DE562536C - Device for monitoring the temperature of ovens - Google Patents

Description

GERMAN EMPIRE

ISSUED ON OCTOBER 26, 1932

REICH PATENT OFFICE

PATENT LETTERING

JVr 562536 CLASS 21h GROUP

WC Heraeus G. mb H. in Hanau a. M. *) Device for monitoring the temperature of ovens

Patented in the German Empire on November 11, 1930

In the case of electric resistance furnaces with automatic temperature regulation, it is of very great importance to exclude any possibility that a certain temperature is exceeded. The automatic temperature regulators usually consist of a temperature measuring element, ζ. Β. Thermocouple that interacts with contact devices, so that when the set temperature is reached, the heating resistors are switched off and when the temperature falls below this Temperature the power is turned on again.

But if the temperature measuring element fails in an automatic temperature controller, is z. B. in the case of a thermocouple, the thermal circuit is interrupted for some reason, in this way, the heating resistors remain switched on even though the temperature exceeds the

ao has exceeded the permissible limit.

It is also known to introduce a fuse into the furnace as a protective fuse for electric furnaces, which fuse is switched into the circuit of a relay or directly into the heating circuit. These fuses respond when normal temperature regulation fails. So far, only fuses above 1000 ^° C. have proven successful, because in this case fusible wires made of precious metal could be used. In the previously known devices of this type, however, it was not possible to use precious metal fuses such. B. gold fuses to use for lower temperatures and to change the temperature for which the thermal fuse is intended. But it is sufficient z. B. in an electric annealing furnace not only the protection of the electric heating coils against overheating, one must also protect the material to be annealed against inadmissibly high temperatures. In this case it is of particular advantage if the temperature fuse can be set according to the respective maximum permissible temperature. The device according to the present invention enables, with particularly simple and reliable means, a change in the respective desired maximum temperature within wide limits.

^{According to the invention, a body 6 1} , which is heated by heat transfer from the resistor or annealing material to be protected and consists of an electrically conductive material and melts at a certain temperature, is connected in series with the control circuit of a relay R and a regulating resistor V. The circuit is fed by a transformer Tr, the secondary voltage is kept so low that can occur during melting of the body-S "no arc. By regulating resistance V, by the way, also

*) The patent seeker named as the discoverers:

Eduard Killius and Dipl.-Ing. Johann Grossinger in Hanau a. M,

can lie in the primary circuit of the transformer Tr , the amperage / is changed. By changing the current strength / one changes the additional heating of the melting body S. Depending on the size of the additional heating current flowing through the temperature fuse, the body 5 ^{1 will} melt at a higher or lower temperature of the furnace. Assuming a constant voltage source, this is the additional heating current and thus the melting temperature of the fuse. depends directly on the size of the variable series resistor V , so that this resistor can be provided with a scale that shows the maximum permissible oven temperature.

The relay R is expediently designed as a bimetallic current relay. Through the strip 2 ?! the control current flows, the strip B ₂ is only used to compensate for room temperature fluctuations. Both strips sit on the same axis A, which, in addition to the power supply line C, also carries the pointer Z. On the pointer of the contact K Z _2, currency-S5 sitting rend the mating contact K ₁ on an isolated on the ZeigerZ attached steel or bronze spring F is attached.

If the relay was de-energized, the pointer Z would be on the right of the scale T and would rotate from right to left, i.e. counterclockwise, depending on the current flowing through the bimetal strip B _1. The stop N, which causes the flexible contact arm to lift off when the relay circuit is interrupted, is on a scale value that is above the desired temperature range. For example, if a temperature range is desired 550 to 900 ⁰ C for the temperature control, so the stop is mounted at the N-scale value of about ⁰ C iooo. Assuming a fuse wire made of gold, the zero point of the currentless relay corresponds to the temperature value of 1063 ^° C. When installing the stop N , the fixed contact arm Z and the springy contact arm F are rotated from the right by a mechanical force (e.g. a weight) to the left, for example, to the scale value of 900 ° C. after completion of the mounting of the stopper N is removed, the additional torque causing weight, and the ZeigerZ now returns to its corresponding one of said zero current initial position back (at a gold wire according to the scale value of 1063 ⁰ C).

The spring F is stopped by the stop N here. When the relay is de-energized, the resilient contact arm F is lifted from the fixed contact arm Z by the stop N.

If now the fuse is put into operation and z. B. is loaded according to the temperature of 900 ⁰ C with 2 amps, then the pointer Z rotates from the right 6g to the left up to the scale value 900 ⁰ , the stop N releases the spring F, and the contacts K ₁ and K ₂ closed.

Depending on the strength of the current /, the strip B ₁ bends, and the pointer Z shows the respective response temperature of the fuse 6 "and thus the maximum furnace temperature on the scale Γ. When the body S melts, the control circuit of the relay R. If the strip B _{1 is} de-energized, the pointer Z returns to its initial position, whereby the spring F is stopped by the stop and the contacts K ₁ and K ₂ , which are normally closed, are separated the heating current of the furnace is switched off in a manner known per se with the aid of the lamp L of a mercury gas switch or some other intermediate relay and a further increase in temperature is prevented. An alarm clock W or the like can be set parallel to the body S. When the body 6 ″ melts, the signal W is automatically activated. By separating the contacts K ₁ and K ₂ , valves, flaps or other auxiliary devices that prevent the temperature from rising can be operated electrically, also with the aid of suitable intermediate relays will.

Claims (3)

Patent claims: 1. Device for monitoring the temperature of ovens with the aid of an electrically conductive body (S) which is arranged in the heated room and which melts at a certain temperature, characterized in that the oven temperature at which the body (S) melts can be changed, that the melting body (S) by an expedient lower a power source voltage sampled, adjustable relay current flowing through it, which flows through a lying with the body (S) in series Bimetallorgan (B ₁₎ which is a the main circuit via an intermediate contactor (L) controlling Relay (R) activated. 2. Device according to claim r, characterized in that the Bhnetallorgan (B ₁ ) via an axis (A) with two attached to this and contacts (K ₁ , K ₂ ) carrying switching arms (F and Z) is in connection, of which one arm (F) designed as a spring moves when the bimetal spring (B ₁ ) is de-energized against an adjustable stop (N) , while the other rigid arm (Z) returns to the rest position and thus lifts its contact from that of the resilient arm. 3. Device according to claim 1 and 2, characterized by a scale on which the rigid contact arm (Z) indicates the response temperature of the fuse (S). 1 sheet of drawings