ISA Certified Automation Professional (CAP) program

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Certified Automation Professionals (CAPs) are responsible for the direction, design, and deployment of systems and equipment for manufacturing and control systems.

CAP question

In a motion control application, which of the following signal types would be able to indicate both direction and velocity?

A. 4–20 mA
B. 3–15 psi
C. ±10 V
D. 0–10 V

CAP Answer

The correct answer is C, “±10 V.”

In order to indicate both direction and velocity, a signal with both positive and negative characteristics is required. Motion controls use either ±10 V or ±5 V signals to accomplish this. Direction is indicated by the sign of the signal; magnitude of velocity is indicated by the magnitude of the voltage.

The other three choices are typical signal types for analog inputs, but none have the ability to easily indicate direction, only velocity. Obviously, a pneumatic (3–15 psi) signal would never be a good choice for motion control applications.

Reference: Trevathan, Vernon L., A Guide to the Automation Body of Knowledge, Second Edition, ISA, 2006.