US2138593A - Thermal controlling device - Google Patents

Description

THERMAL CONTROLLING DEVICE Filed Sept. 28, 1936 2 Sheets-Sheet l I i l l i I 46 L L97 Nov. 29, 1938.

V. W. BREITENSTEIN THERMAL CONTROLLING DEVICE Filed Sept. 28, 1936 2 Sheets-Sheet 2 Patented Nov. 29, 1938 Victor W. Breitenstein,

Chicago, 111., assignor to Illinois Testing Laboratories, Inc., Chicago, 111., a corporation of Illinois Application September 28, 1936, Serial No. 102,864

4 Claims.

The present invention relates to thermal controlling devices, and is particularly concerned with controlling devices of the type adapted to be regulated or controlled by a thermo-couple 5 acting on a galvanometer which is provided with a movable reactance, for example, such as a capacitance reactance or an inductive reactance, affecting a sensitive electronic control circuit.

One of the objects of the invention is the provision of a safe and reliable, supen-sensitive thermal controlling device which is practically foolproof and which may be used without danger of an electric furnace controlled thereby being turned on when the controlling device is disabled.

In certain'of the devices of the prior art, condenser-controlled relays have been used, but such relays as are exemplified in the prior art have the disadvantage that if the galvanometer needle, which carries the movable condenser plates, should move past the fixed condenser plates, as instrument needles often do, then they controlling circuits to the furnace would first be actuated to turn off the furnace, and then again turn the furnace on when the needle has passed the fixed plates.

In such case the furnace would be turned on, and if it would continue to heat up, the controlling thermo-couple would generate a still greater electromotive force tending to cause the needle of the galvanometer to swing still farther past the fixed plates. unstable condition, resulting in overheating of the furnace, since the more heat generated the farther the needle would get away from the fixed plates which control the shut-off of the furnace.

One of the objects of the invention is the provision of an improved reactance controlled circuit maker and breaker which has the safety feature of a reactance arrangement whereby the over-travel of the needle cannot carry the cooperating condenser plates or other devices past each other to such a point that the circuit to the furnace may be turned on again.

In;other devices of the prior art the controlling pulse of electric current which is caused by the proximity of the condenser plates carried by the needle and by a fixed support of the galvanometer. In such case, if the needle over-travels, one impulse is caused in the controlling circuits by the passage of the needle on a rise of temperature, and due to the over-travel and oscillation of the needle another impulse may be caused when the needle returns. This causes the elec- 55 -tromagnetic relays, which control the heating This would be an relays may be such as to be actuated by an im-.

circuit of the furnace, to get out of step with the controlling galvanometer, and on the next cycle of operation the furnace would be turned on as a result of a rise of temperature instead of being turned off, thereby causing thefurnace to overheat and to run away in spite of the controlling devices.

One of the objects of the invention is the provision of an improved reactance controlled circuit maker and breaker for controlling electric m heating circuits or the like, which has the safety feature of assuring the synchronism of operation of the galvanometer movement which actuates the reactance devices, and of the electromagnetic relays which are controlled there- 15 by.

Another object of the invention is the provision of an improved controlling apparatus of the type covered by United States Patent No. 1,861,929, issued to John D. Lowry, dated June '7, 20 1932, including additional practical and safety features which are highly desirable and advantageous adjuncts to the condenser controlled circuit makers and breakers covered by said patent.

Another object is the provision of an improved controlling device of the class described, which has the safety features of being adapted to shut off the electric heating circuit or other circuit controlled thereby whenever a break occurs in the 30 circuits of the controlling thermo-couple. In the devices of the prior art the thermo-couple generates an electromotive force which actuates a moving coil galvanometer. The moving coil 'galvanometer brings into proximity the plates of a condenser which affect a controlling circuit, due to the change in capacity of the circuit. The controlling circuit is then adapted to actuate relays or circuit makers and breakers which open the heating circuit. It will be evi- 40 dent that in the devices of the prior art the opening of the heating circuit is dependent upon the generation of an electromotive force by the thermo-couple, which requires a closed thermocouple circuit. If the thermo-couple circuit becomes broken in those prior devices, then there is nothing to assure the opening of the heating circuit after the furnace attains a predetermined temperature, and the heating circuit will in such prior devices remain closed, producing such an excessive heat that the furnace and controlling devices, and of course the material being treated, will be damaged.

