US3050933A

US3050933A - Device for protecting thermo-dynamic engines

Info

Publication number: US3050933A
Application number: US3828A
Authority: US
Inventors: Fokker Herman
Original assignee: US Philips Corp
Current assignee: US Philips Corp; North American Philips Co Inc
Priority date: 1959-02-11
Filing date: 1960-01-21
Publication date: 1962-08-28
Anticipated expiration: 1979-08-28
Also published as: BE587427A; AT217791B; FR1247734A; NL236024A; GB934634A; NL102934C; DK109698C; CH387383A

Description

Aug. 28, 1962 H. FOKKER r 3,050,933

DEVICE FOR PROTECTING THERMO-DYNAMIC ENGINES Filed Jan. 21, 1960 [:yzs 29 2| F|g.|

\ LLLLH--25u 23 CONTROL FUBEULRgUEPRPLY W I)HHVZ4BURNERVALVES 30-INDICATOR I EEEENWC? 27 N TRANSDUCER e 2e 29 1 g t um luv-U 1 I20 L /l8u i N .2 1' PHOTO h' h' s2 TRANSISTORS 5 l9 a 1 I -l TRANSISTOR TRANSISTOR 3 5 6 7 i I0 I 1 lBb mm TRA I 330 U U f 3 z l I I m {33c Q L INVENTOR HERMAN FOKKER AGENT United States Patent 3,050,933 DEVICE FOR PROTECTING THERMO-DYNAMIC ENGINES Herman Fokker, Eindhoven, Netherlands, assignor to North American Philips Company, inc, New York, N.Y., a corporation of Delaware Filed Jan. 21, 196i), Ser. No. 3,828 Claims priority, application Netherlands Feb. 11, 1959 16 Claims. (Cl. 60-24) This invention relates to a control device for protecting thermo-dynamic apparatus from excessively high and/ or low temperatures.

The construction, operation, and theory of thermodynamic apparatus of the hot-gas reciprocating type are well known and described in the art; see, for example, Air Engines, H. Rinia et a1., and The Construction of the Philips Air Engine, F. L. van Weenen, Philips Technical Review, a publication of the assignee herein, vol. 8, No. 5, pp. 129-160, 1946; and vol. 9, No. 5, pp. 125160, 1947, respectively. Briefly, the cylinder of such type apparatus contains a Working substance usually in the form of a gas such as air, which is subjected systematically to a. cycle of isothermic and isochoric phases in a predetermined manner. In one specific type of the aforementioned apparatus, the cylinder is divided into two parts, one of which is maintained at a high temperature. The other part is maintained at a substantially lower temperature. During the cycle, the working substance is repeatedly transposed between the two parts. During the period that the working substance occupies the part maintained at the low temperature, it is subjected to an isothermal compression. When the working substance is subsequently transformed to the high temperature part of the cylinder, the working substance undergoes an isothermal expansion. Since the isothermal expansion takes place at a high temperature, greater energy is released than that expended to subject the working substance to the isothermal compression at the low temperature. The resulting net energy is utilized to drive a suitable piston and crankshaft arrangement associated with the cylinder. To obtain the required high temperature, heater means are disposed at the location of the high-temperature part of the cylinder and are heated by a suitable source of heat energ as, for example, a burner supplied by a compatible combustible mixture.

To maintain the proper phase relationship between the various steps of the aforementioned cycle, it is obvious that the operating temperatures specified be extremely stable. For example, if the temperature should exceed or decrease from the specified operating high temperature, then the apparatus would malfunction due to the disturbance of the operating cycle. In apparatus of the type described, having multi-cylinders, each of which has an individual associated heater means, and a usually common source of heat energy, the temperature stability problem is further compounded, as it is imperative that each of the cylinders also coact in a proper phase relationship with one another.

An object of this invention is to provide a temperature responsive control circuit device for the protection of a controllable system or apparatus against temperatures above and below a predetermined temperature range.

The invention has for another object the provision of a control device of the kind set forth, which operates rapidly in a reliable manner and which stabilizes the temperature of the aforementioned apparatus.

Still another object of this invention is to provide a temperature responsive control circuit device for the protection of hot-gas reciprocating apparatus against tem- 3,5,933 Patented Aug. 28, 19962 peratures above and below the operating temperature range of the apparatus.

