A common question when it comes to the calibration of instruments is what is the difference between traceable and accredited calibrations.  Understanding the differences between the two will help a lab determine what their products require and making sure that the calibration needs are met.

What is a NIST Traceable Calibration?

A National Institute of Standards and Technology (NIST) traceable calibration is when a manufacturer or calibration laboratory can certify that the standards used to calibrate a device are traceable to the International Systems of Units (SI).  Through an unbroken chain of comparable measurements to the NIST. Traceability recognizes that metrological traceability can be to SI through any recognized national metrology institute.  This type of calibration does not indicate or determine the level of competence of the staff and laboratory that performs the calibrations.  It mainly identifies that the standard used in the calibration is traceable to NIST or another recognized metrology institute (RMI).

What is an ISO/IEC 17025 Accredited Calibration?

It is important to note that an ISO/IEC 17025 accredited calibration is recognized internationally.  ISO 17025 is a statement to the competence of the calibration laboratory.  The standard specifically accesses factors relevant to a laboratory’s ability to produce precise, accurate test and calibration data.  This data includes several types.  Traceability of measurements and calibrations to national standards.  The quality assurance of test and calibration data.  Maintenance of test equipment.  The validity and appropriateness of test methods.  The technical competence of staff.  The appropriate handling and transportation of test items.  Quality of testing environment and sampling.

The ISO/IEC accredited calibration is considered to be a step above the NIST calibration.  This is because of the discipline of calibration is reviewed in addition to the traceability of the standards.  It also not only includes the measurement of traceability, but it also includes the measurement of uncertainties of the calibration results.

How to Choose Between the Two

The choice determination is normally by the maintenance/service personnel at a company.  They can also make the decision depending on how the equipment that requires periodic calibration usage.  An example is in a lab that is using the equipment for critical applications and there could be a risk of liability.  The ISO/IEC 17025 calibration may be the better choice.  If they use the piece of equipment for more reference purposes in a low-risk setting and the measurement just needs to be close enough, an NIST traceable calibration can be adequate.

Applications and Industries That Use Critical Measurements

There are applications and industries that consistently require critical measurements and in these situations, ISO/IEC 17025 calibration must be used.  These critical measurements utilize instruments such as barometers for barometric pressure in airplanes, medical and automotive industries, temperature with portable multifunction calibrators in the natural gas and power industries and electrical calibrations with the use of multimeters to check voltage, current, millivolts, and resistance in the hydro, oil & gas and water/wastewater industries. Pharmaceutical laboratories also require very accurate measurements.

Applications and Industries that Utilize Low-Risk Measurement Devices

While all industries want accurate measurements, there is room for play within low-risk measurement devices.  Some examples where NIST calibration is good for these non-critical devices are process gauges that indicate good or bad.  Also pressure switches and pressure gauges used for air compressors.

Help Determine Which Calibration Fits Your Needs

It is up to the individual business and the needs that are required in their industry to determine if the NIST traceable calibration or the ISO/IEC 17025 calibration is the best choice.  However, if you are unsure about what is best for your specific device and needs, we can help you.  SRP has been helping provide calibration solutions for over 40 years.  We can help you choose the best calibration solution to fit your needs with our on-site laboratory.