Emerging technologies for coating new types of filters, such as linearly variable bandpass filters, urges new kind of measurement systems requiring accurate and time-saving spatially resolved transmittance measurements. On the other hand, one of the main uses of coated filters is standardization use; e.g., as certified reference materials (CRMs) for transmittance and absorbance standards. In this case, the homogeneity assessment is of great interest. To do such measurements with low uncertainty, spatial scanning methods using reference double-beam spectrophotometers are routinely used. High time consumption and relatively high-cost are disadvantages of this traditional method. In this work, we propose a new system based on an imaging technique. The newly developed system comprises a quartz tungsten halogen (QTH)-based illuminator, with collimator and coupling optics, a double-grating monochromator, customized integrating sphere, and scientific highly digitized, high-resolution and dynamic range Si-based CCD (monochrome) camera. The system is time-saving: in one-shot we may measure the spatial transmittance distribution of the samples (e.g. filters) without separately measuring the reference (air), which has many instability issues. Validation measurements using standard filters are presented. Systematic errors may be studied and corrected for. Many types of filters and liquids, for instance chemical reference materials (RMs), may be measured and reported. Uncertainty of spatial, spectral and radiometric components are studied carefully and estimated. The combined uncertainty evaluation has shown that relatively low uncertainty levels may be achieved, specially in the visible range (U < 1 %, k=2 ). Spatially-resolved data with different curves at different positions (spatial points) are shown in the spectral range of 380 nm through 950 nm. The combined uncertainties at some spectral points are presented and proved to be sample- and wavelength-dependent at all the points in the field-of-view (FOV) of the CCD camera.
Accurate measurement of the atmospheric longwave irradiance is important for renewable energy and atmospheric science applications. Pyrgeometers are deployed outdoors all over the world to measure the atmospheric longwave irradiance and presently are calibrated with traceability to the interim standards for atmospheric longwave radiation measurement, the standards are based on four pyrgeometers and their average irradiance is the World InfraRed Standard Group (WISG) which is developed and maintained by The Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center (PMOD/WRC). Since 2013 the InfraRed Integrating Sphere (IRIS) developed by PMOD/WRC and the Absolute Cavity Pyrgeometer (ACP) developed by the National Renewable Energy Laboratory (NREL) have been compared outdoors six times at different locations and the difference between the measured atmospheric longwave irradiance by ACP and IRIS was less than 2 W/m2 with traceability to the International System of Units (SI). During the six comparisons the irradiance measured by the interim WISG was 5 W/m2 lower than the irradiance measured by the average irradiance measured by the ACP and IRIS [1]. Based on this discrepancy, the World Meteorological Organization’s Commission for Instruments and Methods of Observation (CIMO) recommended that the interim WISG should be adjusted to be traceable to SI units [2]. In anticipation of CIMO’s expert team agreement on establishing the world reference using the average irradiance measured by ACP and IRIS in this article we describe a procedure to calibrate pyrgeometers with traceability to SI. One Absolute Cavity Pyrgeometer (ACP95F3) was used to calibrate four pyrgeometers traceable to SI units. Three Eppley PIRs and one Kipp&Zonen CG4 were originally calibrated with traceability to the interim WISG. Using the described procedure below, the responsivity of each pyrgeometer was then adjusted to match the irradiance measured by ACP. Outdoor data was collected during one clear sky nights monitored by the output thermopile voltage of ACP95F3. The irradiance measured by the PIRs was calculated using NREL equation and the CG4 using NREL equation and PMOD/WRC equation. Using the NREL equation, the calculated uncertainty (U95) of the PIRs varied from 2.43 W/m2 to 2.67 W/m2, and for the CG4 using the NREL equation U95 equals 1.97 W/m2, and using the PMOD equation U95 equals 2.88 W/m2 with respect to SI.
Thermal expansion sometimes dominates uncertainty in a precision measurement. A cell-based refractometer has been designed at NIST which targets 10−6 relative uncertainty in the measurement of helium refractivity; in terms of absolute refractive index at ambient conditions, the accuracy goal is 3 × 10−11. To achieve this level of accuracy, the length of a 0.5 m gas cell would need to be known within 100 nm. This is achievable when cell length is measured by coordinate-measuring machine at 20 °C. However, the refractometer will operate at the thermodynamically known fixed-points of water and gallium, near 0 °C and 30 °C, respectively. The cell is made from fused quartz glass, which has a nominal thermal expansion coefficient of 0.4 (μm/m)/K. Therefore, to scale the accuracy of the dimensional metrology across 20 °C to the triple-point of water requires that the thermal expansion coefficient of fused quartz glass is known within 10 (nm/m)/K, or 2.5 %. A method is described to measure the thermal expansion coefficient of fused quartz glass. The measurement principle is to monitor the change in resonance frequency of a Fabry–Perot cavity as its temperature changes; the Fabry–Perot cavity is made from fused quartz glass. The standard uncertainty in the measurement was less than 0.6 (nm/m)/K, or 0.15 %. The limit on performance is arguably uncertainty in the reflection phase-shift temperature dependence, because neither thermooptic nor thermal expansion coefficients of thinfilm coatings are reliably known. However, several other uncertainty contributors are at the same level of magnitude, and so any improvement in performance would entail significant effort. Furthermore, measurements of three different samples revealed that material inhomogeneity leads to differences in the effective thermal expansion coefficient of fused quartz; inhomogeneity in thermal expansion among samples is 24 times larger than the measurement uncertainty in a single sample.
