Calibration

STANDARD

NIST. Each instrument calibrated (including standards)

must bear evidence that it is in calibration. This evidence

A standard is a laboratory-type device that is used

is in the form of a calibration label affixed to the

to maintain continuity of value in the units of measure-

instrument. This label provides the date and place of

ment. Its accuracy is ensured through periodic com-

calibration and the next due date for calibration. The

parison with higher echelon or national standards. A

METCAL program provides for periodic calibration of

standard may be used either to calibrate a standard of

most instruments. The responsibility for assignment of

lesser accuracy or to calibrate test and measurement

these periodic calibration intervals has been given to the

equipment directly.

Metrology Engineering Center (MEC).

The calibration of all measuring devices is based on,

TRACEABILITY

and is dependent upon, the basic international and

national standards of measurement. Since we cannot

Traceability is the unbroken chain of properly

rush off to the NIST every time we need to measure a

conducted and documented calibration of equipment

length, a mass, a weight, or an interval of time, the NIST

from the fleet through higher echelons to the National

prepares and issues a great many practical standards that

Bureau of Standards (NBS).

can be used by government and industry to calibrate

their instruments. Government and industry, in turn,

TEST AND MONITORING SYSTEMS

prepare their own practical standards, which are

applicable to their own requirements. Thus, there is a

Test and monitoring systems (TAMS) are the

continuous linkage of measurement standards that

instruments used for all quantitative measurements

begins with the international standards, comes down

except metrology standards. TAMS can also be referred

through the national standards, and works all the way

to as precision measurement equipment (PME), test and

down to the rulers, weights, clocks, gauges, and other

measuring equipment (T&ME), or test, measuring, and

devices that we use for everyday measurement.

diagnostic equipment (TMDE).

For further information and detailed assignment of

the METCAL program, refer to NAVMAT Instruction

OPERABLE EQUIPMENT

4355.67.

Operable equipment is equipment that before being

submitted to calibration is found by review of its per-

CALIBRATION TERMS AND

formance history and by cursory electrical and physical

DEFINITIONS

examinations to be operational in all its required

Before proceeding, it is necessary for us to discuss

functions.

some of the commonly used terms associated with the

instrument calibration program used by the Navy. It is

INCIDENTAL REPAIRS

important that you understand the meaning of these

terms and use them correctly. Many of these terms will

Incidental repairs are those repairs found necessary

be used throughout this text. Other very important terms

during calibration of an operable equipment to bring it

are listed in the glossary, appendix II. Refer to it as often

within its specified tolerances. These include the

as necessary.

replacement of parts that, although worn sufficiently to

prevent calibration, do not otherwise render the

CALIBRATION

equipment inoperative. This repair work is normally

performed incidental to the calibration of standards.

Calibration is the act of comparing a measurement

system or device of unverified accuracy to a

TRACEABILITY OF STANDARDS

measurement system or device of known and greater

accuracy to detect and correct any variation from

The U.S. Department of Commerce, National

required performance specifications.

Institute of Standards and Technology, located at

The calibration process involves the use of

Gaithersburg, Maryland, is the focal point in the federal

government for maintaining and advancing standards

approved instrument calibration procedures (ICPs). It

includes any adjustments or incidental repairs that are

and technology for the physical and engineering

necessary to bring a standard or an instrument being

sciences. NIST provides the common reference for

Navy scientific measurements and certifies the

calibrated within specified limits.

4-2