Industrial Drive Applications Questions and Answers

Answer: A

Following a programmed path to within microns means a position loop, a fine encoder and a low-inertia machine that can reverse quickly. Permanent magnet servo drives with ball screws or linear motors are the usual answer.

Answer: B

Correct answer: allows rapid acceleration for a given torque

Angular acceleration is torque divided by inertia, so halving the inertia doubles the acceleration for the same torque. A servo machine is therefore built long and slender rather than short and fat, since inertia grows as the fourth power of the radius while torque grows only as the square.

Answer: C

Correct answer: a smoothly rising speed profile as the bobbin fills

As the bobbin builds, the yarn must be delivered and wound at a rate that keeps the twist and the tension right, so the drive follows a profile rather than a fixed speed. Any discontinuity in that profile shows in the finished yarn, which is why smoothness matters as much as accuracy.

Answer: D

Each colour must be laid within a fraction of a millimetre of the last, so the units run in exact and trimmable angular relationship. Electronic line shaft control has replaced the mechanical shaft and its gearing entirely.

Answer: A

Correct answer: the angular position of one unit relative to another

Each colour is printed by a separate unit, and the impressions must coincide on the web to a fraction of a millimetre. Register control makes small continuous adjustments to the angular position of each unit relative to the others, correcting for the stretch and slip of the paper as it runs.

Answer: B

The pressure the screw develops is set by the die and the melt rather than by the speed, so the torque is flat and the power rises with output. Constant flux over the whole range, with generous overload capability for a cold start, is what the drive needs.

Answer: C

Correct answer: the thermal duty of the repeated run-up

Bringing a loaded bowl up to several thousand revolutions a minute takes a large current for a long time, and the heat generated far exceeds anything the steady running produces. Since the cycle repeats, the machine must be rated on the heat of the whole duty rather than on the modest power needed once at speed.

Answer: D

Reducing the speed by a fifth takes nearly half off the power, which is why variable-speed pumping pays for itself so quickly on any duty that spends time below full flow. A positive displacement pump offers no such saving.

Answer: A

Correct answer: the water temperature leaving the tower

The tower exists to cool water to a required temperature, so that is the controlled variable and the fan speed is the means. Controlling on fan speed or motor current would control the actuator rather than the process, and ambient temperature is a disturbance to be rejected rather than a setpoint.

Answer: B

Terminal boxes throughout the building open and close, and holding a duct pressure lets the fan deliver exactly what they are drawing. That is where the saving comes from, since the alternative is a fan at full speed with dampers throttling the surplus.