Abstract 989,177. Electric measuring apparatus. HONEYWELL Inc. April 24,1961 [April 27, 1960], No. 14764/61. Heading G1U. An apparatus for measuring D.C. voltage signals from a thermocouple 2 comprises a signal amplifier 22 having a common mode reference terminal 26 and a differential signal input terminals 20, 24, to which are connected first and second input circuit legs, and a transformer 12 with a primary winding 14 and two secondary windings 16,18, each secondary winding being series connected in a leg of the input circuit. The primary winding is capacitatively coupled between both legs of the input circuit and the common mode reference terminal, through capacitors 28, 30. The primary winding induces in the secondary windings a signal opposing common mode signals in the two legs of the input circuit, so as to eliminate spurious alternating current signals in the legs of the thermocouple, which are caused by grounding the sensing junction. Such signals, termed common mode signals, act as though a constant alternating current generator 36 is connected between the thermocouple juntion and the common mode reference level. The transformer secondary windings are bifilarly wound so as to make them as similar as possible in their individual characteristics and in their relation to the primary winding.
ELECTRICAL MEASURING APPARATUS COMPRISING AN ELECTRICAL MEASURING CIRCUIT INCLUDING A PRIMARY SENSING ELEMENT, SAID MEASURING CIRCUIT HAVING A FIRST LEG AND A SECOND LEG, A DIFFERENTIAL AMPLIFIER HAVING A FIRST AND SECOND INPUT TERMINAL AND A COMMON-MODE REFERENCE TERMINAL, A TRANSFORMER HAVING A PRIMARY WINDING AND TWO SECONDARY WINDINGS, ONE OF SAID SECONDARY WINDINGS BEING SERIALLY CONNECTED BETWEEN SAID FIRST LEG OF SAID MEASURING CIRCUIT AND SAID FIRST INPUT TERMINAL OF SAID AMPLIFIER, THE OTHER OF SAID SECONDARY WINDINGS BEING SERIALLY CONNECTED BETWEEN SAID SECOND LEG OF SAID MEASURING CIRCUIT AND SAID SECOND INPUT TERMINAL, SAID PRIMARY WINDING BEING CONNECTED AT ONE END TO SAID COMMON MODE REFERENCE TERMINAL, AND CAPACITIVE COUPLING MEANS COUPLING EACH OF SAID LEGS OF SAID MEASURING CIRCUIT TO THE OTHER END OF SAID PRIMARY WINDING, SAID PRIMARY WINDING BEING INDUCTIVELY COUPLED TO SAID SECONDARY WINDINGS TO PRODUCE IN SAID SECONDARY WINDINGS A SIGNAL IN OPPOSITION TO COMMON MODE SIGNALS IN SAID MEASURING CIRCUIT.
Claim 2
Dependent Claim
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ELECTRICAL MEASURING APPARATUS COMPRISING AN ELECTRICAL MEASURING CIRCUIT INCLUDING A PRIMARY SENSING ELEMENT, SAID MEASURING CIRCUIT HAVING A FIRST LEG AND A SECOND LEG, A DIFFERENTIAL AMPLIFIER HAVING A FIRST AND SECOND INPUT TERMINAL AND A COMMON-MODE REFERENCE TERMINAL, A TRANSFORMER HAVING A PRIMARY WINDING AND TWO SECONDARY WINDINGS, ONE OF SAID SECONDARY WINDINGS BEING SERIALLY CONNECTED BETWEEN SAID FIRST LEG OF SAID MEASURING CIRCUIT AND SAID FIRST INPUT TERMINAL OF SAID AMPLIFIER, THE OTHER OF SAID SECONDARY WINDINGS BEING SERIALLY CONNECTED BETWEEN SAID SECOND LEG OF SAID MEASURING CIRCUIT AND SAID SECOND INPUT TERMINAL, SAID PRIMARY WINDING BEING CONNECTED AT ONE END TO SAID COMMON MODE REFERENCE TERMINAL, AND CAPACITIVE COUPLING MEANS COUPLING EACH OF SAID LEGS OF SAID MEASURING CIRCUIT TO THE OTHER END OF SAID PRIMARY WINDING, SAID PRIMARY WINDING BEING INDUCTIVELY COUPLED TO SAID SECONDARY WINDINGS TO PRODUCE IN SAID SECONDARY WINDINGS A SIGNAL IN OPPOSITION TO COMMON MODE SIGNALS IN SAID MEASURING CIRCUIT.