Electric cooking apparatus with safety control

Abstract

The improved operating-safety control uses an operating contactor and a safety contactor each having normally open switch contacts and means connect these switch contacts on opposite sides of and in main power series circuits with the electric heating elements of the cooking apparatus effective for controlling electric input to same. An actuating coil is effective for closing each contactor switch contacts, and the control includes an operating thermostat and a safety thermostat each having a heat sensor in the cooking environment and each having a heat sensor in the cooking environment and each having normally closed contacts opened responsive to a set sensed high temperature. The control connects main on and off switch means operatively in series with a parallel hookup connection of the safety contactor actuating coil as one leg and the serially connected operator contactor actuating coil and operating thermostat controlled contacts as the other leg. Thus actuation of said main on and off switch means effectively opens and/or closes the switch contacts of both contactors. The control further connects the safety thermostat controlled contacts operatively with a power series connection through said mentioned parallel hookup connection and in series with the main on and off switch means and operates responsive to the opening of said contacts for deenergizing the actuating coils of both contactors, and means hold the safety thermostat controlled contacts open until reset means is actuated. A signal device is hooked across the main power input lines at locations between the safety contactor switch contacts and heating elements effective to indicate both a power on condition and a faulted closed condition of the operating and/or safety contactor switch contacts.

Description

BRIEF DESCRIPTION OF DRAWINGS DETAILED DESCRIPTION OF THE INVENTION The switch 50 can be located on the front wall of the fryer as shown in FIG. 1.

Power lines L1 and L2 can be identical to any two of power lines X, Y, or Z; or can be at a lower voltage resulting from a step down transformer (not shown), connection with these lines, depending on the local code requirements or on the preference of the installer. The power lines are brought into the interior control section of the fryer in any typical manner and are therefore not shown other than in the schematic. Red indicator light 54 is connected in a parallel hookup across the controlled switch contacts 28 of the safety thermostat control and the same is of such high resistance so that in the normal contacts closed condition there is insufficient current draw to light the indicator light, whereas with the switch contacts 28 open there is sufficient draw to light the indicator light 54 but not enough to energize either actuating coil 46 or 48.

The safety thermostat bellows arrangement is preferably of the type that actuation of the bellows 27 in a manner to open the switch contacts 28 throws an overcenter toggle or the like (not shown) to preclude back movement or closing of the contacts 28 incident to a cool down of the sensed temperature, instead the contacts must be manually shifted such as by actuation of control button 56 for instituting a restart condition of the circuit.

In normal operation of the control circuit indicated in FIG. 2, it will be appreciated that the safety contacts 28 are closed as are normally the operating thermostat contacts 23. Consequently with power in the lines X, Y, and Z, and L1 and L2, closing the main on-off switch 50 simultaneously energizes the actuating coils 46 and 48 of the respective safety and operating contactors 30 and 34 to bring main-line power through the heating elements 17, 18, and 19. At this time the amber indicator light 49 glows indicating that the operating contactor 34 is closed, and the green indicator light 52 glows indicating that likewise the safety contactor 30 is closed. Power is thus carried to the heating elements until the time that the operating thermostat bulb 20 senses the set high temperature and actuates bellows 22 to open the contacts 23 and thereby deenergize the actuating coil 48 and indicator light 49, and thereby open the contactor switches contacts 35, 36, and 37 to deenergize the heating elements. The green indicator light 52 remains on since the safety contactor 30 through energized actuating coil 46 is still closed.

Under normal use the operating thermostat thus cycles to energize and deenergize the heating elements sufficient to satisfy the demand. Should however the contactor 34 or the operating thermostat fail and an over temperature condition be reached, the safety thermostat is activated to open the safety thermostat control contacts 28 to cut power to both actuating coils 46 and 48 of the respective contactors.

When the contacts 31, 32, and 33 open, main power to the heating elements is cut off to stop further heating of the cooking oil. Opening of contacts 28 turns red signal light 54 on indicating an over temperature condition of the cooking oil.

In as much as under normal operation an over temperature condition will not be reached except by the malfunction of the operating contactor 34, the green signal light 52 shall still remain on because of leakage current through closed contacts 35 and 36 and the heating elements 17 and 18. This indicates that main power to the unit is still on; however, this leakage current is insufficient for significant operation of the heating elements and the oil thus cools down.

Power can only be restored by manually resetting the safety control, by depressing the button 56, but this is only after sufficient cool down of the cooking oil, and this closes the safety thermostat control contacts 28 and reenergizes the actuating coils 46 and 48 of the respective safety and operating contactors 30 and 34. If the subsequent operation results in another over temperature condition, the operator is clearly appraised of malfunctioning equipment and can arrange for service of same.