Still another object of this invention is the provision of a control device for hot-gas reciprocating apparatus hav ing a plurality of cylinders which protects the remaining cylinders when one or more cylinders thereof experiences an excessively high and/ or low temperature.

Accordingly, this invention features a temperature responsive control circuit to control the action of a controllable system such as, for example, the heater system of a hot-gas reciprocating apparatus having one or more cylinders. The circuit comprises thermal-electrical transducer means to provide a signal proportional to the temperature sensed thereby and indicator means having a movable member which is responsive to the signal. In addition, a pair of photosensitive transducer means which are associated with compatible output means that are coupled to the controllable system, are adapted for mutually exclusive light energy coupling relationship with a light source. An opaque member, which is coupled to the movable member, is adapted to be disposed between the light source and a predetermined one of the photosensitive transducer means at temperatures below a given temperature range of at least one temperature to stop the action of the controllable system. The opaque member is also adapted to be disposed between the light source and the other of the photosensitive transducer means at temperatures above the given temperature range to stop the action.

Another feature of this invention is to provide a temperature responsive control circuit of the type af0redescribed further comprising a third photosensitive transducer means which is also associated with a compatible output means that is coupled to the controllable system. The third photosensitive transducer means is likewise adapted to be in light coupling relationship with the light source, and the opaque member is further adapted to adjust the light coupling relationship between the third photosensitive transducer and the light source to regulate the action of the controllable system, such as, for example, the aforementioned heater system for a hot-gas reciprocating apparatus, within the given temperature range.

The above-mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective drawing of the control device of this invention which includes a sectional view of the high temperature part of a cylinder of a hot-gas reciprocating apparatus; and

FIG. 2 is a schematic diagram of the control device of this invention; and

FIG. 3 is a schematic diagram of another embodiment of this invention for application with multi-cylinder hotgas reciprocating apparatus.

Referring to FIG. 1, there is illustrated as a sectional view thereof, high temperature part 20 of a hot-gas reciprocating apparatus cylinder. Part 20 comprises cylinder wall 21, piston 22 and chamber 23 which contains the working medium of the hot-gas reciprocating apparatus. Piston 22 is coupled to a suitable crankshaft arrangement, not shown, via the piston rod 22a, in a manner well known to those skilled in the art. Cylinder part 20 has associa-ted therewith suitable heat transfer means, illustrated as heater means 24 comprising, by way of example only, a plurality of orthogonal radiating fins, such as, annular shaped fins 25a and the radial fins 25b, which transfer heat generated from a heat source, illustrated, byway of example only, as annular burner 26. A source 27 of compatible heat energy supply is coupled to the heat source, and is illustrated in FIG. 1 as a source of a combustible fuel mixture for burner 26. Disposed between source 27 and the heat source, are electrically operated control means 28, 29, illustrated in block form, which are compatible to the heat source and source 27 of heat energy utilized by the hot-gas apparatus. In the illustrated example of hot-gas apparatus chosen to teach the principles of this invention, electrically operated control means 23, 29 compose a pair of electrically driven fuel valves, each of which controls the fuel supplied from source 27 to burner 26 in a predetermined manner as will be explained hereinafter. It is to be understood, however, that the heater means and source of heat energy supply, as well as the control means therefor, are chosen by way of example only, and may comprise other types, such as an all electrical system comprising an electrical heat source, a source of electric energy, and compatible electrical control means to control the electrical energy thereof supplied to the electrical heat source.

Referring now to FIGS. 1 and 2, indicator 30, is illustrated, by Way of example only, as a current meter for use in a device according to the invention. Indicator 30 is connected to a suitable thermal-electrical transducer means, and which may comprise, for example, thermoelement 31 which is arranged in the proximity of the heater means 24; as an alternative, it may be connected to a bridge circuit comprising at least one temperaturedependent resistor. Thus, indicator 30 is provided with a suitable movable member 30a that is responsive to temperature variations occurring at the heater means 24. The movable member 30a may comprise a pointer that serves at the same time for the indication of the temperature and it is therefore to be preferred to calibrate the face plate 30b of indicator 30 in degrees centigrade. Behind three openings 1, 2 and 3 in the face plate 3% are placed three lamps 1', 2 and 3', illustrated in FIG. 1 by a dashed outline, which coact with holes I, 2, 3, respectively, to provide a source of light in energy coupling relationship with photosensitive transducer circuit means which comprises elements 5-49, inclusive, of FIG. 2 as will be explained in greater detail hereinafter. In three different positions of movable member 30a, the openings are screened by an opaque member 4, secured to the movable member, so that the light passing through the openings is intercepted and/ or adjusted. It will often be possible to use a single lamp for two or even for the three openings. As is obvious to one skilled in the art, the number of openings and/or lamps are chosen by way of example only and are not intended to limit the scope of the present invention. In front of the openings are arranged photosensitive devices which may be of the vacuum tube variety or, as illustrated in FIG. 2, are, preferably photosensitive current carrier devices such as photo transistors 5, 6, 7. The photosensitive circuit means of FIG. 2 is preferably contained in a suitable housing 32, and is coupled to the aforementioned electrically operated control means 28, 29

