Automation System
Today, programmable controllers:

are more powerful then the first controllers on the market
All of these
can be cost effective even when replacing just a few relays
are relatively low cost compared with the original digital equipment available for industrial control
None of these

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Automation System
Stepping motors:

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

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