Calibrated isothermal assembly for a thermocouple thermometer

• US 6,293,700 B1
• Filed: 09/24/1999
• Issued: 09/25/2001
• Est. Priority Date: 09/24/1999
• Status: Expired due to Term

• Current Assignee: Fluke Corporation (Fortive Corp.)
• Original Assignee: Fluke Corporation (Fortive Corp.)
• Inventors: Parle, Jonathan J., Washburn, Monte R., Lund, John M.
• Primary Examiner(s): Gutierrez, Diego
• Assistant Examiner(s): DEJESUS, LYDIA M
• Application Number:
  US09/404,921
• Time in Patent Office: 732 Days
• Field of Search: 374/181, 374/182, 374/178, 136/230, 136/229, 136/242
• US Class Current: 374/181
• CPC Class Codes: G01K 7/13 Circuits for cold-junction compensation

Abstract

A calibrated isothermal assembly for a thermocouple thermometer is provided to obviate a calibration step after manufacture of the instrument. A compact isothermal block is fabricated on a specialized printed circuit board which includes a thick metal plate to establish sufficient thermal mass and good heat conductivity. A temperature sensor is mounted at the thermocouple reference junction on the printed circuit board to track the reference junction temperature. The calibrated isothermal assembly also includes a current source for the temperature sensor, and a memory device containing stored calibration data specific to the temperature sensor.

Claims

1. A calibrated isothermal assembly for a thermocouple thermometer, comprising:

a base member comprising a metal plate having a high heat conductivity characteristic and sufficient thermal mass to provide an isothermal block, said metal plate having an electrical insulative layer disposed thereon;

a pair of electrical contacts disposed on said electrical insulative layer and forming a virtual reference junction for a thermocouple;

a temperature sensing transistor having a voltage-temperature characteristic curve mounted on said base member proximate said pair of electrical contacts; and

a memory device mounted on said base member, said memory device containing calibration data relating to said voltage-temperature characteristic curve of said temperature sensing transistor.

2. A calibrated isothermal assembly in accordance with claim 1 further comprising a current source for said temperature sensing transistor mounted on said base member.

3. A calibrated isothermal assembly in accordance with claim 1 further comprising a housing mounted on said base member and extending over said pair of electrical contacts.

4. A calibrated isothermal assembly in accordance with claim 1 wherein said metal plate is composed of copper.

5. A calibrated isothermal assembly in accordance with claim 1 wherein said metal plate has a thickness of at least 0.040 inches.

6. A calibrated isothermal assembly in accordance with claim 1 wherein said calibration data includes at least one value of voltage corresponding to at least one predetermined temperature on said voltage-temperature characteristic curve of said temperature sensing transistor.

7. A compact isothermal assembly, comprising:

a metal plate upon which is disposed at least one electrical insulative layer to form a specialized printed circuit board, said metal plate having sufficient thermal mass to provide an isothermal block;

a pair of conductive pads disposed in juxtaposition on a surface of said at least one electrical insulative layer;

a temperature sensing transistor having a voltage-temperature characteristic curve disposed on said surface in close proximity to said conductive pads;

a memory device disposed on a surface of said at least one insulative layer, said memory device containing calibration data relating to said voltage-temperature characteristic curve of said temperature sensing transistor.

8. A compact isothermal assembly in accordance with claim 7 wherein said metal plate has a thickness of at least 0.040 inch.

9. A compact isothermal assembly in accordance with claim 7 wherein said metal plate is copper.

10. A compact isothermal assembly in accordance with claim 7 further comprising a housing mounted on said surface and at least partially enclosing said conductive pads and said temperature sensing transistor.

11. A compact isothermal assembly in accordance with claim 10 wherein a pair of spring clips are attached to said housing, said pair of spring clips each having a free end disposed adjacent a respective conductive pad.