Standard weights are weights that are used as a reference for measuring the weight of other objects. These weights are typically calibrated to a specific weight and are used to verify the accuracy of weighing scales and balances.
Standard weights are often made of materials such as stainless steel or brass and are designed to resist corrosion and wear. They are manufactured to meet specific accuracy standards set by organizations such as the National Institute of Standards and Technology (NIST) in the United States or the International Organization of Legal Metrology (OIML) internationally.
The most common types of standard weights are known as OIML classes E1, E2, F1, F2, M1, and M2. Each class represents a different level of accuracy, with E1 being the most accurate and M2 being the least accurate. The accuracy of a standard weight is typically determined by comparing it to other standard weights using a precision balance or scale.
The Importance of Calibration
Before delving into the role of standard weights, it is essential to understand why the calibration of scales is so crucial. Scales are used in a wide variety of industries, from food production to chemicals and pharmaceuticals. In all of these industries, accurate measurement of product mass is required to ensure quality, safety, and compliance with regulatory standards.
Without proper calibration, scale measurements can be inaccurate, which can result in serious problems such as poor quality products, material loss, non-compliance with regulations, or even safety risks. Therefore, regular and accurate calibration is essential to maintain the reliability and integrity of measurements.
ALSO READ: What is E2 Class Weight Box?
The Role of Standard Weights in Calibration
Standard weights are used as a reference to adjust and verify the accuracy of the scales. These weights are made with extreme precision and are carefully calibrated to have a known mass value traceable to international standards. In other words, standard weights are “known weights” used to compare and adjust the response of scales.
During the calibration process, the standard weights are placed on the scale platform and the reading is recorded. If the scale correctly indicates the expected value of the standard weight, then it is considered to be correctly calibrated. In case there is a difference, adjustments are made on the scale until the values match. This ensures that future measurements on that scale will be accurate and reliable.
How many Types of Standard Weights are there?
Each type of standard weight has specific characteristics and is chosen according to the precision required in each application. These weights guarantee reliable measurements and comply with international standards to ensure traceability.
- Class F: High precision, they are used in laboratories for exact measurements in sectors such as chemistry and pharmacy.
- Class M: They are used in industrial applications to calibrate commercial and production scales.
- Class E: Suitable for calibrating scales in industrial environments, such as manufacturing or logistics.
- Class S: Designed to calibrate large capacity scales, such as those used in cargo transportation.
Calibration Weights or Laboratory Weights or Standard Weights are major components for any labs. They help and ensure that lab balances are giving accurate readings by keeping weighing balances calibrated on time to time basis. However, they are not all made the same. Calibration weights are assigned a class which is based on the accuracy or tolerance of the weight. There are different sets of classes of weights, including ASTM, OIML and NIST Standards. In addition, there are certifications granted to different weights.
ALSO READ: SOP for Calibration of Weight Box
Classes of Weights
There are three main calibration weight class systems that you’ll come across the world:
NIST: National Institute of Standards and Technology (NIST) Class F weights are often used in industrial settings to verify Class III, Class IV, and non-designated scales. They may also be used in warehouses and manufacturing settings to calibrate scales used for the shipping or production of large products. NIST Class F weights aren’t typically used in laboratories as they are not accurate enough to verify the scales used for most laboratory applications.
ASTM: ASTM International (formerly American Society for Testing and Materials) is a nonprofit non-governmental organization that develops voluntary consensus standards. It has developed 10 calibration weight classes as guided by document ASTM E 617: ASTM Class 000 thru ASTM Class 7. The higher the class number, the higher the level of tolerance (and less accurate) the weight will be. Most laboratory applications require ASTM weights of Class 4 or below. ASTM class weights are the most common type of calibration weights used in US laboratories.
OIML: The Organisation Internationale de Métrologie Légale or International Organization of Legal Metrology (OIML) is an intergovernmental organization that provides standards and systems with the goal of harmonizing legal metrology procedures. From lowest (most accurate) to highest tolerance, the OIML classes are E1, E2, F1, F2, M1, M2, and M3. Most laboratory applications require OIML weights of Class F2 or below. OIML class weights are more commonly used outside the US.
Certifications of Weights
While you search for calibration weights, very often you might come across mentions of certifications. Indeed, depending on your application, you may require that your calibration weights come with a certificate confirming that the lab testing the weights is accredited. Here are the terms you’ll commonly see and what they’re referring to.
ISO/IEC 17025: The International Organization for Standardization (ISO) is an independent non-governmental organization comprising a membership of 164 national standards bodies. The International Electrochemical Commission (IEC) is an international standards organization for electrotechnical fields. Together with other liaison organizations, they created the ISO/IEC 17025 standards. This is the international reference to be used by testing and calibration laboratories that want to display their ability to provide reliable results.
NIST/NVLAP: NVLAP refers to a calibration program developed by the National Voluntary Laboratory Accreditation Program (NVLAP) at the (NIST). It provides a means to assess calibration labs for competency, offering accreditation in various fields. It follows the international standard ISO/IEC 17025 (discussed above) when accrediting calibration laboratories.
Tags
Quality Control
