Speed Input on Powerflex 755

[Smell5933]

Hello,

I am new to the PLC world and I have a project where I am using a powerflex 755 drive. This is a compact Logix controller. I need help writing the code that will tell the drive what speed to run. An input from the touchscreen will be in FPM I will then translate the FPM to the drive. What is the best way to go about doing this? I will be sending the signal via Analog output to the 755's 22 series input module, specifically the Speed reference inputs Ai0- and Ai0+. The analog card is a 1768-OF8V. Let me know if you have any information that can help me. I appreciate the help.

 

[jraef]

Seems rather silly to me to be in possession of a controller with Ethernet capabilities, and a VFD with native Ethernet communications, and yet use hard wired analog I/O to control the drive. But that's just me.

First you will need a scaling factor to convert FPM to RPM in your specific machine, then once you know that, you scale the desired RPM to the motor nameplate RPM (slip speed) to get a percent of full speed, then set the analog output of the PLC to equal the percent motor speed you want. You can also do much of this inside of the 755, so you will have to decide first where you want the decisions to take place. Doing it in the PLC means that changing the drive out is easier, because the replacement drive just has to follow the analog signal from the PLC. Doing it inside of the drive however means that if the PLC dies, you can manually run the motor from the keypad of the drive with the same effect. Only you can assess which is better for your machine / user application, but you will have to start there.

 

[Bullzi]

View attachment 33125jraef is correct. I would look into using Ethernet/IP to communicate the speed reference to the VFD.
I just did a job with 3)753 drives and was really freaking out about how to make it all work. It turned out to be way easier than I thought.

When you add the VFD to your project tree a set of tags for the VFD will automatically be added to your Controller Tags. In those tags you will find a bunch of Input Tags with data you can read into the PLC and Output tags that you can write data into from the PLC over the Ethernet link.

Basically to start the drive I set the Drive_NameLogicCommand_Start tag to a 1. I will keep that tag at a 1 until I see that the Drive_Name:IriveStatus_Running tag is true. Then the Start tag drops out.

To Stop the drive I will set the Drive_Name:O:LogicCommand_Stop tag to a 1. I will keep that tag at a 1 unit I see the Drive_Name:IriveStatus_AtZeroSpeed tag is true. I also set the speed reference tag to a 0.

To set the speed of the drive I MOV a RPM value into O:Reference tag.

See the JPG I have attached for some code ideas.

There is some programming in the drive you have to do to tell it to get its speed reference from the Ethernet port. The rest of the drive programming is pretty straight forward.

 

[Bullzi]

Can anyone tell me how to not get the Smiley faces when I do a colon and a D after?

Also how do I post a higher resolution screen shot? The one I posted is impossible to read. I used the Window Sniping Tool?

 

[jraef]

Can anyone tell me how to not get the Smiley faces when I do a colon and a D after?

Also how do I post a higher resolution screen shot? The one I posted is impossible to read. I used the Window Sniping Tool?

Down below your editor page, there is a control box that says "Miscellaneous Options" with two boxes, click on the box that says "Disable smileys in text". You don't see that option in the "Quick Reply" box however, you have to use the "Post Reply" button on the left bottom corner to get the full blown editor.

Not sure if I can help you with the image issue or not. You have to have saved it to your HD at a higher resolution I think, prior to attaching it to the post. But I also think the attachments have size limitations, likely to conserve server space, so you either have to reduce it or it fails to show. But I believe if you save your higher res image to a 3rd party image hosting site, like photobucket, then link to the image URL using the img command, it might show the higher image, as long as it still exists at that URL.

 

[Smell5933]

Thank you for the information. Yes I agree that using the ethernet would be much more simple. But from your information it seems either way will not be difficult to do. Thank you!!

 

[kamenges]

Originally posted by Smell5933

...it seems either way will not be difficult to do.

It is much easier to do over Ethernet/IP. You can skip the analog scaling and possible mismatch in speed basis if you use Ethernet/IP. The speed command output from the plc will be a floating point number is RPM. Granted, set-up is a bit more complicated with Ethernet but once you go down that road I can pretty much guarantee you won't go back.

Keith