Automation System
Light sensors:

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

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Automation System
Time proportioning control:

a and b above.
cannot use a TM990 micro¬computer
is less efficient than normal PID control
can be used on a PM550 programmable process controller
None of these

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