Tham khảo tài liệu 'measurement process characterization_13', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | . Consistent bias 2. Measurement Process Characterization . Uncertainty analysis . Type A evaluations . Type A evaluations of bias . Consistent bias Consistent bias Bias that is significant and persists consistently over time for a specific instrument operator or configuration should be corrected if it can be reliably estimated from repeated measurements. Results with the instrument of interest are then corrected to Corrected result Measurement - Estimate of bias The example below shows how bias can be identified graphically from measurements on five artifacts with five instruments and estimated from the differences among the instruments. Graph showing consistent bias f for probe 5 An analysis of bias for five instruments based on measurements on five artifacts shows differences from the average for each artifact plotted versus artifact with instruments individually identified by a special plotting symbol. The plot is examined to determine if some instruments always read high or low relative to the other instruments and if this behavior is consistent across artifacts. Notice that on the graph for resistivity probes probe 2362 5 on the graph which is the instrument of interest for this measurement process consistently reads low relative to the other probes. This behavior is consistent over 2 runs that are separated by a two-month time period. Strategy -correct for bias Because there is significant and consistent bias for the instrument of interest the measurements made with that instrument should be corrected for its average bias relative to the other instruments. http div898 handbook mpc section5 1 of 3 5 1 2006 10 12 51 AM . Consistent bias Computation of bias Given the measurements on Q artifacts with I instruments the average bias for instrument I say is where Computation of correction Type A uncertainty of the correction Example of consistent bias for probe 2362 used to measure resistivity .
