Position: Ensure that only the weight force is transmitted to each weight load cell. Other forces, including environmental forces such as wind loading, shock loading, vibration, large temperature changes, and pressure differentials, can produce errors in the weight load cell signal and weighing controller.
Wind loading affect.
Wind loading can affect an outdoor weighing controller or a low-capacity indoor system. For example, outdoors, a 30-mph crosswind on a weigh vessel exerts forces on the weight load cells that have nothing to do with weight, causing the windward cells to sense a lighter load and the leeward cells to sense a heavier load. In such a case use higher-capacity weight load cells to prevent overloading the leeward cells. Indoors, an active overhead air conditioning vent can also create inaccurate small-increment (such as 1-ounce) measurements on a low-capacity weighing controller, such as a small platform scale. You can use a Plexiglas cover over the platform scale to block or divert the stray air currents.
For accurate weighing, the weight load cells alone must support all the weight to be measured.
Shock loading affect.
Shock loading occurs when heavy material is dumped onto a weighing controller, causing forces greater than the system's rated capacity and damaging the system. You can use higher-capacity weight load cells that can handle this shock loading, but this will degrade the system's resolution (the smallest increment that the system can weigh). Controlling the material flow onto the weighing controller with a feeder, specially designed loading chute, or other device can prevent shock-loading damage.
Vibration affect. Vibration from process equipment and other sources near the weighing system can cause the weight load cells to measure the weight of material as well as vibration that's transmitted to them, which the cells sense as mechanical noise. You can reduce or prevent vibration effects by isolating the weighing controller from vibration sources when possible or using weighing system instrumentation with algorithms that remove vibration effects.
Large temperature changes affect.
Whether your weigh vessel is indoors or outdoors, large temperature changes can cause it to expand or contract. This causes errors in the weight reading and can damage the weight load cells. If your weighing system is exposed to large temperature shifts, install weight load cells and mounting hardware that can handle the vessel's expansion and contraction.
Pressure differentials.
A pressure differential can create weighing errors by applying unwanted forces to the weighing controller. A pressure differential can occur, for example, when a weigh vessel is installed between a pressurized plant floor and another floor at ambient pressure. To minimize weighing errors, calibrate the weighing load cell to the pressurized floor's constant pressure level. If the pressurization isn't constant, install the weigh vessel elsewhere.
A pressure differential can create weighing errors by applying unwanted forces to the weighing controller and weight load cell.
Another form of pressure differential is created in an unvented weigh vessel: When material flows quickly into a closed weigh vessel, it displaces a volume of air equal to the material volume. If the air can't escape from the vessel through a vent, the flexible connections that attach the material inlet and outlet piping to the weigh vessel will expand as the undisplaced air floods into it, and this expansion will apply side forces to the weight load cells, creating weighing errors. To prevent this problem, properly vent your weigh vessel.
