US1976461A

US1976461A - Control system

Info

Publication number: US1976461A
Application number: US577885A
Authority: US
Inventors: David C Prince
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1931-11-30
Filing date: 1931-11-30
Publication date: 1934-10-09
Anticipated expiration: 1951-10-09
Also published as: GB390776A; DE615713C

Description

Oct. 9, 1934. D. c. PRINCE CONTROL SYSTEM Filed Nov. 30. 1931 Figl.

l lmrm nnrm Patented Oct. 9, 1934 PATENT OFFICE CONTROL SYSTEM David 0. Prince, Swarthmore, Pa., assignor to General Electric Company, a corporation of New York Application November 30, 1931, Serial No. 577,885

9 Claims.

My invention relates to control systems wherein a variable sourceof light is utilized and more particularly to means for controlling the temperature of electric furnaces and the like, and has I for its object the provision of a simple and reliable means for varying the input energy to an electric furnace to maintain the temperature of the furnace at a predetermined value.

More particularly my invention relates to temlo perature control systems employing radiant energy from the furnace or other heated device to activate alight sensitive control device, although it obviously has general application in control systems where a variable source of light is utilized. ll It is an object of my invention to provide a control system of this type giving uniform and accurate response independently of variations in the operating characteristics of the light sensitive device. so In accordance with my invention in one form thereof, I provide means for controlling the temperature of an electric furnace in response to the relative intensity of the light radiated from the furnace and from a standard source of light. My invention also comprehends a control system for an electric valve wherein the electric valve is controlled in response to the relative intensities of a plurality of light sources, one of which is variable.

For a more complete understanding of my invention, reference should be had to the accompanying drawing, Fig. 1 of which is a diagrammatic representation of a temperature control system for a furnace embodying my invention, while Figs. 2-5, inclusive, illustrate curves explanatory of the operation of my invention.

Referring to the drawing, I have shown my invention in one form as applied to the control of an electric furnace provided with a heating resistor 11 which is connected through the coils l2 and 13 of a saturable core reactor 14 to a suitable source of alternating current supply as is indicated by the

supply lines

15 and 16. The reactor 14 is also provided with a coil 17 connected in the output circuit of an electric valve 18, preferably of the type having an inert gas, such as mercury vapor within its envelope and sometimes termed a grid controlled arc rectifier. It will be understood that when the grid 19 is made sumciently positive when its anode 20 is positive the valve or rectifier 18 becomes conductive. As shown a battery 21 is connected in the grid circuitso as to maintain the grid 19 sumciently negative normally to prevent the passage of current through the valves. In order to render the valve 18 conductive under certain conditions of operation, alight sensitive device 22 is connected through a battery 23 to the primary winding 24 of a transformer 25, the secondary 26 of which is connected in the grid circuit of the rectifier.

The temperature of the furnace is controlled by comparing the amount of intensity of light from the furnace with the amount of intensity of the light of a standard source of radiation 27. As shown, the comparison is made by means of a 55 rotatably mounted mirror 29 provided with four reflecting surfaces arranged at right angles with each other to form a cube.

With the mirror29 occupying the full line position one of its reflecting surfaces serves to di- 7 rect light from a tube 31 extending within the furnace 10 to the light sensitive device 22. This tube 31 may be directed to a point on the wall of the furnace and as will be understood by those skilled in the art, the intensity of the light con- 7 ducted through the tube 31 to the mirror 29 will vary with the temperature of the furnace.

If the mirror occupies the position illustrated by the broken lines, light will be directed from the standard 27 to the light sensitive device 22. By rotating the mirror 29 at a speed such that the radiation from the standard 27 is thrown on the light sensitive device 22 while the anode voltage of the rectifier 18 is positive and the radiation from the standard 27 is directed to the device 22 while the anode is negative, the valve or rectifier 19 may be controlled in a manner to govern the temperature of the furnace 10. A synchronous motor 33 is therefore employed to drive the mirror 29. The motor 33 is connected by

conductors

34 and 35 across the

anode supply lines

15 and 16.

The anode or plate 20 is connected by a conductor 36 to the secondary 37 of a transformer 38, the primary 39 of which is connected to the

supply lines

15 and 16.