FIG. 2 schematically shows a circuit arrangement of the electrical system of a control device according to the invention. The lamps 1' and 3' actuate photo-transistors 5 and 6, respectively, the latter being connected in series with a resistor 13 between the supply terminals 18a, 13b which are coupled to a suitable voltage source, not shown. The current circuit of the photo-transistors 5, 6 controls an amplifier, illustrated as a transistor 9, the collector circuit of which includes the coil 11 of a solenoid, the armature 11a of which controls the action of the heat source, which in the instant example comprises burner 26, via electrically operated control means 28. In the specific example chosen to teach the operation, electrically operated control means 28 comprises an electrically operated valve means which cuts-off the supply of fuel from source 27 to burner 28 upon actuation of armature 11a. For example, the armature 11a, upon its actuation, may close a contact switch that causes the electrical driving system, not shown, of means 28 to close the valve thereof. The operation is such, that when opaque member 4 is not disposed between the light source and photo-transistors 5, 6, the latter conduct and their emitter-collector current coact with the input resistors 13, 15 to overcome a cut-off bias appearing at the base input of transistor 9 In turn, the emitter-collector current of transistor 9 energizes coil 9, causing the armature 11a to be placed in a position so as to maintain electrically operated valve means 28 in an open position. When opaque member 4 of the indicator occupies such a position that the light through the openings 1 or 3 is intercepted, the current through the resistor 13 is interrupted, causing transistor 9 to become cut-off. Coil 11, thus, becomes de-energized and releases armature 11a which in turn actuates the electrically operated valve 28, closing fuel supply 27 to burner 26.

In a similar manner, the light from the lamp 2' strikes photo-transistor 7 causing current to flow in the emitter circuit thereof which includes the resistor 14. Resistors 14-, 17 combine to form an input bias circuit for transistoramplifier 1%, such that any variations in the input signal supplied by the emitter current of photo-transistor 7 is reflected in the output of amplifier It} in a manner well known to those skilled in the art. The collector circuit of transistor 10, comprises a current limiting resistor 19 and a coil 12 which is part of a solenoid that operates electrically operated control means 29, by means of the armature 12a thereof. In the particular example, chosen to represent the heat source and source of heat energy supply, control means 29 may be an electric-ally operated control valve that monitors the amount of fuel supplied by the source 27 to burner 26, as will be explained hereinafter.

As is shown in FIG. 1, the opening 1 is provided at the beginning and the opening 3 at the end of the face plate 30b, which represent respectively the lower and upper temperature ranges, approximately, of the indicator 39. By judiciously selecting the position of opening 3 on plate 30b to coincide with excessive temperate range that is deleterious to the associated cylinder and apparatus, and by suitable adjustment of the input threshold level of the photo-transistor 6, the electrically operated control valve 28 will be closed whenever the opaque member 4 is interposed between the photo-transistor 6 and opening 3 in such a manner that the light energy emanating from lamp 3 and intercepted by photo-transistor 6 is attenuated below the selected threshold level.

In order to protect the associated cylinder thereof and the hot-gas reciprocating apparatus from inherent defects such as may arise within the reciprocating apparatus itself or within the control device of the present invention, opening 1 is placed in such a position on plate 30b so as to coincide approximately with the minimum temperature that the high temperature part 20 may safely assume during the operation of the apparatus as, for example, the zero on null markings of the indicator 34]. In any event, opening 1 is in such a position that the pointer, or more properly the opaque member 4-, will intercept the light energy emanating therefrom on returning to its rest position, as for example when there is no signal present at the input of indicator 30 from the element 31. Such defects may arise, for example, from an actual decrease in temperature of the heat transfer means itself, or may arise from a defect in the control device such as a short circuit or the like.

