Fault analysis of silo weighing system

"Continued to work on fixing this scale, as there were complaints from operators that the weights displayed were incorrect. I kept checking the condition of the scale’s load cells, and used a tri-square to ensure that all load cells were at a 90-degree angle, as advised by Mettler Toledo’s technical support. All load cells were found to be in the correct position. The guide bolts and nuts for the load cells were also realigned, and it was confirmed that all such bolts had an acceptable clearance of 1 mm. Additionally, a zero adjustment was made to the output in milliamps from the load cell controller, so that the DCS display showed a value of 0.1 tons."

"Continue removing the mini flexlock units for servicing in the workshop. The mini flexlock unit of load cell No. 3 was removed and serviced there. It was found that both sides of the ball joints were severely corroded and difficult to rotate. The ball joints were kept turning by using a suitable tool while spraying WD-40. Fine sandpaper and an iron brush were used to clean the dusty surfaces of the ball joints, and new grease was injected through the grease fitting. The lock nuts of the mini flexlock units were also loosened. Once the work was completed, the mini flexlock units were reinstalled before removing the next one for servicing. The work on the mini flexlock units of load cells No. 3 and No. 4 is now complete. A zero adjustment was performed on this silo weigher, as the actual zero reading was -2.8 tons, while the reading indicated by the DCS system was 0.0 tons. "

"Continue removing the miniflexlock units for servicing in the workshop. The miniflexlock unit of load cell No. 2 was removed and serviced there. It was found that both sides of the ball joints were severely corroded and hardly rotated. The ball joints were kept turning by using a suitable tool while spraying WD-40. Fine sandpaper was used to clean the dusty surfaces of the ball joints, and new grease was injected through the grease fitting. Both lock nuts of the miniflexlock units were also loosened. Once the work was completed, the miniflexlock units were reinstalled before removing the next one for servicing. The work on the miniflexlock units of load cells No. 1 and No. 2 is finished; the remaining units will be dealt with tomorrow. "

"To check for any issues related to the short filling times – which are around 1 hour and 18 minutes – the following was done: 1. According to the engineer, the DCS indicates 66.7 tons; however, considering the actual filling time, the amount should be around 38 tons. 2. He also mentioned that the filling rate is 50 tons per hour, while the normal rate for batch processing is about 29 tons per hour. 3. With an empty test bin, the DCS indicated 2.0 tons, and the current output was measured to be 4.293 mA. 4. The sum of the output voltages from the 4 load cells was 1.06 mV/V, and the supply voltage of 12 Vdc remained constant. 5. A simulation was carried out by increasing the voltage from 1.06 mV/V to 8.259 mV/V; the DCS then indicated 120 tons. 6. It was confirmed that there were no problems with the zeroing and range settings, as the readings of 4.00 mA for zeroing and 20.00 mA for the range were obtained. 7. The resistance of the cables used for measuring each load cell was measured; the results are as follows: Load cells Gray + Green (with deadload): 1 – 6.302 k ohms, 2 – 6.282 k ohms, 3 – 6.266 k ohms, 4 – 6.262 k ohms. 8. According to the manual, without a deadload, the resistance should be within the range of +/- 650 ohms. 9. The cables connected to each load cell were reorganized inside the summing box, and all cable connections were tightened again. 10. After observing the current output signal for about 30 minutes, it was confirmed that it was more stable. 11. The voltage output of the load cells remained at 1.096 mV/V, while the current output was 4.01 mA. 12. The DCS reading was 0.1 tons. 13. The operation to pack out the contents of silo with lot number E1704D was carried out yesterday, and the result was 37.5 tons. 14. When the silo was filled again, the DCS indicated 66.7 tons; however, calculations suggest that the actual amount is around 40 tons. 15. The operation continued, and this issue will be discussed with the Metel Toledo supplier tomorrow. Note: It’s not possible to fill both test bins at the same time (as suggested by WJM), due to the sequencing requirements."

"To check for any issues related to the short filling times – which are around 1 hour and 18 minutes – the following was done: 1. According to the engineer, the DCS indicates 66.7 tons; however, considering the actual filling time, the amount should be around 38 tons. 2. He also mentioned that the filling rate is 50 tons per hour, while the normal rate for batch processing is about 29 tons per hour. 3. With an empty test bin, the DCS indicated 2.0 tons, and the current output was measured to be 4.293 mA. 4. The sum of the output voltages from the 4 load cells was 1.06 mV/V, and the supply voltage of 12 Vdc remained constant. 5. A simulation was carried out by increasing the voltage from 1.06 mV/V to 8.259 mV/V; the DCS then indicated 120 tons. 6. It was confirmed that there were no problems with the zeroing and range settings, as the readings of 4.00 mA for zeroing and 20.00 mA for the range were obtained. 7. The resistance of the cables used for measuring each load cell was measured; the results are as follows: Load cells Gray + Green (with deadload): 1 – 6.302 k ohms, 2 – 6.282 k ohms, 3 – 6.266 k ohms, 4 – 6.262 k ohms. 8. According to the manual, without a deadload, the resistance should be within the range of +/- 650 ohms. 9. The cables connected to each load cell were reorganized inside the summing box, and all cable connections were tightened again. 10. After observing the current output signal for about 30 minutes, it was confirmed that it was more stable. 11. The voltage output of the load cells remained at 1.096 mV/V, while the current output was 4.01 mA. 12. The DCS reading was 0.1 tons. 13. The operation to pack out the contents of silo with lot number E1704D was carried out yesterday, and the result was 37.5 tons. 14. When the silo was filled again, the DCS indicated 66.7 tons; however, calculations suggest that the actual amount is around 40 tons. 15. The operation continued, and this issue will be discussed with the Metel Toledo supplier tomorrow. Note: It’s not possible to fill both test bins at the same time (as suggested by WJM), due to the sequencing requirements."