Use relays, contactor, button, air switch and travel switch etc low-voltage constitute control circuit called relay contact control circuit.

使用继电器、接触器、按钮、空气开关、行程开关等低压电器构成的控制电路称为继电接触控制电路。

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The paper introduces how to design the PLC non - contact control system in rebuilding electrical system of crane, on the basis of a practical example.

结合实际情况对以PLC为内核的全数字直流调速器电能驱动，进行了起重机的工作机构和电器系统改造实现电器系统无触点控制。

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Normally, aircraft crossing the oceans are in contant contact with traffic control, updating them with details of their route information or location.

正常情况下，飞机飞越大洋时要和控制塔保持联络，需要及时告知飞机的航线和位置等详细信息。

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If staff find themselves too fatigued to continue providing cover on standby, they should contact ambulance control and ask to be stood down.

BBC: NEWS | UK | Wales | Strike threat on ambulance cover

It was a tricky maneuver, and it didn't help that during its approach Messenger had to lose radio contact with mission control while it flew behind the planet.

NPR: NASA Probe Glimpses Unseen Side of Mercury

Businesses have been advised to contact private pest control companies.

BBC: Carlisle traders seek seagull problem solution