US2303110A - Regulating system - Google Patents

Description

1942 w. o. COCKRELL 2,303,110

REGULATING SYSTEM Filed March 20, 1941 Inventor-z William D. CockPeH,

H is Attorney.

Patented Nov. 24, 1942 REGULATING SYSTEM William D. Cockrell, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application 20, 1941, Serial No. 384,335

8 Claims. (Cl. 236-78) This invention relates to regulators for apparatus or systems in which a considerable time lag is present between the departure of the regulated characteristic from the predetermined normal value and the return to such value, such for example, as in the case of heating apparatus like furnaces'and rotary kilns, and it has for an ob- ,lect the provision of a simple, reliable and improved regulator of this character.

In regulating systems in which a substantial time lag is present, attempts to operate the control means directly by a device responsive to the departure of the regulated condition or characteristic from normal value usually result in a serious hunting cycle. For example, in the case of a furnace, in which there may be a time lag of a minute or more, operation of the control by a simple pyrometer in response to instantaneous temperature will result in a very extreme and undesirable hunting cycle. According- 1y, a further object of'the invention is the provision of a regulating system in which the regulator operates to return the regulated characteristic to normal value and in which provision is made for compensating for the efi'ectiv'e time lag.

In carrying the invention into effect in one form thereof, electric valve means having an anode, a cathode, and a control grid are provided for varying the characteristic which is to be regulated, and means responsive to a departure of the regulated characteristic from a predetermined value are provided for varying the relative values of the voltages of the grid and cathode to change the conductivity of the electric valve means and thereby initiate a correcting action to reverse the departure of the regulated characteristic, together with a capacitor connected in the grid cathode circuit of the electric valve means, and means responsive to the change in conductivity of the valve means for applying a voltage to charge the capacitor, and of such polarity as gradually to restore the normal relationship between the grid and cathode voltages as the capacitor becomes charged and thereby to restore the original condition of conductivity of the valve means before the regulated characteristic returns to normal value, and also responsive to the restoration of the original condition of conductivity of the valve means for interrupting the application of voltage to the capacitor.

In illustrating the invention in one form thereof, it is illustrated as applied to a furnace for heating skelp which is being shaped and rolled into the form of a finished steel pipe. The

the regulation of apparatus and processes in which a substantial time lag between departure and restoration is present.

For a better and more complete understanding of the invention, reference should now be had to the following specification and to the accompanying drawing in which Fig. 1 is a simple, diagrammatical illustration of an embodiment of the invention, and Fig. 2 is a simple, diagrammatical sketch illustrating an application of the invention to a furnace for heating skelp.

Referring now to the drawing, a fiat strip of hot steel I0 is shown passing through a furnace I I and being delivered from the furnace to a pair of forming rolls I2 by means of which it is shaped into the form of a finished pipe. Such a strip of steel is usually referred to as skelp. As the skelp leaves the furnace, it is viewed by a photoelectric pyrometer l3 and if the temperature is not correct, the skelp is speeded up or slowed down to permit more or less heat to be absorbed as required to bring the skelp to the correct temperature. Since approximately one minute is required to bring the skelp to the working temperature of 2500 deg. F., any attempt to operat the control means directly by the pyrometer in response to the instantaneous temperature of the skelp results in serious hunt ing. The forming rolls I2 are driven by suitable driving means illustrated as an electric motor I4 supplied from a suitable source which is not shown but which is indicated by the and designation of the leads to the armature. The motor I4 has a field winding la which is supplied from a suitable source which may be and preferably is the same source as that from which the armature is supplied.

A motor driven field rheostat serves to vary the speed of the motor II. This rheostat is illustrated as comprising a resistor I5, connected in series with the field winding I45, a stationary contact rail I6, and a movable contact arm I1 which bridges the rail I6 and the resistor I5 and is mounted on a lead screw I8 so as to be advanced or withdrawn along the screw in response to rotation thereof by a motor I9. This motor I9 is illustrated as a split series field Wind-f runs in one direction and when the motor is It may be assumed that when the motor is energized through the field winding I93, it rotates in such a direction as to move the movable contact arm I! to the left and that when the motor I9 is energized through the field winding l9b, it rotates in such a direction as to move the movable cor tact arm I! to the right. Instead of controlling the speed of the skelp, the motor l9 could be used to control a fuel valve or any other control device.

