Electric heating – Heating devices – With current connection and/or disconnection means
Patent
1987-09-11
1991-08-13
Bartis, Anthony
Electric heating
Heating devices
With current connection and/or disconnection means
38 82, 200 6145R, 219251, 337 3, 337104, H05B 102, H01H 6102, H01H 7704, D06F 7526
Patent
active
050398431
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention is based on a safety cutout device for electric loads, particularly for use in pressing irons and portable heating apparatus.
STATE OF THE ART
Such a device is known from German Offenlegungsschrift 3,506,784. It contains two components which are, on the one hand, a temperature switch which is located in series with the load, opens when overheated and, as a result, switches off the load and, on the other hand, a switch which operates in dependence on position and which is located in parallel with the load, is opened in the normal position of the equipment and has a series resistor which heats the temperature switch when the switch operating in dependence on position closes. Due to the heating, the temperature switch exceeds its switching temperature after some time and opens so that the load is also switched off due to the operating of the position-dependent switch. If it is assumed that the temperature switch is not located in the circuit of the switch operating in dependence on position, the temperature switch, after operating, remains open due to its continuing heating until the equipment is returned to its normal position in which the position-dependent switch opens, as a result of which its series resistor loses its current and gradually cools down. However, during overheating of the temperature switch which does not originate from this series resistor, no provision is made for the temperature switch to remain open after operating, instead it will automatically switch on again after having cooled down, regardless of whether the disturbance which led to the overheating has been eliminated or not.
DISCLOSURE OF THE INVENTION
The invention is based on the object of developing a safety cutout device of the type initially mentioned in such a manner that the temperature switch which switches off the load is automatically kept open after operation, for whatever reason.
The resistance value of the additional resistor is selected, in adaptation to the respective switching and sensing task of the temperature switch and to the resistance value of the load, in such a manner that, when the temperature switch is closed, the predominating proportion of the current flowing through the load takes a direct path via the temperature switch and only a comparatively small proportion of the current flows via the additional resistor so that the resistive heat generated in the resistor is not sufficient for heating the temperature switch to its switching temperature. If, however, the temperature switch operates due to overheating, current only flows through the additional resistor and, possibly, through the series resistor of the switch, which preferably operates in dependence on position and/or in dependence on acceleration, if it is closed. For this reason, the resistance value of the further resistor bridging the temperature switch must be selected, on the other hand, in such a manner that, with the temperature switch open, the resistive heat generated due to the higher current passing through the additional resistor is sufficient for keeping the temperature switch open. The heating power needed for this is typically of the order of magnitude of a few watts. With a feed voltage of 220 volts, suitable resistance values for the additional resistor are of the order of magnitude of 10k.OMEGA., for example between 5k.OMEGA. and 25k.OMEGA.. The series resistor belonging to the switch operating due to position changes or accelerations must be capable of heating up the temperature switch within a suitable time from its normal operating temperature up to above its switching temperature, which requires a somewhat greater heating power than if it is merely kept open. It is therefore recommended to select the resistance value of this series resistor to be slightly lower than the resistance value of the additional resistor which continuously bridges and heats the temperature switch.
In a particularly advantageous arrangement of the two resistors, these bridge the temperature switch whilst being conne
REFERENCES:
patent: 1461878 (1923-07-01), Harvey
patent: 2367985 (1945-01-01), Weeks
patent: 4661685 (1987-04-01), Comtri
patent: 4686352 (1987-08-01), Nawrot et al.
Bartis Anthony
Limitor AG
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