JPH0221760Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a furnace temperature control device for controlling the temperature of a furnace used when heat treating metals and the like.

[Prior Art] Conventionally, furnaces have been frequently used when heat treating metals and the like. Furnace temperature control devices that detect the temperature inside the furnace and control the temperature by feeding back the detection result to the heat generation source of the furnace are widely used in order to perform heat treatment using the furnace with higher accuracy.

Among the furnace temperature control devices mentioned above, those that use thermocouples as a means of detecting the temperature inside the furnace have high detection accuracy despite their low cost, and since the detection output is an electrical signal, the signal processing is accurate. It is widely used in various fields because it has the advantage of being easy to implement.

[Problems to be Solved by the Invention] However, the furnace temperature control device using the above-mentioned thermocouple has the following problems at the same time, and is still not satisfactory.

That is, a thermocouple measures the temperature of a hot junction by detecting a thermoelectromotive force generated due to a temperature difference between a cold junction that provides a reference temperature and a hot junction that provides a temperature at a measurement point. In other words, the temperature inside the furnace is not detected absolutely, but only the relative detection of the temperature difference with the cold junction is performed.

Therefore, thermometers using thermocouples are used with the positive direction defined as the direction in which a positive electromotive force is generated in proportion to the temperature difference when the hot junction is at a higher temperature than the cold junction. The control system that processes the thermocouple output also inputs the positive voltage value to determine that the temperature of the hot junction has risen to the temperature corresponding to the voltage value relative to the cold junction. That's what I do. Therefore, in a furnace temperature control device using such a thermocouple, when the user sets a certain positive voltage as the desired furnace temperature value, the set voltage is compared with the thermocouple output voltage, and the thermocouple is still detected. A basic configuration is adopted in which the capacity of the heat source of the furnace is increased if the output voltage of the pair is low, and the capacity of the heat source is maintained when the two comparison voltage values match.

Due to the above configuration, if the user accidentally connects the output terminal of the thermocouple to the processing device in the opposite direction, the output voltage of the thermocouple will be reversed in polarity and will be applied to the processing device. . In other words, the processing device controls the heat source of the furnace by comparing the positive reference voltage set by the user with the negative voltage detection output from the thermocouple, and how to increase the capacity of the heat source. Furthermore, the thermocouple output only becomes a large negative voltage value, and the two comparison voltages do not match, further increasing the amount of heat generated. If such a condition were left untreated, there was a risk that not only the object to be heat treated would be thermally destroyed, but also the furnace would be destroyed.

Moreover, since the furnace temperature control device is automatic, the user often leaves the area after setting the furnace temperature, and it takes a considerable amount of time to recognize the above-mentioned incorrect connection and take measures. Thermocouple connections required careful attention.

[Purpose of the invention] The present invention was made to solve the above problems. Even if a thermocouple is mistakenly connected in the opposite direction, the furnace temperature control device automatically detects the incorrect connection and performs the heat treatment. The purpose is to provide an excellent furnace temperature control device that can protect the objects to be treated and the furnace itself from destruction.

[Means for Solving the Problems] The configuration of the present invention to achieve the above object is as follows: The temperature inside the furnace is detected using a thermocouple, and the temperature inside the furnace is controlled based on the output of the thermocouple. In the furnace temperature control device, the output of the thermocouple is compared with a predetermined reference voltage of less than zero volts, and when the output is less than the predetermined reference voltage, control of the temperature in the furnace is stopped. The gist is a furnace temperature control device that is characterized by:

[Function] The thermocouple of the present invention may be any thermocouple type thermometer, regardless of the type or combination of metal wires used.

In addition, a predetermined reference voltage of less than zero volts is based on a comprehensive judgment of the detection output characteristics of the thermocouple used, the heat resistance strength of the object to be heat treated, the heat resistance of the furnace itself, and the ability of the heat source. It is determined. In other words, if the thermocouple is connected in reverse, and the furnace temperature is estimated from the negative voltage value output at that time, the negative voltage value is still small enough to not cause destruction of the heated object or the furnace. , and the value is larger than the negative voltage that might be output even if the thermocouple was connected normally before the heat source of the furnace is activated.

Compared to the reference voltage determined as above,
Stopping the control of the temperature inside the furnace, which is executed when the thermocouple output is below the reference voltage, means stopping the control that increases the output to the heat source of the furnace from at least that point, and the furnace temperature The temperature may be maintained from that point on, or the operation of all heat generating sources may be stopped to bring the temperature to room temperature.

Hereinafter, in order to explain the present invention more specifically, the present invention will be described in detail with reference to examples.

[Embodiment] FIG. 1 is a circuit block diagram of a system using a furnace temperature control device which is an embodiment of the present invention.

In the figure, 1 is the furnace, 2 is the heat source of the furnace 1, and 3 is the furnace.
represents the furnace temperature control device. The furnace temperature control device 3 includes a thermocouple 31, a comparison section 32 that compares the output of the thermocouple 31 with a negative reference voltage, and when the user sets a desired furnace temperature, the temperature in the furnace matches the set temperature. It is composed of three parts: a temperature controller 33 that controls the heat source 2 so as to

The thermocouple 31 has the output characteristics shown in FIG.
1B is connected to the input terminal of the comparing section 32.

