Measuring Equipment and Calibration

This section describes the impact that process control equipment can have on system safety. It details activities that are performed to keep equipment and instrumentation within calibration and how that is verified. 

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Measuring equipment and calibration Discusses how control equipment of the system life cycle is defined and ensured to be within specification, especially as it relates to system safety. 

Purchase and control measuring equipment and reference material necessary for internal calibration certification of calibrated instruments. Label them with the date when last calibrated and also date when the next calibration is due. Write a calibration report and, if necessary, an incident report or a calibration variance report. 

The protocol must include directions on selecting or developing the maintenance program, including preventive and corrective action. The maintenance program includes the calibration program of measurement equipment and the replacement of equipment parts. 

ISO TR 14253-2 (1998) Geometrical product specifications (GPS) - Inspection by measurement of work-pieces and measuring equipment -Part 2 Guide to the estimation of uncertainty in GPS measurement, in calibration of measuring equipment and in product verification. ISO, Geneva Kadis R (1998) Accred Qual Assur 3 237-241... 

Abstract Since the uncertainty of each link in the traceability chain (measuring analytical instrument, reference material or other measurement standard) changes over the course of time, the chain lifetime is limited. The lifetime in chemical analysis is dependent on the calibration intervals of the measuring equipment and the shelf-life of the certified reference materials (CRMs) used for the calibration of the equipment. It is shown that the ordinary least squares technique, used for treatment of the calibration data, is correct only when uncertainties in the certified values of the measurement standards or CRMs are negligible. If these uncertainties increase (for example, close to the end of the calibration interval or shelf-life), they are able to influence significant-... 

Stability of the traceability chain in chemical analysis is dependent on the calibration intervals of measuring equipment and shelf-life of CRMs used for the calibration of the equipment. 

CRMs are an important tool for quality assurance and quality control in analytical laboratories. They are used for verification of accuracy and precision (i.e., reliability of the results of analysis, validation of analytical procedures, establishing measurement traceability, and calibration of measurement equipment). Use of CRMs is recommended by the ISO/IEC 17025 standard and therefore it is obligatory for those who wish to obtain and maintain accreditation of the laboratory. 

Production control planning, preparation of materials, traceability and calibration, measurement equipment and methods, assessment of homogeneity and stability, data treatment and certification. 

Accuracy for critical measuring equipment and certificates for calibration as appropriate. 

Evaluation and calibration. A piece of tube was rotated around its own axis during four channel wall thickness mea.surements (Figure 7). The four traces are not identical A rotation apart as should be expected. The calibrations of the four equipment s from the manufacture was not the same. Especially one of the traces has less dynamic than the other three. Based on these observations a dynamic calibration system was suggested using a tube, which could be rotated around its own axis in the measuring system. The values should be verified using traditional mechanical measurement around the tube circumference. The prototype system was permanently installed in the workshop at the production hall. Experimental work was more difficult under such circumstances so our participation in the development work stopped. 

Good measurement practices (GMPs) describe operations specific to a technique. In general, GMPs provide instructions for maintaining, calibrating, and using the equipment and instrumentation that form the basis for a specific technique. For example, a GMP for a titration describes how to calibrate a buret (if nec-... 

The assessor should also find out whether an effective testing program is in place to help ensure the serviceability of process measurement equipment. The successful toller should have an established calibration program to address the accuracy of critical measurement equipment. Safety critical process parameters should be monitored and critical process equipment should automatically interlock when monitoring instrumentation detects safety critical deviations. Interlocks should either facilitate a remedy to the critical deviation or bring the process to the zero energy state. These instruments and interlocking devices should be routinely tested to ensure operational reliability. 

Is all measuring equipment used, tested and calibrated for accuracy at regular intervals ... 

Traceability is also important to control processes. You may need to know which products have been through which processes and on what date, if a problem is found some time later. The same is true of test and measuring equipment. If on being calibrated a... 

Procedures are required for the control and maintenance of inspection, measuring, and test equipment and to cover test software, not only for calibration. This section of the standard is often referred to as the calibration requirement but it goes far beyond mere calibration. In assessing compliance with section 4.11, there are at least 30 requirements to check (see the questionnaire at the end of this chapter) and calibration is only one of them. Figure 11.2 shows the processes needed to control, calibrate, and maintain inspection, measuring, and test equipment. The shaded boxes indicate interfaces with other processes. 

