Hycintia Subash

MDS instruction would not complete

3 posts in this topic

Hany any you of guys dealt with MDS instruction not completing and being stuck on .EN bit but the motor itself just stopped running out of nowhere?

I did read the tech note on this on Rockwell's website. Am mostly wondering if any of you have dealt with this and what you did to fix this.

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Never used an MDS before, presumably for use with motion capable VFDS like a PF527.  General rule of thumb, most motion instructions are looking for a rising edge trigger or a one shot to execute the command.

As for why the drive stops, find the corresponding MDO and inspect the properties and stop action type.  Either way, the MDS EN bit must go low before seeing another rising edge trigger or one shot to execute again.

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The MDS .EN bit goes true when the input conditions on the rung go from false to true. The .EN bit will stay true so long as the rung is true regardless of the condition of the .DN bit.

The .DN bit is set when the drive has been successfully enabled. If the .DN bit is not going true, the MDS instruction is probably not seeing that the servo has been enabled. Does the drive start after the MDS goes true and then stop? Is this a new installation?

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