With the devices constructed according to the invention, the controlling devices will immedi- 66 ately open the heater circuit whenever the thermo-couple circuit is broken, thereby assuring the safety of all apparatus and material under treatment.

Another object of the invention is the provision of a thermo-couple controlling arrangement which will immediately indicate to the operator the fact that any thermo-couple leads have become damaged or open circuited, and in which the thermo-couple circuit may be provided with a cold juncture compensation.

Another object of the invention is the provision of an improved reactance controlled circuit maker and breaker of the class described, which is more sensitive than the devices of the prior art, and which, however, is not affected by the proximity of bodies of metal or persons, which naturally have a certain amount of electrical capacity with reference to other objects.

Other objects and advantages of the invention will be apparent from the following description and from the accompanying drawings, in which similar characters of reference indicate similar parts throughout the several views.

Referring to the drawings accompanying this specification,

Fig. 1 is a diagrammatic view, showing the apparatus and circuits for a thermal controlling device constructed according to the invention;

Fig. 2 is a fragmentary view of a modified form of thermo-couple circuit which may be substituted for the part of the circuit of Fig. 1 whenever it is desired to provide for cold junction compensation.

Fig. 3 is a diagrammatic view, showing the meter arrangement when a photocell and source of light are employed.

Fig. 4 is a diagrammatic view, showing the arrangement when a coil and a magnetic body are employed.

Fig. 5 is a diagrammatic view, showing the arrangement of the meter when two reactance-coils are employed.

Referring to Fig. 1, l indicates in its entirety the thermal controlling device, which in this example of the invention is used for controlling the heating circuit of the heater resistance ll of an electric furnace |2. The heater ll of the furnace has its terminals connected by suitable conductors I3 and I4 to the contacts of one or more electromagnetic relays which may be connected in any conventional manner and which may be connected in cascade.

The relays are indicated by the rectangle I on the diagram. The line conductors I6 and I1 leading to the relays provide the current supply for the heater II and for the electronic control circuit indicated at l8, which may be connected to line by conductors I9 and 20. The electromagnetic controlling relays |5 are in turn controlled by the electronic control circuit |9 by being connected in the plate circuits thereof by means of conductors 2|, 22.

The electronic control circuit l9 may be of the type of an electronic oscillating circuit which is adapted to oscillate at a predetermined frequency, but which is thrown out of tune by the addition of a relatively small reactance to the electronic circuit, thus actuating the relays to' turn off the furnace when reactance is added to the electronic control circuit. The preferred type of electronic control circuit is that disclosed in my copending application, Serial No. 112,644, filed November 25, 1936, relating to further improvements in thermal controlling devices of this type.

The conductors 23 and 24 leading from the electronic control circuit l8 are a part 01' that circuit, and they are connected respectively to the needle 25 of a moving coil type of galvanometer and to the condenser plates 25, 21.

Plate 50 is in conductive relation to-the needle and through its proximity to the meter movement it can be considered as grounded to the instrument case at the frequency used. The coil 30 is, of course, insulated. Lead 23 is therefore generally connected to ground instead 01 to the needle.

The galvanometer 28 is shown diagrammatically and provided with the spindle 29, upon which is mounted the pointer 25 and a spool supporting the moving coil 30. The galvanometer is, of course, provided with a permanent magnet or an electromagnet having its poles in proximity to the moving coil 3|! and with a suitable core inside the coil.. Any suitable construction of moving coil galvanometer may be used.

The furnace I2 is provided with a thermocouple 3|, which may be designated the measuring thermo-couple, and which has its hot junction 32 located inside the furnace in suitable proximity to the heater I I or in contact with or in proximity to the material being acted on by the heater or furnace.

