Automation System
Light sensors:

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

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Automation System
Stepping motors:

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

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Automation System
A venturi tube:

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

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