Automation System
Light sensors:

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

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Automation System
Stepping motors:

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

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Automation System
A venturi tube:

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

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