Integrator with automatic compensation of the variation of the zeropoint

Claim 1

APPARATUS FOR ANALYZING A GAS SAMPLE COMPRISING A SOURCE OF SUPPLY VOLTAGE, FIRST AND SECOND BRANCH CIRCUITS CONNECTED TO SAID VOLTAGE SOURCE, SAID FIRST BRANCH COMPRISING A MEASURING CELL THROUGH WHICH SAID GAS SAMPLE AND A CARRIER GAS FLOWS AND COMPRISING AN ELEMENT HAVING RESISTANCE VARIATIONS AS DETERMINED BY VARIATIONS IN THE COMPOSITION OF SAID GAS SAMPLE FLOWING THEREOVER, SAID SECOND BRANCH COMPRISING A COMPARISION CELL HAVING A SIMILAR TYPE ELEMENT THROUGH WHICH SAID CARRIER GAS FLOWS, MEANS FOR DERIVING A CONTROL VOLTAGE FROM SAID FIRST BRANCH CIRCUIT WHICH VARIES IN ACCORDANCE WITH THE RESISTANCE VARIATIONS OF SAID MEASURING CELL, INTEGRATING MEANS COMPRISING MEANS RESPONSIVE TO SAID CONTROL VOLTAGE FOR DERIVING AN ALTERNATING VOLTAGE HAVING A FREQUENCY WHICH IS DETERMINED BY SAID CONTROL VOLTAGE AND MEANS FOR DETERMINING THE VALUE OF SAID FREQUENCY, MEANS FOR DERIVING A SECOND CONTROL VOLTAGE FROM SAID SECOND BRANCH CIRCUIT WHICH VARIES WITH THE RESISTANCE VARIATIONS OF SAID MEASURING CELL AND SAID COMPARISON CELL FROM A REFERENCE VALUE, AND MEANS FOR SUPPLYING SAID SECOND CONTROL VOLTAGE TO SAID INTEGRATING MEANS, SAID INTEGRATIONG MEANS FURTHER COMPRISING MEANS RESPONSIVE TO SAID SECOND CONTROL VOLTAGE FOR MODIFYING THE FREQUENCY OF SAID DERIVED ALTERNATING VOLTAGE IN ACCORDANCE THEREWITH WHEREBY THE FREQUENCY OF SAID DERIVED ALTERNATING VOLTAGE IS CORRECTED FOR SAID VARIATIONS FROM SAID REFERENCE VALUE.