Automation System
Light sensors:

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

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Automation System
Stepping motors:

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

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Automation System
A venturi tube:

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

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