In the application illustrated, it is required that the temperature of the skelp as it is delivered from the furnace I i be maintained substantially constant at a predetermined value and accordingly, means are provided for maintaining the temperature of the skelpsubstantially constant at this predetermined normal value. This is accomplished as pointed out in the foregoing by varying the speed of the roll driving motor M in response to changes in the temperature of the skelp. These means are illustrated as a device which is responsive to radiant energy of the skelp, such for example, as a photoelectric pyrometer l3, an amplifying device 20, and suitable electric valve apparatus illustrated as a pair of electric valves 2| and 22 controlled by the amplifier 20.

together with suitable switching means illustrated as a pair of electromagnetic contactors 23 and 24 respectivel controlled by the valves 2| and 22 for in turn controlling the pilot motor IS.

The operating coils of electromagnetic contactors 23 and 24 are energized from a source of alternating voltage represented by the supply line 25 through electric valves 2| and 22 and transformers 26 and 21, respectively. The electric valves 2| and 22 are each provided with an anode, a cathode, and a control grid and may be of any of the several types well known in the art. However, it is preferred to use discontinuous control electric valves, such for example, as valves of the vapor electric discharge type. The term discontinuous control electric valves is intended to refer to valves of the type in which the starting of current in the valve may be controlled by the potential on its control grid, but in which the current in the valve may be interrupted only by reducing the anode voltage below a predetermined critical value. In order to control the con ductivity of the valves 2| and 22, there is provided a source of unidirectional control voltage represented by the supply lines 28 and 29 across which is connected a voltage divider 30, and the grids of the electric valves 2| and 22 are connected to the same point on the voltage divider 30 by means of the movable contact arm 30.. Suitable current limiting resistors 2 a and 22. are included in circuit with the grids as illustrated.

There is also provided a second voltage divider connected across the source of unidirectional voltage 28 and 29 comprising a resistor 3|, a resistor 32, an electric valve 20, the conductivity of which is variable and therefore constitutes a variable impedance, and a portion of the voltage divider 30 between the movable contact 301; and the side 29 of the unidirectional source of voltage. The cathodes of electric valves 2| and 22 are connected to electrically spaced terminals on this second voltage divider. They are shown as being connected to points 32:. and 32b of the resistor 32 which comprises one portion of the second voltage divider. The valve 20 is provided with an anode, a cathode. and a control grid. As shown in the drawing, the valve 20 is a pentode and is provided with a screen grid and a suppressor grid in addition to the control grid. Instead of the pentode, the valve 20 may be of the well known three-element types of valve. It is preferred that the valve 20 shall be of the high vacuum, pure electron discharge type. The control grid of the valve 20 is connected to the cathode of the photoelectric cell |3 through a resistor 34.

The photoelectric cell I3 and the pentode amplifier valve 20 constitute a stable amplifier system in which the currents in the anode circuit of the valve 20 increase with increased temperature of the skelp ill. The IR, drop in the resistors 3| and 32 subtracts from the voltage of the source 28 and 29, which may be some suitable value such, for example, as volts, and lowers the voltage of the cathodes of the two electric valves 2| and 22 as the temperature increases. The point 321: to which the cathode of the cold electric valve 22 is connected is 4 the most negative point of the resistor 32, whereas the voltage of the point 32b to which the cathode of the hot electric valve 2| is connected is more positive. The voltage of the point 30a on the first voltage divider to which the grids of the valves 2| and 22 are connected is a preset value which can be adjusted as desired. The voltages of the cathodes are such that at the preset value of the grid voltage, and the correct temperature of the skelp. the "hot valve 2| is non-conducting and the cold valve 22 is conducting. As a result of this condition of conductivity, the operating coil of contactor 23 is deenergized so that its normally open contacts are open as illustrated and the operating coil of contactor 24 is energized so that the normally closed contacts of this contactor are open. For the purpose of preventing hunting, a capacitor 35 is connected in the common grid circuit of the valves 2| and 22. A discharge resistor 36 is connected in parallel with the capacitor. The grid current which flows through resistor 36 is insufficient to cause any appreciable voltage drop across the resistor. When the valve 2| is con ducting, the contactor 23 is picked up and i s normally open contacts 23b are closed to connect the negative side 29 of the unidirectional voltage source to the grid terminal of the capacitor 35, and similarly, when the valve 22 is non-conducting the contacts 241, of contactor 24 are closed and the positive side 28 of the unidirectional voltage source is connected to the grid terminal of the capacitor 35.

