US2250207A - Temperature control system - Google Patents

Description

July 22, 1941.

E. D. SCHNEIDER TEMPERATURE CONTROL SYSTEM Filed Dec. 16, 1939 Fig.2.

. Inventor: Elbert D. Schneider, In W cfJMZW y His. Kt

torney.

energy. As is well known of inert gas such as Patented July 22, 1941 v 'rnmnaaruan coN'raoL SYSTEM ElbertD. Schneider, Scotia, N. Y., assignor to General Electric New York Company, a corporation of Application December 18, 1939, Serial No. 309,693

My invention relates to temperature control systems for the control 01 electrically heated devices, such as iumaces, ovens and the like. and has for its object a simple and reliable system giving close regulation of the temperature.

In carrying out my invention in one form, I

utilize high amperage capacity cold cathode electric discharge devices for controlling the supply of current to the Iurnace or other heated device. These discharge devices are controlled by hot cathode discharge devices which in turn are controlled by saturable core reactor phase shifting means responsive to the temperature of the heated device. For a more complete understanding of my invention, reference should be had to the accompanying drawing, Fig. 1 of which is a diagrammatic view of a temperature control system embodying my invention; while Fla. 2 is a vector diagram of the control voltages for the discharge devices.

Referring to the drawing, I have shown my invention in one form as applied to the control of an electric furnace It provided with a heating resistor or device I l which is supplied with energy from suitable alternating current supply mains or conductors l2 and 13 through two half-wave electric discharge devices I4 and it connected to pass current during alternate half cycles.

The discharge devices l4 and ii are of a cold mercury pool cathode, two element, enclosed type whose current carrying capacity is not limited by a hot filamentary cathode. Such discharge devices have the advantage of the property of passing large currents while the device itself may be physically small. The devices are provided arc will start and will continue indep'endently oi the grid voltage as long as the anode is positive. Furthermore, when the grid voltage is more negative with respecg to the anode voltage than the critical value at which the arc starts, the arc is prevented from starting and no current flows through the discharge device. 1

The discharge devices I8 and I9 are controlled by voltage supplied from the secondary windings.

with starting electrodes It and i1 bymeansfloi which a spot on the surface 0! the mercury pool cathodes lid and Fla is heated to make device, electrically conducting and start the therethrough.

Current is supplied to the starting electrodes l6 and II by two electric valve discharge devices It and I9. These devices are preferably three-element vapor electric discharge-devices of 'the type characterized by a relatively large energy output which is controlled by a small amount oi. grid in the art, the sealed envelope of this device contains a small quantity mercury vapor whereby the device becomes an arc rectifier. The arc between the anode and cathode and hence the conduc-- is controlled by the grid. It that at certain critical values the anode is positive, the

tivity of the device will be understood of grid voltage, when primary core reactor 26, the resistance and reactor being connected in series with each other across the supply mains.

For the purpose of causing a shift in phase of the voltage supplied by the secondaries 20 and II to thereby control the discharge devices I! and IS, the saturation of the reactor 26 is varied by,

means of a direct current, core saturating winding'fl, intermittent or half-wave D. 0. current to which is supplied through a three-element discharge device 28 connected in series with the winding 21 across the mains i2 and I3.

For the control of the device 28, voltage is supplied irom the secondary winding 29 connected across the .cathode and grid of the device 28. The winding 30 01 this secondary is energized in accordance'with the temperature of the furnace II by means of a Wheatstone bridge potentiometer comprising a resistor II connected across the secondary winding 24, a resistor connected across a portion of the secondary winding 24, and a resistor 33 having one end conneqted to a contact arm 34 adiustably cooperating with the resistor 32 and its other end adjustably connected to the resistor 3|. The primary winding 30 is adjustably connected across a variable portion of the resistor 33.

Thus the position of the contact arm 34 on the resistor 32 determines the bridge voltage applied to the resistor 33. Also this voltage may be varied to adjust the temperature setting, i. e., the v change in the energy input to the resistor II, is provided by moving the connection point II for, the coil 30 on the resistor 33. A. capacitor 3. is connected in parallel with the primary winding ll of such value as to draw a leading current to 5 compensate for the lag ing current through the winding 30.

In the operation of thesystem, movement of the contact arm 34 in response to change in the temperature of the furnace varies the voltage api0 plied by the secondary winding 2! to the grid 38 of the discharge device 2. When this voltage becomes sufllciently positive'or rather sumciently less negative with respect to the anode II, the

discharge device passes current substantially pro- 18 portional to the grid voltage during the positive half of each alternating current cycle. This current passes through the coil 21 and varies the saturation of the reactor 28. By thus varying "f the saturation of the reactor and hence its reacso tance, the voltage drop acrom it and across the resistance 25 is varied so as to shift the phime of the voltage applied to the primary winding 22.

