The Back Story
The customer called us in to look at a 6 cell high capacity tank - 50,000 lb maximum net weight tank. The previous scale company was telling them that they needed 2 new loadcells, 2 new junction boxes and maybe a new weight display. It sounded to us like they might be guessing at the problem causing additional expense and down time. So we grabbed the right tools and dug into the details starting without any assumptions.
Initial Inspection
At the heart of any troubleshooting call you always start with a very thorough mechanical and physical inspection before jumping into electrical diagnostics. This will show you all types of potential issues and tells a story about how the device was installed and how it has been maintained if you know what to look for. Most problems will be mechanical issues and once the potential for those is exhausted, you can begin looking into electrical problems.
This issue (cracked loadcell body) while easily visible in the image was hard to see onsite without a very bright inspection light and crawling around the load cell mounts one at a time checking out every detail slowly.
Repairs
So we advised the customer our findings who chuckled and said the other company had been out several times for diagnostics since this problem was reported and hadn't taken this step to inspect the cell.
Once we remove the cell from the mount you can see the discoloration areas along the crack line from the intense corrosion that had eaten into the loadcell weakening it enough to cause it to split in two when loading. This turned out to be the only issue with this tank, the other loadcell that the previous company said was faulty turned out to simply be unloaded as the tank lifted up slightly when this cell failed. They saw a 0 millivolt output and assumed a bad cell, not that it was out of plane and no longer had any dead load from the weight of the vessel. There were no other components needed to return this tank back into service.
Calibration
Once the cell was replaced, this hopper (nor any others at the facility) was not setup well to accept test weights. This is a common issue in mixing and batching environments where space is limited, surfaces are never flat and level, and the proper setup isn't put in place to help scale companies apply the right amount of test weight onto the tanks safely. Initially the only flat and sturdy spot that we had to get weight onto the tank was the top rim.
While this technique might be marginal but still acceptable for lower capacity vessels, it simply would not allow us to get a large enough amount of certified and traceable test weights onto the hopper safely to provide a proper high quality calibrated span point.
Luckily the customer has a great attitude and an even better welder on staff that was able to listen to our recommendation to get some weight mounts built that is compatible with all of their tanks and can easily be installed.
You can see below he built up some mounts that wrap around the tank legs and bolt in place quickly.
This allowed us to safely mount 4,000 pounds of certified test weight onto the tank and more importantly isolate a 1,000 pound load over an individual loadcell for testing and tuning the system to be as accurate as possible.
The end result is a customer with a repaired tank that can rely on accurate readings to make their product faster and with greater accuracy than before.