With the foregoing understanding of the apparatus and its organization in the system, the operation of the complete system itself will readily be understood from the following detailed description: Assuming that the skelp Ill leaving the furnace II in the zone viewed by the photoelectric cell I3 is at the correct desired temperature and that the movable contact 30- is at the proper point on the voltage divide 30, the voltage drops across the portions of the resistor 32 of the second voltage divider are such that the valve 2| is nonconducting and the valve 22 is conducting, as explained in the foregoiiv'. As a result, the contacts of both contactors 23 and 24 are open and there is no movement of the contact arm driving mot-or l9.

If the temperature of the skelp rises above the desired predetermined temperature, the current through the photoelectric cell l3 will increase and this will increase the voltage drop across the resistor 33 so that the voltage of the control grid of the valve 20 is increased relative to its cathode. As a result, the impedance of the valve 20 is decreased and the anode current is increased. This results in increasing the current flowing through the resistors 3| and 32 with the result that the voltages of the. cathodes oi the valves 2| and 22 are decreased relative to their grid voltages. This has the same effect on the valves 2| and 22 as making the grid voltages of these valves more positive. In other words, it tends to make the valves 2| and 22 conducting. However, the valve 221s already conducting and consequently, th only effect is to render the valve 2| conducting. In response to valve 2| becoming conducting, contactor 23 closes its normally open contacts 233 and 23b. Contacts 23a in closing connect the contact driving motor |9 to the source 28, 29 through the split 'fleld winding I93 so that the motor I9 is energized in such a direction as to move the contacts H to the left and thereby increase the amount of the resistor IS in circuit with the field winding of the motor II which advances the skelp. This weakens the field of the motor l4 and causes its speed to be increased with the result that the speed of the skelp I through the furnace H is increased and less heat is absorbed by the skelp.

Simultaneously with the closing of the contacts 23a to increase the speed of the skelp through the furnace, the contacts 23b are also closed to connect the grid'terminal oi the capacitor 35 to the negative side of the unidirectional voltage source. As a result, the voltage between the contacts 30a on the voltage divider 30 and the negative side 29 of the source is applied to the capacitor and a charge begins to build up on the capacitor. A resistor 31 in circuit between the grid terminal of the capacitor 35 and the source limits the charging current of the capacitor to a predetermined value. As the charge builds up on the capacitor, the grid terminal becomes more and more negative as the charge increases and this negative voltage is applied to the grids of the valves 2| and 22 thereby to restore the original normal relationship between the voltages of the grids and cathodes of the valves 2| and 22 which existed before the skelp temperature departed from the correct value. The restoration of the original relationship between the grid and cathode voltages of valves 2| and 22 restores the original condition of conductivity of the valve 2|. In other words, the valve 2| becomes non-conducting, thereby deenergizing the operating coil of contactor 23. In response to deenergization. contactor 23 opens its normally open contacts 23a to deenergize the 'contact driving motor I! and also to disconnect the grid terminal of the capacitor 35 from the negativeside of the unidirectional voltage source, thereby interrupting the charging of the capacitor. Since the resistor 36 is connected in parallel with the capacitor 35, the opening of contacts 231, permits the capacitor 35 to lose its charge slowly and therefore the relationship between the grid and cathode voltages of the valves 2| and 22 is maintained. However. the capac tor 35 does discharge through the resistor 36 at a rate which is dependent upon the ohm c resistbe so related to the natural heating cycle of the furnace and skelp that the grid voltages return to normal value at the same rate that the oathode voltages return to normal and thus the original normal relationship between the grid and cathode voltages of the valves 2| and 22 is maintained as the temperature of the skelp returns .to the normal desired value. If the proper value of charging and discharging resistors is chosen, it is' possible to match the natural time cycle of the process closely enoughso that but a single corrective operation takes place for any moderate deviation of the temperature from the nor;

mal desired value.