A calibration technique was developed to predict nickel plating thickness of a manufactured part. The technique was used to replace a destructive scanning electron microscope (SEM) measurement, with a nondestructive X-ray fluorescence (XRF) measurement. The XRF measurement was used to screen suspect parts from a rejected lot, and to replace lot-by-lot sampling with screening for ongoing product acceptance. The key to this approach was calibration and quantification of prediction uncertainty. Guardbanding, based on prediction uncertainty, was used to minimize the probability of accepting defective product. A significant number of suspect parts from a rejected lot were screened and deemed acceptable for use in next assembly with minimal risk.
Increasing regulatory pressure is being placed on the environmental storage conditions of perishable products during manufacture, storage, and transportation. These requirements are established by, the Food and Drug Administration (FDA), Center for Disease Control and Prevention (CDC), Code of Federal Regulations (CFR), United States Pharmacopoeia (USP), American Association of Tissue Banks (AATB), as well as other US and non-US counterparts. Compliance with agency regulations may be reactive or proactive. A reactive response would follow the proper and accurate monitoring methodologies and only occurs after an alert or other notification. In contrast, proactive compliance would employ data analytics that provides the user with methods by which monitoring and management of the collected storage data may be accomplished. These methods would show strengths and weaknesses in monitoring and managing overall compliance, thus allowing the user to focus on addressing any potential liability and preventing loss due to non-compliance. Critical-temperature monitoring drives the requirement for thermal buffering. The lack of specification associated with the guidance to this practice leaves the size, material, and geometry up to the user's discretion. This practice results in errors in representing the temperature of the contents and will, at a point, lead to improper notification alerts. These shortcomings and inaccuracies are overcome using Virtual Temperature Buffering™ (VTB). VTB is a mathematical algorithm that operates on air temperature. This highly accurate model preserves the air temperature while computing the buffered temperature in real-time. The measurement and recording of the air temperature are accomplished per the CDC guidance [1] by placing the measurement probe in the center of the storage unit. The buffered temperature value may be calculated for any volume and geometry desired. If desired, the air temperature will be available for post-process for a specific geometry.
The test uncertainty ratio (TUR) is often used to ensure false-accept risk is minimal for a given measurement. The commonly used guidance requires either a TUR greater than 4, or appropriate guardbanding, to result in a global false-accept probability of less than 2 %. However, this guidance assumes the distribution of units under test is centered between the tolerance limits and fails to achieve 2 % false accept probability when the product distribution is shifted toward one of the limits. A new guardbanding calculation is proposed that accounts for this potential bias in the product distribution. This guardband method may be applied when no assumptions should be made, and no information is available about the bias of the product distribution and works to ensure a 2 % or lower false accept probability for all TURs (including TURs greater than 4) in the presence of modest product bias.
This paper presents the ultrasonic flaw detectors calibration system at Standards and Calibration Laboratory (SCL) developed in accordance with the Group 2 tests of ISO 22232-1:2020. The calibration system contains a delay-pulse generator, a function generator, an amplifier, an oscilloscope and a set of tunable attenuators. The measurement setup, model and uncertainty components for each tests are presented. The difference in test parameters from the preceding international standard EN 12668-1:2010 are also reviewed and compared.
The Standards and Calibration Laboratory (SCL) in Hong Kong has developed a system for calibration of quarter-inch working standard (WS3) microphones which automates the measurement process and generates digital calibration certificates (DCC) to meet the growing demand for microphone calibration services in Hong Kong. This paper describes (i) the method of determining the pressure sensitivity of a microphone combination unit from 20 Hz to 20 kHz by the comparison technique in accordance with the International Standard IEC 61094-5, (ii) the measurement model and uncertainty evaluation, and (iii) the automatic system which facilitates the calibration process and generation of a digital calibration certificate.
This paper presents the ultrasonic flaw detectors calibration system at Standards and Calibration Laboratory (SCL) developed in accordance with the Group 2 tests of ISO 22232-1:2020. The calibration system contains a delay-pulse generator, a function generator, an amplifier, an oscilloscope and a set of tunable attenuators. The measurement setup, model and uncertainty components for each tests are presented. The difference in test parameters from the preceding international standard EN 12668-1:2010 are also reviewed and compared.