With the above understanding of the elements and their organization with respect to each other in the system, the operation of the system itself and the manner in which the light sensitive device 22 accurately controls the temperature of the furnace 10 due to the difierence in the intensity of the, light rays from the furnace with the light rays from the standard will be readily understood from the description which follows:

It. will be assumed that the

supply lines

15 and 16 are suitably energized from an alternating current source of supply (not shown) and that the standard light source 27 has been adjusted by means of the battery 32 to produce radiant energy having an intensity the same as the radiant en- 1 ergy directed by the tube 31 on the light sensitive device 22 when the temperature of the furnace has reached a predetermined value. As I have stated, the motor 33 drives synchronously the mirror 29 with respect to the anode voltage so that the light from the standard 27 is directed to the light sensitive device 22 during one half of a cycle of anode voltage while light from the furnace 10 is directed to the device 22 during the other half cycle of anode voltage.

Referring now to Fig. 2, the anode voltage is represented by the curve 40, while in Fig. 3 the condition is represented when the furnace is cold and consequently no light rays from the furnace are directed to the light sensitive device 22 during the negative half cycle of anode voltage. However, during the positive half of the cycle, the light rays from the standard are directed on the device 22 to cause a response from the photoelectric cell which, for the sake of clarity of description, is represented by the straight lines 41 and 42. The resulting voltage wave obtained at the terminals of the secondary winding 26 of the transformer 25 may therefore be represented by drawing a sinusoidal like curve 43 with the zero axis represented by the broken line 44 half way between the line 41 and the line 45 representing the zero axis.

It will be observed that the positive half of the cycle occurs while the anode is positive. The transformer 25 is therefore connected so that the grid 19 of the rectifier 18 is caused to be positive when the anode 20 is positive. The rectifier 18 therefore becomes conductive and saturating current flows through the coil 17 of the reactor 14.

Consequently the reactor permits current to flow through its coils 12 and 13 to the heating resistance 11.

As soon as the temperature of the furnace 10 increases radiant energy is produced which is directed on the device 22. This condition is represented in Fig. 4. During the negative half of the cycle of anode voltage the light rays from the furnace are directed on the device 22 to cause the light sensitive device 22 to respond as indicated by the

lines

46 and 47. The response of the device 22 due to the radiation from the standard 27 remains the same as before and is againrepresented by the lines 41 and 42.

The resulting wave form 48 of secondary voltage has the same phase relation with respect to the anode voltage as before but its amplitude has been decreased due to the response of the device 22 to the radiations from the furnace.

As soon as the temperature of the furnace increases so that its radiation as directed on the light sensitive device 22 is greater than that of the standard 2'7, the phase of the grid voltage reverses and control of the electric valve 18 is thereby obtained. This condition is represented in Fig. 5, the lines 41 and 42 again representing the response of the device 22 to the standard, while the lines 49 and 50 represent the response from the furnace radiation. In this case it will be observed that the peak of the voltage wave 51 of the secondary voltage occurs during the negative half cycle of anode voltage while in the previous cases (Figs. 3 and 4) the peak occurred during the positive half cycle of anode voltage. The result is a reversal in the phase of the grid voltage with respect to its anode voltage, which reversal renders the valve or rectifier 18 non-conductive. Consequently the saturation of the reactor 14 disappears thereby substantially preventing current flow through the heating resistance 11.

The control of the heating current or the rate of heat generation therefore depends on the relative intensities of the light rays from the standard 22 and the furnace 10. The effect of any variations in the response of the light sensitive device 22 as well as any variations of voltage of the battery 23 do not affect the temperature control of the furnace because it is the relative light radiation that eil'ectuates the temperature control of the furnace. In other words the response of the light sensitive device to the two sources of light will vary by equal amounts and result in the same grid control voltage for a given relative intensity of the two light sources, regardless of the sensitivity of the device 22.

It will be observed that the amount of light received by the device 22 is not constant over a half cycle of anode voltage. In the positions shown, the maximum amounts of light are directed to the light sensitive device 22. For instance, considering the full line position of the mirror it will be seen that the intensity gradually decreases as the mirror is rotated until no light from the furnace is directed to the device 22. In the same manner, the light directed by the mirror 29 from the standard 27 gradually increases to a maximum and then decreases to zero.