Of significance in the subject invention is the fact that the main on-off switch 50 and the contacts 28 of the safety control thermostats 28 thermostat are effectively in series and each is effectively in a parallel hookup with the actuating coils 46 and 48 and of contactors. This means that each of the contactors is actuated responsive to the operator opening the on-off switch 50 such as at the end of the cooking day. Consequently both contactors should open and should take power away from the heating elements, and the green light 52 should thus turn off. If the safety contactor 50 should malfunction fused closed, then a circuit is established from lines X and Y through the closed contacts 31 and 32 to the indicator 52, and the illuminated indicator warns the operator that such a malfunction exists and repair of same is in order. It should be appreciated that the contactors are of such physical construction that should any pair of separate contacts become fused together none of the contacts can be separated since the operating mechanism of the contacts acts in unison responsive to the single pull of the actuating coil and/or of a return spring not shown.

A second embodiment of the invention is disclosed in FIG. 3, and this embodiment uses a thermostat of the automatic resetting type and the control itself acts to maintain the thermostat disabled until a reset device is manually actuated. Thus there is provided normally opened start switch 60 and normally closed stop switch 62; and there further is provided an operate relay 54 and the safety relay 56. The relays are of typical construction and have a pair of movable leaf switches each which can be connected across opposing contacts for completing or breaking circuits through the moving leaf, and an actuating coil is used to shift the movable leaf. Specifically, the operate relay has actuating coil 70 and a pair of moving leafs 71 and 72; whereas the safety relay has actuating coil 74 and a pair of moving leafs 75 and 76. The start and stop switches can be located on the front wall of the fryer forward of the fat container to allow an operator to actuate them without reaching over the fat container.

The control circuit is completed, upon a momentary closing of the start switch 60, from the line L1 through the switch 60 to junction 78, and through operate relay coil 70 and closed leaf contact 76 to the line L2. The energized coil 70 shifts the leaf contacts 71 and 72 closed, against contacts 81 and 82, respectively, whereupon a holding circuit is maintained through the normally closed stop switch 62 to junction 80, and through the now closed leaf 71 to the junction 78 and through the energized operate relay coil 70 as noted. The power at the junction 78 further is carried by the now closed leaf 72 through the operating thermostat switch contacts 23 and the actuating coil 48 of the operating contactor 34 to line L2. Power is carried further from the common hot junction 78 and across the safety control thermostat switch leaf 84 and engaged contact 85 through the actuating coil 46 of the safety contactor 30 to line L2. Consequently upon the operate relay being energized, circuits are completed through the respective actuating coils 46 and 48 to shift the contactors 30 and 34 thereby applying power through the heating elements 17, 18, and 19. During this power on condition the amber light 49 glows because of the energized coil 48; and the green indicator light 52 glows because of the closed safety contactor contacts. Also, cycling of the operating thermostat contacts 23 as dictated by demand cycles the heat elements on and off.

The safety thermostat as noted includes a movable leaf 84 which, responsive to the sensing bulb 25 indicating the set oversafe overheat temperature , is shifted from against contact 85 to against normally open contact 86 and this . This brings power through the safety relay coil 74 to line L2, and this further illuminates red indicator light 54 in a parallel hookup connection with the coil 74. Upon the safety relay coil 74 being energized the leaf contacts 75 and 76 are shifted and the opened leaf 76 breaks the circuit through the operate relay coil 70 to deneergize the operate relay and thus allow the leaf contacts 71 and 72 to return to their positions as shown; and secondly the closed leaf contact 75 establishes a safety relay hold circuit through coil 74 by means of the closed leaf 75 to junction 80 and through and the normally closed stop switch 62.

The thus opened leaf contacts 71 and 72 deenergize both actuating coils 46 and 48 of the safety and operate operating contactors respectively and thereby terminates power input to the heating element elements . The energized safety relay maintains the operate relay deenergized and the latter cannot be energized unless and until the safety relay is first deenergized, and this can only happen after the cooking oil has cooled sufficiently to allow the contact 84 to shift back against contact 85 and then subsequent to this condition of manually opening stop switch 62. Thus when the safety relay coil 74 is energized, the unit cannot be started by closing the start switch 60, and likewise during the unsafe condition when the over temperature condition exists and contact 86 is engaged by moving leaf 84, the safety control cannot be deenergized merely by opening the stop switch 62 . . . since immediately upon the same closing the stop relay will then be reenergized. The deenergized safety control relay allows the safety relay leafs 75 and 76 to shift to their normal positions shown, so that a subsequent cycle can be instigated upon momentarily closing the start control switch 60.

