| 摘要 |
An arrangement for determining the level in a container includes a capacitive probe disposed in the container, a measuring transducer arranged in the vicinity of the container, and a remote evaluation apparatus. The measuring transducer produces a signal corresponding to the capacitance between the probe and the container. This signal, which is indicative of the level in the container, is transmitted from the transducer to the evaluation apparatus via a two-wire line, which also transmits the current supply DC voltage from the evaluation apparatus to the transducer. The transducer includes a switch for periodically switching from the probe capacitance to a test capacitance. The evaluation apparatus comprises a time control circuit which periodically varies or interrupts the DC voltage on the two-wire line, and the transducer includes a control circuit which responds to the voltage changes to actuate the switch. This permits control of the test operation by the evaluation apparatus over the same two-wire line which also carries the measuring signal and the current supply voltage. |
