# Powerflex comms loss alarm



## mpetro (Jan 6, 2016)

Hey everyone,


Just as a preface, I have fairly limited VFD programming experience.



Working on a project with a few critical Powerflex 753s in a DLR configuration, communicating to a ControlLogix through a 1756-EN2TR card. We're looking to send an alarm to the plant DCS if the drive sees a loss of Ethernet comms, without stopping the drive with a fault (obviously other faults will still cause the drive to trip). The drives are controlled through hardwired I/O, the network is only for supervisory purposes, so the drive can keep operating if the I/O is still present.


I guess my question is how exactly is the easiest or simplest way to do this? I can't seem to find anything in the controller tags in the PLC program under the drive I/O (DriveStatus, etc), and the only thing I can find in the drive parameters is parameter 33 under the port 5 Ethernet/IP host parameters, labelled Comm Flt Action. My gut says to change this parameter to "Hold Last" but I'm not sure of the finer details of how this interaction works.


Any insight would be greatly appreciated.


----------



## MDShunk (Jan 7, 2007)

Yes, there's a way to do it. I've got all my ethernet com cards in PowerFlex drives (maybe a thousand?) set up that way. When I get into work tonight I'll screenshot some logic. You don't actually montor the drive. You monitor the COMM-E card in the drive.


----------



## mpetro (Jan 6, 2016)

MDShunk said:


> Yes, there's a way to do it. I've got all my ethernet com cards in PowerFlex drives (maybe a thousand?) set up that way. When I get into work tonight I'll screenshot some logic. You don't actually montor the drive. You monitor the COMM-E card in the drive.



Great, thanks. I figured it was something to do with the comms card specifically but I can't seem to find exactly what I'm looking for.


Appreciate it


----------



## MDShunk (Jan 7, 2007)

mpetro said:


> Great, thanks. I figured it was something to do with the comms card specifically but I can't seem to find exactly what I'm looking for.
> 
> 
> Appreciate it


no problem. Someone might beat me to it and link you to a knowledgebase article or something before then. Don't hold it against me if I don't get to it tonight. I never quite know what I'm walking into on any given day. That's what makes my job genuinely fun.


----------



## splatz (May 23, 2015)




----------



## Rora (Jan 31, 2017)

If the VFD loses connectivity, it can't communicate that to the PLC, so the PLC must monitor its connection to the VFD. I believe Splatz screenshot identifies the connection status variable "EntryStatus" for the PowerFlex_700S_AC_Drive... there should a similar variable in your PLC which will reflect the Ethernet connection status to the VFD that can be utilized to trip an alarm.

Even if that wasn't available, it would be possible to monitor the timestamp of the most recent feedback (via Ethernet) from the VFD as a keepalive, and send an alarm if the elapsed time exceeds a certain amount. That would insinuate the health of not only the Ethernet link L2/L3 but also the relevant functionality at the "application layer"


----------



## mpetro (Jan 6, 2016)

Rora said:


> If the VFD loses connectivity, it can't communicate that to the PLC



Duh, that should have been pretty obvious that I need to be looking at the PLC. Thanks!


----------



## Rora (Jan 31, 2017)

mpetro said:


> Duh, that should have been pretty obvious that I need to be looking at the PLC. Thanks!


Very understandable considering it's the only problem equipment can have that can't be reported by said equipment. Finding the relevant variable is the hard part, though... I'd imagine it will look similar to what's seen in the screenshot Splatz posted, since they're both Powerflex 700 series. The MEQ function compares the string to what you'd see when it's connected and reduces it to an on/off value that can be used to trigger the alarm. Best of luck!


----------



## mpetro (Jan 6, 2016)

Rora said:


> Very understandable considering it's the only problem equipment can have that can't be reported by said equipment. Finding the relevant variable is the hard part, though... I'd imagine it will look similar to what's seen in the screenshot Splatz posted, since they're both Powerflex 700 series. The MEQ function compares the string to what you'd see when it's connected and reduces it to an on/off value that can be used to trigger the alarm. Best of luck!



Yes we'll try out what Splatz posted, it looks to be what we want to do.


Thanks again guys!


----------



## JRaef (Mar 23, 2009)

Inside of the 753, there is PLC code available called “DeviceLogix” and in there, you can also write a routine that checks whether the comms are active and if not, trigger another routine. I use it for when I have network control, but want hard wire as a backup. So the first line of that code is to check comms, and if active, ignore the rest of the code. But as soon as the network doesn’t respond (after a time out to make sure), the internal code is executed using the I/O brought into the drive. This works especially well for Pump Control Valves where the circuit to control the valve resides inside of the drive AND the PLC, so if the comms are ever lost, the drive still has control of the valve.


----------



## JRaef (Mar 23, 2009)

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/ra-um003_-en-p.pdf


----------



## mpetro (Jan 6, 2016)

JRaef said:


> Inside of the 753, there is PLC code available called “DeviceLogix” and in there, you can also write a routine that checks whether the comms are active and if not, trigger another routine. I use it for when I have network control, but want hard wire as a backup. So the first line of that code is to check comms, and if active, ignore the rest of the code. But as soon as the network doesn’t respond (after a time out to make sure), the internal code is executed using the I/O brought into the drive. This works especially well for Pump Control Valves where the circuit to control the valve resides inside of the drive AND the PLC, so if the comms are ever lost, the drive still has control of the valve.



This is great, I have a couple of options to explore now. Thanks!


----------



## MDShunk (Jan 7, 2007)

JRaef said:


> Inside of the 753, there is PLC code available called “DeviceLogix” and in there, you can also write a routine that checks whether the comms are active and if not, trigger another routine. I use it for when I have network control, but want hard wire as a backup. So the first line of that code is to check comms, and if active, ignore the rest of the code. But as soon as the network doesn’t respond (after a time out to make sure), the internal code is executed using the I/O brought into the drive. This works especially well for Pump Control Valves where the circuit to control the valve resides inside of the drive AND the PLC, so if the comms are ever lost, the drive still has control of the valve.


That's what I call a real belt with suspenders approach. 

I'll keep it in mind if I ever have to setup a drive for cooling water in a nuclear power plant. :biggrin:

Even though we use feedback tops on valves and outlet pressure sensors to prevent pump dead heading at the plant I'm at, all that is for naught if comms are lost. On critical pumps, we have a pressure relief from outlet back to inlet in case things really go haywire, essentially just stirring the product round-and-round in that case. The preference is to shear product from overpumping rather than blow pump seals or blow pipe flanges apart.


----------

