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Discussion Starter · #1 ·
Any one ever work on scales? We package almonds, I have a scale that is used to weigh 4'X4' plastic bins of almonds. The bins are set on a scale and are fed by a stainless steel hopper. As the almonds fill the bins we experience static electricity. This causes the scale control boards to go out due to the static electricity. The building is 2 years old with a ufer ground. I have grounded all posable points of equipment with ground wire and chair lugs. We are still having issues. Any ideas?
 

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Any one ever work on scales? We package almonds, I have a scale that is used to weigh 4'X4' plastic bins of almonds. The bins are set on a scale and are fed by a stainless steel hopper. As the almonds fill the bins we experience static electricity. This causes the scale control boards to go out due to the static electricity. The building is 2 years old with a ufer ground. I have grounded all posable points of equipment with ground wire and chair lugs. We are still having issues. Any ideas?
Do you know for sure it is static, or are you assuming it is because it only happens when the almonds drop into the bin? Because if what is making that happen is a VFD, and the wiring of it is not done right, EMI/RFI can cause transducers to go all squirrelly like that, I've experienced it many times. The big culprit is people using SO cable to wire the VFD, because it needs to be flexible, but sometimes it's because they use plastic conduit and plain wire (not shielded). Unshielded wiring on a VFD turns into a local radio transmitter. Piezo elements, like those used in scales, strain gauges and pressure transducers, are especially susceptible to RF.
 

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If all of the equipment is metal and is call bonded together, than about the only other thing you can do is increase the humidity in the area.
If you have non-metallic parts in the transfer system, you need to replace them with conductive parts. They do not have to be metallic, but they have to be conductive enough to prevent the build up of static.

How is the static getting to the scale boards?
 

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Discussion Starter · #5 ·
JRaef said:
Do you know for sure it is static, or are you assuming it is because it only happens when the almonds drop into the bin? Because if what is making that happen is a VFD, and the wiring of it is not done right, EMI/RFI can cause transducers to go all squirrelly like that, I've experienced it many times. The big culprit is people using SO cable to wire the VFD, because it needs to be flexible, but sometimes it's because they use plastic conduit and plain wire (not shielded). Unshielded wiring on a VFD turns into a local radio transmitter. Piezo elements, like those used in scales, strain gauges and pressure transducers, are especially susceptible to RF.

All of the equipment wiring in this building is done overhead in cable tray. They used cable tray wire in the attic and all wire dropping down to the equipment is ran in rigid conduit. They did not strip the wire coming down the conduit. All of the cable tray cable is in the conduit. I believe the hoppers are fed by cablevay I will have to check other possibilities causing this.

The bins are lined with big plastic bags so when the almonds load up in the bin the friction of the bag in the plastic bin seems to cause the static. When I stand next to the box as it is getting filled I can feel the static on my arm. It seems to get stronger as it fills to the top.
 

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Discussion Starter · #6 ·
When I say they did not strip the wire coming down the pipe I'm referring to them not removing the outer black sheeth that keeps the colored wire together. The cable is like SO cable but it is made to be used in cable tray.

This is done to all of the 480V, 208V and control wiring used for the equipment in the building.
 

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The bins are lined with big plastic bags so when the almonds load up in the bin the friction of the bag in the plastic bin seems to cause the static. When I stand next to the box as it is getting filled I can feel the static on my arm. It seems to get stronger as it fills to the top.
They make conductive bags so that will not happen. That being said, I don't see how that is causing damage to the scale system. The static should just bleed off via the conductive parts after it jumps off the plastic bag.
 

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Discussion Starter · #8 ·
don_resqcapt19 said:
They make conductive bags so that will not happen. That being said, I don't see how that is causing damage to the scale system. The static should just bleed off via the conductive parts after it jumps off the plastic bag.
Could an operator carry the static charge to the controller? The operators have complained about getting shocked when they touch the control board.
 

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Could an operator carry the static charge to the controller? The operators have complained about getting shocked when they touch the control board.
If they are getting shocked, they are transferring the charge. They could wear conductive shoes or something like that to prevent a charge transfer.
 
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