E1C01 09/14/2010
15:40:35 Page 28
A chart for converting between units is included inside the text cover. Table 1.2 lists the basic
standard and some derived units used in SI and the corresponding units used in the I-P and
gravitational metric systems.
Hierarchy of Standards
The known value applied to a measurement system during calibration becomes the standard on
which the calibration is based. So how do we pick this standard, and how good is it? Obviously,
actual primary standards are impractical as standards for normal calibration use. But they serve as a
reference for exactness. It would not be reasonable to travel to France to calibrate an ordinary
laboratory scale using the primary standard for mass (nor would it likely be permitted!). So for
practical reasons, there exists a hierarchy of reference and secondary standards used to duplicate the
primary standards. Just below the primary standard in terms of absolute accuracy are the national
reference standards maintained by designated standards laboratories throughout the world. These
provide a reasonable duplication of the primary standard but allow for worldwide access to an
extremely accurate standard. Next to these, we develop transfer standards. These are used to
calibrate individual laboratory standards that might be used at various facilities within a country.
Laboratory standards serve to calibrate working standards. Working standards are used to calibrate
everyday devices used in manufacturing and research facilities. In the United States, NIST
maintains primary, reference, and secondary standards and recommends standard procedures for
the calibration of measurement systems.
Table 1.2 Dimensions and Units
a
Dimension
Unit
SI
I-P
Primary
Length
meter (m)
inch (in.)
Mass
kilogram (kg)
pound-mass (lb m )
Time
second (s)
second (s)
Temperature
kelvin (K)
rankine (
R)
Current
ampere (A)
ampere (A)
Substance
mole (mol)
mole (mol)
Light intensity
candela (cd)
candela (cd)
Derived
Force
newton (N)
pound-force (lb)
Voltage
volt (V)
volt (V)
Resistance
ohm (V)
ohm (V)
Capacitance
farad (F)
farad (F)
Inductance
henry (H)
henry (H)
Stress, pressure
pascal (Pa)
pound-force/inch
2 (psi)
Energy
joule (J)
foot pound-force (ft-lb)
Power
watt (W)
foot pound-force/second (ft-lb/s)
a SI dimensions and units are the international standards. I-P units are presented for
convenience.
28 Chapter 1 Basic Concepts of Measurement Methods
15:40:35 Page 28
A chart for converting between units is included inside the text cover. Table 1.2 lists the basic
standard and some derived units used in SI and the corresponding units used in the I-P and
gravitational metric systems.
Hierarchy of Standards
The known value applied to a measurement system during calibration becomes the standard on
which the calibration is based. So how do we pick this standard, and how good is it? Obviously,
actual primary standards are impractical as standards for normal calibration use. But they serve as a
reference for exactness. It would not be reasonable to travel to France to calibrate an ordinary
laboratory scale using the primary standard for mass (nor would it likely be permitted!). So for
practical reasons, there exists a hierarchy of reference and secondary standards used to duplicate the
primary standards. Just below the primary standard in terms of absolute accuracy are the national
reference standards maintained by designated standards laboratories throughout the world. These
provide a reasonable duplication of the primary standard but allow for worldwide access to an
extremely accurate standard. Next to these, we develop transfer standards. These are used to
calibrate individual laboratory standards that might be used at various facilities within a country.
Laboratory standards serve to calibrate working standards. Working standards are used to calibrate
everyday devices used in manufacturing and research facilities. In the United States, NIST
maintains primary, reference, and secondary standards and recommends standard procedures for
the calibration of measurement systems.
Table 1.2 Dimensions and Units
a
Dimension
Unit
SI
I-P
Primary
Length
meter (m)
inch (in.)
Mass
kilogram (kg)
pound-mass (lb m )
Time
second (s)
second (s)
Temperature
kelvin (K)
rankine (
R)
Current
ampere (A)
ampere (A)
Substance
mole (mol)
mole (mol)
Light intensity
candela (cd)
candela (cd)
Derived
Force
newton (N)
pound-force (lb)
Voltage
volt (V)
volt (V)
Resistance
ohm (V)
ohm (V)
Capacitance
farad (F)
farad (F)
Inductance
henry (H)
henry (H)
Stress, pressure
pascal (Pa)
pound-force/inch
2 (psi)
Energy
joule (J)
foot pound-force (ft-lb)
Power
watt (W)
foot pound-force/second (ft-lb/s)
a SI dimensions and units are the international standards. I-P units are presented for
convenience.
28 Chapter 1 Basic Concepts of Measurement Methods