6.2 Production of Reference Materials
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the employment of highly qualified personnel. After the production, the RM must be
stored under appropriate conditions, and the manufacturer is also obliged to periodically check whether the reference value has not changed. A single batch of produced
material is often sold over many years, which significantly increases the cost of the
individual package and extends the amortization periods for investment.
It is also important to know how different RMs are certified by individual manufacturers. For CRMs, the reference value can be determined in different ways, for
example:
– Assigning a value a priori (by formulation);
– Assigning a value derived as a result of interlaboratory comparisons;
– Using primary or reference measurement procedure.
In any case, the reference value should be accompanied with a corresponding
uncertainty. It is also important to consider how close the certified value meets the
requirements described in the definition of measurement traceability. Where it is
possible to set the value with the primary method, the measurement traceability is
ensured with the clearly described measurement procedure. In other cases, measurement traceability is related to the conventionally accepted values for which it is not
always possible to refer to the standard of a higher order.
6.3 Types of Reference Materials
RMs can be divided according to their position in the metrological hierarchy. It should
be noted that the position of the given material within the level in this hierarchy does
not relate directly to their usefulness and quality. The hierarchy of metrological patterns is considered for the allocation of their reference value and assigned uncertainty.
The metrological quality of the standard/reference material must always be selected
for a given purpose and justified both logically and economically.
Primal measuring standard is a standard that has the highest metrological quality and whose value is accepted without reference to other higher standards of a
given quantity. By contrast, the secondary measuring standard is one whose value is
determined by comparison with the primal standard of a given quantity.
In the measurements of physical quantities, the most common primary standard is
associated with the respective natural phenomena. For example, the primary standard
for time is the second defined by fixed numerical value of the cesium frequency Δν Cs ,
the unperturbed ground-state hyperfine transition frequency of the cesium 133 atom,
as 9,192,631,770 when expressed in the unit Hz, which is equal to s
−1 . The realization
of this unit is carried out by the respective laboratory at BIPM and selected NMIs.
In the measurement of the chemical quantity, primary RMs, the highest in the
metrological hierarchy, are materials whose properties are determined by definitive
methods (also called primary methods). Primary RMs produced by NMIs are traced to
SI units and are assigned an uncertainty in accordance with the procedure described in
71
the employment of highly qualified personnel. After the production, the RM must be
stored under appropriate conditions, and the manufacturer is also obliged to periodically check whether the reference value has not changed. A single batch of produced
material is often sold over many years, which significantly increases the cost of the
individual package and extends the amortization periods for investment.
It is also important to know how different RMs are certified by individual manufacturers. For CRMs, the reference value can be determined in different ways, for
example:
– Assigning a value a priori (by formulation);
– Assigning a value derived as a result of interlaboratory comparisons;
– Using primary or reference measurement procedure.
In any case, the reference value should be accompanied with a corresponding
uncertainty. It is also important to consider how close the certified value meets the
requirements described in the definition of measurement traceability. Where it is
possible to set the value with the primary method, the measurement traceability is
ensured with the clearly described measurement procedure. In other cases, measurement traceability is related to the conventionally accepted values for which it is not
always possible to refer to the standard of a higher order.
6.3 Types of Reference Materials
RMs can be divided according to their position in the metrological hierarchy. It should
be noted that the position of the given material within the level in this hierarchy does
not relate directly to their usefulness and quality. The hierarchy of metrological patterns is considered for the allocation of their reference value and assigned uncertainty.
The metrological quality of the standard/reference material must always be selected
for a given purpose and justified both logically and economically.
Primal measuring standard is a standard that has the highest metrological quality and whose value is accepted without reference to other higher standards of a
given quantity. By contrast, the secondary measuring standard is one whose value is
determined by comparison with the primal standard of a given quantity.
In the measurements of physical quantities, the most common primary standard is
associated with the respective natural phenomena. For example, the primary standard
for time is the second defined by fixed numerical value of the cesium frequency Δν Cs ,
the unperturbed ground-state hyperfine transition frequency of the cesium 133 atom,
as 9,192,631,770 when expressed in the unit Hz, which is equal to s
−1 . The realization
of this unit is carried out by the respective laboratory at BIPM and selected NMIs.
In the measurement of the chemical quantity, primary RMs, the highest in the
metrological hierarchy, are materials whose properties are determined by definitive
methods (also called primary methods). Primary RMs produced by NMIs are traced to
SI units and are assigned an uncertainty in accordance with the procedure described in