Automation System
Light sensors:

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

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Automation System
Stepping motors:

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

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Automation System
A venturi tube:

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

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