METHOD AND APPARATUS FOR DETECTING THE OPEN-CIRCUIT CONDITION OF A THERMOCOUPLE BY SENDING A PULSE THROUGH THE THERMOCOUPLE AND A REACTIVE ELEMENT IN SERIES

• US 3,590,370 A
• Filed: 04/09/1969
• Issued: 06/29/1971
• Est. Priority Date: 04/09/1969
• Status: Expired due to Term

• Current Assignee: Donald W. Fleischer
• Original Assignee: Donald W. Fleischer
• Inventors: Fleischer, Donald W.
• Application Number:
  US04/818,466
• Time in Patent Office: 811 Days
• US Class Current: 324/537
• CPC Class Codes: G01K 7/026 Arrangements for signalling failure or disconnection of thermocouples
• CPC Class Codes: G01R 31/52 Testing for short-circuits, leakage current or ground faults
• CPC Class Codes: G01R 31/54 Testing for continuity

Abstract

A pulse is sent serially through the thermocouple and the primary of a pulse transformer. The pulse has a duration longer than that sufficient to charge the distributed capacity in the thermocouple and leadwire. At the end of the pulse period the thermocouple is disconnected and the transformer primary is provided with a discharge path. The resulting potential across the secondary indicates a good thermocouple. If that potential does not appear, an open circuit is indicated. The transformer can be replaced by a capacitor which becomes charged only when the thermocouple is a complete circuit.

Claims

1. A method for high speed checking of thermocouples connected by long leadwire comprising sending a pulse serially through the thermocouple to be checked and a reactive element, said pulse being of duration such that the capacity between the long leadwires is charged before the end of the pulse so that a reactive field within said reactive element is present at the end of said pulse only when said thermocouple forms a complete circuit, releasing said reactive field by providing a current discharge path for said reactive element after the termination of said pulse, and detecting the flow of said discharge current, said flow being indicative of a complete circuit through said thermocouple.

2. A circuit for the high speed checking of thermocouples having long leadwire connections comprising an inductor, means for passing a unidirectional pulse serially through said inductor and the thermocouple to be checked, said pulse being of duration sufficient to charge up any capacity between said long leadwires before the end of said pulse so that a reactive field is present in said inductor at the end of said pulse only when said thermocouple forms a complete circuit, means providing a path for the discharge of current by said inductor to allow the collapse of the reactive field after the termination of said pulse, and means for detecting the flow of discharge current upon the collapse of said reactive field, the flow of said current being indicative of a complete circuit through the thermocouple being checked.

3. A high speed thermocouple continuity checking circuit comprising a transformer having a primary winding and a secondary winding, a DC power source, switching means connected in series with said DC power source for applying a unidirectional pulse serially through the primary winding and the thermocouple to be checked, said pulse being of duration sufficient so that a magnetic field is set up only when said thermocouple forms a complete circuit, a diode connected across the primary winding and poled in a direction opposite to that of the DC power source for providing a path for the discharge of current by the primary winding during the collapse of the magnetic field after the termination of said pulse, a flip-flop circuit normally maintained in one state, and means for applying to the flip-flop circuit during the collapse of the magnetic field the output of the secondary winding resulting from the flow of discharge current in the primary winding to change said flip-flop circuit to an opposite state indicative of a complete circuit through said thermocouple to be checked.