Measurement is all around us – be it the distance to Grandma’s house, cloth length or transistor width on a computer chip – from measuring grandmas house distances and lengths, cloth length or transistor width on computer chips, cloth length measurements or any physical signals which must be converted into known quantities for comparison purposes. To measure something accurately we must differentiate its dimensions or frequencies and create a comparison signal of known quantity that can then be converted back into comparison signals that represent that object being measured.
Definitions
There are various technical terms related to meters and measurements that must be understood clearly and defined accurately, including accuracy, uncertainty, precision, and sensitivity. Though some of these have universally accepted definitions, others undergo constant change due to advances in technology. It is essential that users understand these definitions when selecting mass properties measurement instruments as well as when comparing instruments among themselves.
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- Temperature compensation refers to any correction applied to a pressure measurement instrument that reduces errors caused by temperature variations in either the media being measured or its surroundings. Also referred to as temperature compensation.
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- Repeatability refers to how closely an instrument’s indication matches up with what it measures – usually, measurand – which can be called its indication. Precision should not be mistaken for repeatability as precise devices may still produce consistently inaccurate results.
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- Nominal dimensions are written onto drawings or CAD models as nominal dimension values that will serve as comparison points against which any measured part can be measured. Nominal dimensions play an integral part in Geometric Dimensioning and Tolerancing, the system of symbols and language for defining acceptable limits (tolerances) within physical dimensions
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- The financial penalty imposed for minor offenses that do not warrant criminal prosecution is often paid directly to the Crown for tax purposes and is commonly known as amercement.
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- Maximum deviation from a specified value that can be expected under specific conditions typically expressed in terms of +/- percent of full-scale output or reading.
Units of Measurement
Units of measurement are standardized quantities used to express physical properties like length and weight. They often fall under a specific system of measurement such as the metric system or United States customary units; within such systems, they serve as standards against which other quantities may be measured and their values assessed.
- As early humans developed, units of measurement were first created to meet basic human needs such as building homes, fashioning clothing, and trading food and raw materials. With scientific advancement came an increased need to compare different traditional systems of measurement to advance knowledge; eventually this led to modern systems like the metric system, imperial system, and US customary system being established.
- Factors that influence the selection of physical units include size, availability, and convenience. For instance, the metric system uses grams, liters, and meters as its measurements of weight, volume, and distance respectively; its decimal system based on 10 units has become widely adopted worldwide; by contrast, imperial measurement systems employ inches, feet, and pounds instead.
- Standardized measurements play an essential role in both public safety and infrastructure, including road design. Engineers rely on units of measurement established by engineering professionals when creating road and highway networks. Furthermore, measurements help regulate commerce as well as inform policymaking on topics like industrial emissions, water consumption, and ecological effects.
- A unit of measurement refers to any specific kind of quantity; any other kind can be expressed as multiples of that unit, for instance, the length of a ruler can be measured by comparing it against known units like yardsticks.
- Many items are quoted and purchased in packaged quantities that specify both a minimum and multiple (min/mult) order quantity. For instance, surface mount resistors are often sold and stored in reels of 5,000 pieces; it would not be practical to create an entirely new unit of measurement such as “5,000-pc tape & reel” for this use – industry standards usually reference “each”.
Measurement Instruments
Measuring involves some interaction between an object or quantity to be measured and a measuring instrument, with its sensor converting physical input variables into signal variables that can then be transmitted to recording or other output devices. Voltage is often used as the signal variable in electrical circuits while displacement or force may be more appropriate in mechanical systems. Signal variables can either be physical (pressure, temperature, or vibration), electrical (current or power), or both (both may use physical measurements for measurements).
- An essential function of any measurement instrument is its capacity to record raw score data generated during its measurement procedure, either physically on paper or via computer memory storage. Furthermore, some recording systems include methods for physically transmitting this information elsewhere on Earth.
- An effective measurement instrument typically features the capability of calibrating its sensor output with the true value of an accepted standard reference value, known as calibration.
- Calibration is essential in maintaining accurate readings from its sensor; accuracy refers to how closely its readings match up with expected values – usually measured through repeatability and reproducibility measurements.
- An instrument designed for measurement will usually include specific properties in its design such as linearity and range of readings. Ideally, such instruments should produce output readings that resemble straight lines (or almost so). Non-linearity in instruments is an undesirable trait that can be measured using its sensitivity drift or zero/span drift measurements.
- Repeatability and reproducibility are also critical aspects of an instrument, which describes its output readings being consistent over time with similar input. To achieve this consistency, methods, observers, instruments, locations of use as well as stability should all be consistent and monitored using tools like an autograph or check weigher should all remain the same.
Measurement Uncertainty
Uncertainty associated with measured quantities is an integral component of metrology, defined as unknown and thus uncorrected random deviations from desired results. This includes errors associated with both measuring instruments as well as measurement processes themselves as well as factors that might alter measurement outcomes, such as environmental temperature or operator skill.
- Unfortunately, not everyone who needs medical help receives it on time and at an affordable price. The standard uncertainty of a measurement is an estimate derived by statistically weighting each component of uncertainty to create an average estimate, taking into account knowledge about input quantities gleaned through repeat measurements (“Type A evaluation of uncertainty”) or scientific judgment/information regarding possible values for that quantity (Type B evaluation of uncertainty).
- The combined standard uncertainty also referred to as an expanded uncertainty, consists of the sum of individual contribution terms’ standard uncertainties multiplied by their coverage factors – numerical values equaling the positive square root of the product of variances and covariances weighted according to how changes affect measurement result uncertainty. Coverage factors used to express measurement uncertainty can be calculated in various ways depending on the circumstances.
- They could range from simple numbers such as the mean of distribution, or they could use statistical confidence intervals like those commonly seen in statistics, commonly referred to as Z scores or Z values.
General best practice suggests selecting a coverage factor which encompasses 95% of values within the measurement uncertainty distribution, although this may not always be feasible due to resource restrictions and availability. A coverage factor can then be compared with its respective reference standard uncertainty value in BIPM Key Comparison Database in order to ensure it exceeds this reference value.
Though error and uncertainty are frequently used interchangeably, they have distinct definitions according to GUM, VIM, and other international guidance documents. A measurement error refers to any random variation from what would have been desired or expected value; while uncertainty estimates a range within which lies the true value of measurand. A +- or a sign after measurement results represents error while symbols after uncertainty statements represent coverage factors.