According to documentary standards for the performance evaluation of Laser Trackers (LT), long length reference artifacts are required. In this paper, we discuss the design, construction, and calibration of a long length artifact called step gauge of nests (SGN). The SGN has several nests in line to place the LT probe; the two extreme nests of the SGN are at a distance of 3 m approximately. The documentary standard establishes that the gauge's length must be known no matter the orientations it takes. However, for long gauges, factors like gravitational force, fixturing forces, change in the environmental conditions, among others, deforms the gauge, and its length changes when its orientation changes. To evaluate these factors, in the design stage, we use a finite element simulation of the SGN to predict such deformations (mainly length variations between the two extreme nests). The simulation takes into account the used material, its stiffness, straightness, distribution of the nest's weight, and geometry's change of the SGN to reduce the variations in its length. For the construction stage, we describe how the SGN was manufactured and how using high module carbon fiber, we reduce the influence of the temperature factor. The results of the finite element simulation show a length variation of around 20 ppm between the horizontal and vertical SGN positions. That variation was validated with the calibration results using two different methods. The first uses the line of sight (LOS) method, which involves the same LT under evaluation. The second uses an accurate CMM, using the overlap method for calibration. The traceability of the LOS method is accomplished with the wavelength calibration of the LT interferometer; meanwhile, the overlap method uses a CMM evaluated with a laser interferometer with calibrated wavelength.
The physical model of the spectral responsivity of trap detectors consists of multiple parameters such as the internal quantum efficiency and the spectral reflectance. In some measurement models, the spectral reflectance of trap detectors is approximated by fitting a wavelength dependence equation which does not consider the effect of the oxide thickness of the silicon photodiode. To analyze the uncertainty due to the oxide thickness variation, a thin film reflectance model is set up in the Standards and Calibration Laboratory (SCL) for the evaluation of the spectral reflectance of trap detectors. The model is based on the Fresnel coefficients of a three-layer thin-film structure which consists of air and a thin-film oxide layer on a silicon substrate. The reflectance model was implemented as user-defined functions to calculate the spectral reflectance at different oxide thicknesses. It was also integrated with the SCL’s MCM program to evaluate the uncertainty of the spectral responsivity of trap detectors.
Fluke Calibration is accredited for gas flow measurements in the range of 0.1 sccm to 6000 slm in nitrogen and air. Traceability is maintained directly through a gravimetric f low standard but only recently from 1 sccm to 10 sccm. The traceability of flow in the range of 0.1 sccm to 1 sccm is based on extrapolation of the use of laminar flow elements (LFE) below 1 sccm. This part of the range has never been completely verified through interlaboratory comparisons, proficiency testing or other means of measurement assurance. In an internal document from DH Instruments in the early 1990s it was suggested that a piston gauge might improve traceability for very low gas flows. In order to prove out traceability in this range an attempt was made to use a piston gauge using a piston-cylinder size of 35 mm diameter as a reference. One reason for choosing a piston gauge as a reference is its pressure control. This is crucial when measuring gas flow through a LFE in this design and range. In addition, the effective area is known to within 0.001 %, leaving the vertical displacement of the piston to dominate the uncertainty of the dimensional part of the flow test. This was a challenge because the measurements required absolute mode and the internal piston position sensor supplied with the piston gauge did not have sufficient precision. This paper describes the theory and design of the gas flow measurement system, the current results, and improvements desired or suggested. Two different designs are discussed, one with a single piston gauge as a reference and one with two piston gauges measuring flow on either side of the laminar flow element. Note: sccm (standard cubic centimeters per minute) is an industry accepted alternative to kg/s [1]. It is used out of convenience to normalize flow rates of gases with significant differences in density.
Facilitating the uptake of established methodologies for risk-based decision-making in product conformity assessment taking into account measurement uncertainty by providing dedicated software is the aim of the European project EMPIR CASoft(2018–2020), involving the National Measurement Institutes from France, Sweden and the UK, and industrial partner Trescal (FR) as primary supporter. The freely available software helps end-users perform the required risk calculations in accordance with current practice and regulations and extends that current practice to include bivariate cases. The software is also aimed at supporting testing and calibration laboratories in the application of the latest version of the ISO/IEC 17025:2017 standard, which requires that“…the laboratory shall document the decision rule employed, taking into account the level of risk […] associated with the decision rule and apply the decision rule.” Initial experiences following launch of the new software in Spring 2020 are reported.
In this article, probabilities are described for decisions that can be made from medical tests to determine whether a patient is sick or not. Methods for constructing and combining these probabilities are also applicable to tests in other areas where binary decisions of this kind are made. To provide a basis for discussion, we focus on testing for the presence or absence of a given hypothetical illness infecting a specified population, such as a community, age group, medical history or other relevant grouping.
