Ramping a digital speed reference


Thread Starter

Mike Trombley

I have a system in service that uses a MMI to set the speed of 12 ABB drives over a Profibus network. It incorperates the use of a timer
accumulated value to guide the digital refernce up until the timer is done and the system is at the desired speed. If the operator needs to
make speed adjustments after the ramp time has been completed the reference changes immediately, no ramp. The operator enters the ramp time
on the MMI and it goes to the timer preset, they also set the speed, it scales the max digital reference. Any suggestions.
Hi Mike,

I'm not sure I understand your problem, but from what I make of it, it sounds like whoever wrote the program didn't account for any speed changes made AFTER the initial startup. Am I close?

If so, I would think you can just add a new ramp timer (or timers) to be used during post-startup speed changes (or reconfigure the existing
timer(s)). The greater the difference in current speed vs. new speed selected, the higher the ramp timer preset becomes. For example, if the ramp
from 0 to 2000 RPM is 20 seconds, that's a 100 RPMs per second increase. Therefore, if the machine is currently running at 500 RPM, and the operator selects a new speed of 1400 RPM, your timer preset would automatically be set to: The difference in speed (900 RPM), divided by the RPMs per second increase (100), which is 9 seconds. This is only a simple example, but the
basic principle remains the same, no matter how much you refine it. The RPMs per second increase should be the variable which the operators set on the HMI , NOT the total ramp time. The total ramp time would be calculated by applying the two variables... 1.) The difference between current and target RPM, and 2.) The "RPMs per second" value

This can be used for decreases in speed as well. I may be able to help more but I need to know what's commanding the drives? The HMI or a PLC? and what brand?

Hope this helps... Or at least gets you headed in the right direction? ;o)

- Eric Nelson
[email protected]
Packaging Associates Automation Inc. [email protected]
Rockaway, NJ, USA

Mike Trombley

Hi Eric,
I decided to make things easier on myself. Since the system uses profibus to send commands and change settings at the drives I decided to
send the ramp time to the drives. Rather than allow the timer to guide the digital speed reference up I would write the ramp time to the
accel parameter in the drives and do the same for the decel. Thanks for your suggestions.