Total Combined Error
All measurement devices will have some degree of error that is unavoidable. This is acceptable as long as the error is less than the error tolerance of the device. (0.05 lb.)
Dramatic temperature changes cause metal to warp. Traditional load cells are built using strain gauges, which are delicate metal pieces. Dramatic temperature changes will affect the function of the strain gauge, and therefore the load cell. If the load cell is exposed to cold nights and then hot, direct sunlight, or surrounding equipment heats up the area, this can cause inaccuracy. You might consider shielding the equipment from the sun if it is causing dramatic temperature shifts.
If a load cell remains under pressure for a long period, it becomes susceptible to creep. This isn’t a problem in for operations less than one-minute intervals, but load cells measuring for extended periods, such as filling a bucket on the scale, will need to account for creep.
Load Cell Response
All load cells require a set time to return to zero before they can accurately measure a new load. If the process begins to refill the vessel before the load cell(s) return to zero, the measurement won’t be accurate within the error tolerance. Allow enough time between measurements for the load cells to stabilize and response time.
The load must be properly balanced on the load cell. In short, the scale should be level and the bucket placed in the center of the scale plater.
Excessive vibration, usually from passing trucks or equipment, can disrupt the reading.
Air currents exert force on a load cell that can disrupt the weight of the load alone. Usually, this is not enough to cause significant inaccuracy, but strong, consistent wind can disrupt the reading.
When the load cell transmits its electrical signal to the weight controller, interference, or noise, can disrupt it. Radio signals and electromagnetic signals both cause noise, which includes electrical currents, other data transmission signals, even strong wireless signals.
Moisture can also inhibit the signal from the load cell to the weight controller. Moisture, perhaps from steam, excessive humidity, or equipment washing, most often enters the load cell through the cable entry area.
A number of factors can cause the weight signal from a load cell to move unsteadily upward (or downward) instead of in a smooth line. The bucket’s movement while weighing, fruit and produce settling, or the uneven contents, an agitator preventing sticking, or unshielded noise can all cause the signal to fluctuate.
Damaged Load Cell Connections
Often, multiple load cells are used to measure a load. When these load cell signals are not combined and summed properly at the weighing instrument, it can cause noticeable error. This can occur due to faulty connections between the load cells and the instrument. Corrosion from acids or salts can cause connections to corrode, thereby disrupting the signal.
Most load cells use a strain gauge, layers of very thin, conductive metal, to measure weight. Just as moisture can disrupt the load cell’s function, so can conductive metal dust and debris. If the load cell seal is damaged, it is not properly sealed and environmental metal dust or salt.
Though a load cell can be reinforced to withstand difficult environments, the internal components are delicate. A heavy impact, as well as corrosive chemicals or salts, can damage the inner workings of the load cell and cause it to malfunction. If you notice intermittent misreadings, or if there is more error than usual, the strain gauge or capacitor within the load cell may be damaged.
To stay accurate, load cells require regular calibration. A regular maintenance schedule is the best way to stay on top of necessary maintenance. If the load cell is not calibrated, it is more susceptible to every form of disruption. When making repairs to the load cell, remember to recalibrate afterwards