US3819950A - Reference voltage generator for thermal processes having an exponential temperature-time characteristic - Google Patents
Reference voltage generator for thermal processes having an exponential temperature-time characteristic Download PDFInfo
- Publication number
- US3819950A US3819950A US00361551A US36155173A US3819950A US 3819950 A US3819950 A US 3819950A US 00361551 A US00361551 A US 00361551A US 36155173 A US36155173 A US 36155173A US 3819950 A US3819950 A US 3819950A
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- United States
- Prior art keywords
- regulator
- input
- capacitor
- exponential
- output
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- Expired - Lifetime
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- 238000000034 method Methods 0.000 title claims abstract description 16
- 230000008569 process Effects 0.000 title claims abstract description 16
- 239000003990 capacitor Substances 0.000 claims abstract description 22
- 230000008878 coupling Effects 0.000 claims description 8
- 238000010168 coupling process Methods 0.000 claims description 8
- 238000005859 coupling reaction Methods 0.000 claims description 8
- 238000007493 shaping process Methods 0.000 claims description 2
- 230000000630 rising effect Effects 0.000 abstract description 3
- 230000000694 effects Effects 0.000 abstract description 2
- 239000013643 reference control Substances 0.000 description 3
- 230000033228 biological regulation Effects 0.000 description 2
- 230000001276 controlling effect Effects 0.000 description 2
- 229910000831 Steel Inorganic materials 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
Images
Classifications
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D23/00—Control of temperature
- G05D23/19—Control of temperature characterised by the use of electric means
- G05D23/1902—Control of temperature characterised by the use of electric means characterised by the use of a variable reference value
- G05D23/1904—Control of temperature characterised by the use of electric means characterised by the use of a variable reference value variable in time
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D23/00—Control of temperature
- G05D23/19—Control of temperature characterised by the use of electric means
- G05D23/20—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature
- G05D23/22—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature the sensing element being a thermocouple
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Automation & Control Theory (AREA)
- Control Of Temperature (AREA)
- Feedback Control In General (AREA)
Abstract
An improved arrangement is described for generating an exponential reference voltage for comparison in a suitable regulator with a value proportional to the measured temperature output of a thermal process having a desired exponential temperature-time characteristic. The generator includes an R-C circuit chargeable via a DC source wherein the time constant of the R-C circuit is chosen to equal the thermal time constant of the exponential thermal process. The voltage increase across the capacitor during charge or the voltage decrease across the capacitor during a subsequent discharge is employed selectively as a reference voltage for controlling, respectively, a rising and a falling exponential temperature-time characteristic of the thermal process. A cathode follower or other input buffer amplifier is coupled to the output of the capacitor to isolate the R-C circuit from the loading effect of the input of the regulator.
Description
United States Patent Korntheuer June 25, 1974 REFERENCE VOLTAGE GENERATOR FOR THERMAL PROCESSES HAVING AN EXPONENTIAL TEMPERATURE-TIME CHARACTERISTIC [75] Inventor: Friedrich Korntheuer, Kapfenberg,
[2l] Appl. No.: 361,551
[30] Foreign Application Priority Data May 18, 1972 Austria 4331/72 [52] US. Cl. 307/149, 307/152 [51] Int. Cl. G05d 23/00 [58] Field of Search H05b/23/0O; 307/149, 152;
[56] References Cited UNITED STATES PATENTS 3.010,035 ll/l96l Calvert et al. 307/152 Primary Examiner-L. T. Hix Attorney, Agent, or FirmArthur O. Klein 5 7 ABSTRACT An improved arrangement is described for generating an exponential reference voltage for comparison in a suitable regulator with a value proportional to the measured temperature output of a thermal process having a desired exponential temperature-time characteristic' The generator includes an R-C circuit chargeable via a DC source wherein the time constant of the R-C circuit is chosen to equal the thermal time constant of the exponential thermal process. The voltage increase across the capacitor during charge or the voltage decrease across the capacitor during a subsequent discharge is employed selectively as a reference voltage for controlling, respectively, a rising and a falling exponential temperature-time characteristic of the thermal process. A cathode follower or other input buffer amplifier is coupled to the output of the capacitor to isolate the R-C circuit from the loading effect of the input of the regulator.
