VFD motor control causing soft error in microcontroller flash memory
VFD motor control causing soft error in microcontroller flash memory
(OP)
The basic setup is a microcontroller that is providing a 0 - 10 DC voltage level to the VFD. The VFD is connected to a 120VAC fan motor (small horsepower). The problem that is occuring is the flash memory in the microcontroller is getting corrupted. Reprogramming the device corrects the corruption problem.
I would like to be able to recreate the problem in the shop, but haven't had any luck. How can I corrupt the flash memory? I haven't been able to see any frequency in the field that might cause the problem. As anyone else experienced this type of problem?
I would like to be able to recreate the problem in the shop, but haven't had any luck. How can I corrupt the flash memory? I haven't been able to see any frequency in the field that might cause the problem. As anyone else experienced this type of problem?





RE: VFD motor control causing soft error in microcontroller flash memory
RE: VFD motor control causing soft error in microcontroller flash memory
RE: VFD motor control causing soft error in microcontroller flash memory
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: VFD motor control causing soft error in microcontroller flash memory
RE: VFD motor control causing soft error in microcontroller flash memory
Several questions:
Is the flash capable of being "self modified" by the CPU?
If it is, you would be more likely,(like a million times),to be having a software bug that is commanding a bad self modification.
Or a soft error that causes the same thing to happen.
Otherwise your boards must be experiencing a RAD of ionizing radiation that is in the process of frying the entire processor.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: VFD motor control causing soft error in microcontroller flash memory
That's rather futile.
Instead. Get your scope and HF probes (isolated) as well as a Fischer HF clamp and stick it in your car. Also, get loads of capacitors, chokes, ferrites, hose-clamps, filters, shielded cables, EMC glands, braids, bolts, washers and nuts and tools and whatever you need to work in the field.
Kiss bye to wife and children and go there. Be prepared to stay for a week - at least. If you have an installation with 500 units that fail once a day - you have a serious problem. That is nothing you can solve in your lab.
I would go to management and tell them that this is something they have to solve once and for all. Not a piecemeal job.
Gunnar Englund
www.gke.org
RE: VFD motor control causing soft error in microcontroller flash memory
To answer your questions:
The flash has a boot rom which can allow in application programming. I'm going to bring this up again with the CTO.
Our station controller was basically a 3 speed fan controller. It pulled on a different relay for the different windings in the motor. This had worked fine for years. When we installed a VFD to allow quieter fan operation we started seeing the devices memory getting altered. The station controller has been installed all over the world for many years and in the thousands without a problem. Of course, they are not being used as VFD controllers.
I would like to rule out the fact that the flash memory is being directly altered by EMI if possible. I haven't been able to find very much information on the subject.
If the problem would occur on a more regular basis at an individual station at the site, it would be easier to monitor the problem. It is too random for anyone to stay there waiting for it to happen.
RE: VFD motor control causing soft error in microcontroller flash memory
I agree that the memory is not changed directly by any EMI. It is most probably something that happens either via the power supply or via the reset circuit. Another possibility is that the address gets corrupted so that the processor goes to never, never land and that something happens on the way there.
Is changing the flash memory the only thing that happens? Or do you have other problems like frequent restarts or changes of operation modes? Do you have to restart the equipment often?
I did not mean that you should go on site and try to catch the thing when it happens. I mean that you should check things like interference on power supply lines, ground potential, reset circuit and such things. If you find interference there when the VFD is running it is a good starting point. Make modifications while monitoring interference levels. You will hopefully find the main road that the interference is taking and also a way of blocking it. Then, there may be another, less important, road that also needs blocking. But usually, there is just one thing that needs to be done to make the equipment more reliable.
Good luck! And please leave some feed-back on how things are going.
BTW: Did I misunderstand the number of units in one place? Are there 500 of them? And about one of them being disturbed every day? That is, as I see it, a serious situation.
Gunnar Englund
www.gke.org
RE: VFD motor control causing soft error in microcontroller flash memory
These tricks and details are learned by most through diligence and the school of hard knocks. I was in on a project that put the first microcontrollers into rail cars to control refrigeration. Having some of the problems like the one you're describing on a fleet of 300ton boxes that are uniformly distributed across the country taught me some very hard lessons.
I would suggest you have someone go over the design if you are still making them.
Otherwise you are going to have to shotgun solutions on all of them which may be a huge expensive headache.
Are you talking about a bunch of units here and there that all worked fine until each one was hooked to a VFD or one VFD gets added to a site and all the units start being victimized?
What kind of processor are we talking about?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: VFD motor control causing soft error in microcontroller flash memory
I know railcars are heavy and getting heavier but not 300 tons!!!!!
RE: VFD motor control causing soft error in microcontroller flash memory
RE: VFD motor control causing soft error in microcontroller flash memory
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: VFD motor control causing soft error in microcontroller flash memory
The whole properties of 500 stations each have their own VFD controller. All the stations worked fine before the installation of the VFDs.
A number of people from the team have been out to the site to monitor the devices. We’ve designed 2 different filters without success. A common mode disturbance has been ruled out. The latest tests we are running are for brown-out conditions.
