responsiveness such as a muffle furnace is raised, the control signal CS2 by the measured temperature in the furnace 3 is compared with the control signal CS1 by the measured temperature of an electric heat generating body 1, a low signal selector 7 selects the CS1 or CS2 , whichever is smaller, and the process value to determine the control signal of a power adjuster 5 is automatically switched to eliminate the power disconnection of TIA due to overheating in the conventional temperature rise and the cycling of the temperature accompanied thereby.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a temperature control method for an electric resistance type or lamp type heating furnace, and more particularly to a temperature at the time of heating in an electric heating furnace having a relatively low response such as a muffle furnace. In the control, the control signal by the temperature measurement of the furnace temperature,
By comparing the control signals obtained by measuring the temperature of the electric heating element and automatically switching the process value that determines the control signal of the electric heating element, the current interruption due to overheating at the time of heating is eliminated and the heating time is increased. The present invention relates to a heating furnace temperature control method that can be shortened.

[0002]

2. Description of the Related Art In a vacuum furnace or a furnace for heating a special gas, the temperature inside the furnace is controlled as shown in FIG. 2 by setting the electric heating element 1 of the heating source so as not to affect the atmosphere or the medium to be heated. The heating source container 2 which is the first container is sealed, the heating source container 2 is installed inside the second container, that is, the heating furnace 3, and the internal temperature of the heating furnace 3 is kept constant at a predetermined temperature. In general, the controller TIC outputs a temperature control signal to the power controller 5 according to the internal temperature of the heating furnace 3 measured by the thermometer 4 to control the amount of electricity supplied to the electric heating element 1. .

In such a heating furnace, when the temperature inside the furnace is rising or has risen to a predetermined temperature, the outer surface of the heating source container 2 has reached a temperature higher than the position of the thermometer 4, that is, the temperature inside the furnace 3, The temperature of the electric heating element 1 in the heating source container 2 is even higher. For this reason, there is a risk that the temperature of the electric heating element 1 or the heating source container 2 will rise above the allowable value. In order to avoid this danger, when the temperature of the electric heating element 1 is detected by the thermometer 6 and reaches a predetermined temperature, a signal is issued from the alarm setter TIA to forcibly cut off the power supply to the heating element 1. The method has been adopted.

[0004]

However, even if the power supply is cut off by the alarm setter TIA, the temperature of the electric heating element 1 has a significantly larger heat capacity than the medium in the heating source container 2, and in general, the heat of the medium is high. Since the conductivity is low, the heat of the electric heating element 1 is continuously released, and the surface temperatures of the medium and the heating source container 2 continue to rise for a while.

For this reason, the temperature inside the heating furnace 3 rises following it, so that the signal output of the controller TIC drops significantly, but during this period, the temperature of the electric heating element 1 continues to drop,
When the temperature falls below the operating point of the alarm setter TIA, the detection end temperature of the alarm setter TIA reaches a predetermined lower limit temperature.

However, since the temperature of the electric heating element 1 is lower than the required temperature at this point in time, even if the alarm signal output of the alarm setting device TIA is canceled and the power supply is resumed, it is necessary to recover the required temperature. Takes time. During this period, the surface temperature of the heating source container 2 continues to further decrease, and the temperature in the heating furnace 3 begins to decrease, but the regulator TIC generally has an integral element, so the set output is not immediately increased. For this reason, it is inevitable that it takes a long time for the temperatures of the electric heating element 1 and the heating source container 2 to recover to the predetermined values.

Such a situation is repeated, and the frequent ON / OFF of the alarm setting device TIA and the cycling of the temperature in the heating furnace 3 are inevitable, and the heating time of the electric heating element 1 becomes discontinuous. Therefore, the average amount of heat supplied decreases, and the time required to raise the temperature inside the heating furnace 3 to a predetermined temperature must be extended. In addition, it is indispensable to raise the temperature in the heating furnace 3 as quickly as possible, and the frequent operation of the alarm setting device TIA and the cycling of the controller TIC cause various problems. Therefore, it is desirable to avoid this.

According to the present invention, in the method of controlling the temperature of the heating furnace, the alarm setting device for interrupting the electric power supply to the electric heating element is not operated as much as possible, the temperature cycling is eliminated, and the amount of heat input is maximized so that It is an object of the present invention to provide a temperature control method capable of raising the temperature of a furnace by a smooth temperature change.

