An example of a primary standard is the international prototypekilogram (IPK) which is the master kilogram and the primary mass standard for the International System of Units (SI). The IPK is a one kilogram mass of a platinum-iridium alloy maintained by the International Bureau of Weights and Measures in France.
Another example is the unit of electrical potential, the volt. Formerly it was defined in terms of standard cell electrochemical batteries, which limited the stability and precision of the definition. Currently the volt is defined in terms of the output of a Josephsonjunction, which bears a direct relationship to fundamental physical constants.
In contrast, the reference standard for the meter is no longer defined by a physical object. In 1983, the standard meter was redefined as the distance which light travels in a vacuum during 1/299,792,458 of a second.
Secondary reference standards
Secondary reference standards are very close approximations of primary reference standards. For example, major national measuring laboratories such as the US's National Institute of Standards andTechnology (NIST) will hold a national standard kilogram, which is periodically calibrated against the IPK.
Working standards
Although the SI definition of the «meter» is based on a laboratory procedure combining the speed of light and the duration of a second, a machine shop will have a physical working standard (gauge blocks for example) that is used for checking its measuring instruments. Working standards and certified reference materials used in commerce and industry have a traceable relationship to the secondary and primary standards.
Ex. 2. Answer the following questions
1. What is standard?
2. What types of standard do you know?
3. What is working standard?
4. What is the advantage of the elimination of artifacts?
5. What is IPK?
Ex. 3. Are these sentences true or false?
1. Gauge blocks are used as a wo rking standard to check the calibration of measurement tools such as micrometers.
2. The unit of magnetic potential is the volt.
3. Today the unit of electrical potential is determined in terms of standard cell electrochemical batteries.
4. In the science of measurement, a standard is an object, system, or experiment that bears a defined relationship to a unit of measurement of any quantity.