The thermo-couple 3| comprises a pair of conductors of dissimilar metal 33, 34, which are conresistance 31 and the cold Junction 38 of another thermo-couple 39, respectively.

The thermo-couples 39 and 49 may both have their hot junctions 4| and 42 arranged to be acted on by a heater 43, which has a thermal controlling device, such as a bi-metallic element switch 44 adapted to control the heater 43 in such manner that the hot junctions 4|, 42 may be kept at any suitable elevated temperature, such as, for example, from 100 to 250 degrees 'F. Thermo-couple 39 has one of its leads connected at the point 38 to conductor 36, and the other of its leads connected to the other end of resistor 31 at the point 45. Thermo-couple 49 has its two leads'connected in series with the conductor and a conductor 49, which is connected through the spring 41 to one end of the moving coil 30 of the indicator.

The end 45 of resistance 31 and one lead 01' thermo-couple 39 are connected by conductor 43 to the other spring 49 of the galvauometer movement, thereby being placed in connection with the other end of the moving coil 39. The resistance 31 is relatively high with respect to the resistance of the moving coil 39' so as not to impair the sensitivity of the instrument and to cause the major portion of thecurrent which is generated by the thermo-couples to pass through the moving coil 33.

The thermo-couples 39 and 49 are so connected in circuit that the electromotive forces generated thereby oppose each other in the circuit which includes the measuring thermo-couple 3|. The hot junctions 4|, 42 of thermocouples 39 and '40 being kept at the same elevated temperature and the cold junctions thereof being kept at the same room-temperature, the electro-motive forces generated by thermo-couples 39 and 49. will be equal and opposite, thereby canceling out the efl'ects of these thermo-couples in the normal operation of the circuit. The moving coil indicating instrument 2. will then be acted on under the normal conditions by the electromotive force of the measuring thermocouple 3I.

The galvanometer 28 is preferably provided with the moving condenser plate 60, which is carried by the needle of the galvanometer and connected to the conductor 23 leading to the electronic control circuit. The condenser 60 may consist of one or a .number of condenser plates so arranged with respect to the condensers 26 and 21 that they come into suitably spaced proximity with each other when the needle moves into proper position.

I desire it to be understood that instead of movable and fixed condenser plates, which constitute a capacitative reactance, I may also employ an inductive reactance in the'form of fixed and movable inductance coils or I may use fixed and movable bodies of paramagneticmaterial adapted to come into proximity with each other to change the reluctance of a magnetic circuit,

or I may use a suitable light beam or beams in-' stead of the reactance members 26 and 21 acting on a light responsive member, with a shield replacing the member 50, or a mirror carried by the galvanometer for reflecting the light beam in a predetermined manner to accomplish the same result.

Figs. 3 to 5 are illustrations of the foregoing embodiments, including, respectively, photocell (Fig. 3), the reactance coil and core (Fig. 4), and movable coils (Fig. 5).

Referring to Fig. 3, I00 indicates an amplifier for a photocell ml, and exciter lamp and housing, I02 a photocell, I03 a lens, I04 the instrument scale, I05 the instrument pointer, I08 a movable supporting arm, and I01 an intersecting, opaque vane. II2 indicates the light beam.

Referring to Fig. 4, I08 indicates an amplifier of the oscillator type, I09 indicates a paramagnetic body; IIO indicates a coil which is in circuit with the oscillator amplifier I06.

Referring to Fig. 5, III indicates a short-circuited coil carried by pointer I05 and adapted to be brought in proximity to coil IIO by movement of the pointer I05.

The operation of the modifications of Figs. 3, 4 and 5 will be evident from the description of the operation of the principal embodiment.

In the case of the use of a reactance, the capacitative reactance 26 may consist of a substantially U shaped metal member having the two plates which are adapted to embrace the plate 50, carried by the needle 25 and arranged at the zero end of the scale and range of movement of the needle.

