Post-test calibration

J.L. Wise, P.K. Kammer, and J.A Murray, Post-test calibration of single-use, antimony, 24-hour ambulatory esophageal pH probes is necessary. Dig. Dis. Sci. 49, 688-692 (2004). 

Beside technical aspects mentioned above, there are additional considerations for selecting NDT methods for a specific purpose. Cost, frequently, is decisive and major cost factors are (1) test duration, including time used for setup and post-test analysis and assessment (2) type of equipment, its sophistication, calibration, and maintenance (compatibility with previous records from periodic inspection may require costly maintenance of aging equipment) (3) equipment operator, specifically operator training and certification (191) (4) accreditation of test agency (5) qualification or validation of the NDT method (192) and (6) accuracy and precision estimates required by test standards or quahty management systems. 

Part of the confusion surrounding the model testing and validation process is largely because different meanings have been attached to the terms calibration, verification, validation, and post-audit in the technical literature. As a result of the Pellston conference, I have adopted the following relationship among these terms ... 

Thus, the process of model testing and validation (considered synonymous) should ideally include the steps of calibration (if necessary), verification, and post-audit analyses. I indicate "ideally" because in many applications existing data will not support performance of all steps. In chemical fate modeling, chemical data for verification is often lacking and post-audit analyses are rare (unfortunately) for any type of modeling exercise. 

The experimental setup for diode-laser sensing of combustion gases using extractive sampling techniques is shown in Fig. 24.8. The measurements were performed in the post-flame region of laminar methane-air flames at atmospheric conditions. A premixed, water-cooled, ducted flat-flame burner with a 6-centimeter diameter served as the combustion test-bed. Methane and air flows were metered with calibrated rotameters, premixed, and injected into the burner. The stoichiometry was varied between equivalence ratios of = 0.67 to... 

Even once a method is standardized, erroneous results can still be generated. As a result, it is critical to have robust quality control procedures in place. Here, careful attention should be paid to identify opportunity for in-process control measures such as internal standards, calibration, control plates, replicates and so on as opposed to post-processing data review steps. Inline QC approaches allow sources of error to be identified and remedied much more rapidly and help limit costly re-tests, or the possibility of erroneous data leaving the laboratory. 

ISO 17025 1999, which covers the general requirements for the competence of testing and calibration laboratories, or ISO 15189 2002, which includes particular requirements for quality and competence in medical laboratories extending to post-analytical aspects including the reporting of results. 

Preparation of the patient, sampling of specimens Pre-analytical handling of specimens Accurate and precise analytical performance Selection of appropriate, sensitive and specific methods Calibration of analytical systems Internal and external quality assurance Post-analytical handling of test results Clinical interpretation of test results Reporting process... 

In the test for oxygen binding, 02-electrode measurements were made by diluting samples of oxygenated sea water with equal-sized volumes of either deaerated sea water or deaerated vanadocyte suspensions. If vanadocytes could bind 02, the concentration of dissolved 02 should be lower in the sample diluted with vanadocytes, than in the one diluted by deaerated sea water. However, no difference in the post-dilution sea water oxygen concentration was found between the two the results fell on the calibration curve. This finding has now been extended to tunicate blood cells rich in iron, rather than vanadium64. ... 

Underwater acoustics is routinely used in laboratory-scale test facilities for flaw detection, transducer calibration, material property evaluations, and acoustic visualization. In a typical underwater acoustic study, an object of interest is submerged in a water filled tank and acoustically illuminated (insonified). The acoustic signals scattered by the object are then measured and analyzed. If the tank used is not sufficiently large, these measured acoustic signals will include spurious echo components due to extraneous wall reflections. Since the effect of these contaminating echoes usually cannot be removed from the resulting data set by post analysis, they must be prevented from occurring at their source. One cost... 

A UTCHEM chemical flood model was built based on history-matching core flood experiments. The chemical parameters were calibrated through matching experiments. The calibrated parameters were used to build a field sector model to simulate the ASP pilot test. In the model, detailed alkaline reactions were considered. It was probably the hrst time such an ASP model was applied in a real held scale. The model was used to optimize injection schemes. For example, the model showed that when the post-flush slug volume was in the range of 0.15 to 0.35 PV, the pilot performance was insensitive to the slug size. Therefore, 0.15 PV of post-flush slug was selected for the injection scheme. 

Calibration program summary. The instrument calibration program should describe calibration policy for validation of test equipment, pre- and post-calibration, and NIST traceability of calibration standards. The responsibility of calibration shall be defined. 

In practice, a three-person crew is required to perform these measurements. One person walking ahead locates the pipeline with a pipe locator to ensure that the potential measurements are performed directly overhead the pipeline. This person also carries a tape measure and inserts a distance marker (a small flag) at regular intervals over the pipeline. The markers serve as distance calibration points in the survey. The second person carries a pair of electrodes that are connected to the test post by means of a trailing thin copper wire and the potential measuring instrumentation. This person is also responsible for entering specific features as a function of the measuring distance. Such details (road, creek, permanent distance marker, fence, rectifier. 

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