There are two widely used high-precision data acquisition methods,they are I/F convert and A/D convert,because of they all convert analog signal to digital signal,they become the bridge of analog and digital.

I/f converter of electric locomotive running monitor and recorder;

The I-F converter in the weak current measurement;

In order to solve the HVDC bus voltage measurement parameters,the output analog voltage signal of DC voltage transformer was turned into pulse-frequency signals by High-precision V/F converter,which go through the optical transmitter module,optical fiber and optical receiver modules to achieve the function of pulse frequency signal optical transmission.

The paper discusses the accuracy offset when using the timer to sample periodical signals in common A/D transform circuit composed of V/F converter,and proposes an improved circuit which adopts pre- positve signal regulation to makes the change of input signals consistent with that of the period of output signals.