The Role of Metrology Laboratory

3.16.
There is a need for exacting methods, procedures and equipment for verifying the various
dimensional elements of the gauges. The accuracy of the measuring and test equipment can be
controlled only by establishing and maintaining a calibration system. The calibration system
available in metrology laboratory should be coordinated with the Inspection or Quality control
systems and be designed to provide adequate accuracy in use of measuring and test equipment. The
calibration system should also provide for the prevention of inaccuracy by ready detection of
deficiencies and timely positive action for their correction. It is essential that the written description
of the calibration system covering measuring and test equipment and measurement standards are
properly documented and maintained. All measurements should be traceable to National Stand-
ards. For meeting all these objectives the need of an independent metrology laboratory in industry
is justified.
The independent metrology laboratory is designed to’ furnish to the end user (i) traceability
of measurement, (ii) proper environment, (Hi) appropriate measuring equipment, and (iv) standard
measuring procedures consistent to the state of the art.
The standards established for calibrating the measuring equipment used in controlling
product quality should have the capabilities for accuracy, stability and range required for the
intended use.
Environment controls for measuring and test equipment and gauges should be calibrated in
an environment controlled to the extent necessary to assure continued measurements of required
accuracy giving due consideration to temperature, humidity, vibration, cleanliness and other
controllable factors affecting precision measurement.
The ideal environmental conditions in metrology laboratory for dimensional measurements
of reference standards are;
Temperature 20°C ± 0.3°C
Temperature rate of change Less than 0.5°C per hour
Relative humidity 35%—55%
(constant within 2% around a regulated point)
Dust (particle count) Less than 3.3 x 105 parts per m3 over 1.0 micron, and
less than 16.5 x 104 parts per m3 over 0.5 microns.
Vibration 0.001 g
(The instrument mount must provide such stability that
readings can be consistently obtained to an accuracy of at
least the value indicated for each unit)
Lighting (at bench level) 100 ft candles
Acoustic noise 50 db max.
The measuring equipment required in metrology laboratory depends on the requirements ;
however the following minimum equipment must be provided.
Gauge blocks of grades AAA and AA
Gauge block measuring machines
Basic measuring machine
Thread measuring wires
Gear measuring wires
Internal measuring machines
Optical projector
Lead testing machine
Master thread setting plug gauges
Surface plates
Indicator tester
Master sequare
Digital height gauges
Co-ordinate measuring machine
Electronic amplifiers, etc.
The laboratory should maintain a set of standard procedures showing the equipment
required to calibrate, control requirements, a step by step procedure on how to make the actual
calibration and disposition of gauges.
The laboratory should furnish a test report for each gauge calibrated showing measurable
or visual condition. The report should also tell the user the actual measurement or master size. The
report should also reflect temperature, masters used, etc.