The condenser plates 26 and 21 are all curved on the same radius as the radius of the condenser plate 50 with respect to the spindle 29, and the condenser plates 21 may be of the same shape as described with respect to the condenser plates 26, but are preferably elongated and arcuate in shape.

The needle 25 is also preferably provided with a lateral extension 5| adapted to be used as a pointer in connection with a scale 52, which may be carried by a metal shield 53. The memben 54 is another metal shield of the same shape, having a similar curvature to the shield 53, both of these shields being curved with respect to the axis of the spindle 29.

Of course, any number of fixed and movable condenser plates may be used.

The shields 53, 54 are of sumcient width and length so as to enclose the condenser plates 26,

21 and 60 and prevent their being affected by the proximity of other metallic bodies or bodies having electrical capacity. The capacity of the hand or body of a person, for example. with respect to the members 26, 21, 60 would be so small in comparison to the effect of the shields 63. 54 as to prevent any effect of the body of the person on the instrument. The shields 63, 64 are grounded, as is the body of any person who comes into proximity with the instrument.

The scale 62 may be of any suitable range, but is preferably provided with a red field 65 at the zero end, in order to indicate the condition of the instrument when circuit leads of the thermocouple 3| are broken. The point at which the heating circuit to the furnace is to be opened is that corresponding to the left end 66 of the elongated reactance elements 21. I

The operation of the thermal controlling device is as follows: The thermo-couples 39 and 40 have their junctions kept at an elevated temperature by the heater 43, controlled by thermostat 44 and energized through conductors 51, 68 leading to the line. The circuit from the line is, of course, provided with a manual switch 59. When the line circuit is closed and the indicating instrument is so adjusted that its pointer 5I is located approximately at room temperature and out of the red field 55, the heating circuit to the furnace will be closed by the relays I5.

The electronic control circuit I8 will, for example, be in a state of oscillation, being ener- Thermo-couple 3I generates an electromotive force which-acts on the moving coil of the instrument 20, causing a flow of current in the moving coil and resulting in a field which reacts with the field of the galvanometer resulting from the permanent or electromagnet of the instrument. This causes the needle 25 to move in a counterclockwise direction in Fig. 1, indicating the elevated temperature of the furnace, and the heater II is thus kept turned on until the furnace reaches a predetermined temperature.

When the pointer 25 indicates such a temperature that the condenser plate 50 enters between the plates 21 at the point 56, then an additional amount of capacitative reactance is added to the electronic control circuit I8, which throws this circuit out of tune, and oscillation of the circuit ceases. This actuates the electromagnetic relays I5 which control the furnace heater II to shut off the heater circuit.

There is a lag between the arrival of a thermocouple at a predetermined temperature and the action of the furnace, and after the heater II is shut off the temperature of the furnace may continue to rise for a short time, during which time the needle 25 will continue to move toward the right in Fig. 1, but its relation to the electronic control circuit will be unchanged, since the condenser plate 50 will continue to be located within the fixed condenser plates 21.

Incidentally, the condenser plates 26 and 21 may both be mounted for suitable adjustment to adjust the characteristics of the instrument and the temperatures at which it will act. Thus, the needle 25 may over-travel without any danger of turning on the furnace II again, and therefore without any danger of. the furnace running away due to over-travel of the needle or the galvanometer getting out of synchronism with the controlling relays I5.

When the temperature of the furnace drops and the electromotive force generated by-the thermo-couple 3| decreases sufficiently, the needle 25 may again move to the left, moving the condenser plate 50 out of proximity to the condenser plates 21 and removing from the electronic control circuit the capacitative reactance caused by condenser plates 50, 21. The furnace is then again turned on, and the cycle of operations may be repeated, the furnace being turned on whenever necessary to supply heat.

In the event a break occurs in the leads 35. 36 of the measuring thermo-couple 3|, then the thermo-couple 39 is out of circuit also, but the thermo-couple 40 is in the circuit. The thermocouple 40 is then adapted to impress upon the moving coil 30 such an electromotive force that it moves the needle 25 to the left in Fig. 1, the pointer 5| being in the red field 55 and indicating that the thermo-couple circuit is out of order.

