| 摘要 |
PURPOSE:To detect a liquid surface or level, by detecting an electromagnetic wave from a transmitting antenna in the form of variation in electromagnetic induced voltage at a receiving antenna according to fluctuations of the liquid level or surface of liquid or bulk material to be monitored which contacts the circumference of the transmitting antenna. CONSTITUTION:When the transmitting antenna 3 uses an antenna bar and the receiving antenna 4 uses a receiving coil, a high frequency signal from an oscillating circuit 1 is impressed to the antenna bar 3. When this signal is detected by the receiving coil 4, the voltage induced across the coil 4 varies with the specific dielectric constant epsilon and conductivity sigma of the circumferential material of the receiving coil 4. In other words, the specific dielectric constant epsilon and conductivity sigma of the circumferential material are measured by the voltage V induced across the receiving coil 4. When there is no dielectric material at the circumference, the output voltage V is high. For this purpose, a proper intermediate voltage (v) is set to a voltage comparator 2 to decide on whether the circumferential dielectric material is present or not and to detect the liquid level or surface level. |