It is not necessary to calibrate all test and measuring equipment. Some equipment may be used solely as an indicator, such as a thermometer, a clock, or a tachometer other equipment may be used for diagnostic purposes, to indicate if a fault exists. If such devices are not used for determining the acceptability of products and services or process parameters, their calibration is not essential. However, you should identify such devices as for Indication Purposes Only if their use for measurement is possible. You don t need to identify all clocks and thermometers fixed to walls unless they are used for measurement. Having observed that you record the time when observations were made, a zealous assessor may suggest that the clock be calibrated. If the time is not critical to product or process acceptability, calibration is unnecessary. 

ISO 10012 requires that the integrity of measuring equipment be confirmed at appropriate intervals established on the basis of stability, purpose, and usage. With new equipment it is customary to set the frequency at 12-month intervals unless recommended otherwise by the manufacturer. Often this frequency remains despite evidence during calibration that accuracy and precision is no longer stable. Such action indicates that the calibration staff have not been properly trained or that cost rather than quality... 

The standard requires the supplier to maintain calibration records for inspection, measuring, and test equipment and the supplementary requirements specify the content of these records. 

Unlike the other requirements, which only referred to inspection, test, and measuring equipment, this clause adds test facilities. Facilities include the equipment and the area or room in which it is kept or used. Test facilities are any room, area, or complex in which tests are carried out. Inspection, measuring, and test facilities include functional and environmental test laboratories, test and inspection chambers, calibration rooms. 

The only statistical techniques which need control are those used to determine the acceptability of a product or service or the capability of a process that produces the product or service. Any activity where you rely on statistical evidence rather than physical measurement is an activity which should be governed by these requirements. The use of recognized techniques is important to the confidence one has in the result. It is similar to the use of measuring equipment that has been calibrated against known standards of accuracy. Unless you actually check every product, measure every attribute or variable you cannot be 100% certain. But that is costly and you can be 99.99% certain by using statistical techniques 99.99% may be sufficiently accurate for your needs. 

Control of Monitoring and Measuring Devices (Calibrate measuring equipment for valid results)... 

Control of monitoring and measuring devices - Maintain and calibrate measuring equipment... 

Sec. 820.72 Inspection, measuring and test equipment - Use traceable calibration standards and maintain caiibration records for measuring equipment... 

In the cases where liquid formulations are applied, calibration is normally performed by collecting the output volume over a given time period. Generally a minimum of three such measurements should be taken in order to estimate output consistency. Where output is collected from multiple nozzles or outlets, each nozzle or outlet should be evaluated in order to ensure uniformity of output across all the nozzles or outlets. If the deviation from the manufacturer s recommended value is not within 5% (or the value specified in an appropriate SOP), the nozzle or outlet should be replaced. The use of a patternator allows the droplet distribution pattern of the nozzles or outlets to be measured accurately, and this check should be conducted annually. Having estimated the output of the equipment, the time required to treat a specific area with a known quantity of test item solution can be calculated. 

A plan is draw up detailing how checks will be made to ensure that the critical limits are not exceeded. It shows how often the checks are made, how and by whom, so that it is clear who is responsible that it is done correctly. It also specifies regular inspections and calibrations of measuring equipment such as thermometers. 

The case of Oetzi (or the Iceman), the frozen mummy found in 1991 on the Alps on the border between Austria and Italy and now kept at the Archaeological Museum of Bolzano (Italy), is also well known. AMS radiocarbon measurements from the laboratories of Zurich[78] and Oxford[79] on tissue and bone samples from the Iceman dated him to 4550 19 years BP. When calibrated, this radiocarbon age corresponds to three probable calendar time intervals between 3350 BC and 3100 BC. Consistent measurements were obtained by dating some of his equipment and also botanic remains from the discovery site. [80] In this context, it is important to note that dating of Oetzi represents a good example of the relevance of the behaviour of the calibration curve in the final precision of a radiocarbon measurement. Actually, in this case, despite a very high precision of the radiocarbon age ( 19 years), the special trend in the calibration curve around the dated period, i.e. in particular the so-called wiggles, prevents a more exact and unambiguous absolute age determination. 

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