leitmotif
Member
OK my opinion and experience with load cells was asked for.
I worked in a food processing faclity where we used load cells extensively. We had them on floor scales. We had them retrofit installed on machines (mixers and steam heated kettles) total load somewhere around 5 to 10,000 lb and batch weight was around 1,000. We also had them as factory original weighing integrated with conveyers - these weighed finished containers - less than one or two pounds.
All of our load cells read only to a display. Multiple cells (one on each leg of steam kettle or mixer) fed to a integrator (I guess you would call it that) which took each cell signal computed total reading and then sent that to a display. We did not have these tied into a PLC. Each display had a zero function where the reading could be rezeroed for actual conditions - this waas needed because things did change and the readout had to be rezeroed frequently.
Actual calibration was done by vendor using known weights.
The reason I mentioned attachments - When we adapted kettles we could not get one to calibrate. When we cut a bracket for the decking from the kettle it worked much better.
Our biggest problem with load cells was water. Equipment was constantly exposed to water and hosed down nightly (read that as drowned). Cells mounted near the floor were the most problematic - now is that not a surprise.
Cells were potted but water still got in. We believed water migrated thru or around the potting or thru the cable. We sealed the cell and cable for six inches back from cell - we used 3M 6100 (I think was number) and then ran cable thru plastic conduit. This effort seemed to reduce or resolve the problem. It did not reoccur from the time I dreamed up this solution to the time I left - approx six months.
For best results
1. Do not let supervisors near them.
2. Train the operators how to properly input data as their product changes.
3. Have a good step by step manual for maintenance showing button pushing sequence (I never was able to memorize the damn things and manuals were useless)
4. Do not let cells get wet.
5. Do not let the integrator boxes get wet.
6. Consider factory sealing as non existant.
7. Do not mount load cells near floor. WATER is on floor
8. Make sure the load the cell is measuring is able to free float and as much as you can take into account product left in fill and drain lines etc. This is where zero and tare buttons are handy.
9. If you want to tinker with the cells themselves get a good VOM that will read down to 0.1mV.
10. Run load cell cable in a plastic conduit. (that increases pallet jack mashing survivability from one to four or five)
11. IF you are satisfying QC requirements and government weighing regulations I recommend walking in at random once a week and handing operator a known weight standard different from one he uses and have him demonstrate abiltity to change machine settings within his authority.
I think load cells are a perfect solution to many problems / challenges. They appear to have good precison and good repeatability. They reduce handling and will payoff from reduced operator contamination and ergonomic considerations.
Dan Bentler
I worked in a food processing faclity where we used load cells extensively. We had them on floor scales. We had them retrofit installed on machines (mixers and steam heated kettles) total load somewhere around 5 to 10,000 lb and batch weight was around 1,000. We also had them as factory original weighing integrated with conveyers - these weighed finished containers - less than one or two pounds.
All of our load cells read only to a display. Multiple cells (one on each leg of steam kettle or mixer) fed to a integrator (I guess you would call it that) which took each cell signal computed total reading and then sent that to a display. We did not have these tied into a PLC. Each display had a zero function where the reading could be rezeroed for actual conditions - this waas needed because things did change and the readout had to be rezeroed frequently.
Actual calibration was done by vendor using known weights.
The reason I mentioned attachments - When we adapted kettles we could not get one to calibrate. When we cut a bracket for the decking from the kettle it worked much better.
Our biggest problem with load cells was water. Equipment was constantly exposed to water and hosed down nightly (read that as drowned). Cells mounted near the floor were the most problematic - now is that not a surprise.
Cells were potted but water still got in. We believed water migrated thru or around the potting or thru the cable. We sealed the cell and cable for six inches back from cell - we used 3M 6100 (I think was number) and then ran cable thru plastic conduit. This effort seemed to reduce or resolve the problem. It did not reoccur from the time I dreamed up this solution to the time I left - approx six months.
For best results
1. Do not let supervisors near them.
2. Train the operators how to properly input data as their product changes.
3. Have a good step by step manual for maintenance showing button pushing sequence (I never was able to memorize the damn things and manuals were useless)
4. Do not let cells get wet.
5. Do not let the integrator boxes get wet.
6. Consider factory sealing as non existant.
7. Do not mount load cells near floor. WATER is on floor
8. Make sure the load the cell is measuring is able to free float and as much as you can take into account product left in fill and drain lines etc. This is where zero and tare buttons are handy.
9. If you want to tinker with the cells themselves get a good VOM that will read down to 0.1mV.
10. Run load cell cable in a plastic conduit. (that increases pallet jack mashing survivability from one to four or five)
11. IF you are satisfying QC requirements and government weighing regulations I recommend walking in at random once a week and handing operator a known weight standard different from one he uses and have him demonstrate abiltity to change machine settings within his authority.
I think load cells are a perfect solution to many problems / challenges. They appear to have good precison and good repeatability. They reduce handling and will payoff from reduced operator contamination and ergonomic considerations.
Dan Bentler