From the foregoing it will be clear that for slow temperature changes, the contactor will be operated only long enough to obtain the smallest desired increment of control (perhaps a single button on the motor operated field rheostat l5) before the charging of the capacitor 35 has restored the original normal relationship between the voltages of the grids and cathodes of valves 2| and 22. For more rapid temperature changes a longer control time results. Thus the control as described has the ability to respond instantly to temperature changes and to apply a corrective action fairly proportional to the correction required.

If the temperature of the skelp ill decreases 1 below the desired normal value, the operation will be similar but opposite to that described in the foregoing. Thus if the temperature of the skelp ||l decreases below the desired normal value, the current flowing in the circuit of the photoelectric cell l3 decreases and this decreases the positive voltage of the control grid of electric valve 20. Decrease-of the positive voltage of the control grid of valve 20 increases its impedance and thereby decreases the current flowing through the resistors 3| and 32 of the secondvoltage divider. The result of this'is to make the voltages of the cathodes of valves 2| and 22 more positive with respect to the voltages of the grids which has the same eifect as making the grid voltage more negative. The increasing cathode voltage of valve 22 causes the valve to become non-conducting and thereby to deenergize the operating coil of contactor 24 which in response to deenergization closes its normally closed contacts 249. and 24b. Contacts 249. in closing cause the motor l9 to run in a direction to move the movable contact arm to the right thereby to decrease the speed of the motor I4 and thereby to decrease the speed of the skelp ||J through the furnace The decrease in the speed of the skelp I0 allows it to absorb more heat and as a result, the decrease in temperature is checked and reversed.

The closing of the contacts 24b connects the grid terminal of the capacitor 35 to the positive side 28 of the unidirectional voltage source and as a result, the capacitor 35 is charged in a positive direction and an increasing positive voltage is applied to the grids of the valves 2| and 22.

When the original relationship between the voltages of the grids and cathodes of valves 2| and 22 is restored, valve 22 again becomes conducting and the operating coil 'of contactor 24 is energized. In response to energization, the contactor opens its contacts 245 and 24b. The opening of contacts 24:, terminates any further increase in the corrective action of rheostat motor I9, and the opening of contacts 24b disconnects the grid terminal of the capacitor 35 from the unidirectional voltage source. The remainder of the operation is similar but opposite in sign with respect to that described in the foregoing as applicable to the case of increasing temperature.

Although in accordance with the provisions of the patent statutes, this invention is described as embodied in concrete form and the principle thereof has been explained together with the best mode in which it is now contemplated applying that principle, it will be understood that the aption, means for controlling said apparatus to vary said characteristic comprising an electric valve provided with an anode, a cathode, and a control grid, means responsive to a departure of said characteristic from a predetermined value for varying the relative voltages of said grid and cathode to change the conductivity of said valve and initiate a correcting action to counteract said departure of said operating characteristic, a capacitor in the grid cathode circuit of said valve, 2. source of unidirectional voltage, a connection from one side of said source to one terminal of said capacitor, means responsive to said change in conductivity for completing a connection from the other side of said capacitor to said source thereby gradually to restore the original relationship between said grid and cathode voltages in response to the charging current of said capacitor thereby'to restore the original condition of conductivity of said valve and responsive to the said condition for disconnecting said capacitor from said source and a discharge path for said capacitor for maintaining said normal values of said grid and cathode voltages as said characteristic returns to said predetermined value.

2. A regulator for apparatus having an operating characteristic to be maintained constant comprising in combination means for controlling said apparatus comprising a first electric valve for increasing the magnitude of said characteristic, a second electric valve for decreasing the magnitude of said characteristic, each of said valves having an anode, a cathode and a control grid, means responsive to a predetermined value of said operating characteristic for energizing one of said valves and deenergizing the other of said valves and responsive to a departure of said characteristic for simultaneously varying the relative voltages of the grids and cathodes of said valves to change the conductivity of one of said valves to counteract said departure of said characteristic from said predetermined value, a voltage divider connected in the cathode grid circuit of said valves, a capacitor in said cathode grid circuit having one of its terminals connected to an intermediate point of said voltage divider, a unidirectional source of voltage, means respons ve to said change in conductivity of one of said valves for connecting the other terminal of said capacitor to one side or the other of said source thereby gradually to restore the original relationship of the grid and cathode voltages and to terminate the correcting action of said valve and responsive to the termination oi said correcting action for disconnecting said capacitor from said source and a capacitor for maintaining said original relationship of said grid and cathode voltages as said characteristic returns to said predetermined value.