Similarly, the position of opening 2 on plate 30b is selected as an intermediary one and so placed as to coincide with the normal operating temperature range of the cylinder part 20. With the light energy emanating from the opening 2 focussed upon photo-transistor 7, the emitter current thereof will be responsive to attenuations in the light energy emanating from lamp 2 by virtue of the movement of the opaque member 4 from its normal operating temperature of the cylinder part 20. \As a consequence thereof, the collector current of transistor-amplifier 10 will also vary proportionately causing a corresponding movement in the armature 12a. Electrically operated control valve means 29, which may include, for example, as a part thereof a fuel valve operated by an electric motor whose field excitation is controlled by a rheostat having a variable arm which is coupled to the armature 21a, in a manner well known to those skilled in the art, is adjusted thereby to control the amount of fuel required by the burner 26 to maintain cylinder part 20 at the normal operating temperature. In the event that control means 28 becomes closed, provision is made for the clo sure of control means 29, as will be explained hereinafter.

As illustrated in FIG. 2 the lamps 1', 2', 3' are serially connected across the negative supply terminal 18a via current limiting resistor 16 and coil 11. In the event either photo-transistor 5 or 6 becomes non-conductive, as explained herein-above, transistor-amplifier 9 is cut off. As a consequence, no current flows in the collector circuit of transistor 9 and lamps I, 3', 2' are extinguished causing electrically operated valve means 28 to remain in the closed position. Even if the movable member were subsequently to move into a position in which the opaque member 4 no longer covered the openings 1 or 3, means 28 would still remain closed. Upon the occurrence of this event, electrically operating control means 29 may be so arranged to cause a similar closure therein, thus insuring against the possibility of any fuel from source 27 being supplied to burner 26. A switch 8 is shunted across photo transducers 5, 6 and upon its closure, as for example after correction of the defect, causes a negative voltage to appear at the input of transistor-amplifier 9 sufiicient to overcome the cut ofi bias thereat. As a result, transistor 9 conducts causing lamps l 2' 3 to become operative and thereby recycles the control device of this invention.

If a hot-gas reciprocating apparatus comprising a plurality of cylinders is to be provided with a control device, use may advantageously be made of the control device shown in FIG. 2 with a slight modification. It is necessary in this case to provide a control device for each cylinder, since the cylinders, i.e., their individual heat sources, are separately fed and controlled. The use of the arrangement shown in FIG. 3 provides the extra advantage that when the fuel supply to a heat source of one or more of the cylinders is closed, the fuel supply to the remaining heat sources of the other cylinders is also interrupted. To this end it is sufficient to connect the second lamp 3a of the first device 33a in series with the first lamp 1!) of the second device 3312, the second lamp 3b of the second device 3312 in series with the first lamp 310 of the third device 33c, and so forth, the second lamp 3n, not shown, of the last device, not shown, being connected in series with the first lamp in of the first device 33a. These connections are designated in FIG. 3 by

conductors

34, 35, 36. In this case the current interruption in the circuit of phototransistors of the first device is automatically attended with the current interruption in the corresponding circuit of the second device, and so on.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made by way of example only and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

1. A temperature responsive control circuit to control the action of a controllable system, said circuit comprising thermal-electrical transducer means to provide a signal proportional to the temperature sensed thereby, indicator means having a movable member responsive to said signal, a source of light, a pair of photosensitive transducer means having output means associated therewith coupled to said controllable system, each of the photosensitive transducer means of said pair being adapted for mutually exclusive light energy coupling relationship with said source, and an opaque member coupled to said movable member adapted to be disposed between said light source and a predetermined one of the photosensitive transducer means of said pair at temperatures below a given temperature range to stop said action and to be disposed between said light source and the other of the photosensitive transducer means of said pair at temperatures above said given temperature range to stop said action, said given temperature range having at least one predetermined temperature.

2. A temperature responsive control circuit according to claim 1 further comprising selector means to recycle said circuit means whenever said action is stopped.

