# US 2014/0153606 A1 · High temperature furnace having reconfigurable heater circuits > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0153606 A1 - Document ID: US20140153606A1 - Status: Published application - Kind: A1 - Application number: 13/764,578 - Filed: 2013-02-11 - Published: 2014-06-05 - Earliest claimed: 2012-12-05 - Assignees: Fluke Corporation - Applicants: Fluke Corporation - Inventors: Richard W. Walker; Tian Xia; Jiajun Yan - Web page: https://patentgrep.com/patent/US20140153606A1 ## CPC - H05B 1/02: Automatic switching arrangements specially adapted to apparatus {; Control of heating devices} (thermally-actuated switches H01H37/00) - F27B 17/02: specially designed for laboratory use - F27D 11/00: Arrangement of elements for electric heating in or on furnaces - G01K 15/005: {Calibration} - H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL - F27B: FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS - F27D: DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE - G01K: MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR (radiation pyrometry G01J5/00) ## Abstract The core of a high temperature furnace has an elongated central test cavity for testing/calibration of a temperature-sensitive component, such as the probe of a thermocouple. At least three electrical heating elements as positioned adjacent to the test cavity, including two elements adjacent to the opposite end portions of the test cavity, respectively, and a center element between the end elements. A uniform temperature profile is maintained in the cavity by control circuitry that manages the supply of electrical power to the heating elements, by periodically configuring interconnections of the elements during multiple phases of a duty cycle. The duty cycle includes a first phase in which current is passed through the center element, a second phase in which current is passed through the end elements in series, and a third phase in which current is passed through one of the end elements and also through the center element without passing current through the other end element. ## Claims ### Claim 1 A high temperature calibration furnace comprising: a core having an elongated central test cavity for testing/calibration of a temperature-sensitive component, the core having at least three electrical heating elements adjacent to the test cavity for heating of the test cavity by a supply of electrical power to the heating elements, the heating elements including a first end heating element adjacent to a first end portion of the test cavity, a second end heating element adjacent to a second end portion of the test cavity opposite the first end portion thereof, and a center heating element between the first and second end heating elements; and control circuitry for managing the supply of electrical power to the first, second and third electrical heating elements, the control circuitry having operating means for periodically configuring interconnections of the first, second and third heating elements during multiple phases of a duty cycle, including a first phase in which electrical current is passed through the central heating element, a second phase in which current is passed through the first and second end heating elements in series, and a third phase in which current is passed through one of the first and second end heating elements and also through the central heating element without passing current through the other of the first and second end heating elements. ### Claim 2 (depends on 1) The furnace defined in claim 1, in which the center heating element does not overlap either of the end heating elements. ### Claim 3 (depends on 1) The furnace defined in claim 1, in which the operating means includes a microprocessor controlling the interconnections of the heating elements during the duty cycle. ### Claim 4 (depends on 1) The furnace defined in claim 1, in which the operating means configures the interconnections of the heating elements so that the first and second phases are performed at least partially simultaneously. ### Claim 5 (depends on 1) The furnace defined in claim 1, in which the operating means configures the interconnections of the heating elements so that the phases are performed consecutively. ### Claim 6 (depends on 1) The furnace defined in claim 1, in which the control circuitry includes a first circuit branch in which a first solid state relay is connected in series with the center heating element, and a second circuit branch in which a second solid state relay is connected in series with the first end heating element and the second end heating element, and in which a third solid state relay is connected between the first and second branches at a first point between the first solid state relay and the center heating element and a second point between the first end heating element and the second end heating element, the operating means controlling the interconnections of the heating elements by periodically controlling the conditions of the solid state relays. ### Claim 7 (depends on 1) The furnace defined in claim 1, in which the control circuitry includes a first circuit branch in which a first solid state relay is connected in series with the center heating element, and a second circuit branch in which a second solid state relay is connected in series with the first end heating element and the second end heating element, and in which a third solid state relay is connected between the first and second branches at a first point between the first solid state relay and the center heating element and a second point between the first end heating element and the second end heating element, the operating means including a microprocessor controlling the interconnections of the heating elements during the duty cycle by periodically controlling the conditions of the solid state relays. ### Claim 8 (depends on 6) The furnace defined in claim 6, in which the duty cycle has a duration of 0.5 second to 2 seconds. ### Claim 9 A method of operating a high temperature calibration furnace having an elongated central test cavity for testing/calibration of a temperature-sensitive component, said furnace having three electrical heating elements each adjacent to the test cavity including a first end heating element adjacent to a first end of the test cavity, a second end heating element adjacent to a second end of the test cavity opposite the first end thereof, and a central heating element between the first and second end heating elements, said method comprising managing the supply of power to the three electrical heating elements by periodically configuring interconnections of the three heating elements during multiple phases of a duty cycle, including: during a first phase, passing electrical current through the central heating element; during a second phase, passing electrical current through the first and second end heating elements in series; and during a third phase, passing electrical current through the central heating element and one of the first and second end heating elements without passing current through the other of the first and second end heating elements. ### Claim 10 (depends on 9) The method of claim 9, including performing the first and second phases at least partially simultaneously.