单选题The limit switches on a ships survival-craft winch system（）.A stop the winch just before the craft reaches the final stowage positionB limit the amount of cable on the drumC limit the ascent rateD stop the winch in case the craft weighs too much

In order to limit the introduction of alien species by ship, ____was adopted on 13 Feb, 2004 at the IMO.

A.Revised MARPOL annex I

B.Revised MARPOL annex II

C.International convention for the control and management of ships' ballast water and sediments

D.ISPS Code

A ______ system placed between the company network and the outside world may limit outside access to the internal network.

A．firewall

B．modem

C．gateway

D．key

Pedestal cranes have limit switches to restrict the movement of which function?______.

A.Luff rate limits

B.Slew travel limits

C.Swivel power limits

D.Slew rate limits

While cranking out a quadrantal davit，slippage of the quadrant due to excessive wear or failure of the teeth in the quadrant will cause the ______．

A.Davit arm to pivot on the traveling nut and the head to fall outboard

B.Traveling nut to lock up in place on the worm gear

C.Limit switch to engage and hold the traveling nut in position

D.Winch brake to lock in position and prevent lowering the boat

A(75)system placed between the company network and the outside world may limit outside access to the internal network．

A．firewall

B．modem

C．gateway

D．key

Pedestal cranes have limit switches to restrict movement of which function（s）________．

A.Hoist upper & lower limits

B.Luff travel limits

C.Rider block hoist upper & lower limits

D.All of the above

第一组

An automatic system usually consists of a control system and an information system. A control system is a system which measures the condition of some entity and, with the information, governs the state of a variable; i.e., speed, temperature, pressure, position, etc. The open-loop system is the simplest form. a control system may assume. It is distinguished from the closed-loop system by the lack of an input which measures the state of the controlled variable; such an input is called a feedback. In modern ships the open-loop system has practically disappeared and the closed-loop system which operates with a feed-back is extensively used. An information system serves the parallel function of monitoring system or plant performance. The monitoring function may serve a number of purposes; specifically it may indicate values of controlled variables to guide remote control operations, warn of off-limit conditions and provide record of performance. In many cases a visual and audible alarm may be provided to warn of off-limit conditions on board ship and, associated with this, the important variables will be recorded on demand. The automatic control system can be more sophisticated by incorporating digital-processing equipment, that is, a computer. This computer is usually fed with signals from all sensors. It scans the values of the sensors and generates alarm signals for off-limit conditions, acting as a super-supervisor. Sometimes, it can even make necessary and take the necessary action to optimize performance without human intervention.

The closed-loop system differs from the open-loop system by

A.the lack of a feedback

B.the presence of a feed back

C.the lack of a computer

D.the presence of a computer