[0009]

[Means for Solving the Problems] In the temperature control at the time of raising the temperature of an electric heating furnace having a relatively low response such as a muffle furnace, the inventors have tried not to operate the alarm setting device as much as possible and maximize the input heat amount. As a result of various studies aimed at possible methods, when outputting the temperature control signal to the power regulator, the control signal for measuring the temperature inside the furnace and the control signal for measuring the temperature of the electric heating element were compared and By automatically selecting the smaller output signal, the power can be adjusted before the alarm setter is activated, the power interruption due to overheating during temperature rise can be eliminated, and the amount of heat can be continuously input. The inventors have completed the present invention by finding that the temperature rising time can be shortened.

That is, according to the present invention, the electric heating element is housed in the furnace, the amount of heat generation can be adjusted by the power regulator, and the interruption means for interrupting the electric power to the heating element when the overheating temperature is detected. In a temperature control method of a heating furnace, which measures the temperature of the inside of an electric heating furnace or a passing medium temperature and outputs a temperature control signal for setting the temperature to a predetermined temperature to a power regulator, The temperature control signal of the first control system is compared with the temperature control signal of the second control system, which outputs the temperature control signal to the power regulator in order to set the temperature of the electric heating element or its vicinity to a predetermined temperature, and outputs the smaller one. This is a temperature control method for a heating furnace in which the amount of electric power to the electric heating element is determined by a signal.

[0011]

1 is an explanatory diagram showing an example of a control circuit for carrying out a temperature control method for a heating furnace according to the present invention. A heating source container 2 accommodating the electric heating element 1 is arranged in the heating furnace 3, and the temperature inside the heating furnace 3 is measured by a thermometer 4 and adjusted by a temperature controller TIC _{1 in the} furnace to bring it to a predetermined temperature. The output CS ₁ is output to the power conditioner 5, and here, the low signal selector 7 is provided between the output CS ₁ and the power conditioner 5.

A thermometer 6 for detecting the temperature in the heating source container 2
Outputs a temperature signal to the alarm setting device TIA and the heating source container temperature controller TIC ₂ , and when the alarm setting device TIA detects a predetermined upper limit temperature, it shuts off the power from the power regulator 5 to generate the heating source container temperature. The controller TIC ₂ outputs the control output CS ₂ to the low signal selector 7 in order to bring the temperature inside the heating source container 2 to a predetermined temperature.
It is configured to output to the power regulator 5 via the.

In the above structure, the temperature controller TI in the furnace
C ₁ , heating source container temperature controller TIC ₂ , alarm setting device TI
Assuming that the set temperatures of A are t ₁ ℃, t ₂ ℃, and t ₃ ℃, respectively, the furnace temperature controller TIC ₁ is
The signal input of the thermometer 4 inside is compared with the set value t ₁ to output the control output CS ₁ , and the heating source container temperature controller TIC ₂ is
The signal input of the thermometer 6 in the heating source container 2 is compared with the set temperature t ₂ to output the control output CS ₂ .

On the other hand, the low signal selector 7 compares the input control outputs CS ₁ and CS ₂ and outputs the smaller signal as it is to the power regulator 5. When the temperature measured by the thermometer 4 in the heating furnace 3 and the temperature measured by the thermometer 6 in the heating source container 2 are set to t _1p ℃ and t _2p ℃, respectively, by the setting of the temperature controller used and the automatic learning function, etc. Is t
CS ₁ and C are calculated according to the absolute value of the difference between _1p −t ₁ and t _2p −t _2.
Since the magnitude relationship with S ₂ may not be determined in some cases, it is desirable to select the condition setting or the like so that the low signal selector 7 performs the above-mentioned function.

The alarm setter TIA monitors the signal of the thermometer 6 in the heating source container 2, and outputs an alarm signal when the set temperature t ₃ is exceeded, and the power regulator 5 supplies power to the electric heating element 1. Shut off forcibly. Here, the set temperature, for example, the set temperature t ₃ of the alarm setter TIA is set to be several tens of degrees higher than the set temperature t ₂ of the temperature controller TIC ₂ in the heating source container,
Further, the set temperature t ₂ is set to a temperature higher than the set temperature t ₁ of the in-furnace temperature controller TIC ₁ by several 100 ° C.

The temperature control method according to the present invention comprises a heating furnace 3
A particularly remarkable effect is exhibited when the internal temperature is raised from room temperature to a predetermined high temperature. When the temperature in the heating furnace 3 is low, the atmospheres in the furnace temperature gauge 4 and the thermometer 6 in the heating source container 2 are also low, and when heating is started here, the furnace temperature controller TI
Since both C ₁ and the heating source container temperature controller TIC ₂ have large temperature deviations from the set temperature, both the control outputs CS ₁ and CS ₂ have the maximum output to the power controller 5.

