PLC Motion Control & Drive Systems 2

Question 1

What is the primary function of an encoder in a servo motor system?

Accepted Answer

To provide real-time position and velocity feedback to the servo controller

Answer

An encoder provides continuous position and velocity feedback to the servo controller, enabling the closed-loop control required for precise positioning applications.

Question 2

What fundamentally distinguishes a servo drive from a standard VFD?

Accepted Answer

Servo drives use encoder feedback for precise closed-loop position and torque control

Answer

Servo drives utilize encoder or resolver feedback for tight closed-loop control of position, velocity, and torque, while VFDs are primarily used for open-loop or simple closed-loop speed regulation.

Question 3

In PLC motion control, what does performing a 'homing' routine accomplish?

Accepted Answer

It establishes a known reference position so the controller knows the axis's absolute location

Answer

A homing routine moves the axis to a defined reference point (home position) so the motion controller establishes a coordinate origin for all subsequent absolute position moves.

Question 4

A quadrature incremental encoder outputs two channels (A and B) that are 90° out of phase. What information does the phase relationship between A and B provide?

Accepted Answer

Direction of rotation (clockwise vs. counterclockwise)

Answer

The 90° phase offset between channels A and B allows the controller to determine the direction of rotation — if A leads B the motor turns one way; if B leads A it turns the other way.

Question 5

What is the purpose of a 'jog' command in a PLC motion control application?

Accepted Answer

Move the axis continuously at a slow speed only while the command signal is held active

Answer

A jog command moves the axis at a controlled, low speed only while the discrete input or button is held active, allowing operators to manually position equipment during setup or maintenance.

PLC - Programmable Logic Controller Certification Practice Test

PLC - Programmable Logic Controller Certification Practice Test

PLC Motion Control & Drive Systems 2