单项选择题

The two most common gases used in pneumatic system are （）

A.compressed air and nitrogen
B.helium and nitrogen
C.oxygen and hydrogen
D.oxygen and acetylene

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单项选择题

Restrictions occurring in the small orifices of pneumatic control system components can be used by （）

A.moisture in the compressed air supply
B.excessive dryness in the compressed air supply
C.pressure surging in the compressed air receiver
D.insufficient lubrication of the system components

单项选择题

In a pneumatic automation system, a unit producing a signal to govern the position of the controller of the measured variable, relative to the value of the measured variable, is said to have（）.

A.reset action
B.proportional action
C.two position action
D.rate action

单项选择题

In an automation system, the effect of a control action sensed by a controller is known as （）

A.command input
B.set point signal
C.output
D.feedback