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Old October 8th, 2018, 08:05 AM   #1
phuz
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Best practice for VFD control backup (if PLC fails)

I just installed 3 PowerFlex 755 VFDs for a customer's fresh water booster pumps, and converted the three PowerFlex 400 well pump VFDs over to Ethernet, and all control is done via a 5069-L306ER. Given the critical nature of the systems (needs 24/7 uptime), we are examining all possible failures, including losing the PLC. One of the options would be putting HOA switches on the door, but I've never done this when using Ethernet. Is there a way to provide a quick switch in the event we lose the PLC control source without needing to change 'Start Source' and 'Speed Source' in the VFD parameters?
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Old October 8th, 2018, 08:28 AM   #2
cardosocea
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If the drive "sees" no PLC comms are up, can you program it to run at a set speed?

In my case, the VFD's have a digital signal from the PLC that in the event of a PLC failure, will switch and they'll run at a set speed. If you have a pressure sensor or something like that, you could potentially wire it into the VFD and use that as a very rough setpoint. It's not a PID, but would allow some control.
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Old October 8th, 2018, 08:32 AM   #3
Mad_Poet
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You might also consider what happens if the VFD goes out.

I know of a conveyor system which was ran off VFD's . . . and it had a backup
system whereby the motors could be ran off 'house power'. Three phase 220V 60 Hz.
Poet.
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Old October 8th, 2018, 08:34 AM   #4
phuz
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Quote:
Originally Posted by cardosocea View Post
If the drive "sees" no PLC comms are up, can you program it to run at a set speed?

In my case, the VFD's have a digital signal from the PLC that in the event of a PLC failure, will switch and they'll run at a set speed. If you have a pressure sensor or something like that, you could potentially wire it into the VFD and use that as a very rough setpoint. It's not a PID, but would allow some control.
I think the best bet would be to use a rocker switch that would go do a digital input and run a preset speed. But if the start source is already programmed for 'Comm Port', how can you use a digital input without changing parameters?
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Old October 8th, 2018, 08:35 AM   #5
phuz
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Quote:
Originally Posted by Mad_Poet View Post
You might also consider what happens if the VFD goes out.

I know of a conveyor system which was ran off VFD's . . . and it had a backup
system whereby the motors could be ran off 'house power'. Three phase 220V 60 Hz.
Poet.
Not a concern. There are 3 well pumps and 3 booster pumps. One can fail and the plant can still run.
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Old October 8th, 2018, 11:24 AM   #6
Lynx777
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I've set up a couple 755's to run like this.

Step one is to program the drive so that it does not fault when it looses communications.

After that there are a couple of different ways to proceed. In your case I think I would set up an output from the plc (this can be over enet) that stays on as long as the PLC is communicating. When you loose that input to the VFD it would then switch over to local control and either run at it's last speed or it could be programmed to run at a set speed.

We also added an I/O card to the drives and use an HOA switch so that maintenance can take over control when needed.
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Old October 8th, 2018, 11:31 AM   #7
phuz
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Quote:
Originally Posted by Lynx777 View Post
I've set up a couple 755's to run like this.

Step one is to program the drive so that it does not fault when it looses communications.

After that there are a couple of different ways to proceed. In your case I think I would set up an output from the plc (this can be over enet) that stays on as long as the PLC is communicating. When you loose that input to the VFD it would then switch over to local control and either run at it's last speed or it could be programmed to run at a set speed.

We also added an I/O card to the drives and use an HOA switch so that maintenance can take over control when needed.
I think just the idea of the HOA switch would be enough, but how is that programmed when using Ethernet control?
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Old October 8th, 2018, 12:56 PM   #8
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A contact of the HOA switch is fed into the VFD to an input programmed to change the control point and speed reference point.


For the PowerFlex 755, download the Reference Manual, 750-RM002A-EN-P, it shows you how to do that on Page 32.


For the PF400, because there is a Hand - Local selector on the keypad, the instructions are a little different, but start on page 50 of the User Manual.
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Old October 8th, 2018, 01:01 PM   #9
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Quote:
Originally Posted by jraef View Post
A contact of the HOA switch is fed into the VFD to an input programmed to change the control point and speed reference point.


For the PowerFlex 755, download the Reference Manual, 750-RM002A-EN-P, it shows you how to do that on Page 32.


For the PF400, because there is a Hand - Local selector on the keypad, the instructions are a little different, but start on page 50 of the User Manual.
Thanks, you're awesome. I figured it out for the 400, but missed that section on the 755. That'll be perfect.
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Old October 9th, 2018, 06:37 AM   #10
Lynx777
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Quote:
Originally Posted by jraef View Post
A contact of the HOA switch is fed into the VFD to an input programmed to change the control point and speed reference point.


For the PowerFlex 755, download the Reference Manual, 750-RM002A-EN-P, it shows you how to do that on Page 32.


For the PF400, because there is a Hand - Local selector on the keypad, the instructions are a little different, but start on page 50 of the User Manual.
Thanks jreaf for adding the reference material. I was going to add it to my post, but life interrupted. (Granddaughter swallowed a penny, I had to help manage the panic)
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Old October 9th, 2018, 08:50 AM   #11
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Quote:
Originally Posted by Lynx777 View Post
Thanks jreaf for adding the reference material. I was going to add it to my post, but life interrupted. (Granddaughter swallowed a penny, I had to help manage the panic)
Been there, done that, got the t-shirt and the hat...


I'm hoping for you that it didn't get stuck in her throat. Bananas help move it along if it made it safely to the stomach. Took my daughter 3 days to pass it, which itself was a somewhat traumatic event too...
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Old October 9th, 2018, 10:21 AM   #12
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Quote:
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Been there, done that, got the t-shirt and the hat...


I'm hoping for you that it didn't get stuck in her throat. Bananas help move it along if it made it safely to the stomach. Took my daughter 3 days to pass it, which itself was a somewhat traumatic event too...
Thankfully no choking, just had to reassure Nana and Mom that there precious jewel was not going to die from copper poisoning or something worse. LOL
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Old October 9th, 2018, 12:15 PM   #13
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You may panic though if your child or grandchild swallows one of those miniature batteries, like in watches or small toys. Don't wait for those to exit on the other end. They can kill you, not because of the chemicals directly but rather to the reactions that will occur in the tissue due to electrical currents, however small they are. Make them throw up, no matter which way, if not get to a doctor/hospital quickly.
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Old October 10th, 2018, 12:44 PM   #14
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Quote:
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Thankfully no choking, just had to reassure Nana and Mom that there precious jewel was not going to die from copper poisoning or something worse. LOL
Heh, there's hardly any copper left in a penny... Since the 1980s pennies are mostly zinc. It is potentially harmful, but only if the penny doesn't come out; not enough zinc dissolves in the stomach to be harmful. So that's the worst part, having to monitor your child's "output" for a week looking for the penny (or taking them for an x-ray a week later to make sure). By the way when it comes out, the copper will most likely be gone and it will be grey.
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Old October 10th, 2018, 01:15 PM   #15
Lynx777
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Thanks for the intel. I'll tell Nana & Mom to keep there eyes open for a grey penny!
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