Weighing is a critical process in any food production facility. It is used to dispense ingredients and ensure that all the required quality requirements are met.
Good laboratory practices, standards, and balances are necessary for obtaining accurate mass measurements. However, there are many sources of error that can occur during weighing.
Accuracy
Weighing accuracy is a key criterion for many applications. It’s a function of the quality of your load cells, weight controller, and weighing instrument. Selecting top-quality components especially designed for your application will go a long way toward ensuring the best possible weighing accuracy for your system.
The primary source of error in a load cell is mechanical, which can be minimized by selecting an appropriate size and location for your weighing system. Keep it away from sources of vibration and large temperature changes. Consider using a feeder or custom-designed loading chute to prevent shock loads, which can exceed the load cell’s rated capacity and damage it.
Another important factor is eliminating electromagnetic interference, which can be caused by nearby electronic devices, power lines, radio signals, and natural phenomena like lightning. This can confuse the sensors and components in your weighing system and cause it to provide inaccurate readings. ISO defines accuracy as the proximity of measurement results to their true value, while precision describes the consistency of measurements over time or between different instruments and operators.
Safety
Weighing equipment installed in hazardous areas must be designed to comply with regulations set forth by government agencies. This typically means weighing systems are fitted with intrinsically safe electrical components. These components limit the amount of electricity available in circuits that could cause an explosion under normal or fault conditions.
The general weighing process must take place in a clean environment with low levels of vibration, air current and noise. The weighing chamber must also be scrupulously clean to prevent cross contamination of samples and errors in readings. Add a printer to the balance to automatically print out weight slips and keep them on file along with your laboratory records.
If a direct weighing method is used, the balance must be tared before adding the sample. The chemical should be added to the tared container that will hold it and not directly to the pan or weighing paper. This technique helps to avoid temperature changes that can change the chemical’s mass.
Error Reduction
Many of the errors that occur during a weighing process cannot be avoided, but there are ways to reduce their impact. One method is through error reduction during the calibration process.
Procedures currently in use typically compare the device error associated with a single test position to a governmental standard. The present invention, on the other hand, compares the summed error of several selected test positions to a designated tolerance level. The summed error may be a measure of the maximum possible measurement error or it may be a desired measure of correspondence between measured weight and actual product weight.
Traditional balance testing can be a waste of time and resources if it doesn’t take into account the four significant components of measurement uncertainty. A science-based calibration protocol, such as Mettler Toledo’s Good Weighing Practice (GWP), includes tests to evaluate these four factors and optimize routine testing procedures. The GWP program also helps users avoid unnecessary testing and erroneous results.
Efficiency
Weighing is a vital process that provides valuable information for your entire production process. Whether you’re measuring ingredients for lean manufacturing or regulatory compliance, accurate and repeatable results are important to your quality standards.
To ensure the best weighing results, you should use the correct procedures for your specific material. For example, fine powders are sensitive to static charge and may require the use of an antistatic device. Weighing dishes should be cleaned carefully after each use and used with care when handling hot objects. Using an empty weighing dish to weigh the material eliminates the potential for error caused by the weight of the container itself and also prevents the loss of water from hygroscopic materials.
Weighing by difference is one of the most accurate methods for liquid weighing. This technique requires the scale to be completely zeroed with nothing on the weighing pan and then the substance is added. The initial reading is then subtracted from the second, eliminating any errors in the scale calibration.