In Fig. 2, the vector ll indicates the line voltage across the winding II, the vector ll the as time during the respective half cycles that the "85 discharge devices lland ll supply currart to the starting electrodes II and II. It will be observed that each of the devices II, II is connected across the mains i2 and il in series with the respective starting electrode,'the mercury pool terminal of" the discharge device I or II, and the furnace resistor ll. t

The discharge devices II and II each start in operation to pass current almost instantly after its respective starting discharge device II or "'45 starts topass current and the devices I4 and II each pass current during the remaining portion of its half oi the alternating current wave. .Tjhus two-wave pulsating direct current is supplied to the resistor H.

As the furnace temperature rises, the arm is actuated by the temperature responsive device 44 which may be of any suitable type and as is shown asa bulb andbeliows type device. With increase in temperature, the voltage applied to' 86 y the primary winding II is thereby decreased un- I ti 1 finally when the predetermined furnace temperature for which the equipment is adi -S ed is reached.thesaturationofthereactorliissuch that the phase angle or the control voltage sup-\ co plied to the discharge devices II and II causes these devices to start alternately durtng the respective positive and negative halvesof the current waves at such times in these waves that the current supplied to the resistor during the re-ss maining portions of the waves is just sufiicient to supply the furnace heat losses and maintain the desired furnace temperature. As the temperature rises, the energy inputio the furnace is decreased gradually and, consequently, the desired furna'ce temperature is reached with very little overshooting of temperature.

-In the event that the furnace temperature falls below the predetermined value to be maintained, I as might be caused by the lhtmdueuoh-cr a cold Bychang-So .charge into-tllefln-nace,thecontactarmis movedtocausethedcviceslland lltosupply current over greater portions of their half-waves andthussupplymore nergytothefurnace. In the event that the furnace temperature becomes toohigh,thecontactarmflreducestheenergy inputtoavaluelessthanrequiredtomaintain.

WhiIeLI have shown a particular embodiment of my invention, it will be understood, of course,

'thatIdonotwishto belimitedtheretmsince manymodiiimtionsmaybemade,and1,thereforecontempiatebytheappendedclaimstocovcr anysuchmodiflcationsasfailwithinthetnlc spiritandsoopeofmyin whatlclaimasncwanddesiretosecureby IettersPatentoftheUnitedStatesis:

2.Atemperaturecontrolsystunforelectricaily heated devices, comprising an electric heating resistor, a-cold cathode electric discharge device connectedinseries withsaidresistorfos c'ontroliingthesupplyofheatingcunenttosaid a vapor electric discharge device for startingsaidcoldcathodedcvicaphasesbifting startingmeam fm'saidvaporelectricdcvioein- Y cludingasatura'blecorereacto.andtunpcntu-e responslvemea'nsiorcmtroliingsaidphassshiftingmeansinresponsetothetempcratureofthe heateddevice.

3.Atemperaturecontrolsystemfor electrically heated devices, m electric heating mmnaacoldcathode Whammconnectedinserieswithsaidheatingmeansfa' ccslh'oisystemforeiectricvheated devicca'anelecn-leheasing resistor, a cold cathode am discharge deviceconnectedinscrieswith-saidresistorfor controllingthesuppiyofheatingcurrulttosaid resistor, a'vapor electric discharge devicefor starting said cold cathode device, phase shifting m connected across starting means for said vapor electric device including a saturable corereactor, a saturating a transformer having a primary windsaid conductors, a second transformer having a primary winding connected between an intermediate point on said first priductors,

winding for said reactor, control discharge means 5 mm winding and a point between said tfor supplying a saturating current to said winding, a Wheatstone bridge potentiometer including a variable resistance, means responsive to the voltage across said bridge for controlling ance and said saturable core reactor, a secondary winding on said second transformer connected to said vapor electric device to control said device to pass current, a saturating windsaid control discharge device, and means for ing g said reactor, control m-1 discharge varying said variable resistance in' response to the temperature of the heated device.