3 Claims, 2 Drawing Figures PAIEIHHIzs lam REFERENCE VOLTAGE GENERATOR FOR THERMAL PROCESSES HAVING AN EXPONENTIAL TEMPERATURE-TIME CHARACTERISTIC BACKGROUND OF THE INVENTION In the control of furnaces, e.g. those employed in the fabrication of steel products, it is often advantageous to employ a closed-loop temperature regulator of the furnace using a rising or falling temperature-time characteristic. In general, the regulation of such furnaces in this manner employs a themiocouple or other thermoelectric element which continually samples the temperature of the furnace and provides a proportional electrical signal, generally in the millivolt range. Such measured signal is continually compared at the regulator input with a reference electrical signal whose amplitude-time characteristic is mechanically varied in a manner that generally tracks the desired exponential variation of the thermal process. An error signal derived from such comparison is employed to vary the quantity of heat supplied to the furnace in such a manner as to minimize the error signal.
In presently known reference voltage generators for those applications, the required exponential variations of the amplitude characteristic is accomplished by mechanically driving, in a suitable manner, the wiper arm of a potentiometer whose input is coupled across a DC source. Unlike the far simpler case where the desired FIG. 1 is a curve showing a typical exponential temperature-time variation suitable for certain types of controlled furnaces; and
FIG. 2 is a block diagram of an arrangement in accordance with the invention for generating a reference control voltage proportional to the exponential temperature-time relationship of FIG. 1.
A closed-loop temperature regulation system of a type appropriate for instrumenting the temperaturetime characteristic of FIG. 1 is shown in FIG. 2. The quantity of heat to be applied to a furnace 7 to be regu lated is controlled by a conventional furnace regulator 6. The regulator is responsive to an error signal obtemperature characteristic of the furnace is to be linear (wherein the drive mechanism for the wiper arm can be instrumented in a straightforward way by a motor driven in accordance with velocity step function), the requirement of an exponential temperature variation requires, for the mechanically instrumented reference ,voltage generator, not only a motor but also mechanical motion-changing devices such as curved cams which are complicated and expensive.
SUMMARY OF THE INVENTION An improved arrangement for generating the required exponentially varying reference voltage for controlling thermal processes without the necessity of complex mechanical components is provided by the instant invention. In one embodiment, the input of an R-C electric circuit chosen to have an RC time constant corresponding to the thermal time constant of the desired temperature-time characteristic of the furnace is coupled across a DC source. The output voltage vari BRIEF DESCRIPTION OF TI-IEDRAWING The invention is further set forth in the following detailed description taken in conjunction with the appended drawing in which:
tained by a comparison, at the regulator input, between a first electrical quantity representative of the actual temperature of the furnace at each instant, and a second electrical quantity representative of the desired temperature (in accordance with the curve of FIG. 1) at that instant. Accordingly, such second quantity ideally has an amplitude that decays exponentially, with a time constant corresponding to Ta.
The first quantity mentioned above is the voltage output of a thermocouple or other thermoelectric element 8, which is disposed in thermal communication with the furnace 7. The second quantity is the voltage output of an exponential voltage generator 10.
In accordance with the invention, the furnace control system shown in FIG. 2 employs, as the reference generator 10, an all-electric arrangement including a waveshaping R-C circuit 3 having a resistor 11 and a capacitor 12. The input of the circuit 3 is connected to the output of a DC voltage source 1 via a switch 2. (The source 1 may be made adjustable if desired). The output of the circuit 3 is taken from the capacitor 12.
It will be recognized that once the capacitor 12 has been charged to the voltage of the source 1 by closure of the switch 2, a subsequent discharge of the capacitor (initiated, eg by closure of a switch 13 which may be controlled by the furnace regulator 6), will cause the capacitor voltage to decrease exponentially from its initial value with a time constant Tf= RC.
Consequently, the desired reference control voltage for the furnace 6 may be obtained from the capacitor output by so selecting the values of the resistor 11 and the capacitor 12 that Theoretically, the capacitor output voltage could be applied directly to the input of the regulator as the desired reference voltage without intervening circuitry. However, in order to prevent the input resistance of the regulator from loading the output of the capacitor 12 and thereby shifting the effective value of the time constant Tf from the desired value Ta, a bufier amplifier 4 having a high input impedance (e.g. an impedance that preferably is at least 10 times as large as the'resistance of resistor 11) is coupled to the output of the circuit 3. Such amplifier 4 may typically be a cathode or an emitter follower.
Moreover, since the output voltage from the amplifier 4 may typically be at least one order of magnitude greater than the millivolt range output of the thermcouple 8 to which the reference voltage is to be compared, an adjustable voltage divider 5 of suitable reduction ratio may be provided as shown between the output of the amplifier 4 and the associated input of the regulator 6.