While I have described what I at present consider the preferred embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention and I, therefore, aim in the appended claims to cover all such changes and modifications as fall withk vided with input and output circuits, a source of alternating current supply for said output circuit, a standard source of light, a variable source of light, and means including a light sensitive member and a member for directing light thereto alternately from said standard source and from said variable source for impressing an alternating voltage on the input circuit of said valve varying in phase relation with respect to the voltage of said alternating current supply in accordance with the relative intensities of the light from said standard source an from said variable source. 2. In a control system, a grid controlled electric valve provided with input and output circuits, a source of alternating current supply for said source of alternating current for successive- 1y directing light from said sources to said light sensitive device, and means responsive to said light sensitive device for impressing on said input circuit a voltage varying in phase relation with respect to the voltage of said source of alternating current in accordance with the relative intensities of the light from said standard source and from said variable source.

3. In combination, a furnace, a heating resistor therefor, a grid controlled electric valve the conductivity of which is arranged to be controlled by variation of the phase relation between the grid and anode voltages, means responsive to said valve for controlling the energization of said resistor, a standard source of light rays, a light sensitive device, means for alternately directing light rays from said furnace and from' said standard source to said light sensitive device, and means responsive to said light sensitive device for varying the phase relation between the grid-and anode voltage of said valve.

4. A temperature control system comprising a furnace, a heating resistor therefor, a reactor for controlling the heating current of said resistor, a grid controlled rectifier for controllin the degree of saturation of said reactor, a source of alternating current for the anode of said rectifler, a standard source of light and means including a light sensitive device responsive to radiations .from said furnace and from said standard for controlling the phase relation between said grid and anode voltages whereby the saturation of said reactor is controlled so as to maintain a substantially constant temperature within said furnace.

5. In combination, a furnace, a heating resistor therefor, a standard light source, a light sensitive device, means for alternately directing radiations from said furnace and said standard source to said light sensitive device, a grid controlled rectifier arranged to control the energize.-

-tion of said resistor, means for electrically connecting said light sensitive device in the grid circuit of said rectifier so that said grid is positive with respect to the anode so long as the light rays from one of said sources of radiation of said rectifier has a greater intensity than the other of said sources.

6. In combination, a furnace having light emitting characteristics varying with its temperature, a heating resistor for said furnace, alight sensitive device, an arc rectifier having an anode and having input and output circuits for controllin the energization of said resistor, connections for connecting said light sensitive device to said input circuit, a source of 'alternating current supply for said output circuit providing a voltage on said anode, a standard source of light, a reflecting device having a plurality of movable reflecting surfaces, means for moving said surfaces in synchronism with said anode voltage to reflect light to said light sensitive device alternately from said furnace and from said standard, and means responsive to said light sensitive device for impressing on the input circuit of said rectifier a voltage varying in phase relation with respect to said anode voltage in accordance with the relative intensities of the light from said sources.

I. In combination, a furnace having light emit- -ting characteristics varying with its temperature, heating means for said furnace, an arc sectifler having input and output circuits for controlling said heating means, a. light sensitive device, connections for connecting said light sensitive device to said input circuit, a standard source of light, a source of alternating current for said output circuit, a reflecting device having a plurality of reflecting surfaces mounted for rotation to bring said surfaces into positions alternately to reflect light to said light sensitive device from said furnace and from said standard, means for rotating said reflecting device in synchronism with said output voltage so that when the anode of said rectifier is positive, light is reflected from said standard to said light sensitive device, and when said anode is negative, light is reflected from said furnace to said light sensitive device.

8. In combination, a furnace having light emitting characteristics varying with its temperature, a heating resistor for said furnace, a saturable core reactor for controlling the energization 'of said resistor, an arc rectifier having grid and anode circuits for controlling the saturation of said reactor, a source of alternating current supply for said anode circuit, a. light sensitive device connected to said grid circuit, a standard light source, a rotatably mounted reflecting device having a plurality of reflecting surfaces movable to interrupt light alternately from said furnace and said standard and to reflect it on said light sensitive device, a motor connected to said supply source for driving said reflecting device in synchronism with said supply source so that said light sensitive device alternately receives light from said standard and said source, and a transformer connected to said light sensitive device 0 and said grid circuit for impressing on said grid circuit a voltage varying in phase relation with respect to said anode circuit in accordance with the relative intensities of the light from said light sources.

9. The method of controlling a tube having input and output circuits by a light sensitive device, a standard source of light and a variable source of light, which consists in alternately directing light from said standard source and from 120 said variable source on said device, causing said device to generate a voltage varying in phase relation with respect to said output circuit in accordance with the relative response of said device to said sources, and causing said voltage to be 125 impressed on said input circuit so as to render said tube conductive when one of said sources has a greater light intensity than the other of said sources.

DAVID c. PRINCE. m