Automation System
Light sensors:

come in a wide variety of mounting styles
cannot be used a s limit switches.
never use infrared light as light source
None of these
work in direct sunlight

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Automation System
Stepping motors:

can run at varying speeds
can run both clockwise and counterclockwise
can be built to index different amounts by changing the pole configuration
do not require commutators
All of these

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Automation System
A venturi tube:

None of these
is made only of metal
is extremely difficult to use
measures the presence of a liquid
can be used to measure gas or liquid flow rates

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