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Bilge Rat
motors and controls.........
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Discussion Starter · #1 ·
I was called to troubleshoot a VFD today, it was the feed belt to a rock crusher.

The VFD in question was an Allen Bradley PowerFlex 4, or maybe a PF 40; I can't remember. Near as I can tell, it's been in operation for several years without issue.

It has a speed pot up in the control house, and the operator stated that even with the pot turned all the way down, the belt ran too fast and would overload the crusher.

The speed pot is basic 0 - 10 V. 0 volts on one side, 10 volts on the other, and the wiper goes to an analog input that's set for voltage.

With the pot all the way down, I had 0 volts from the wiper to the analog common, and 10 volts to the + 10DC. With it turned up a bit, I had 3 volts to common and 7 volts to +10.

Pot is likely ok.

The display was set to HZ, and it read 20.0 with the pot all the way down. The belt usually runs around 13 - 18, hence the overload on the crusher.

So I figured the minimum speed was set at 20HZ. The parameter for this is p034 (I think.....), so I went there and sure enough it's set to 20. I reset it to 0, saved the change, and the VFD operated exactly as it is supposed to.

Oooooookkk.......now the real question here is just exactly how did it get set to 20HZ? I very seriously doubt that any of the plant guys could set a parameter in a VFD. At this plant, I'll be called out to make even the simplest changes to their VFDs.

Of course, I could spend a lot of time and very likely never find the answer, but it bugs me nonetheless.

And even worse, the problem may or may not be solved......
 

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I run into phantom program changes on VFD's and Honeywell controllers all the time, I can only figure people try to troubleshoot something before they call someone in, maybe do a quick google search, and start hitting buttons. If it doenst work out right (it never does) then they call you in and never mention the part where they created a bigger problem so now you have to figure out how to un-**** what they did AND try and figure out the initial problem that was there in the first place.
 

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zap
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I can't remember if ab has preloaded operating parameters, like default pump or fan settings, if they do i would bet that is what happened. frustrated worker/maintenance guy started smashing buttons and ended up using one of the pre configured settings. Or the line side power was cycled enough times the vfd was reset the the factory defaults.

Just some wild guesses

Edit: looking thought the pf4 manual, default min hz is 0.
 

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I don't have any experience with the AB drives but I've done a lot of ABB units. I've had a few situations now where some machine wasn't working right and the maintenance guy went in and started pushing buttons and wound up changing the application macro to something else. That resets everything to default values.

Don't know if AB has something similar
 

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I can't remember if ab has preloaded operating parameters, like default pump or fan settings, if they do i would bet that is what happened. frustrated worker/maintenance guy started smashing buttons and ended up using one of the pre configured settings. Or the line side power was cycled enough times the vfd was reset the the factory defaults.

Just some wild guesses

Edit: looking thought the pf4 manual, default min hz is 0.
I'm in this camp for sure. I can't count the number of times this issue has come up for me, all makes, all models. It cannot possibly be random bit flipping across such a wide variety. It's wannabe technicians, often guys taking a night course in electrical maintenance or something, and they play around with the equipment when nobody is looking, only to get themselves in trouble, then claim no knowledge of it because it means losing the grunt labor job they have before they finish the training for a new job.

The only caveat would be if these drives are set up with communications to a higher level system like a PLC, which might be writing values to control registers inside the drive. Sometimes, if power is failing at the exact moment a register is being communicated to, there can be errors in the addressing and or values that are sent and you get weird random things like this happen. I've noticed it mostly on systems where portable generators are used (ie crushers). People often shut a system down by killing fuel to the engine but are too lazy to open the breaker first. So the generator slowly loses voltage AND frequency at the same time, which creates crazy noise and erratic behavior in the switched mode power supplies connected to the PLC.

Did a huge job a Boeing once where Yaskawa drives kept coming up with random changes to programming, some of them downright dangerous because they were on hoists. We ended up installing magnetic switches in the enclosure doors and monitoring them with the PLC and a time stamp. Caught the guy in about a month through the process of elimination on shift schedules. He was a crane maintenance tech who's crew had initially been charged with making the cranes work, but they pulled the plug and hired us after 9 months of failure, then laid off some of the crane maintenance techs until we got them all working. Apparently he was pissed and wanted to make it look like we didn't know what we were doing either.
 

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We ended up installing magnetic switches in the enclosure doors and monitoring them with the PLC and a time stamp. Caught the guy in about a month through the process of elimination on shift schedules.
please jraef explain how this works

Sent from my HUAWEI Y210-0100 using Tapatalk 2
 

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please jraef explain how this works

Sent from my HUAWEI Y210-0100 using Tapatalk 2
Just installed a magnetically actuated door switch, like on an alarm system, mounted so that when the door was closed, the switch was held in an Open state by the steel of the door and when someone opened it, the contact Closed. It was then wired to an input of the PLC, then in programming we just logged the change of that switch in the PLC with a time and date stamp every time it was actuated. When we came to work every morning, we looked at the log in the PLC and saw what time the box was opened. We then compared those logs to who was working that night, and eventually we eliminated all but one guy.
 

