| 摘要 |
PURPOSE:To make it possible to detect the level of a frequency stably even if the frequency changes by detecting the level of an object to be detected from the ratio of a period of time during which input voltage exceeds a specified value and a period of time during which input voltage stays below a specified value. CONSTITUTION:Alternating current V is input into a level division circuit 5 through a full wave rectifying circuit 1, and it becomes a signal 5a which is high during the period of time in which the voltage exceeds VL and is low during the period of time in which the voltage does not go over VL. This signal 5a is integrated by an integrator 6 during the period of low and the integrated output 6a is supplied to a judgement circuit 7. When the level of the input is small, the signal 6a partially exceeds the voltage VRe of return level of the judgement circuit 7, but does not reach its operation level VOp with the signal staying low. On the other hand, when input level is large, the signal 6a sometimes goes over the voltage VOp and the judgement circuit 7 outputs high signal 7a. In this way it becomes possible to make detection level unchanged by the frequency of an object to be detected. |
