| 摘要 |
<p>To prevent non payment in self service petrol stations an electrically controlled pneumatically actuated anti-reversal system ensures that motor vehicles can enter only at one end and, after filling, leave only past the cashier. The anti-reversing device is a triangular steel frame, pivoted from one edge and pneumatically actuated so that in normal usage it lies flush with the road surface, but if required tilts upwards offering a vertical face to obstruct the vehicle. Two detectors sense the direction of motion of the vehicle and if the vehicle is travelling in the wrong direction actuate the obstruction control which is a solenoid valve in the compressed air supply line. An audible warning is then activated.</p> |