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JRaef said:
It's wannabe technicians, often guys taking a night course in electrical maintenance or something, and they play around with the equipment when nobody is looking, only to get themselves in trouble, then claim no knowledge of it because it means losing the grunt labor job they have before they finish the training for a new job.
Hell! That sounds like me back in the day!
 

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Hell! That sounds like me back in the day!
Hey, nothing wrong with it, everyone has to learn somehow. Just own up to it! I am very forgiving of ignorance and always willing to help someone with a desire to learn. If you F'd up in the process, that's OK to me, just don't try to hide it and claim it is some kind of "ghost in the machine"... That just wastes everyone's time.

"Hey, I tried to program this myself and got in trouble, please help me out".

No problem, let's just clear everything to defaults and start over clean. Saves a lot of time compared to trying to find a condition that caused the problem, where none ever existed.
 

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Bilge Rat
motors and controls.........
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Discussion Starter · #12 ·
Even though every one of the guys at the plant claims to be deathly afraid of anything electronic, it is completely possible that one of them was messing around with it.

The VFD is a stand-alone, it has a 2 wire DI for run, a 3 wire AI for speed control, and a 2 wire AO that may or may not go anywhere.

The plant is on POCO power, and the drive is de-energized every night.

For now, I'm going to go with the tinkering theory.........
 

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Bilge Rat
motors and controls.........
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9,383 Posts
Discussion Starter · #13 ·
Hey, nothing wrong with it, everyone has to learn somehow. Just own up to it! I am very forgiving of ignorance and always willing to help someone with a desire to learn. If you F'd up in the process, that's OK to me, just don't try to hide it and claim it is some kind of "ghost in the machine"... That just wastes everyone's time.

"Hey, I tried to program this myself and got in trouble, please help me out".

No problem, let's just clear everything to defaults and start over clean. Saves a lot of time compared to trying to find a condition that caused the problem, where none ever existed.
I'm the same way. But I find it's nearly impossible to get anyone to admit that they messed with anything.

If they do though, I will gladly lead them through the process.
 

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Where I work they have over ten differant types of drives,
i just swaped out an AB drive, it was so easy.
Some of the older drives they cant find any more or be repaired, so it alway fun to see what i can find to replace it with.
Im alway learning.
:thumbup:
 

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Just installed a magnetically actuated door switch, like on an alarm system, mounted so that when the door was closed, the switch was held in an Open state by the steel of the door and when someone opened it, the contact Closed. It was then wired to an input of the PLC, then in programming we just logged the change of that switch in the PLC with a time and date stamp every time it was actuated. When we came to work every morning, we looked at the log in the PLC and saw what time the box was opened. We then compared those logs to who was working that night, and eventually we eliminated all but one guy.
intresting might use this somewhere.
there was a time my boss wanted to monitor the downtime hrs of a machine most operators would just switch of the machine at nyt so affecting production. I remember we wired the control of the motor through a relay to the input of a plc so it could record day and time. it was off.

I had never thought of such a excellent way to catch a troublesome dude who is messing with drives. thanks

Sent from my HUAWEI Y210-0100 using Tapatalk 2
 

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In our plant we have many VFDs (70) running all our machines. I program them all and no one else is supposed to mess with them. The operators watch me set them up and say that looks easy. When I am not in the area they were playing with the buttons and really screwing things up. Took a few days to figure out why my programs were changing, Now I put a lock code so none of the buttons on the controller work any more. We are set up with external control so they do not have to push any buttons on the VFDs . Fixed that problem real fast.
It was a real nightmare on some machines with 3 controllers tied into a closed loop system. If they messed with the master unit it was a real pain so I take the keypad all the way off the master just in case. We use all TB Woods VFD units and they give me that option. Saves on me pulling my hair out with program problems.
 

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In our plant we have many VFDs (70) running all our machines. I program them all and no one else is supposed to mess with them. The operators watch me set them up and say that looks easy. When I am not in the area they were playing with the buttons and really screwing things up. Took a few days to figure out why my programs were changing, Now I put a lock code so none of the buttons on the controller work any more. We are set up with external control so they do not have to push any buttons on the VFDs . Fixed that problem real fast.
It was a real nightmare on some machines with 3 controllers tied into a closed loop system. If they messed with the master unit it was a real pain so I take the keypad all the way off the master just in case. We use all TB Woods VFD units and they give me that option. Saves on me pulling my hair out with program problems.
Yep, several drive brands offer that option, a blank filler plate for the keypad which totally eliminates the ability for curious minds to experiment. The problem is, to troubleshoot it the qualified technician has to have a real HIM to plug into it, and Murphy's Law says that the day you need it will be the day AFTER someone lost it.
 
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