Weighing processes are a critical part of any industrial application. The correct technique is essential to avoid errors and maximize accuracy.
Chemical and pharmaceutical industries often require measurement precision down to the microgram. Weighing by difference is the preferred method in these scenarios to ensure minimal errors.
Whenever possible, a weighing system should be installed at a level and within a structure that can resist flexing. This prevents unwanted horizontal forces on load cells that can impact weighing accuracy.
Workspace Preparation
Weighing workspaces must be sterile to prevent contamination of the sample or the balance. If the weighing process involves volatile chemicals, a fume hood or specialised isolator should be used. Otherwise, a sanitary weighing room should be maintained with an ISO 7 LAF (Large Area Filtration).
The work surface must be cleaned to remove debris and residue from previous weighing operations. Static charge can also build up on surfaces, especially with fine powders, and must be eliminated before a suitable weighing can be made. Using an antistatic device may help to minimize static charge, depending upon the sensitivity of the material.
If precision is the top priority, Weighing by Difference is preferred, but direct weighing can offer convenience and speed for recipes that don’t demand pinpoint accuracy. Whichever method is chosen, the resulting measurement must be equivalent to the original material.
Equipment Calibration
As time passes, equipment calibration can begin to drift. This can cause inaccurate test results that may impact important processes.
It’s especially important to keep up with calibrations when working with potentially dangerous materials or creating solutions for medical purposes. In these situations, small inaccuracies could lead to safety issues and other costly problems.
With advanced software solutions, managing the calibration process becomes a breeze. It helps reduce production downtime and facilitates seamless communication and collaboration across multiple company locations.
For mass calibrations, it’s vital to ensure that the instruments are in thermal and environmental equilibrium prior to weighing. Generally, the objects to be weighed and the reference standards must be placed in or near the balance for 24 hours in order to achieve this state. This will help minimize temperature fluctuations that could affect the calibration. The calibration process will generally require comparison weighing, which involves substituting the unknown instrument with an identically sized mass standard.
Sample Placement
Process weighing requires a combination of methods and careful attention to detail. Cutting corners with less quality weighing equipment can result in poor performance and inaccurate results.
It is important to always use the correct capacity load cell for a given application. COOPER Instruments & Systems can help with proper load cell selection and installation for process weighing applications.
When a sample needs to be transferred, the tried-and-true method is called “weighing by difference.” The empty balance is tared and then the solid is added to the weighing bottle with its cap off. The weighing bottle is then re-tared, subtracting the original mass to get the new weighed value.
After the weighing is complete, the final tare weight is recorded and the balance door closed. It is important to not touch or breathe on the weighing platform, since even slight air pressure changes can affect the measurement. The weighing results should be recorded directly into the laboratory notebook.
Data Recording
In this phase, the data is recorded in either a hard or electronic format. Whether it is in the form of notes, spreadsheets, or photos, this record serves as documentation of the work that has been performed.
It’s important to understand that even when the weighing process is done correctly, errors may still occur. These errors could be caused by improper balance operation, air currents, temperature changes, lack of thermal equilibrium, and magnetic or electrostatic fields.
Weighing methods are designed to eliminate these types of errors, ensuring that the results you receive are accurate and precise. When working with sensitive substances, such as pharmaceuticals and chemicals, precision is key. Weighing by Difference is the best method for these scenarios, providing a high level of accuracy while reducing contamination concerns. For more routine applications, Direct Weighing offers simplicity and speed for situations where precision is not a priority. Both methods can be optimized for the unique characteristics of your samples, allowing you to get the most out of your weighing process.