Furthermore, the condenser plate 50 is brought into proximity to the condenser plates 26 at the zero end of the instrument, and the electronic control circuit is affected in the way described above to actuate relays l5 and turn off the circuit to the heater ll. Thus, a break in the thermo-couple circuit causes the heater to be turned off and causes a suitable indication to be made on the scale of the galvanometer.

It should be understood that instead of an electric heating resistance H and electrical circuit makers and breakers for controlling resistance H, the furnace may be provided with a suitable oil burner or a gas burner, in which case the relays I5 would control valves for controlling the supply of liquid or gaseous fuel, and circuit makers and breakers or pilot lights for effecting suitable ignition.

In other embodiments of the invention the furnace may be provided with solid fuel, such as coal, supplied constantly by a stoker, which is provided with any suitable kind of electrical control, except that in this case the fuel in the furnace is kept in a constant state of ignition, but its combustion is regulated by the supply of air with suitable thermally controlled fans and the supply of fuel, also thermally controlled.-

In the case of an automatic controller the features of the thermo-couples 39, 40 may be employed by holding the temperature of the hot ends 4| and 42 of the auxiliary thermocouples higher than the temperature to be controlled.

In this case, if a break occurs in the measuring thermo-couple circuit, the unopposed electromotive force of the thermo-couple 40 will push the pointer and control element to the right of the scale, bringing the condenser'plates 50 and 21 into proximity, and shutting off the heat supply in the same way as if the temperature for which the instrument was set had been reached by the furnace.

' Referring to Fig. 2, this is a fragmentary circuit diagram which may be substituted for the thermo-couple arrangement of. Fig. 1 at the conductors 4B and- 48, which bear the same indicia. L1 this case the measuring thermo-couple 3| is arranged in the same manner, but it is connected by a conductor 60 in series with one of the leads 6| of an auxiliary thermo-couple 62, the other lead 63 being connected to conductor 48.

The conductor 46 is connected to the'other lead of measuring thermo-couple 3|. The thermo-couple 62 is a reference thermo-couple, whose hot junction 64 is kept at a constant elevated temperature of about to 250 degrees F. with a heating arrangement 43, 44, similar to that previously described.

The cold junctures of both thermo-couples are included in the same housing 65 so that they will all be kept at the same temperature.

The reference junction box 65 may then be located anywhere between the instrument and the measuring thermo-couple. The connections between the instrument and reference iunction may be copper leads, and the Junction box 65 may be suitably located to keep the cost of the leads between the thermo-couple II and the junction box 65 low.

The instrument movement 28 is so adjusted, by means of a zero adjustment screw that the pointer 5| comes to rest in the red field 55 under conditions of zero input or open circuit. The electromotive force of the reference thermocouple 62 at its constant temperature is such that it brings the pointer to the prevailing temperature of the cold junction. as indicated on the scale 52, whereas the measuring thermocouple 3l adds the necessary electromotive force for the difference between the cold junction and the hot-junction of measuring thermo-couple ll.

In this arrangement both thermo-couples are connected in the sense that the instrument will indicate the sum of their electro-motive forces. Any break in the leads anywhere between the instrument, reference junction, and measuring junction will open-circuit the instrument, which immediately returns the pointer to the red field A of Fig. 1, and indicates through its position the damaged thermo-couple leads. In the case of an automatic controller, as described with respect to Fig. 1, thezero position may actuate a contact maker and breaker to shut off the power or the supply of fuel to the furnace. In case the copper leads between the thermo-couple 3| and the instrument become short-circuited, the instrument also returns to" zero position for lack of any electromotive force, and automatically indicates damaged leads, or shuts off the power or fuel to the furnace.

