russrmartin
Member
I have not had a lot of experience with load cell installations. I have a certain load cell which when installed, will be very difficult to calibrate. We have calibrated the cell in a press using all the existing hardware that will be used in it's working condition from the amplifier and PLC end. Using the press we have for this, the load cell was dead nuts, and very repeatable. My question is this. When installed, the load cell will see the load differently than it did in the press we used to calibrate it. However, this load will be applied exactly the same every time. I expect that when all is installed, due to existing hardware being attached to the load cell, the zero position will need adjustment. Can I simply create a zero offset in the PLC to "tare" the load cell to zero and expect that it will be linear and correct throughout the whole range? Or will the load cell react differently because the load is applied to it differently. If it should be off by the same amount, I'd rather not have to adjust zero and gains again, due to not having anything really reliable to use as a force reference.
Example. Now, 0-1000 lbs. is right on. When mounted, zero is off by say 75 lbs. Should I expect that when 1000 more lbs is applied that the cell will show me 1075? Or is it a likely possibility that because the load cell is recieving the load differently than it did in the calibration press that the whole scale may be off. Something like 0=75, 1000=875. The whole point of this would be that if this is linear, our calibration procedure would be to remove the load cell, calibrate in press, and reinstall. Then create what we consider zero lbs. state, and adjust offset to get a zero value.
Edit: FYI, this is actually for a nip roll. Right now, we have no way to apply a calibrated force to the sensing roll because of it's mounting setup. The load cell is mounted horizontally to a frame with the butt of a cylinder attached to it. The cylinder pushes on a rod, roughly in the center causing it to rotate around a pin. The end of the rod opposite the pin hosts the nip roll. There is one of these on each end of the nip roll. Due to other rolls and equipment for the process being in the way, there is no easy way to create a horizontal force by hanging weights or the like.
Example. Now, 0-1000 lbs. is right on. When mounted, zero is off by say 75 lbs. Should I expect that when 1000 more lbs is applied that the cell will show me 1075? Or is it a likely possibility that because the load cell is recieving the load differently than it did in the calibration press that the whole scale may be off. Something like 0=75, 1000=875. The whole point of this would be that if this is linear, our calibration procedure would be to remove the load cell, calibrate in press, and reinstall. Then create what we consider zero lbs. state, and adjust offset to get a zero value.
Edit: FYI, this is actually for a nip roll. Right now, we have no way to apply a calibrated force to the sensing roll because of it's mounting setup. The load cell is mounted horizontally to a frame with the butt of a cylinder attached to it. The cylinder pushes on a rod, roughly in the center causing it to rotate around a pin. The end of the rod opposite the pin hosts the nip roll. There is one of these on each end of the nip roll. Due to other rolls and equipment for the process being in the way, there is no easy way to create a horizontal force by hanging weights or the like.
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