Er, the answer is in the question except that it is a setting, and not a calibration: the zero of the equipment and the span range.
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"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Do the temperature and barometric pressure swing, then?
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"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Technically, either the load cell or the controller can drift. Of these two, the load cell is the most susceptible to drift. However, if there are any analog components in the controller capable of drift (e.g. resistors or capacitors in the analog-to-digital converter) then the calibration procedure compensates for that as well.
Putting it into the simplest possible terms, any portion or component of a measurement system that is analog in nature is susceptible to drift. A purely digital component or system cannot really drift.
Another important consideration in the calibration of any weighing system are the mechanical components transferring the product's weight to the load cell. If any bearings, flexures, or any other moving component fails, this may show up as random "drift" that cannot be corrected by any calibration procedure. Even something as simple as a heavy layer of dust collecting on a beam may be capable of skewing the calibration of a weigh system.
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They call me "lightning" when wielding a hammer, because I never strike twice in the same place
At zero you set in the weight of the holding device (container / tank / platform / whatever) in the unloaded state as a zero. (in my work it is always an empty tank) At span you take a known set weight and place it on / in which ever above you have. Say you put on / in 100Kg, then you have a zero that is the weight of the holding device and at span you have 100 Kg. Now you are set to measure whatever in between the 2 points very accurately, and a bit above this range, if the system is capable of it, too. Therefore what you measure is just what you have added or placed on / in the holding device, without the weight of the holding device.
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Remember when reading my post: (-1)^½ m (2)^½
In a load cell system, the load cell strain gauges generate a millivolt signal equivalent to the weight distorting the cell.
The adjustments that you do have to do more with the adjusting the transmitters zero and span to match the millivolt signals of the load cells, since these do not have any adjustments.
I use load cells of various manufactures for tension control for web handling.
Some are extremely stable. Others tend to have their readings drift with temperature, or if there is an impact loading "zero" will no longer be 'zero".
Some load cells are sensitive to side loading, so if bearings etc do not allow for thermal expansion the readings are messed up.
For the machines we recommend daily observation of the zero point - the operators can see the load is removed and it no longer reads zero, and at least an annual calibration when known tensions are applied and the zero point and full scale range adjusted.
Thanks all for the good answers, reason for my question is because I am considering doing an electronic calibration as per the controllers manual. The information needed are mV/V ,capacity of the load cell and finally you have to do a Zero.A two point weight calibration is not possible, I guess an electronic calibration is better than nothing.
Some electronic calibrations are superb - the ones by KELK have been especially good. They sell many of their load cells "legal for tender" and come with individual calibration cards for every unit.
I always follow with a test with known weights, especially if it is critical such as being "legal for tender".
If +/- 5% is not critical then don't worry about it.
For web handling I like an annual calibration with weights or calibrated load cells using straps following the web path. That way I can verify not only are the load cells correct, but the calculations for web path geometry are also OK.
Weighing System
Re: weighing system
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