| 摘要 |
PURPOSE:To reduce noise in a minimum integral time corresponding to a power supply frequency component at the time of changing the power supply frequency by detecting the power supply frequency component superimposed on a measuring signal, selectively setting the integral time of an A/D CONVERTER in accordance with the power supply frequency component. CONSTITUTION:A power supply frequency component superimposed on a measuring signal applied to an input terminal 11 is inputted to a waveform shaping circuit 18 after a part of direct current is cut off by a capacitor 17, and from the circuit the waveforms of noise components are outputted to a counter 19. The counter 19 counts the noise component waveforms and outputs the counted results to a discrimination circuit 20. The circuit 20 discriminates whether the power supply frequency is, for example, 50Hz or 60Hz to output the results to a control circuit 15. On this basis, the circuit 15 sets an adequate integral time of an integrator 14. By operating an A/D converter in a minimum integral time corresponding to the driving power supply frequency, the effect of the power supply frequency component on noise can be reduced. |
