Automation System
An aneroid barometer

None of these
can measure only atmospheric pressure
can be used to measure gas or liquid flow rates
is very unreliable
measures pressure by sensing deflection of an evacuated chambers.

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Automation System
Digital signals:

have a sinusoidal shape.
are assigned values of 1 or 0 depending on the voltage level
None of these
have a frequency measured in units of hertz
can have three possible levels

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