Weighing is a common process in manufacturing. It can be used for level measurement, inventory control and batching.

Choose the right weighing system for your application. Then be sure to understand how factors can affect your weighing results. PCEs clients profit from German engineering, manufacturing and maintenance in nearly all kinds of industrial weighing applications.

Methods

A weighing process requires a stable and reliable scale to ensure accurate results. It is important to have a balance that can be zeroed by taring (setting it to 0.00 by placing a piece of paper on the pan).

The ordinary commercial method of putting weights in one hand and the commodity in the other is not acceptable for scientific weighings, because it may result in errors. The error is corrected by a technique known as double weighing, in which the scale is tested with two standard weights and then the commodity is added.

Level or inventory weighing applications involve monitoring how much material is in a storage vessel such as a tank, silo or bin. These systems typically transmit the weighing information to a PLC or DCS for local display and control.

Batching weighing processes typically use a combination of load points, pipes, valves and electrical hardware in a fully integrated system. These systems can be sequential (gain-in-weight) or simultaneous.

Instruments

In order to ensure that weighing systems operate correctly, they must be equipped with high-quality instruments. This could include anything from scales or load cells to electrical hardware & software to make the system work properly. Michelli Weighing & Measurement can develop a variety of quality control weighing systems for food processing plants, including inspection & batching & mixing systems.

Depending on the application, these systems may be equipped with a range of instrument types, from simple balances to complex microbalances. In general, these systems are designed to calculate mass by converting linear spring displacement into a dial reading.

When handling large weights, workers should take special care to avoid touching them with bare hands, as the oil on your fingers can affect the measurement. Moreover, the weights should be stored in a clean room that’s free of moisture, corrosive gases & dust. This will prevent them from rusting or becoming dirty, which can affect the readings they produce.

Calibration

Calibration is the process of establishing a relationship between an instrument’s measurement technique and a set of known values. By comparing the instrument to these values, it can be made to produce more accurate measurements than would otherwise be possible.

This process is often performed in a calibration lab where specialized equipment can be used. The lab may be a facility run by the national measurement institute (NMI, such as NIST in the United States) or an independent laboratory that offers calibration services.

When considering the calibration of a weighing system, it is important to take into account uncertainty components. These uncertainties can come from many sources and can be added together to create a total uncertainty budget for the calibration. This budget helps to ensure that the weighing process is performed as accurately as possible. This can help to improve efficiency, compliance, and safety while reducing waste, risk, and emissions. Using software such as AutoCal+ makes keeping up with your calibrations much easier and more manageable.

Errors

A number of errors are introduced during the weighing process, either by human error or because of mechanical and environmental factors. In order to minimize these errors, it is important to follow the manufacturer’s instructions for operating a precision balance and to calibrate the balance regularly.

Moisture can wick into the load cell’s junction box, reducing capacitance between signal lines and creating electrical noise that affects weighing accuracy. It is also important to use a balance with a sealed junction box that does not leak and to plug any unused junction box holes.

Temperature differences between the material being weighed and the temperature of the balance can cause a loss or gain in weight and create thermal currents in the weighing pan, leading to an inaccurate determinate error. To avoid this, make sure that all chemicals are weighed in their correct tare container and that the tare container is small enough to prevent heat currents from occurring.