| 摘要 |
PURPOSE:To give information when a secondary voltage on the side of a main core does not become zero V due to the occurrence of an error and to accurately meansure the quantity of electric power through appropriate compensation, by monitoring a voltage which appears in the error compensation circuit of a current detection unit. CONSTITUTION:A current detection unit comprises a current converter 21, a voltage comparator 22 and an error information section 23. The current converter 21 is provided with an error compensation circuit so that the secondary voltage across a secondary winding 15 around a main core 11 is eliminated by a voltage which appears across a secondary winding 13 around an auxiliary core 12. When the voltage between a grounded point 25 and another point 24 on the secondary side of the main core 11 does not become zero V due to a cause such as the change in the circuit constant of the error compensation circuit in the current converter 21 or the deterioration of the core, the voltage comparator 22 acts and its output changes from ''L'' to ''H''. As a result, the error information section 23 acts to indicate an error occurrence warning signal. Thus, error occurrence in the current detection unit of a wattmeter can be quickly discriminated and an appropriate measure can be taken. |