3. A temperature responsive control circuit to control the action of a controllable system, said circuit comprising thermal-electrical transducer means to provide a signal proportional to the temperature sensed thereby, indicator means having a movable member responsive to said signal, a source of light, first and second photosensitive transducer means having output means associated therewith coupled to said controllable system, each of said first and second photosensitive transducer means being adapted for mutually exclusive light energy coupling relationship with said source, an opaque member coupled to said movable member and adapted to be disposed between said light source and a predetermined one of said first and second photosensitive transducer means at temperatures below a given temperature range to stop said action and to be disposed between said light source and the other of said first and second photosensitive transducer means at temperatures above said given temperature range to stop said action, and third photosensitive transducer means having output means associated therewith coupled to said controllable system, said third photosensitive transducer means being adapted for light energy coupling relationship with said source, said opaque member being further adapted to adjust the light energy coupling relationship between said third photosensitive transducer and said source to regulate said action within said given temperature range, said given temperature range having at least one predetermined temperature.

4. A temperature responsive control circuit according to claim 3 further comprising selector means to recycle said circuit means whenever said action is stopped.

5. A temperature responsive control circuit adapted to control the action of a controllable system with a plurality of other similarly constructed circuits, said controllable system having a plurality of temperature controllable portions, each of said circuits comprising thermal-electrical transducer means to provide a signal proportional to the temperature sensed thereby, indicator means having a movable member responsive to said signal, a source of light, a pair of photosensitive transducer means having output means associated therewith coupled to one of the temperature controllable portions of said controllable system, each of the photosensitive transducer means of said pair being adapted for mutually exclusive light energy coupling relationship with said source, an opaque member coupled to said movable member adapted to be disposed between said light source and a predetermined one of the photosensitive transducer means of said pair at temperatures below a given temperature range to stop said action at said one portion and to be disposed between said light source and the other of the photosensitive transducer means of said pair at temperatures above said given temperature range to stop said action at said one portion, :said given temperature range having at least one predetermined temperature, and means to stop said action at said one portion whenever another of said plurality of other similarly constructed circuits stops said action at the respective temperature controllable portion coupled to said another circuit.

6. A temperature responsive control circuit according to claim 5 further comprising selector means to recycle said circuit means whenever said action is stopped.

7. A temperature responsive control circuit adapted to control the action of a controllable system with a plurality of other similarly constructed circuits, said controllable system having a plurality of temperature controllable portions, each of said circuits comprising thermal-electrical transducer means to provide a signal pro portional to the temperature sensed thereby, indicator means having a movable member responsive to said signal, a source of light, first and second photosensitive transducer means having output means associated therewith coupled to one of the temperature controllable portions of said controllable system, each of said first and second photosensitive transducer means being adapted for mutually exclusive light energy coupling relationship with said source, and an opaque member coupled to said movable member and adapted to be disposed between said light source and a predetermined one of said first and second photosensitive transducer means at temperatures below a given temperature range to stop said action at said one portion and to be disposed between said light source and the other of said first and second photosensitive transducer means at temperatures above said given temperature range to stop said action at said one portion, said given temperature range having at least one predetermined temperature, third photosensitive trans ducer means having output means associated therewith coupled to said one portion of said controllable system, said third photosensitive transducer means being adapted for light ener y coupling relationship with said source, said opaque member being further adapted to adjust the light energy coupling relationship between said third photosensiti ve transducer and said source to regulate said action at said one portion Within said given temperature range, and means to stop said action at said one portion whenever another of said plurality of other similarly constructed circuit stops said action at the respective temperature controllable portion coupled to said another circuit.

8. A temperature responsive control circuit according to claim 7 further comprising selector means to recycle said circuit means whenever said action is stopped.

9. A temperature responsive control circuit to control the action of a heater system for a hot gas reciprocating apparatus having at least one cylinder, said circuit comprising thermal-electrical transducer means disposed in a predetermined spatial relationship with said apparatus to provide a signal proportional to the temperature sensed thereat, indicator means having a movable member responsive to said signal, a source of light, a pair of photosensitive transducer means having output means associated therewith coupled to said heater system, each of the photosensitive transducer means of said pair being adapted for mutually exclusive light energy coupling relationship with said source, and an opaque member coupled to said movable member adapted to be disposed between said light source and a predetermined one of the photosensitive transducer means of said pair at temperatures below a given temperature range to stop said action and to be disposed between said light source and the other of the photosensitive transducer means of said pair at temperatures above said given temperature range to stop said action, said given temperature range having at least one predetermined temperature.

