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3ph Motor Speed Control

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I have an application where I need to be able to control a motor speed accurately and economically. My application uses the speed of a 1/4HP or 1/2HP 240/3/60 hz motor to control the feed rate of an industrial process. The RPM of the motor on a per second basis is critical so I need the motor speed to be as consistent as possible. What I had envisioned is using a 60 pulse/rev. sensor on the motor shaft and feed that signal back into a PID Loop. I would then like to use a PI or PID loop to aim for a specific number of Pulses per time interval. The setpoint of this loop (pulse/time interval) would then be driven by my process to give me a cascading PID Loop where I am actually controlling the process reaction by varying the feed rate of the motor.

I realize that there are many 3ph drives out there that offer closed loop motor control which may give me better accuracy however, I would like to utilize one of the many built in PID loops in the PLC to keep costs down and at the same time, hope to achieve comparable accuracy. My goal is to achieve accuracy of .5% to .25% (or better) from the setpoint. As an additional note: I am using a V350 with a remote IO-TI8-RO8 equipped with a 5K high speed pulse input.

My questions are:

- What is the best way to go about feeding my 60 PPR sensor into the PLC to best gauge my feedback?

- Would I be better off using a PI or PID control loop?

Any help would be greatly appreciated!



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Short answers:

1. you need ot use High Speed Counter of the controller itself. You can set it to High speed countert (HSO) only or to Encoder. See hardware configuration of your project for details.

2. FB PID offers full PID control. PI is partial option - Td = 0. In my point of view, it depends on your system, but te tool is the same.

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