It will thus be observed that I have invented an improved thermal controlling device which has the safety feature that the'furnace can never run away or become overheated due to a failure of the controlling device. Any failure of the controlling circuits in my invention causes the furnace to be turned off and a suitable indication to be given at the instrument.

Furthermore, the present thermal controlling devices are very sensitive and are adapted to keep the temperature of the furnace within very? close limits. The devices may be constructed at a low cost, and are practically fool-proof in operation. Where embodied in an automatic control, the present controlling devices require no attention from a safety point of view, as the furnace will be shut off in case anything goes wrong.

There is no possibility of the present capacity actuated circuit maker and breaker being affected by the proximity of other bodies having capacity, as in the devices of the prior art, and no possibility of the electromagnetic relays getting out of synchronism with the galvanometer controlling instrument, as might be the case in over-travels.

sire to avail myself of all changes within the scope of the appended claims.

Having thus described 'my invention, what I claim as new and desire to secure by Letters Patent of the United States, is:

1. In a thermal controlling device, the combination of a moving coil electrical instrument with a measuring thermo-couple having its terminals connected to said instrument, a pair of auxiliary thermo-couples, one of which is connected in series with each conductor leading from the measuring thermo-couple to the said instrument, said auxiliary thermo-couples having their hot junctions kept at an elevated temper ture and having their electromotive forces opp sing each other, and a conducting path lo cated between the leads from the measuring thermo-couple and between the auxiliary thermocouples whereby one of said auxiliary thermocouples is adapted to actuate said moving coil instrument when the leads from the measuring thermo-couple are on open circuit, whereby a break inthe leads in the measuring thermocouple is indicated on said instrument.

2. In a thermal controlling device, the combination of a main thermo-couple adapted to be subjected to the heat of a control heater with an auxiliary thermo-couple having its terminals arranged in series with the conductors leading from the main thermo-couple, the electromotive forces of said thermo-couples being additive, said auxiliary thermo-couple having its hot junction maintained at a constant elevated temperature which is adapted to serve as a reference temperature to assure the uniform operation of the main thermo-couple in a controlling circuit, said thermo-couples being connected to a moving coil type of electrical instrument, and

said auxiliary thermo-couple being adapted to move the indicatingelement of said instrmnent an amount corresponding to the prevailing temperature of the cold junctions of said thermovided with means at both ends of a predetermined range of movement on its scale for controlling the shut-ofi of the heat of a furnace to which the main thermo-couple is subjected,

whereby the furnace is controlled at a predetermined elevatedtemperature and is shut off when the thermo-couple leads are broken.

3. In a thermal controlling device, the combination of a main thermo-couple adapted to be subjected to the heat of a control heater, with a pair of auxiliary th'ermo-couples, each of said auxiliary thermo-couples being in series with one of the leads from the main thermoi-couple,

- and the leads having a resistance shunt across them between the connections to said auxiliary thermo-couples, with means for indicating the temperature at the main thermo-couple, said circuit also including a heater and an auxiliary heater at substantially constant temperature for said auxiliary thermo-couples whereby they are maintained at a predetermined elevated temperature at their hot junctions to serve as a reference temperature for the main thermo-couple, and whereby when either of the leads to the main thermo-couple is broken the indicating device may be actuated by-one or the other of said auxiliary thermo-couplea 4. In a thermal controlling device, the combination of a main thermo-couple adapted to be subjected to the heat of a control heater, with a pair of auxiliary thermo-couples, each of said auxiliary thermo-couples being in series with one of the leads from the main thermo-couple, and the leads having a resistance shunt across them between the connections to said auxiliary thermo couples, with means for indicating the temperature at the main thermo-couple, said circuit also including a heater and an auxiliary heater at substantially constant temperature for said auxiliary thermo-couples whereby they are maintained at a predetermined elevated temperature. at their hot junctions to serve as a reference temperature for the main thermo-couple, and

whereby when either of the leads to the mainthermo-couple is broken the indicating device may be actuated by one or the other of said auxiliary thermo-couples.

VICTOR W. BREI'I'ENSTEm.

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