10. A temperature responsive control circuit according to claim 9 further comprising selector means to recycle said circuit means whenever said action is stopped.

11. A temperature responsive control circuit to control the action of a heater system for a hot gas reciprocating apparatus having at least one cylinder, said circuit comprising thermal-electrical transducer means disposed in a predetermined spatial relationship with said apparatus to provide a signal proportional to the temperature sensed thereat, indicator means having a movable member responsive to said signal, a source of light, first and second photosensitive transducer means having output means associated therewith coupled to said heater system, each of said first and second photosensitive transducer means being adapted for mutually exclusive light energy coupling relationship with said source, an opaque member coupled to said movable member and adapted to be disposed between said light source and a predetermined one of said first and second photosensitive transducer means at temperatures below a given temperature range to stop said action and to be disposed between said light source and the other of said first and second photosensitive transducer means at temperatures above said given temperature range to stop said action, and third photosensitive transducer means having output means associated therewith coupled to said heater system, said third photosensitive transducer means being adapted for light energy coupling relationship with said source, said opaque member being further adapted to adjust the light energy coupling relationship between said third photosensitive transducer and said source to regulate said action within said given temperature range, said given temperature range having at least one predetermined temperature.

12. A temperature responsive control circuit according to claim 11 further comprising selector means to recycle said circuit means whenever said action is stopped.

13. A temperature responsive control circuit adapted to control with a plurality of other simlarly constructed circuits the action of a heater system for a hot gas reciprocating apparatus having a plurality of cylinders, said heater system having a plurality of heater portions to heat said cylinders, each of said circuits comprising thermaleiectrical transducer means disposed in a predetermined spatial relationship with one of said plurality of cylinders to provide a signal proportional to the temperature sensed thereat, indicator means having a movable member responsive to said signal, a source of light, a pair of photosensitive transducer means having output means associated therewith coupled to the respective heater portion of said heater system that heats said one cylinder, each of the photosensitive transducer means of said pair being adapted for mutually exclusive light energy coupling relationship with said source, an opaque member coupled to said movable member adapted to be disposed between said light source and a predetermined one of the photosensitive transducer means of said pair at temperatures below a given temperature range to stop said action at said respective heater portion and to be disposed between said light source and the other of said photosensitive transducer means at temperatures above said given temperature range to stop said action at said respective heater portion, said given temperature range having at least one predetermined temperature, and means to stop said action at said respective heater portion whenever another of said plurality of other similarly constructed circuits stops said action at the respective heater portion coupled to said another circuit.

14. A temperature responsive control circuit according to claim 13 further comprising selector means to recycle said circuit means whenever said action is stopped.

15. A temperature responsive control circuit adapted to control with a plurality of other similarly constructed circuits the action of a heater system for a hot gas reciprocating apparatus having a plurality of cylinders, said heater system having a plurality of heater portions to heat said cylinder, each of said circuits comprising thermalelectrical transducer means disposed in a predetermined spatial relationship with one of said plurality of cylinders to provide a signal proportional to the temperature sensed thereat, indicator means having a movable member responsive to said signal, a source of light, first and second photosensitive transducer means having output means associated therewith coupled to the respective heater portion of said heater system that heats said one cylinder, each of said first and second photosensitive transducer means being adapted for mutually exclusive light energy coupling relationship with said source, an opaque member coupled to said movable member adapted to be disposed between said light source and a predetermined one of said first and second photosensitive transducer means at temperatures below a given temperature range to stop said action at said respective heater portion and to be disposed between said light source and the other of said first and second photosensitive transducer means at temperatures above said given temperature range to stop said action at said respective heater portion, third photosensitive transducer means having output means associated therewith coupled to said respective heater portion of said heater system, said third photosensitive transducer means being adapted for light energy coupling relationship with said source, said opaque member being further adapted to adjust the light energy coupling relationship between said third photosensitive transducer and said source to regulate said action at said respective heater portion within said given temperature range, said given temperature range hav- 16. A temperature responsive control circuit according to claim 15 further comprising selector means to recycle said circuit means whenever said action is stopped.

References Cited in the file of this patent UNITED STATES PATENTS 2,340,605 MacLaren Feb. 1, 1944 2,664,698 Van De Poll et al Oct. 9, 1954 2,765,986 Pompetn' et a1 Oct. 9, 1956 2,894,368 Van Heeckeren July 14, 1959