JPS6135113A - Leakage detector of high temperature furnace - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an earth leakage detection device for a high-temperature furnace, which is suitable for application to a firing furnace for materials such as ceramics, a vacuum high-temperature furnace, and the like.

[Prior art]

Carbon Cool is used as an insulator for high-temperature furnaces where the temperature inside the furnace reaches 2000°C or higher. In this case, since carbon wool is a good conductor and there is no insulating material that can be used at temperatures above 2000° C., an insulating space is provided between the carbon wool and the heater. This space exhibits an almost infinite resistance value in the low temperature range.

[Problem that the invention seeks to solve]

By the way, as the temperature of the insulating space rises, the current due to thermionic radiation and the ionic current generated by collision with thermionic electrons increase, and when the temperature exceeds 1800°C, these leakage currents increase rapidly, and finally There is a problem in that a discharge phenomenon occurs and damages the heater, heat insulating material, etc.

This invention attempts to solve the above problems.

[Means for solving problems]

In order to solve the above problems, the present invention calculates the actual load resistance value including the heater by dividing the output voltage of the transformer that supplies current to the heater by the output current, and uses this resistance value as the reference value. The gist is to determine the magnitude of leakage current by comparing it with the value and output an alarm. Further, the present invention is characterized in that the reference value is changed depending on the temperature inside the furnace to perform more appropriate leakage detection.

[Effect]

In the above configuration, the output voltage of the transformer is V, the output current is T, and the actual resistance value of the heater is R1.The value of the resistance (leakage resistance) corresponding to the leakage current is Ra. , Ra are connected in parallel (see Figure 1), so the combined resistance value r of these is connected to the output terminal of the transformer, and the following holds true. Then, when the temperature inside the furnace is not very high, Ra-→ω may be set, so r = R...
・・・・・・・・・River・・・・・・・・・・・・ (2)
Therefore, the combined resistance value r matches the heater resistance value R. Here, as shown in Figure 2, the resistance value R of graphite heaters widely used in high-temperature resistance heating furnaces increases approximately linearly above a certain temperature, so the combined resistance value r also increases approximately linearly. Rise.

By the way, when the temperature inside the furnace rises, the leakage resistance value Ra gradually decreases due to thermionic current and ion flow, and rapidly decreases immediately before discharge. Therefore, the combined resistance value r also decreases rapidly, and when this value becomes smaller than the reference value C (
r (at the time of c), the W signal is output, and it is possible to prevent damage to the heater and the heat insulating material due to discharge.

In this case, the methods for setting the reference value include (1) the first method in which a predetermined constant value 01 is used as the reference value (see Figure 3), and (2) a value that changes depending on the furnace temperature (e.g. There is a second method (see FIG. 4) in which c2 (a value that increases linearly depending on the furnace temperature) is used as a reference value. That is, when the degree of vacuum in the furnace is low or when there is atmospheric gas, the leakage resistance value Ras and hence the combined resistance value r decrease rapidly, so that the first method described above cannot sufficiently detect the leakage resistance. However, in the case of a high vacuum, although the thermionic current is large, there are few gas molecules, so the leakage resistance value R1 and the combined resistance value r decrease slowly and cannot be detected by the first method. Therefore, the objective is achieved by a second method of changing the reference value according to the temperature inside the furnace. In this way, by properly using the eleventh and second methods depending on the manner in which the furnace is used, reliable leakage detection can be performed.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an emergency embodiment of the present invention. In this figure, reference numeral 1 indicates a transformer, and a heater 2 (resistance value R) is connected to the output side (secondary side) of the transformer. This heater 2 has a leakage resistance 3 (resistance value Ra) corresponding to the leakage current caused by thermionic current or ion flow, and is in the form of a parallel IJ.If the current flowing through the heater 2 is 11, the transformer The current ■ flowing out from l is r = r, 10r, ・・・・・・・・・・・・・・・
...(3). This output current is detected by a current transformer 4, and then converted by a current converter 5 to a value suitable for a subsequent electronic circuit. The output voltage V of the transformer 1, which has been converted into an appropriate value by the voltage converter 6, is then supplied to the divider 7, where the calculation of V÷min is performed, and the combined resistance shown in equation (1) is The value r is determined. In this way, the combined resistance value r output from the divider 7 is supplied to the comparators 8 and 9, and compared with the reference values CI and 02, respectively. Here, the reference value C1 is a constant value, the reference value 02
is a value that increases with temperature at a constant slope a, and the reference value C2 is a value that is determined by the function generator 11 based on the furnace temperature signal lO.
is formed and supplied to the comparator 9. Then, the combined resistance value r
When δ becomes smaller than the reference value C1, the comparator 8
When the value becomes smaller than 2, the comparator 9 outputs the OR gate 1.
2, the alarm 13 is activated and sounds.

In such a configuration, when the temperature inside the furnace rises and the leakage resistance value R8 suddenly decreases, the output current of the transformer 1 increases rapidly, and the combined resistance value r suddenly decreases (Fig. 3, 4
(see figure). As already mentioned, when the degree of vacuum in the furnace is high, the comparator 9 detects r(c2 and the alarm 1
On the other hand, if the degree of vacuum in the furnace is low or there is atmospheric gas, the comparator 8 detects r (01 and alarm 1
Start 3. As a result, an alarm is output from the alarm 13, and the output voltage V of the transformer l is automatically or manually set.
Measures can be taken to rapidly reduce the output voltage or cut off the output current, thereby preventing damage to the beater and insulation material due to discharge.

〔Effect of the invention〕

As explained above, in this invention, the output voltage of the transformer that supplies current to the furnace heater is divided by its output current, and an alarm is issued when this value deviates from the reference value. Damage to the heater and heat insulating material due to discharge can be prevented.

Particularly, by changing the above reference value depending on the temperature inside the furnace, it becomes possible to perform accurate leakage detection even in a high-temperature furnace with a high degree of vacuum.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention;
Figure 2 is a graph showing the relationship between the temperature and resistance value of a graphite heater, and Figure 3 is a graph showing the relationship between the combined resistance value r and the furnace temperature when the degree of vacuum in the furnace is low or there is atmospheric gas, and the standard. A graph showing the value cl, Figure 4 shows the relationship between the combined resistance value r and the furnace temperature when the degree of vacuum in the furnace is high, and the reference value C2
This is a graph showing. l...Transformer, 2...Heater, 3...Leakage resistance,
4... Current transformer, 5-2. Current converter (4 and 5 above are current detection means), 6... Voltage converter (voltage detection means),
7... Divider (calculation means), 8, 9... Comparator (comparison means), 11... Function generator (reference value generation means),
13...Alarm, Ql, 02...Reference value.

Claims (2)

[Claims] (1) In a high-temperature furnace comprising a heater installed in the furnace and a transformer that supplies current to the heater, current detection means for detecting the current flowing out from the transformer; The present invention is characterized by comprising voltage detection means for detecting an output voltage, calculation means for dividing the output voltage by the current, and comparison means for activating an alarm circuit when the division result deviates from a reference value. Earth leakage detection device for high temperature furnaces. (2) The high-temperature furnace according to claim 1, further comprising a reference value generation means for forming the reference value based on the temperature of the high-temperature furnace and supplying the reference value to the comparison means. Earth leakage detection device.