Abstract: An ultrasonic level sensor (1) for monitoring the level of a liquid in a vessel comprises a main housing (3) having a lower part (5) and an upper part (6). An ultrasonic transducer (19) having an output face (25), through which ultrasonic signals are transmitted and received is housed in a sub-housing (39) located in an engagement recess (17) in the lower part (5). A communicating aperture (24) accommodates ultrasonic signals transmitted by the ultrasonic transducer (19) to and from the liquid surface, the level of which is to be monitored. The sub-housing (39) comprises a cylindrical side wall (40) extending upwardly from a protective element (35) for protecting the ultrasonic transducer (19).

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.