The comparator 32 is mainly composed of two operational amplifiers (hereinafter referred to as OP amplifiers) A1 and A2, a transistor TR, and a relay R, and receives the input signal of the thermocouple 31 in a high impedance state. , compare whether it is below the negative reference voltage or not, and when the output voltage of the thermocouple 31 is below the reference voltage, stop the operation of the relay R and cut off the power supply to the temperature controller 33. Operate.
The OP amplifier A1 performs impedance conversion, and constitutes an impedance converter by inputting the positive voltage output terminal of the thermocouple 31 to its non-inverting input terminal and feeding back the output to its inverting input terminal. The output voltage of the thermocouple 31 thus inputted is inputted to the non-inverting input terminal of a comparator constituted by the next-stage OP amplifier A2.
Further, a negative voltage that is appropriately adjusted by a variable resistor 32A for setting a reference voltage is input to the inverting input terminal of the OP amplifier A2. Point P in Figure 2 is this
It shows the negative voltage input to the inverting input terminal of OP amplifier A2. As shown, point P is approximately -
The voltage is about 5 mV, and at this time the temperature difference between the cold junction and the hot junction is about -100°C. This OP amp A
2, when the output voltage of the thermocouple 31 is lower than the potential at point P, that is, when it becomes -5 mV or less, the power supply to the base of the transistor TR is stopped, the transistor TR is turned OFF, and the power is supplied to the relay R. By cutting off the , the contacts of relay R are opened. The contacts of relay R are connected to temperature controller 33 as shown in the diagram.
When the contact point of relay R is opened, the power supply to the temperature controller 33 is stopped and it becomes inoperable, the heat generating part 2 stops generating heat, and the furnace returns to normal temperature.

Under normal circumstances, the furnace temperature will never drop below -100°C, and relay R will always be in the ON state. Therefore, the temperature controller 33 inputs a comparison voltage corresponding to a predetermined temperature set by the user from the variable resistor 33A. For example, in FIG. 2, if the user desires 600°C,
Input the positive voltage S by adjusting the variable resistor 33A,
This voltage S is compared with the output voltage of the thermocouple 31, and if the output of the thermocouple 31 is smaller than S, the capacity of the heat source is increased, and conversely, if the output of the thermocouple 31 is greater than S, the capacity of the heat source is set to be lowered. It operates to maintain a temperature of 600℃.

As described above, according to the furnace temperature control device 3 of this embodiment, if the output terminal of the thermocouple 31 is connected normally, the thermocouple 31 outputs a voltage equal to or lower than the negative potential P, i.e. It is virtually impossible for the furnace temperature to drop below -100°C, so the relay R operates and the temperature regulator 33 normally controls the furnace temperature using the comparison voltage S as a reference. On the other hand, if the user accidentally connects the output terminal of the thermocouple 31 in the opposite direction, first, if the furnace temperature is near normal temperature, the relay R is activated and the heat source 2 is activated by the temperature controller 33. The temperature begins to rise. However, thermocouple 3
1 is connected in the opposite direction, so it outputs an apparently negative voltage to the comparator 32 as the furnace temperature rises. The absolute value of that voltage is shown in Figure 2.
When P'(P'=|P|), the comparator 32 stops supplying power to the relay R and stops the operation of the temperature controller 33 and the heat source 2.

As a result, an abnormal rise in the furnace temperature due to incorrect connection of the thermocouple 31 can be avoided, and there is no risk of damage to the heated object and the furnace itself due to heat.

[Effects of the invention] As described above in detail with reference to the embodiments, the furnace temperature control device of the invention compares the output of the thermocouple with a reference voltage of less than zero volts, and when the output is lower than the reference voltage, the furnace temperature control device This feature is characterized by discontinuing temperature control.

Therefore, if the thermocouple is connected correctly, it will operate without any problems as a normal furnace temperature control device, and even if the thermocouple 31 is connected in the opposite way, the furnace temperature will still rise to some extent. This is an excellent furnace temperature control device that automatically detects misconnection of thermocouples at an early stage, stops the furnace temperature from rising, and prevents the heated material and the furnace itself from thermal damage.

[Brief explanation of drawings]

FIG. 1 is a system circuit block diagram using a furnace temperature control device which is an embodiment of the present invention, and FIG. 2 is a graph showing the output characteristics of the thermocouple. DESCRIPTION OF SYMBOLS 1...furnace, 2...heat source, 3...furnace temperature control device, 31...thermocouple, 32...comparison section, 33...
Temperature controller.

Claims (1)

[Claims for Utility Model Registration] A furnace temperature control device that detects the temperature inside the furnace using a thermocouple and controls the temperature inside the furnace based on the output of the thermocouple, the output of the thermocouple being set to zero. A furnace temperature control device, characterized in that it is configured to stop controlling the temperature in the furnace when the output is below a predetermined reference voltage compared to a predetermined reference voltage of less than volts.