Gas and liquid flow difficult? Get an understanding of the basic terms.
Process of experimentally obtaining one or more quantity values that can reasonably be attributed to a quantity. Measurement implies comparison of quantities or counting of entities. A measurement needs a calibrated measuring system operating according to the specified measurement procedure, including the measurement conditions.
The science of measurement and its application including all theoretical and practical aspects of measurement, whatever the measurement uncertainty and field of application.
Principle of measurement is a phenomenon serving as a basis of a measurement. The phenomenon can be of a physical, chemical, or biological nature.
Example 1 Thermoelectric effect applied to the measurement of temperature.
Example 2 Energy absorption applied to the measurement of amount-of-substance concentration.
Generic description of a logical organization of operations used in a measurement. Measurement methods may be qualified in various ways such as:
• substitution measurement method
• differential measurement method
• null measurement method
or
• direct measurement method, and
• indirect measurement method.
Detailed description of a measurement according to one or more measurement principles and to a given measurement method, based on a measurement model and including any calculation to obtain a measurement result. A measurement procedure is usually documented in sufficient detail to enable an operator to perform a measurement. A measurement procedure generally aims to get the same result when the circumstances are equal. A measurement procedure can include a statement concerning a target measurement uncertainty. A measurement procedure is sometimes called a standard operating procedure, abbreviated SOP.
Set of quantity values being attributed to a measurand (substance or object to be measured). Together with any other available relevant information. This requires knowledge of the kind of quantity, description of the state of the phenomenon, body, or substance carrying the quantity, including any relevant component, and the chemical entities involved.
A measurement result is generally expressed as a single measured quantity value and a measurement uncertainty. If the measurement uncertainty is considered to be negligible for some purpose, the measurement result may be expressed as a single measured quantity value. In many fields, this is the common way of expressing a measurement result.
Closeness between a measured quantity value and a true quantity value of a medium. The concept ‘measurement accuracy’ is not a quantity and is not given a numerical quantity value. A measurement is said to be more accurate when it offers a smaller measurement error. The term “measurement accuracy” should not be used for measurement trueness and the term “measurement precision” should not be used for ‘measurement accuracy’, which, however, is related to both these concepts. ‘Measurement accuracy’ is sometimes understood as closeness of agreement between measured quantity values that are being attributed to the measurand.
Measurement trueness is the opposite of the systematic measurement error (mathematically the inverted value). It is however not related to random measurement error. “Measurement trueness” is not the same as “measurement accuracy”.
Closeness between measurement values obtained by replicate measurements on the same or similar objects under specified conditions. Surprisingly, measurement precision is usually expressed by imprecision, such as standard deviation, variance, or coefficient of. Sometimes “measurement precision” is erroneously used to mean “measurement accuracy”.
The measured quantity minus a reference quantity (the amount too much or too less measured).
This is not the error of an instrument. It’s the error which occurs due to measurement circumstances or execution.
Example:
“The temperature measurement error was 10% or worse because the instrument wasn’t properly shielded from sunlight.”
It generally consists of 2 components: a systematic “measurement error” and a “random measurement error”. In day-to-day practice the measurement error is often not known, but assumed to be little or stable.
Measurement error is often defined in calibration facilities, where measurements are executed by means of a measurement standard.
An operation that establishes a relation between the quantity values (with measurement uncertainties) provided by measurement standards and corresponding indications (with associated measurement uncertainties).
The calibration uses this information to obtain a measurement result from an indication.
The result of a calibration may be expressed by a statement, calibration function, calibration diagram, calibration curve, or calibration table. In some cases, it may consist of an additive or multiplicative correction of the indication with associated measurement uncertainty.
[illustratie door diagram met k-factoren uit thermische flowmeting bij capilair meetinstrumenten, met onzekerheid daarbij]
Calibration should not be confused with adjustment of a measuring system, often mistakenly called “self-calibration”.
The amount of something that’s measured. Quantity value can have any physic entity, i.e.: speed, weight, flow.
Is a component of measurement error that in replicate measurements remains constant or varies in a predictable manner. The cause of a systematic measurement error is not always known, but because it remains constant, a correction can be applied to compensate for this error. Systematic measurement error equals “measurement error” minus “random measurement error”.
The systematic measurement error is not an error of the instrument, it’s only related to the procedure, execution or circumstances of a measurement.
Example:
The direction of gravity is not straight to the ground when measuring in the neighborhood of a large mass such as a mountain. A measurement uses an instrument that only measures gravity in the direction of the ground. This results in an error, the measured gravity is too low. This error is always the same and has nothing to do with the accuracy of the instrument. It’s a systematic measurement error.
A component of measurement error that in replicate measurements varies in an unpredictable manner. Random measurement error equals “measurement error” minus “systematic measurement” error.
A change over time in indication, due to changes in the properties of the instrument. It not related to a change in the quantity being measured. And it is not caused by a change in operating conditions.
A (more or less) constant deviation in reading with respect to a reference quantity value.
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