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shield
A grounded covering device designed to protect a circuit or cable from electromagnetic
interference. Also see "guard".
SI System of Units
The accepted International System of Units. See also "units," "base units," and "derived
units."
specifications
A precise statement of the performance of a measurement or stimulus device.
square law
Defines the response of a device whose output is proportional to the squareof the applied
stimulus. Thermocouple-type transfer devices have a square-lawresponse.
stability
A measure of the freedom from drift relative to a reference value, over time and over
changes in other variables such as temperature. Note that stability is not the same as
uncertainty.
standard
A device that is used as an exact value for reference and comparison.
standard cell
A primary cell that serves as a standard of voltage. The term "standard cell" often refers
to a "Weston normal cell", which is a wet cell with a mercury anode, a cadmium mercury
amalgam cathode, and a cadmium sulfate solution as the electrolyte.
systematic error
Any error that remains constant or varies in a predictable manner as successive
measurements of the same quantity are made under effectively identical conditions. Note
that a known systematic error can be compensated for with a correction, whereas a
random error cannot. Also see "random error".
temperature coefficient
A factor used to calculate the change in indication or output of an instrument as a result
of changes in temperature. Changes in temperature contribute to instrument uncertainty
by an amount determined by the temperature coefficient.
test uncertainty ratio
The numerical ratio of the uncertainty of the measurement system or device being
calibrated or verified, and the uncertainty of the measurement system or reference device.
thermal emf
The voltage generated when two dissimilar metals joined together are heated.
traceability
The ability to relate individual measurement results to legally defined national standards
through an unbroken chain of comparisons. Traceability requires evidence produced on a
continuing basis, such as calibration records, that the measurement process is producing
results for which the total measurement uncertainty relative to national standards is
quantified.
transfer
See "ac-dc transfer."
transfer error
Error induced by the process of comparing one standard or instrument with another. This
does not include the uncertainty of the transfer standard.
Glossary of AC-DC Transfer Related Terms
Appendices
A
A-7
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