3. A regulator for apparatus having an operatand having one terminal connected to an inter mediate point of said divider, means responsive to a predetermined value of said characteristic for energizing one of said valves and deenergizing the other of said valves and responsive to a departure of said characteristic from a'predetermined value for simultaneously varying the relative voltages of said grids and cathodes thereby to change the conductivity of one of said valves and to initiate a correcting action to counteract said departure, a switching device responsive to said change in conductivity for connecting the other terminal of said capacitor to one side or the other of said source thereby gradually to restore the original relationship between said grid and cathode voltages in response to the charging current of said capacitor and to terminate said correcting action and responsive to the resulting change in conductivity of said one of said valves for disconnecting said capacitor from said source and means providing a discharge path for said anode, a cathode and a control grid, a source of unidirectional voltage, a voltage divider connected across said source, a capacitor having one terminal connected to an intermediate point of said voltage divider and having the other terminal connected to both said grids, means responsive to a predetermined value of said characteristic for rendering one of said valves conducting and the other nonconducting and responsive to a departure of said characteristic from said predetermined value for simultaneously varying the voltages of said cathodes relative to said grids thereby to change the conductivity of one of said valves and initiate a correcting action to counteract said departure, switching devices individually responsive to changes in the conductivity of said valves for connecting the grid terminal of said capacitor selectively to the positive or negative side of said source to restore the original relationship 01 said grid and cathode voltages to terminate said correcting action and responsive to the resulting change in conductivity of said valves for disconnecting said capacitor from said one side of said source and a discharge path comprising a resistance connected in parallel with said capacitor for maintaining said original relationship between said grid and cathode voltages as said char-. acteristic returns to said predetermined values;

5. A regulator for apparatus having an operat discharge path for said 75 ing characteristic to be regulated comprising in combination a source of unidirectional voltage, a first voltage divider connected across said source, a second voltage divider including a variable impedance device connected across said source, means responsive to said characteristic for varying said impedance device, a pair of electric valves each having an anode, a cathode and a control grid, said grids being connected to the same point of said first divider and said cathodes being connected to different points of said second divider such that when said characteristic has a predetermined normal value one of said valves is conducting and the other is nonconducting and departure of said characteristic from said normal value changes the relative values of the voltages of said grids and cathodes thereby to change the conductivity of one of said valves and initiate a correcting action to counteract said departure, a I

capacitor in the common grid circuit, means responsive to said change in conductivity for applying a voltage to charge said capacitor thereby gradually to restore the original relationship of said grid and cathode voltages and terminate the action of said one valve and responsive to the termination of said action for interrupting the application of voltage to said capacitor and means providing a discharge path for said capacitor to maintain said original relationship between said grid and cathode voltages as said characteristic returns to said predetermined normal value.

6. A regulator for apparatus having an operating characteristic to be regulated comprising in combination a source of unidirectional voltage, a first voltage divider connected across said source, a second voltage divider including a variable impedance device connected across said source, means responsive to said characteristic for varying said impedance device, a pair of electric valves each having an anode, a cathode and a control grid, said grids being connected to an intermediate point of said first divider and said cathodes being connected to different points of said second divider such that for a predetermined value of said characteristic the voltages of the grid and cathode of each of said valves have normal relative values and departure of said characteristic from said predetermined value changes the relative values of said grid and cathode voltages thereby to change the conductivity of one of said valves and initiate a correcting action to reverse said departure, a capacitor connected between said grids and said first voltage divider, means individually responsive to a change in conductivity of one of said valves for selectively connecting one terminal of said capacitor to the positive or negative side of said source thereby gradually to restore said normal relative values of said grid and cathode voltages in response to the charging current of said capacitor thereby to restore the original condition of conductivity of said valves and responsive to the restoration of said original conditions of conductivity for disconnecting said capacitor from said source, and a discharge path for said capacitor for maintaining said normal values of said grid and cathode voltages as said characteristic returns to said predetermined value.

