# ISA Interchange

Welcome to the official blog of the International Society of Automation (ISA).

This blog covers numerous topics on industrial automation such as operations & management, continuous & batch processing, connectivity, manufacturing & machine control, and Industry 4.0.

The material and information contained on this website is for general information purposes only. ISA blog posts may be authored by ISA staff and guest authors from the automation community. Views and opinions expressed by a guest author are solely their own, and do not necessarily represent those of ISA. Posts made by guest authors have been subject to peer review.

# AutoQuiz: Which Signal Type Indicates Direction and Velocity in a Motion Control Application?

### Subscribe Here!

AutoQuiz is edited by Joel Don, ISA's social media community manager.

This automation industry quiz question comes from the ISA Certified Automation Professional (CAP) certification program. ISA CAP certification provides a non-biased, third-party, objective assessment and confirmation of an automation professional's skills. The CAP exam is focused on direction, definition, design, development/application, deployment, documentation, and support of systems, software, and equipment used in control systems, manufacturing information systems, systems integration, and operational consulting. Click this link for more information about the CAP program.

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
e) none of the above

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.

The correct answer is C, “±10 V.”

Reference: Nicholas Sands, P.E., CAP and Ian Verhappen, P.Eng., CAP., A Guide to the Automation Body of Knowledge. To read a brief Q&A with the authors, plus download a free 116-page excerpt from the book, click this link.