| 摘要 |
PURPOSE:To execute power supply and signal output through the same signal line and actually reduce the influence of noise in a signal processing of electrostatic capacity to be measured by using a circuit suppressing pulse variation down to its minimum limit. CONSTITUTION:The titled device is provided with a switch 32 synchronously discharging a capacity 11 to be measured which is to be charged by charging circuits 81, 12, a comparator 13 comparing the terminal voltage of the capacity 11 with a reference voltage 14 and outputting a pulse signal having the time width corresponding to the charging time constant of the capacity 11, an LPF 41 converting an output pulse from the comparator 13 into DC voltage, a voltage setting circuit 20 outputting DC voltage set in accordance with a fixed capacity component included in the capacity 11, a differential amplifier 60 fetching the difference between respective output voltage of the LPF 41 and the circuit 20, and a circuit 70 outputting a measuring signal obtained by adding DC voltage 67 which sets the zero point and span of the measuring signal to the output of the circuit 60 through two lines also to be used as power supplying lines. |
