Abstract: 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.

Abstract: Apparatus for indicating the oil level in a central heating oil tank comprises a battery powered monitoring unit (1) for mounting on the oil tank which determines the oil level by an ultrasonic signal transmitter/receiver (18). A first microprocessor (14) in the monitoring unit (1) determines the oil level from the ultrasonic transmitter/receiver (18) and operates a primary transmitter (12) for transmitting a radio signal which includes data indicative of the oil level. A remotely mounted mains electricity powered receiving unit (3) comprises a primary radio receiver (15) for receiving the transmitted signal, and a second microprocessor (16) in the receiving unit (3) controls the operation of a visual display unit (10) for graphically displaying the oil level. The monitoring unit (1) and the receiving unit (3) are operable in a teaching mode initially on power-up of the receiving unit (3) during which the monitoring unit (1) teaches the receiving unit (3) its address.