Thanks again for the support.
RE: VFD motor control causing soft error in microcontroller flash memory
The very first problem that you get when you hammer a micro is a reboot. Next would be the occasional data bit flip. next would probably be a changed register value.
Let me suggest you get another designer to look at your system with a fresh eye.
Please keep us informed elarson.
Good luck!
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: VFD motor control causing soft error in microcontroller flash memory
If you are in Europe, there are Euronorms (EN 61800-3 for instance) that say how much EMI a VFD is allowed to spit out. It is obvious that the VFDs in question are emitting a lot more than allowed - or that your design is so lousy that it cannot take any EMI at all. I rule out the latter.
If you were in Europe, you would have an EMC consultant measure the conducted emission and when you have the numbers - they are probably way above what is allowed, they usually are - then you demand that the VFD supplier/installer do something to reduce EMI. A mains filter is usually what is needed.
What make are the VFDs? What filters have been installed? Is there any EMC declaration?
Gunnar Englund
www.gke.org
RE: VFD motor control causing soft error in microcontroller flash memory
It is highly unlikely that the EMC type interference would be able to directly alter the memory contents.I think that you can discount that possibility.
If the firmware is being altered, then it is most surely being done by the processor itself.
The most common cause of this, is poor pcb design and layout, particulary around the rest input.
With the 8051 family, you must hold the rest line for at least 12 cycles to be sure that you have fully reset the processor. If you reset for less than this, you will reset part of the chip but not all of it and the processor can disappear into it's own version of the firmware. This could enable the bootstrap or part of it.
I have a few suggestions that need to be looked at.
1. Use a fast special purpose micromonitor to control the rest input to the micro. This should have an accurate voltage threshold that is appropriate for the micro so that it causes a reset if the supply voltage begins to drop, well before the uC gets into an undetermined state. - DO NOT rely on the old RC rest circuit!
2. Use a good continuous ground plane under and around the uC
3. Apply good chip type bypass capacitors from the supply pins to the ground plane.
4. Position the micromonitor as close to the uC as possible and bypass well to the ground plane.
4. Use an earthed shield between the primary and secondary windings on the transformer supplying the uC, or use a cetre tapped secondary with the center tap connected to the uC ground plane. A lot of the HF noise can be cpacitively couple through the supply transformer and once in the circuit, it is hard to get rid of.
Best regards,
Mark Empson
http://www.lmphotonics.com
RE: VFD motor control causing soft error in microcontroller flash memory
RE: VFD motor control causing soft error in microcontroller flash memory
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: VFD motor control causing soft error in microcontroller flash memory
RE: VFD motor control causing soft error in microcontroller flash memory
The easiest experiment to implement IMHO would be to find your worst offender and replace that portable cord with some properly shielded VFD cable or put it into steel conduit. If the problem goes away, no need to redesign the controller.
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: VFD motor control causing soft error in microcontroller flash memory
I would watch the power lines to the memory. If you don't have a 'scope, try a capacitor and headphones. If the motor comes on during a write, that could cause problems. A simple ferrite bead
on an interconnecting wire, a ferrite flat on a ribbon, could make a difference. If there are inputs to the system, digital or analog, seriously consider making these inputs (and signals) differential. I found this in a PID servo motor controller system with encoder feedback.
Since the wires to the motor were in parallel with lightly loaded digital (encoder) lines, the lines had to be differential to shed the induced noise from the signals which drove the motor.
It's safe to treat the flash device as infallible with regard to cosmic rays. I take it that you have observed this failure more than once.
I can't preclude bad software or something about the setup. Say some interupt occurs every 70 mseconds.. and should the controller be performing a write when the interrupt occurs, some flash controller timing condition is violated and the write operation fails, should any signals arrive late.
The circuitry perhaps could benefit from having a ground plane close by, if not within the board itself.
This serves in a sense to anchor electric fields locally
reducing interaction with more distant sources.
Putting a ferrite bead on the fan power line might be worth a try.
Though it's a tough call, I place my 50 cents on 'scat in the power rails', an occasional spike or heavily impressed 60-cycle voltage in the ground.
It may be possible to misconfigure a wake-up timer to run continuously.
Leprechauns?
RE: VFD motor control causing soft error in microcontroller flash memory
Putting power line filters on all the computers might help, and on the programmers' power supplies.
An industrial building could have a lot of large relatively slow transients... spikey power lines. Occasional confluence of effects results in a rare power event.
With 500 stations, it sounds like the output is fairly high, so rare power events equate with once/day failure rates. Lowering the data rate, if that works, might cut production enough to make reprogramming once a day are minor imposition.
Inadequate static control measures could be in the list of suspects I suppose.
If you have to go to the site, I would bring some fancy gear to monitor their power circuits. Some systems could be on noisy circuits.
I would take the port data rate down a notch and see if they have any errors that week. AC power filters to the devices on either side of the link (programmer, computer)
might be a better solution, since it might allow the higher data rate. Optically isolating the data links on one end could work.
Hope that helps.
Geoff