Claims

1. In an electric cooking unit having electric heating elements element means disposed to heat a cooking environment, an improved operating-safety circuit comprising main on and off switch means, an operating contactor and a safety contactor each including normally open switch contacts and an actuating coil effective for closing same, an operating thermostat and a safety thermostat each having a heat sensor in the cooking environment and each having normally closed contacts opened contact means shifted between operative dispositions responsive to the sensed set high temperature temperature demand and higher temperature satisfied and overheat conditions, means connecting the operating contactor switch contacts and the safety contactor switch contacts on opposite sides of and in main power series circuits with the heating elements element means effective for controlling electric input to same, an operate control including means connecting the main on and off switch means operatively in series with a parallel hookup connection of the safety contactor actuating coil as one leg and the serially connected operator operating contactor actuating coil and operating thermostat controlled contacts contact means as the other leg, so that in the temperature demand conditions actuation of said main on and off switch means simultaneously energizes and deenergizes both actuating coils and thereby opens and closes the switch contacts of both contactors, a safety control including means connecting the safety thermostat controlled contacts contact means operatively with power series connection through said mentioned parallel hookup connection and in series with the main on and off switch means operable responsive to the opening of said contacts for shifting of said controlled contact means for opening the parallel hookup connection and thereby simultaneously deenergizing the actuating coils of both contactors, and means effectively holding said parallel hookup connection open and manual reset means for releasing the said holding means, and a signal device hooked across the main power input lines at locations between the safety contactor switch contacts and heating elements effective to indicate both a power on condition and a faulted closed condition of the safety and operator contactor switch contacts.

2. An operating safety circuit according to claim 1, wherein the means effective for holding the parallel hookup connection open includes having the safety thermostat of the type that remains in its set position until shifted by an outside force so that once the same has been operated responsive to the set high sensed temperature overheat condition and the thermostat contacts are opened and contact means are shifted the same contacts remain open contact means remain shifted until manually reset by actuation of the reset means.

3. An operating safety circuit according to claim 1, wherein the means effective for holding the parallel hookup connection open includes a safety relay having a coil in a circuit including normally opened contacts of the safety thermostat contact means which relay is energized upon a sensed over overheat temperature condition and said relay having normally closed contacts opened upon the energizatio of the relay coil, and means operatively connecting the said normally closed relay contacts in a circuit that precludes actuation of the operate contactor actuating coil.

4. An operating safety circuit according to claim 3, wherein the means precluding actuation of the operate contactor actuating coil includes an operate relay having a coil operatively connected in series with the safety relay normally closed contacts and having normally open contact means operatively connected in series with the operating contactor actuating coil, effective when the safety relay is energized to preclude energization of the operate relay and thus the actuation of the operating contactor actuating coil.

5. An operating safety circuit according to claim 3, wherein circuit means is provided through the safety relay normally opened contact means and the safety relay coil and the main on and off switch means effective when the safety relay is energized to hold the same as such until it is released by actuation of the main on and off switch means.

6. An operating safety circuit according to claim 5, wherein said cooking unit is a deep fat fryer having a cooking container for the fat and a wall forwardly disposed from the cooking container, and wherein said main on and off switch means is located on the said forwardly disposed wall to allow actuation of same without reaching over the cooking container.

7. An operating-safety circuit according to claim 1, further providing that the operating and safety contactors each has two pairs of such switch contacts simultaneously closed by said respective actuating coil, that there are two such electric heating element means, and that said connecting means provide through the pairs of operating and safety contactor switch contacts a pair of independent main power circuits for controlling electric inputs to the heating element means, and further including a signal device hooked across the main power input circuits at locations between the safety contactor switch contacts and the operating contactor switch contacts where said circuits are normally at different potentials when the switch contacts are closed, effective to indicate both a power on condition and a faulted closed condition of the safety and operating contactor switch contacts.

8. An operating safety circuit according to claim 7, wherein the signal device comprises a neon type glow lamp.

9. In an electric cooking unit having at least two electric heating element means disposed to heat a cooking environment, an improvement operating-safety circuit comprising the combination of two contactors, each contactor including at least two sets of switch contacts and means effective for opening and closing same, means establishing an independent power series circuit through each of the heating element means by connecting one set of switch contacts of each contactor on each side of the respective heating element means between the different electric potentials and the heating element means whereby at least two such independent power series circuits are defined, and a signal device connected across two such power series circuits at locations between the contactor switch contacts relative to the different electric potentials and where a diffferential in potential exists between the circuits when all switch contacts are closed, effective to indicate both a power on condition when both contactors are closed and a faulted closed condition of either contactor.