This paper details the development of an automated procedure to conduct calibrations of power supplies at Jet Propulsion Laboratory, California Institute of Technology (JPL). The fundamentals of power supply calibrations are given, and discussion on the method by which this custom software handles that calibration. Additionally, this technique provides real time uncertainty quantification of the calibrations. This automated system has demonstrated a time savings over existing automated techniques in use today.
This paper presents a t wo-dimensional 10 x 10 LED array system developed in-house at t he Standards and Calibration Laboratory (SCL) for the calibration of timing parameters of still image cameras and video cameras. In this paper, the circuit design and the calibration methods for cameras of different shutter types (rolling shutter or global shutter) are presented. This LED array may also be used to verify the shutter type of cameras. The frequency of the clock signal applied in the calibration is traceable to the SI through the cesium beam frequency standard maintained at SCL.
Whether calibrating equipment or inspecting products on the factory floor, metrology requires many complicated statistical calculations to achieve a full understanding and evaluation of measurement uncertainty and quality. In order to assist its workforce in performing these calculations in a consistent and rigorous way, the Primary Standards Lab at Sandia National Laboratories (SNL) has developed a free and open-source software package for computing various metrology calculations from uncertainty propagation to risk analysis. In addition to propagating uncertainty through a measurement model using the well-known Guide to Expression of Uncertainty in Measurement or Monte Carlo approaches, evaluating the individual Type A and Type B uncertainty components that go into the measurement model often requires other statistical methods such as analysis of variance or determining uncertainty in a fitted curve. Once the uncertainty in a measurement has been calculated, it is usually evaluated from a risk perspective to ensure the measurement is suitable for making a particular conformance decision. SNL’s software can perform all these calculations in a single application via an easy-to-use graphical interface, where the different functions are integrated so the results of one calculation can be used as inputs to another calculation.
Where practicable, the total end-to-end test-and-calibration program cost would serve as the ultimate measurement quality metric (MQM). Total cost includes both the capitalization and ongoing costs that support product quality (sometimes called cost of quality) and the consequence costs (sometimes called cost of poor quality) that result from imperfect measurement and products. End-to-end means capturing costs from the entire traceability chain: from measurement standards to end products. Minimizing this MQM, total end-toend cost (TETEC), equates to optimizing measurement quality assurance (MQA). Lacking easily available measurement and performance data automatically fed to modeling software, organizations have found cost metrics unimaginable or impracticable, so their measurement programs instead target more easily computed MQMs, such as false-accept risk or simpler proxies thereof, setting minimum, but sub-optimal, quality levels. However, modern computing systems and software, such as laboratory management systems with testpoint- level traceability, rapidly approach the point at which the TETEC MQM will become practicable. Preparing for this eventuality, the NCSLI 173 Metrology Practices Committee has developed models that relate costs to measurement program information such as product specifications, test and measurement uncertainties, calibration intervals and reliability targets. Applications include optimizing overall program MQA, but also estimating the value of metrology and return on equipment investments, selecting instruments, designing test and calibration processes, designing products. This paper applies the cost models to case studies and examples to illustrate some applications.
There are two methods generally used for calibration of micropipettes: the gravimetric method described in ISO 8655-6:2002 and the photometric method described in ISO 8655-7:2005. In order to validate the photometric method, several micropipettes of different capacities from 0.1 µL to 1000 µL were calibrated using both methods (gravimetric and photometric) in two different laboratories, IPQ (Portuguese Institute for Quality) and Artel. These tests were performed by six different operators. The uncertainty for both methods was determined and it was verified that the uncertainty component that has a higher contribution to the final uncertainty budget depends on the volume delivered. In the photometric method for small volumes, the repeatability of the pipette is the largest uncertainty component, but for volumes, larger than 100 µL, the photometric instrument is the most significant source of uncertainty. Based on all the results obtained with this study, one may consider the photometric method validated.
Infrared ear thermometers allow users to measure body temperature quickly and non-invasively by inserting a probe into the patient’s ear canal. The effectiveness of tympanic ear thermometers is dependent on how accurate their measurement is. This prompts the demand for accurate and reliable calibration of ear thermometers. Developing capability and providing traceability to the health care facilities in South Africa have become crucial, as there is no calibration laboratory that provides such a service. A standard ear-thermometer black-body source system that is traceable to ITS-90 temperature has been constructed and assembled at the NMISA temperature laboratory. The ITS-90-traceable measurement system developed has a measuring capability of 40 mK (k=2) to 70 mK (k=2) in the temperature range of 35.5 °C to 41.5 °C. At the human body temperature of 37 °C an uncertainty of 45 mK (k=2) is achieved.
