| 摘要 |
<p>The petrol dispenser individually records the flow through a particular meter and comprises a number of these instruments in rows. Each meter has its co-ordinates defined by master keys controlling each horizontal row and each vertical row. To prevent fraudulent operation, both sets of key units are wired in series, one horizontal and one vertical contact being required to complete a circuit. This is achieved by using a contactor behind each key unit and operated by inserting and turning the key to activate the pump through the selected meter.</p> |
