Differentiating amplifier having a variable time constant

Claim 1

IN A PERIODMETER FOR NUCLEAR REACTORS, OF THE TYPE COMPRISING A COMPENSATED NEUTRON IONIZATION CHAMBER AND A LOGARITHMIC AMPLIFIER; A DIFFERENTIATING AMPLIFIER HAVING AN INPUT FOR CONNECTION TO THE LOGARITHMIC AMPLIFIER AND AN OUTPUT; SAID DIFFERENTIATING AMPLIFIER ING: A FIRST AUXILIARY INTEGRATION CIRCUIT AND AN OPERATIONAL AMPLIFIER SERIES-CONNECTED WITH ONE ANOTHER AND CONNECTED WITH SAID INPUT AND OUTPUT, RESPECTIVELY; SAID FIRST AUXILIARY INTEGRATION CIRCUIT COMPRISING FIRST RESISTANT MEANS CONNECTED TO SAID INPUT, AND A FIRST CAPACITOR SERIES-CONNECTED BETWEEN SAID FIRST RESISTANT MEANS AND SAID OPERATIONAL AMPLIFIER; A FIRST RESISTOR PARALLEL-CONNECTED WITH SAID OPERATIONAL AMPLIFIER; A VOLTAGE DIVIDER HAVING ONE END CONNECTED BETWEEN SAID OUTPUT AND THE OTHER END CONNECTED WITH ONE SIDE OF SAID FIRST RESISTANT MEANS, AND COMPRISING TWO RESISTANT PORTIONS, SERIES-CONNECTED WITH ONE ANOTHER THROUGH A COMMON POINT, THE RATIO OF THE RESISTANCE VALUES OF SAID TWO PORTIONS BEING VARIABLE ACCORDING TO THE POTENTIAL DIFFERENCE BETWEEN SAID TWO ENDS; AND A SECOND CAPACITOR CONNECTED BETWEN SAID COMMON POINT AND THE INPUT OF SAID OPERATIONAL AMPLIFIER, THE CAPACITANCE OF SAID SECOND CAPACITOR BEING LESS THAN THAT OF SAID FIRST CAPACITOR; SAID FIRST RESISTOR CONSTITUTING WITH SAID FIRST CAPACITOR A DIFFERENTIATING CIRCUIT,AND, WITH SAID SECOND CAPACITOR A SECOND AUXILIARY INTEGRATION CIRCUIT; THE INTEGRATION OBTAINED BY MEANS OF THE FIRST AUXILIARY INTEGRATION CIRCUIT BEING SOLELY A FUNCTION OF THE NUCLEAR PERIOD.