This circuit is a complete ultra long time-constant charge integrator circuit. The integration current IIN is

produced by input VIN and is directly proportional to VIN, given by IIN = VIN/R. The feedback integration

capacitor C is charged with this integration current. Assuming there is no loss of charge at the negative input

terminal of the integrator Amplifier the time required in charging the integrating capacitor depends directly on

the magnitude of 1/VIN and is proportional to the product of R and C. This integrator circuit utilizes 2 separate

relays to control the integration and the reset cycles. Initially, at the beginning of a charge cycle, Relay 1 is

closed to preset the negative input to the Operational Amplifier to a preset voltage. When sufficient time has

been allowed for the preset voltage to charge the integrating capacitor C, Relay 1 is opened. Then Relay 2 is

closed to start the integration cycle. In order to generate ultra long time-constant, select a large value for both

R and C. Select a large value for R consistent with leakage currents permitted on the printed circuit board, and

select large value for C based on size, cost and internal leakage specification requirements. Key selection

criteria for an Operational Amplifier are a) extremely low input leakage currents b) low input offset voltage c)

sufficient slew rate and output current to charge the capacitor for the time-constant desired.

Recommended Components

ALD1712 ALD1721 ALD1722 ALD2711 ALD2722 ALD2726

produced by input VIN and is directly proportional to VIN, given by IIN = VIN/R. The feedback integration

capacitor C is charged with this integration current. Assuming there is no loss of charge at the negative input

terminal of the integrator Amplifier the time required in charging the integrating capacitor depends directly on

the magnitude of 1/VIN and is proportional to the product of R and C. This integrator circuit utilizes 2 separate

relays to control the integration and the reset cycles. Initially, at the beginning of a charge cycle, Relay 1 is

closed to preset the negative input to the Operational Amplifier to a preset voltage. When sufficient time has

been allowed for the preset voltage to charge the integrating capacitor C, Relay 1 is opened. Then Relay 2 is

closed to start the integration cycle. In order to generate ultra long time-constant, select a large value for both

R and C. Select a large value for R consistent with leakage currents permitted on the printed circuit board, and

select large value for C based on size, cost and internal leakage specification requirements. Key selection

criteria for an Operational Amplifier are a) extremely low input leakage currents b) low input offset voltage c)

sufficient slew rate and output current to charge the capacitor for the time-constant desired.

Recommended Components

ALD1712 ALD1721 ALD1722 ALD2711 ALD2722 ALD2726

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