PURPOSE: To reduce the effect of common mode noise by connecting a noise voltage compensation element to either input system so that a generated voltage by a noise current in a floating input system is equal to that in other input system.
CONSTITUTION: A capacitor CC acting like a noise voltage compensation element is connected between ground and one system A (floating input system) of an input terminal of a preamplifier PA. When a common mode noise is superimposed on a measurement signal, since a noise current IA flowing to the system A is almost equal to a noise current IB flowing to a system B, a noise voltage IA×RA generated in the system A is equal to a noise voltage IB×RB generated in the system B. As a result, the difference of the noise voltages applied to the preamplifier PA as a line noise voltage is almost zero and the measurement error due to normal mode noise is almost zero, then the measurement with high accuracy is implemented.
KURIYAMA TETSURO
YUHARA HITOSHI
