| 摘要 |
A non-contact system (10) for sensing a property of a passing web of material (W) includes first and second sensors (14, 16) positioned on opposite sides of the web. The opposing sensors are repelled from the web and each other by gas bearings (22, 24) formed between the sensors and the web and attracted to each other by one or more polarized magnets (26, 25a, 25d, 25a', 27a-27d, 27a') embedded in the sensors. The resultant net force properly spaces the sensors from the web to ensure reliable and accurate sensing. The repelling force enables the sensors to react substantially instantaneously to changes in the pass line of the web. An automatic actuator/retractor (30) can be provided to withdraw the sensors, extend the sensors to or retract the sensors from adjacent the feed path. |
