| 摘要 |
<p>An air freshener unit comprises first and second pressurised canisters (12, 14) containing a fragrant substance, and a control circuit (16) for controlling the valve mechanisms (20, 21) of the first and second canisters to regulate the release of the fragrant substance. A fragrant substance is released from canister (12) until the canister is exhausted at which time a sensor detects inadequate flow and switches the control circuit (16) to ensure that release of fragrant substance will continue from canister (14). An indicator (32) shows when the canister (12) is empty, thus allowing replacement whilst canister (14) is still in operation.</p> |
