VFD vs other type of motor control/monitoring


Thread Starter

Steven Keller

The application is a conveyor in a sand plant. The conveyor has a 20hp motor on. I would like to be able to monitor how much power the motor
is pulling and the speed of the motor. I am aware that Allen Bradley and Cutler Hammer sell motor starters that will give this type of information over Device Net. The type of network connection is not all that important at this point.

Could a VFD be used for the same purpose? Plus gain the added benefit of a soft start? The speed would always be set at 60Hz. Besides maybe price what do you think the pros/cons would be between a VFD and an Intelligent motor starter for motor monitoring? Does anyone have any suggestions besides these two?

Ultimately the information will be used to control the load on the conveyor and if there are any abnormal conditions (Belt broke, overloaded, stalled, etc.).

Thanks for your help

Hi Steve: I design systems for plants of this type. My $0.02, keep it simple. Monitor amps or kw. Motor RPM will not vary much with load, but amps or kw [more linear] will. For existing installation, add ct/transducer or kw sensor, and connect to your controller. Low cost and effective. Please contact me by e-mail for more discussion. [email protected]

David W. Spitzer


Applying a VSD should almost always be based upon process and economic considerations. The manner with which the process should (eventually) be
controlled will have a bearing on this decision. See my VSD book (published by ISA) for more information.


David W Spitzer, PE
Copperhill and Pointer, Inc.

BR Guruvaiah

Dear Steve? KW monitor with analogue output suitable for load changing controller can be used. Please let me know how you want to change the load? BRGuruvaiah