Efficient Quality Management in a Regulated Environment Ensuring compliance with quality management and regulatory standards such as ISO or GMP, requires an understanding of parameters influencing the accuracy of weighing processes. In highly regulated industries where consumer safety is at stake such as food, cosmetics, pharmaceutical or automotive production it can also mean being subjected to frequent audits. Thorough risk analysis before acquiring weighing systems and instrument verification between service visits can help put regulatory guidelines into effective practice while reducing costs and increasing productivity and product safety. Helpful actions include: determining required process tolerances selecting appropriate technology documenting compliance setting adequate testing and calibration schedules choosing appropriate performance measures Instituting relatively simple weighing tests as part of standard operating procedures (SOPs) can help assure top quality product and audit results. Good Weighing Practice (GWP ) the global weighing guideline developed by METTLER TOLEDO can help, regardless of the manufacturer of a particular scale or balance. Contents 1 Putting quality management in perspective 2 Establishing an appropriate weighing practice 3 Matching instrument accuracy to process tolerance 4 Understanding process risks in regulatory context 5 Verifying equipment accuracy 6 Summary 7 Additional resources
1 Putting quality management in perspective Weighing process quality was once primarily a question of accuracy. But it has become increasingly concerned with risk evaluation and management and is the daily preoccupation of quality managers worldwide. Quality assurance complexity often arises from the regulations themselves. They give only a vague framework on performance targets. No concrete implementation information is given based on the assumption that the user knows his or her process best and can therefore choose the best solution to any issue. Questions left to interpretation include: How should verification be made? At what interval? Using which standard? How should validity of results be assessed? Recorded? What action should be taken? Putting the weighing process itself at the center of the quality management equation can help establish helpful, documentation-ready SOPs that pass audits and improve productivity and profitability. METTLER TOLEDO s GWP offers a framework in nearly any regulatory scenario, regardless of a weighing system s manufacturer. Take for example this weighing practices excerpt from ISO 9001: ISO 9001: 7.6 Control of monitoring and measuring devices Measuring devices shall be calibrated or verified at specific intervals, or prior to use, against measurement standards traceable to international or national measurement standards. The organization shall assess and record the validity of the previous measuring results when the equipment is found not to conform to requirements. The organization shall take appropriate action on the equipment and any product affected. 2 METTLER TOLEDO - White Paper - Quality Management
2 Establishing an appropriate weighing practice METTLER TOLEDO s GWP offers a framework to establish a weighing practice that works. The five basic GWP steps follow. STEP 1: Good Evaluation Evaluating the process from a metrological perspective to establish parameters such as smallest net weight and required process accuracy. These parameters set expectations for a given instrument. STEP 2: Good Selection Selection of a scale fulfilling the preceding requirements. Or, matching accuracy to process needs. The minimum weight concept is used as a basis for selection. Good Evaluation Good Selection STEP 3: Good Installation Documenting that appropriate installation unpacking, set-up, configuration, calibration, adjustment and operator training has taken place and that the equipment still fulfills selection requirements. Good Installation STEP 4: Good Calibration Calibrating a scale in its operating environment. Documenting scale performance and issuing applicable certificates at regular intervals is the qualified technician s task. Good Calibration STEP 5: Good Operation Establishing SOPs and test schedules help guarantee weighing process criteria are fulfilled between service visits. Good Operation Each step involves assessment of process parameters to ensure equipment can meet tolerances and quality requirements. 3 METTLER TOLEDO - White Paper - Quality Management
3 Matching instrument accuracy to required process tolerance A weighing system s life starts with assessing process requirements from a metrological perspective. This means establishing process parameters such as: Weighing range Smallest net weight Process tolerance Applicable regulations Need for safety margin Other important concerns include ruggedness of the construction, mechanical stress when loading the scale, environmental conditions such as humidity, temperature, ingress protection, explosion/corrosion protection, and hygiene and connectivity. Quality will be assured if an instrument s measurement uncertainty is always better than the acceptable process tolerance. For example, measuring 1kg with a tolerance of 1% is only possible with a scale providing a measurement uncertainty better than 1% (<1%) at the given net load of 1kg. The relative measurement uncertainty of any measuring instrument particularly a scale can be assured by considering the following characteristics. Minimum Weight In the low range, there will be a limit under which any measurement will have an uncertainty greater then the acceptable tolerance. This is called the minimum weight characteristic. Smallest Net Weight The smallest net weight of the weighing process under consideration has to fulfill the required process toler- ance requirement. As each scale will have its own absolute and relative measurement uncertainty curve (see figure 1 on next page), the only scales that are appropriate are those where the minimum weight characteristic is smaller than the smallest net weight of the respective process. In the example (figure 1), it is obvious that Scale 3 is not appropriate, because its relative measurement uncertainty is greater then to the required relative tolerance at the smallest net weight. Scale 2, taking into account only the minimum weight, could be a candidate. Relative uncertainty becomes bigger at smaller weights U [kg] = U0 + Constant x Weight Absolute measurement uncertainty [kg] Uncertainty U [kg or- %] Process tolerance (%) Relative measurement uncertainty [%] Weight [kg] Max For smaller weights, the relative measurement uncertainty can be so high that the weight cannot be trusted anymore! 4 METTLER TOLEDO - White Paper - Quality Management
