單項(xiàng)選擇題This arrangement is （） if the elements are directly connected to one another and the control action takes place without human involvement.

A.a manual closed loop
B.a manual opened loop
C.an automatic closed loop
D.an automatic opened loop


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1.單項(xiàng)選擇題Bourdon Tube is probably the most commonly used （） measuring instrument.

A.the absolute pressure
B.the gauge pressure
C.the vacuum pressure
D.the differential pressure

3.單項(xiàng)選擇題When two different metals are joined to form a closed circuit and exposed to different temperatures at their junctions （） which can be used to measure temperature.

A.a current will flow
B.a power will develop
C.a heat will flow
D.a pressure will produce

4.單項(xiàng)選擇題（） is provided to alternators, in the event of prime mover failure to ensure that the alternator does not act as a motor.

A.Reverse current protection
B.Reverse power protection
C.Synchronising device
D.Frequency meter

5.單項(xiàng)選擇題To parallel an incoming machine to a running machine therefore it is necessary to ensure firstly that （）.

A.two frequencies must be brought into phase
B.the incoming machine accepts a small amount of load
C.the running machine must be unload
D.both voltages are equal