In the foregoing, the invention has been described in connection with a preferred arrangement thereof. Many modifications and variations will now occur to those skilled in the art. For example, if the furnace 7 is to have an exponentially decreasing temperature-time characteristic, the corresponding exponentially increasing reference control voltage can be obtained from the arrangement of FIG. 2 by extracting the output voltage from the capacitor 12 during the charging thereof from the source 1 via the switch 2. Accordingly, it is desired that the scope of the appended claims not be limited to the specific disclosure herein con-v time is converted to a first proportional electrical signal which is compared continually at the input of a furnace regulator with a second electrical reference signal whose amplitude-time characteristic is proportional to the desired exponential characteristic of the process to generate an error signal employed by the regulator to control the quantity of heat supplied to the process, an improved arrangement for generating the referenced signal, which comprises:
an electrical wave shaping path including a resistor and a capacitor in series, the values of the resistor and the capacitor being chosen so that the resulting time constant of the path is equal to Ta:
means for coupling the input of the path to a DC source; and means for coupling the output of the capacitor to the input of the regulator to constitute the reference voltage.
2. A system as defined in claim 1, in which the coupling means comprises a high input impedance buffer amplifier.
3. A system as defined in claim 2, in which the coupling means further comprises a voltage divider disposed between the output of the buffer amplifier and the input of the regulator.
Claims (3)
1. In a closed-loop system for controlling a thermal process whose desired temperature-time characteristic is an exponential function having a time constant Ta, wherein the actual temperature of the process at any time is converted to a first proportional electrical signal which is compared continually at the input of a furnace regulator with a second electrical reference signal whose amplitude-time characteristic is proportional to the desired exponential characteristic of the process to generate an error signal employed by the regulator to control the quantity of heat supplied to the process, an improved arrangement for generating the referenced signal, which comprises: an electrical wave shaping path including a resistor and a capacitor in series, the values of the resistor and the capacitor being chosen so that the resulting time constant of the path is equal to Ta: means for coupling the input of the path to a DC source; and means for coupling the output of the capacitor to the input of the regulator to constitute the reference voltage.
2. A system as defined in claim 1, in which the coupling means comprises a high input impedance buffer amplifier.
3. A system as defined in claim 2, in which the coupling means further comprises a voltage divider disposed between the output of the buffer amplifier and the input of the regulator.
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AT433172A AT322239B (en) | 1972-05-18 | 1972-05-18 | CIRCUIT FOR THE GENERATION OF A TIME VARIOUS COMPARATIVE VOLTAGE AS A SLIDING SETPOINT IN ELECTRONIC TEMPERATURE CONTROLLERS |
Publications (1)
Publication Number | Publication Date |
---|---|
US3819950A true US3819950A (en) | 1974-06-25 |
Family
ID=3562613
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US00361551A Expired - Lifetime US3819950A (en) | 1972-05-18 | 1973-05-18 | Reference voltage generator for thermal processes having an exponential temperature-time characteristic |
Country Status (6)
Country | Link |
---|---|
US (1) | US3819950A (en) |
AT (1) | AT322239B (en) |
CH (1) | CH559391A5 (en) |
DE (1) | DE2322694C3 (en) |
FR (1) | FR2185291A5 (en) |
IT (1) | IT985072B (en) |
Families Citing this family (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE3153413C2 (en) * | 1981-03-06 | 1988-06-30 | Rene Muraz Ch Rossier | Method for controlling the supply and the extraction of energy in material phase |
DE3108470A1 (en) * | 1981-03-06 | 1982-09-30 | Schweizerische Aluminium AG, 3965 Chippis | Method for controlling the supply and removal of energy, and use of the method |
DE3139199A1 (en) * | 1981-10-02 | 1983-04-21 | Braun Ag, 6000 Frankfurt | Method and arrangement for controlling and regulating the heating power of an electrical heating and/or drying apparatus |
-
1972
- 1972-05-18 AT AT433172A patent/AT322239B/en not_active IP Right Cessation
-
1973
- 1973-04-18 CH CH584273A patent/CH559391A5/xx not_active IP Right Cessation
- 1973-05-05 DE DE2322694A patent/DE2322694C3/en not_active Expired
- 1973-05-15 FR FR7317454A patent/FR2185291A5/fr not_active Expired
- 1973-05-16 IT IT50004/73A patent/IT985072B/en active
- 1973-05-18 US US00361551A patent/US3819950A/en not_active Expired - Lifetime
Also Published As
Publication number | Publication date |
---|---|
IT985072B (en) | 1974-11-30 |
DE2322694C3 (en) | 1978-04-13 |
CH559391A5 (en) | 1975-02-28 |
DE2322694A1 (en) | 1973-11-29 |
DE2322694B2 (en) | 1976-11-04 |
FR2185291A5 (en) | 1973-12-28 |
AT322239B (en) | 1975-05-12 |
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