Scale 1 Scale 2 Scale 3 Quality Management Tolerance (in %) Smallest net weight Process tolerance (%) Load [kg] Process Tolerance & Safety Margin Instrument performance is strongly influenced by the environment. Certain environmental factors such as air currents, temperature changes and vibrations can lead to a reduction in instrument performance resulting in less accurate weighing. So some safety margin must be anticipated to prevent external influences from throwing measurements out of tolerance. Max. 60 kg Figure 1 Relative measurement uncertainty (%) of 3 scales of 60 kg Upon further investigation, however, we will see that Scale 1 is the proper selection. A safety factor on the Minimum Weight must be applied. In other words, the Minimum Weight of a scale at a given tolerance should be at least half of the smallest net weight to be measured (safety factor >2). A safety factor >2 is recommended if risk analysis determines accuracy is critical. Using these criteria, in this example, only scale 1 can fulfill all process requirements. 4 Understanding process risks in regulatory context Industrial processes always carry risk. Errors may impact the company (increased costs, loss of image, loss of production time), consumers, the environment or all of the above. Errors as a result of a weighing inaccuracy may result in over- or under filling, waste of production materials, over-paying for materials, quality issues and customer complaints, which may lead to financial losses for the company. Mistakes across complex industrial processes may be difficult to detect. Identifying, describing and minimizing operational risks has become the focus of most current regulations and quality systems such as ISO or GMP. High risk and a narrow process tolerance may call for frequent instrument accuracy verification. Even under a more frequent testing schedule regulators determine an instrument s uncertainty principle based on an assumption that proper installation and calibration actions have been performed. Therefore, proper installation and calibration are critical to comply with the standards. How Operator Training Impacts Audits Installation includes unpacking, set-up, configuration, calibration, adjustment, training and documentation of all these actions. The manufacturer can install a system in good order and document that the equipment will perform the task for which it was selected. However, many users invest large sums in instrumentation but neglect end-user training. Since the user is often the biggest source of measurement uncertainty, this can be a costly error in terms of lost production and audit failures. Establishing Audit Proof Documentation Calibrating a scale in its operating environment helps document performance under the influence of environmental factors. Documenting scale performance at regular intervals is the task of an authorized and trained technician. He or she will determine the value of the different contributions to the measurement uncertainty such as scale sensitivity, weighing 5 METTLER TOLEDO - White Paper - Quality Management
repeatability, eccentricity deviation and non-linearity. The scale will also be serviced so any deviation from original specifications is minimized or alleviated. 5 Verifying equipment accuracy Inappropriate use, accidental damage, changes in environment conditions, or humidity water ingress can alter instrument accuracy. Since calibration is normally only carried out once or twice per year, users typically perform process-specific verifications between formal service visits themselves. Users determine which tests to perform taking into account process risks and tolerances. Ideally, this means establishing: A test list (sensitivity, repeatability, eccentricity) Testing frequency Weights used SOPs to be followed for the tests Test weight verification/recalibration frequency Verification of tolerance, control and warning limits A calibration certificate establishes links to applicable standards and proves compliance. For critical instruments, documentation demonstrating measurement uncertainty under additional tolerance and safety factors may be valuable. For its clients, METTLER TOLEDO issues a Minimum Weight Certificate to establish bulletproof documentation that helps in passing audits. Regulations like ISO, GMP, and GFSI-based standards remain silent on determining these parameters. Here again, concepts developed under the GWP guideline work. Test frequency should be determined by risk level and process tolerance as depicted in the following diagram. 0.01% Weighing Accuracy 0.1% 1% 10% Higher Risk = More Testing Low Medium High Impact 6 METTLER TOLEDO - White Paper - Quality Management
If a measurement mistake has no impact on the process (low risk) and required tolerance is wide (>10%), there is almost no verification need. Conversely, if a mistake would impact consumer health (high risk) and process accuracy has a narrow tolerance (<0.1%), a verification procedure with higher frequency is necessary. More risk plus stricter tolerance equals higher testing frequency. Service technician calibration is the only method to establish national and international standards compliance and also determines measurement uncertainty so that it can be confirmed that process tolerances can be achieved. But to determine if an instrument will satisfy process tolerance on a daily basis, an operator can: appeal to instrument functions and self-tests, or use weights to perform simplified routine testing. Verification tests only work if an operator can obtain appropriate weights. METTLER TOLEDO has developed two-weight sets that are sufficient to conduct all tests required to ensure scale accuracy called CarePacs and can also supply high-quality reference weights for testing any capacity scale. Because a larger and more expensive weight set is not required, the initial investment is reduced. Costs associated with maintenance and recalibration are lowered as well. METTLER TOLEDO can assist with the appropriate combination of tests as well as the selection of test weights themselves. 6 Summary Efficient quality management helps increase productivity and reduces costs. Choosing the right weighing system, establishing testing frequency based on risk and tolerance, and training internal personnel to spot-check accuracy can help a manufacturer pass required audits, assure quality and keep rejects or worse, recalls to a minimum. Establishing characteristics such as weighing range, smallest net weight, process tolerance and safety margin helps guide weighing system selection. Other important concerns include ingress protection, explosion/ corrosion protection, hygiene and connectivity. Service technician calibration establishes national and international standards compliance. However, routine self-testing on an established schedule can help with regulatory compliance and improve day-to-day operations. If weighing mistakes are low-risk and tolerance is wide, verification needs are few. However, if issues such as company reputation or consumer health are at stake, higher testing frequency is required. Testing costs and operator experience are integrated into METTLER TOLEDO Good Weighing Practice TM (GWP ), a reality-based weighing practice model that can be applied in any scenario where accurate weighing is used crucial to product quality and safety. 7 METTLER TOLEDO - White Paper - Quality Management
7 Additional resources For more about Good Weighing Practice, risk evaluation or effective scale operation, log onto www.mt.com/gwp For more about CarePacs and their role in establishing cost-effective, highly accurate scale testing practices, visit www.mt.com/carepacs www.mt.com/ind-food-productivity-guide2 For more information Mettler-Toledo AG CH-8606 Greifensee Switzerland Phone +41 44 944 22 11 Fax +41 44 944 30 60 Subject to technical changes 08/2011 Mettler-Toledo AG MarCom Industrial