The weighing process involves the use of a balance to determine mass or weight. It is a simple process of placing objects on one plate and subtracting them from the other to find the mass of the object being tested.
It is important to exercise the balance first by placing a known weight on it and taking a reading. This will help improve the repeatability of the readings.
Accuracy
The best way to reduce systematic errors is to calibrate the instrument and use certified calibration weights. These are the only ways to guarantee that the measurement uncertainty is based on internationally correct methodology.
The accuracy of your digital weighing system is determined by the quality of the load cell (also called a load sensor or transducer). This piece of machined metal bends when weight is applied and converts mechanical force into an analog electrical signal that a controller converts to a digital weight measurement.
The accuracy of the load cell can also be affected by temperature, humidity and air currents, which may cause the instrument to fluctuate or produce inaccurate readings. It is important to place your analytical or semi-micro balance in a location with minimum exposure to these factors. Adam offers anti-vibration tables for many of its instruments that can help reduce these effects on the weighing results. The sensitivity test, which is performed at the high end of the weighing range, is another routine calibration procedure that is often omitted.
Errors
Weighing errors or omissions can occur from the use of substandard techniques, the use of improper equipment, or even the simple act of handling and moving the sample to and from the analytical balance. These errors can be large or small depending on the value of the measurement and the accuracy required.
Other errors can be caused by environmental conditions, including temperature changes. Many load cells are temperature-compensated to help reduce these errors.
To minimize the possibility of weighing errors, make sure your workspace is clean, organized, and free of contaminants. Avoid touching the scale or breathing on it while it’s in use. Record the weight directly into a lab notebook to prevent transcription errors and be sure to wear disposable gloves. If possible, tare the balance before each use. Allow the balance and sample to settle for 24 hours before a mass calibration to ensure thermal equilibrium. A lack of thermal equilibrium can lead to convection currents on the weigh pan and produce erroneous readings.
Safety
Weighing equipment needs to be operated carefully, as excessive shock can damage the instrument. This is especially true for analytical balances, which require gentle operation to ensure repeatable results. Handles should be kept free of grease, lint & other contaminants to prevent influencing the readings. It is also helpful to keep the environment stable, as humidity & temperature changes can affect the readings.
Many industrial weighing applications are conducted in hazardous environments, including formulation, filling, dispensing & blending processes. Load cells & weighing systems used in these environments must be specifically designed to meet international standards, such as European ATEX & U.S. NFPA regulations.
Often, data tracking capabilities are built into the weighing system to record information automatically. This enables managers to view quality data such as the number of products that are over & under weight, how these products were rejected & why. This allows companies to identify a problem & correct it, improving overall product quality.
Maintenance
Maintenance measures are crucial in keeping a weighing system operating at optimal levels. Regular servicing and calibration reduces the likelihood of costly emergency breakdowns. Trained technicians are able to spot issues before they escalate into a major problem.
Ensure the weighing equipment is protected from extreme temperatures and moisture. Using a damp, lint-free cloth, clean the glass draft shields and stainless steel weighing platforms regularly. Alternatively, you can use a cleaning solution that is recommended by the balance manufacturer.
A closed-end service plan is a more cost-effective option for industrial scales that require frequent preventive maintenance. These plans feature fixed monthly, quarterly or annual charges for the weighing system, and extra costs above the plan amount are borne by the service company. This eliminates the need for the customer to pay upfront fees for repair services, making it a better fit for many industrial scale owners.