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Click Here to Learn More!Static buildup is the #1 reason for corrupted memory. Corrupted memory can cause your system to perform erratically and/or lock-up. To protect your system from static it is imperative that you follow good grounding procedures. Directing static electricity to earth ground on all scales and control systems ensures you will not experience a high static buildup.
Your ground system needs to be common to all points. This will allow excess energy a path to earth ground and minimize static charge build up. This common point must be earth ground to prevent any floating ground situations. Using a ground cable to every point required and then just tying those cables together will not prevent corrupted memory. This will cause unstable weight readings and poor system performance due to ground loops.
Your vessel and PLC should also be at the same earth ground potential as your weight controller. The resistance reading between the chassis of the controller and the vessel should read less than 1 ohm.
Flexible ground straps should be used to connect the vessel to earth ground. It is preferrable to use a braided ground strap as solid copper wire may cause weighing errors due to binding issues. The ground strap does not have to be a large gauge. Providing an electrical path to drain/discharge static as it builds is all that is required. We also suggest multiple ground points on a scale. The idea is to block or divert any energy build up away from the load cell that will transport that high energy to the weight controller as a very high weight reading. See attached pdf drawing for additional information.
Weighing systems (both portable and stationary) need to have a method to discharge static buildup. A fork truck may need to have a drag chain installed and ground bars in the flooring. Vessels that do not have load cells can still be a source of static buildup. When static buildup does not have a path to ground potential it will continue to build to a point where energy discharges to a path that could include load cells of a nearby vessel.
As the static builds-up and seeks a path to ground there is a voltage divider affect. This is where the built-up charge finds the best path to ground to discharge the majority of the charge. All other possible paths will receive a portion of the charge. This discharge can be strong enough to disable or damage a weighing system! Symptoms include erratic weight readings, drifting and controller lock-up/rebooting.
Mounting a system in concrete does not ensure proper grounding. You need to verify the shield wires are connected in the summing junction box and at the controller. The summing junction box is not a grounding point, only a pass-through termination point.
Use proper C2® certified shielded cable from Hardy Instruments to connect the summing junction box to the weight controller. The load cell shield wires normally do not make contact with the load cell body. The shield should act as a drain for EMI/RFI noise from the load cell end to the ground at the controller.
Verify proper grounding with a resistance reading
Disconnect the load cell shield wire in the summing junction box and verify it reads read open when measured to ground. Reconnect the load cells and measure the same shield connection to earth ground at the summing junction box and the resistance reading should be less than one ohm. Go to the controller and disconnect the C2 cable shield from the ground point. Return to the summing junction box and again measure shield to earth ground.
