| 摘要 |
<p>PURPOSE: To enhance an instrument transformer in accuracy of measurement restraining it from varying in voltage transformation ratio due to a change in its winding resistance with a temperature change. CONSTITUTION: The temperature coefficient of resistance of the feedback resistors R21 and R22 of an operational amplifier included in a current-voltage transforming circuit is set nearly equal to that of the combined resistance of the resultant primary-equivalent winding resistance and the current limiting resistor R1 of an instrument transformer PT. An instrument transformer is comparatively large in winding resistance, and if an input current varies with a change in an ambient temperature, a current-voltage transforming circuit of an operational amplifier provided on the secondary side of the instrument transformer makes correction on the input current, so that the instrument transformer is capable being kept constant in voltage transformation ratio and high in accuracy of measurement independent of an ambient temperature change.</p> |
