Static discharge beating up my 1769-WS

[OkiePC]

Thanks for all the replies so far.

My new 1769-WS module should arrive tomorrow or the next day, so I am going to rule out a flaky module before I go further. If the new module is just as sensitive, then I will try to get some experienced help in here with a meter.

 

[OkiePC]

The new module arrived today, and the symptoms were exactly the same. It was a little disappointing, and also a relief that I know for sure the module is ruled out as a possible cause.

So, asking around among the guys, I found out we use tinsel on a bag making machine and stock a 21" long piece in spare parts. So, I added that to the infeeding conveyor so that it touches the plastic belt and the cartons just as they enter the scale conveyor.

This did not appear to help. So I got my meter out again and began probing the cases, the conveyors, the drive rollers, etc...looking for potential between some of the moving parts and the frame. I found that the outfeed belt was generating 4 to 10 volts on its drive rollers. This is a short rubber coated belt that was once upon a time a gap creating belt, but it is really not even needed anymore (if we extend the next conveyor a bit). It has three static generating drums near the output of the scale conveyor, and they are all making juice. There are two rear idler rollers and a take-up roller.

So, I rigged up some short pieces of copper wire and bolted them to the bearing blocks and bent them around in such a way that they are discharging the voltage from these rollers. Sparks are evident here when I touched copper to spinning roller.

End result is that is has been 30 minutes so far with no errors. Tomorrow, after checking the alarm logs, I will try removing the tinsel from the infeed and see if it's just the static from the outfeed that has been kicking my a$$.

I am not calling this one solved just yet, but it is definitely progress...

 

[OkiePC]

Whipped!

No alarms since 2:05 yesterday. It was the outfeed belt all along, and it's "fixed" with $0.02 worth of copper wire!

Thanks for the feedback on this, everyone!

 

[sthompson]

No alarms since 2:05 yesterday. It was the outfeed belt all along, and it's "fixed" with $0.02 worth of copper wire!

Thanks for the feedback on this, everyone!

I am glad to hear you were able to resolve it. Thanks for the update Paul.

Stu.....

 

[The Plc Kid]

We use these products http://www.haug-static.com/ the ion blowers on winders other wise in the summer getting your body to within 12 inchs of the material will reach out and get you in a visible fashion.

Funny when they are not on or a good fist day gag for noobs

 

[milldrone]

So, I rigged up some short pieces of copper wire and bolted them to the bearing blocks and bent them around in such a way that they are discharging the voltage from these rollers. Sparks are evident here when I touched copper to spinning roller.

I do not know how dust free your environment is but in my old facility the "free" or pointy ends of the collector wires collect a lot of dust. Just like the high voltage areas of a CRT screen system.

Van De Graaf generators are constant current devices. The current however small remains the same. The voltage keeps on rising until a discharge occurs. When the drain wires or collectors are placed in close proximity, the discharge happens at a lower voltage due to the size of the air gap. The discharge also goes to ground directly instead of through your sensitive equipment.

The outfeed belt is rubber and straight and short.

Just a shot in the dark here: I'm guessing it is not black. Carbon black is a very common coloring and anti static additive for rubber conveyor belts.

 

[OkiePC]

I do not know how dust free your environment is but in my old facility the "free" or pointy ends of the collector wires collect a lot of dust. Just like the high voltage areas of a CRT screen system.

It is very clean except for a very gradual build-up of cardboard dust from the 10,000 cases of product we process each day.

Van De Graaf generators are constant current devices. The current however small remains the same. The voltage keeps on rising until a discharge occurs. When the drain wires or collectors are placed in close proximity, the discharge happens at a lower voltage due to the size of the air gap. The discharge also goes to ground directly instead of through your sensitive equipment.

Yes, I am sure the potential was much greater than the 10volts I read on my Fluke with the probe touching the roller. It would spark at a distance of about 3/8", and the belt itself is only about 1/2" from the scale belt.

Just a shot in the dark here: I'm guessing it is not black. Carbon black is a very common coloring and anti static additive for rubber conveyor belts.

Actually, it is black (on the main system HMI it's called the "2nd Black Belt") But, I really don't know the composition of the thing. It is textured and designed to grip the boxes and pull a gap between them. We aren't using it for that purpose anymore. I think I will try to gather the materials to extend the next downstream intralox belt and do away with this one altogether at our next shutdown. That would be one less motor/reducer and 8 fewer bearings to deal with. It would also give me the opportunity to increase the space between these belts and my scale conveyor to about 1 inch.

We replaced what was the "1st Black Belt" with this checkweigher a few weeks ago, and it was a close fit without modifying things too much, but it put my sensitive scale too close to the other belts. The mfg of the checkweigher wanted 10 grand to add the module to have it talk to our SLC for sorting, and their code would not have worked very well in this high volume area with limited package spacing, so I took on the project of replacing their electronics with my own design using CompactLogix and the Hardy Instruments 1769-WS plus a Red Lion G306A for the HMI and data logger. Aside from this static problem, it really turned out well.

 

[JeffKiper]

Paul is that belt like suction cups on the box contact side? I worked at UPS for a while doing Maintenance and that belt would light you up if it was on a UHMW bedpan.

How do you like the Hardy interface? I was looking at it not to long ago for a web handling application. It was going to be my tension feedback input from a load cell. We decided to use a stand alone controller that had some algorithem in it.

PLC Kid we use some static bars as well. Getting the new foreman that wanted to change the world was always the funniest. They would wait a month or so until tje got to know them. Then watch out. Like a damn electric fence just jumped out 18" and bit you.

 

[OkiePC]

Paul is that belt like suction cups on the box contact side? I worked at UPS for a while doing Maintenance and that belt would light you up if it was on a UHMW bedpan.

No, it is textured, and on a steel plate, but the bearings are composite housings, insulating the four 4" diameter rollers from discharging. I will get the bearings changed to stainless steel housings when (if) we get a down day to do the changes.

How do you like the Hardy interface? I was looking at it not to long ago for a web handling application. It was going to be my tension feedback input from a load cell. We decided to use a stand alone controller that had some algorithem in it.

Overall, I really like it. The program examples are imperfect, but they're just examples, and easy enough to fix. The manual is just average, some of the command status and feedback states aren't listed as bits, but as hex codes, so you have to read between the lines a bit to figure out what's what. Almost all the info is in there. One thing I called tech support for was to understand why my readings were freezing due to static. There is a counter in the input table that should increment each time the module successfully does an A/D conversion. If that counter stops, the module is resetting, but the backplane connection remains intact. I just tied that counter to a timer so if it failed to change for 30ms, I latched a fault bit. It has not faulted since I fixed the static. The module is very fast with 10ms update rates for a 24 bit channel. I don't know if there's a millivolt module that can compete. For tension control, the features might not apply all that well, but for any type of scale I would definitely recommend it. The lead time for the module was almost 2 weeks though, so order your spares early.

PLC Kid we use some static bars as well. Getting the new foreman that wanted to change the world was always the funniest. They would wait a month or so until tje got to know them. Then watch out. Like a damn electric fence just jumped out 18" and bit you.

In my past experiences with static, it was always a safety concern, but never managed to infect our controls. In the tire industry we made 4000lb capacitors at 400fpm rolling up rubber coated steel sheets for ply and belt stock. I have seen and felt the thick bright sparks that will leap two feet to get you.