Patent ID: 7990302

Claim:
An analog input device comprising: isolating transformers each for outputting, while a primary side switch is controlled in a closed state and an analog signal is applied to a primary side, a pulse-like signal with amplitude corresponding to the analog signal from a secondary side; secondary side switches connected to the secondary sides of the isolating transformers; an amplifier for amplifying the pulse-like signal output from the secondary side of one of the isolating transformers while one of the secondary side switches is controlled in a closed state; a capacitor connected to a negative feedback loop across an input and output of the amplifier; timing control means for controlling the primary side switch of one of the isolating transformers into the closed state, then for controlling the corresponding secondary side switch into the closed state, and for controlling after that the secondary side switch into an open state at timing simultaneous with the primary side switch or earlier than the primary side switch; and an AD converter for converting, after the timing control means controls the secondary side switch into the open state, an output signal of the amplifier to a digital signal.