| 摘要 |
The invention refers to a level transducer for conductive liquids, which has a capacitive sensor (Cx) that is made up of a thin brass rod (1) covered with a lacquer film (2) with good dielectric properties. The rod is fixed inside a thin stainless steel tube (3) which accommodates the liquid column (4) whose level (hx) must be measured. The measurement is done ratiometrically, by comparison with the capacity of a reference condenser (Cr) which is made up of a brass disc (5) covered with a lacquer film (6), having the same dielectric as the capacitive sensor (Cx). The reference condenser (Cr) is kept immersed in the liquid (4) at all times, and the ratio (Cx/Cr) between the capacities of the capacitive sensor (Cx) and the reference condenser (Cr) is calculated by means of the (Ux/Ur) ratio of the voltages (Ux, Ur) at the terminals of the capacitive sensor (Cx) and of the reference condenser (Cr), with the help of an analogue divider (D), preceded by two capacity-voltage converters (CTx, CTr). At the output, the divider gives a voltage (U0) that is proportional to the measured level (hx) of the liquid (4), but is independent from the inductive capacity (ε) of the lacquer film (2) and the instability of the activation voltage (U).
|