'I. A temperature regulating system for heating apparatus and the like comprising in combination, a pair of electric valves and means conpedance device, a pair trolled thereby for increasing or decreasing said temperature in response to selective changes in the conductivity of said valves, each of said valves having an anode, a cathode and a control grid, a source of unidirectional voltage for applying voltages to said grids and cathodes having a normal relationship when said temperature has a predetermined value, photoresponsive means responsive to a departure'of said temperature from said predetermined value for varying the relationship of said grid and cathode voltages to change the conductivity of one of said valves and initiate a temperature correcting action, a voltage driver connected in the cathode grid circuit of said valves, a capacitor connected in the grid circuit of said valves and having one terminal connected to an intermediate point of said voltage divider, means responsive to said change in conductivity for connecting the other terminal of said capacitor to one side or the other of said source to charge said capacitor and gradually restore said normal relationship of said grid and anode voltages in response to the charging current of said capacitor thereby to restore the original condition of conductivity of said valves and terminate the action of said valve and responsive to the restoration of said original condition for terminating the application of voltage to said capacitor and means providing a discharge path for said capacitor to maintain said original condition of conductivity of said valves as said temperature returns to said predetermined value.

8. A temperature regulating system for heating apparatus and the like comprising in combination a source of unidirectional voltage, a first voltage divider connected across said source, a second voltage divider including a variable impedance device connected across said source, photoresponsive means responsive to the temperature of said apparatus for varying said imof electric valves each having an anode, a cathode and a control grid, said grids being connected to an intermediate point of one of said dividers and said cathodes being connected to different points of the other of said dividers such that for a predetermined value of said temperature the grid and cathode voltages of each of said valves have normal relationships causing one of said valves to be conducting and the other of said valves to be nonconducting and departure of said temperature from said predetermined value changes the relative values of said grid and cathode voltages thereby to change the conductivity of one of said valves and initiate a correcting action to reverse said departure, a capacitor in the grid circuit of said valves, means responsive to said change in conductivity for selectively applying a positive or negative voltage to charge said capacitor and gradually restore the normal relationships of said grid and cathode voltages to restore the original condition of conductivity of said valves and responsive to the restoration of said condition for interrupting the application of voltage to said capacitor and means providing a discharge path for said capacitor to maintain said original condition as said temperature returns to said predetermined value.

WILLIAM D. COCKRELL I CERTIFICATE OF CORRECTION. Patent No. 2,505,110. November 2 9 4 WILLIAM D. COCKRELL.

it is hereby certified that error appears in-the printed'specificationof the above numbered patent requiring" correction as follows; Page 1;, first colmnn, line 51;, claim 1, for-other'side of said capacitor to said source read --other terminal of said capacitor tojche other side of said source";

page 5, second column, line 15, claim Y-Q for driver read d n; and that the said Letters Patent should be read with this correctionthere in that the same may conform to the record of the case in the Patent fice. Q t

Signed and sealed this 26th da of January, A. D. 19%.

Henry Van Arsdale,

(Seal) Acting Commissioner of Patents.

CERTIFICATE OF CORRECTIOI.

Patent 'No. 2,505,110. N vember 21;, 19kg,

' WILLIAM D. COCKRELL.

jlt is hereby certified that error appears 'iri-the pr of the ebove numbe colmsn, line 51L, claim 1, for-other'side of said capacitor to said source" (1 --other terminal of said capacitor tojzhe other side second column, line 15, c1aim 7, for "driver" read 1' hould be read with this correctionthere' res P 5: and that the said Letters Patent 8 in that the same may conform to the record of the case in the Patent fice s Signed and sealed this 26th dsy of January, A. ;D. 1914.5;

Henry Van Arsda1e,

(Seal) Acting Commissioner of Patents.

irited'specificationred patent requiring correction as follows: Page h, first of said source"; I

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