| 摘要 |
Apparatus (1) for monitoring liquid level in a tank comprises a battery powered monitoring unit (2) for mounting in or on the tank, and a remote display unit (3) which is mains powered. The monitoring unit (2) comprises a microcontroller (8) which operates the monitoring unit (2) alternatively in one of a first operating mode and a second operating mode. During the first operating mode an ultrasonic transducer (7) determines the liquid level at third predefined time intervals of fifteen seconds and operates a radio transceiver (10) to transmit a signal indicative of the liquid level at first predefined time intervals of one hour to the display unit (3). For so long as the microcontroller (8) determines that the liquid level is constant or falling at a normal draw-off rate, the monitoring unit (2) is operated in the first operating mode. On the microcontroller (8) determining that the liquid level is falling at a rate greater than a normal draw-off rate or is rising, the monitoring unit (2) is operated in the second operating mode. In the second operating mode the microcontroller (8) operates the ultrasonic transducer (7) to determine the liquid level at second predefined time intervals of half of one second and operates the transceiver (10) to transmit a signal indicative of the liquid level at the second predefined time intervals for reception by the remote display unit (3). A visual display screen (15) in the remote unit (3) displays a graphical representation of the liquid level in the tank. The monitoring unit (2) may be provided with a visual display screen which would also display a graphical representation of the liquid level. The monitoring unit (2) may be operated in a third operating mode for determining if signals received from the ultrasonic transducer (7) are spurious signals.
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