6. A temperature control system for electrically heated devices comprising an electric heating resistor, a pair of cold cathode electric 'discharge devices oppositely connected in series with said resistor for supplying two-wave pulsatcurrent to said resistor, a

ing direct heating pair of oppositely connected vapor electric discharge devices for devices, phase. shifting starting means for said vapor electric devices including a saturable core reactor, a saturating winding for said reactor, control discharge means for supplying a saturatstarting said cold cathode ing current to said winding, a Wheatstone bridge potentiometer including a variable resistance, means responsive to the voltage across said bridge for controlling said control discharge device, and

temperature responsive means for varying said variable resistance in response to the temper- 0 ature of the heated device thereby to vary the voltage across said bridge.

7. A temperature control system for electrically heated apparatus, comprising electric heating means, a'cold cathode electric discharge device for supplying half-wave pulsating direct current to said heating means, a vapor electric discharge device for starting said cold cathode device, supply conductors for supplying an alternating voltage for said heating means, a saturable core reactor connected in series with, each other across said conductors, a transformer having a primary winding connected across said conductors, a second transformer having a pria resistance and 40 mary-winding connected between an intermediate. point on said first primary winding and a point between said resistance and said saturable core reactor, a secondary winding on said second transformer connected to said vapor electric device to control saturating winding for said reactor, 9. control electric discharge device for supplying current to said saturating winding, a. secondary winding associated with a primary winding of said first said device to pass current, a

transformer, a second resistance connected across at least a portion of said secondary winding, means responsive to the temperature of the heated device for varying said second resistance,

and connections for applying a varying voltage '7 to control the grid from said second resistance of said control electric discharge device and thereby control the saturation of said reactor whereby the phase angle of the voltage supplied by the secondary winding of said second transformer is shifted to control said vapor electric device.

8. A temperature control. system for electrically heated apparatus, comprising electric-heating means, a cold cathodeselectric discharge dea resistance and a saturable core reactor connected in series with each other across said convice for supplying current to said heating means, 7

device for supplying current to saidsaturating winding, a secondary winding associated with a primary winding of said first transformer, a second resistance connected across said secondary winding, a third resistance connected across at least a portion of said secondary winding, a fourth resistance connected to intermediate points of said second and third resistances, means responsive to the temperature of the-heated device for moving the point of connection between said fourth resistance and said third resistance to vary thereby the potential across said fourth resistance, andconnectionsfor applying the voltage across at least a portion of said fourth resistance to control the grid of said control elec-.

. tric discharge device. and thereby control the saturation of said reactor whereby the phase angle of the voltage supplied by the secondary winding of said second transformer is'shifted to control said vapor electric device.

a 9. A temperature control system for electrically heated apparatus, comprising an electric heating resistor, a pair of cold cathode electric discharge devices oppositely connected in series with said resistor for supplying half-wave pulsating direct-current to said resistor, a pair of vapor electric discharge devices for starting.

said cold cathode devices, supply conductors for supplying alternating voltage for said resistor, a resistance and a saturable core reactor connected in series with each other across said conductors, a transformer having a primary winding connected across said conductors, .a second transformer having a primary winding connected between an intermediate point on said first primary winding and a point between said resistance and said saturable core reactor, two secondary windings on'said second transformer oppositely connected to said vapor electric devices to control said devices to pass current alternately, a saturating winding for said reactor, a control electric discharge device for supplying pulsating direct current to said saturating winding, a secondary winding associated with the.

primary winding of said first transformer, a secv ondresistance connected across said secondary winding, a third rmistance connected across at least a portion of said secondary winding, a fourth resistance connected to intermediate points ,of said second and third resistances, means responsive to the temperature of the heated device for moving the point of connection between said fourth resistance and said third resistance to varyithereliythe potential across said fourth resistance, and a third transformer having one winding connected across at least a portion of said fourth resistance and a second'winding associated with said first winding connected to control said control electric discharge device and thereby control thesaturation of said reactor whereby the phase angle of the voltages supplied by the secondary windings of said second transformer is shifted to control said vapor electric devices.

rtions, a

transformerhavingaprimarywinding connectedbetweenan control system for electum-11y heating heated apparatus, comprising electricmeans, supply connection; for supplying an alternating voltage,

an electric discharge device for supplying pulsating direct current from. said sumly connections to said heating means, a second electric discharge device for starting said first discharge device, a resistance and a saturable core reactor connected in series with each other across said supply connections,

, a first winding connected across said supply connections, a transformer having a primary winding connected between an intermediate point on said first winding and a point between said resistance and said saturable core reactor, a

secondary winding on said transformer connected of said reactor whereby the phase angle of the voltage supplied by said secondary winding of said second transformer is shifted to control said second electric device.

ELBERT n. scnmsmm.

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