Then, within a short time, the temperature inside the heating source container 2 rises, the deviation between the signal input of the thermometer 6 and the set temperature t ₂ rapidly decreases, and the temperature controller inside the heating source container TIC ₂ The control output CS ₂ of No. ₁ starts to decrease and tries to control the temperature inside the heating source container 2 to a predetermined temperature. When this control is insufficient and overruns, the set temperature t ₃ is exceeded and forced power cutoff occurs, but the values of the set temperatures t ₁ and t ₃ are selected, and P of the heating source container temperature controller TIC ₂ is set. The alarm setting device TIA is not activated by appropriately setting the I, C elements.

In this way, the temperature in the heating source container 2
That is, the temperature of the electric heating element 1 can always be maintained at the set temperature t ₂ . This control output CS ₂ is not affected by the in-furnace thermometer 4 at all, but in order to optimize the set temperature, the signal level of the control output CS ₂ from the heating source container temperature controller TIC ₂ is almost the same. Is kept constant.

On the other hand, as the temperature of the thermometer 4 in the heating furnace 3 approaches the set temperature t ₁ of the furnace temperature controller TIC ₁ , the control output CS ₁ decreases. If the control output CS ₂ becomes larger than the control output CS ₁ , the control output CS ₂
When the input of the electric heating element 1 is continuously controlled by, the thermometer 4 in the heating furnace 3 overshoots. Therefore, when the control output CS ₁ is below the control output CS ₂ , The temperature must be reduced. As described above, the low signal selector 7 selects the smaller _{one of} the control outputs CS ₁ and CS ₂ to control the electric power of the electric heating element 1, so that the temperature rise in the heating furnace 3 in the optimum shortest time is increased. Can be achieved.

In the above example, the case where the temperature inside the furnace of the closed heating furnace is raised is shown.
The present invention can be applied to various known heating furnaces for heating a gas or a material arranged in the furnace, in addition to a heating furnace through which a gas of the embodiment passes, such as a halogen lamp. The method shows a remarkable effect even in the case of a stepwise temperature increase in which the temperature is raised and held for a certain period of time and further raised, and the above-mentioned control circuit can be applied to control for keeping a constant temperature. It is also possible to use a control method for keeping the heat of.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The heating furnace temperature control method according to the present invention using the heating furnace control circuit shown in FIG. 1 is equivalent to the conventional heating furnace temperature control method using the heating furnace control circuit shown in FIG. It carried out on the same conditions using the electric heater of the output. Atmosphere gas was passed through the heating furnace at a predetermined speed, and in order to maintain the temperature of this gas at 350 ° C., the two types of heating furnaces described above were simultaneously heated from room temperature to 350 ° C.

The conventional heating furnace temperature control method is 350 ° C.
It took about 7 hours to raise the temperature up to, but in the temperature control method of the heating furnace according to the present invention, the required time is about 5 hours and about 3 hours.
It was possible to shorten by 0%.

[0023]

As described in the embodiments, the present invention provides a control signal for measuring the temperature inside the furnace and an electric heating element in the temperature control when raising the temperature of an electric heating furnace having a relatively low response such as a muffle furnace. By comparing the control signal based on the temperature measurement and automatically switching the process value that determines the control signal for the electric heater, it is possible to eliminate the current interruption due to overheating during temperature rise and the accompanying temperature cycling. By maximizing the amount of heat input from the electric heater, there is an advantage that the temperature can be raised smoothly and quickly and the temperature rise time can be greatly shortened.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a control circuit for carrying out a heating furnace temperature control method according to the present invention.

FIG. 2 is an explanatory view showing an example of a control circuit for carrying out a conventional heating furnace temperature control method.

[Explanation of symbols]

1 electric heating element 2 heating source container 3 heating furnace 4,6 thermometer 5 power regulator 7 low signal selector TIA alarm setting device TIC controller TIC ₁ furnace temperature controller TIC ₂ heating source container temperature controller

Claims (2)

[Claims] 1. An electric heating furnace comprising an electric heating element housed in a furnace, the amount of heat generation of which can be adjusted by an electric power regulator, and interruption means for interrupting energization to the heating element when an overheating temperature is detected. In a temperature control method for a heating furnace, which measures a temperature of a medium in a furnace or a passing medium and outputs a temperature control signal for setting the temperature to a predetermined temperature to a power regulator, a first method for controlling the temperature in the furnace
The temperature control signal of the control system is compared with the temperature control signal of the second control system, which outputs the temperature control signal to the power regulator to set the temperature of the electric heating element or its vicinity to a predetermined temperature, and the smaller output signal A method for controlling the temperature of a heating furnace that determines the amount of electric power to the electric heating element. 2. The temperature control method for a heating furnace according to claim 1, wherein the electric heating element is housed in a closed container, and the temperature inside the closed container is a control target of the second control system.