Track your unbroken chain to NIST

-January 02, 2013

Resistance/Capacitance/Inductance
At our local calibration house, standard resistors, capacitors, and inductors are used to calibrate the DMMs, RLC and capacitance meters. These standards are sent out to higher level labs for comparison of their stated values.  

A multifunction calibrator uses artifact calibration techniques, so a resistor with an accurate value is critical for setting the internal resistance. The same is true for multiproduct calibrators for inductance and capacitance. 

Temperature
The lab’s Fluke 80TK temperature probe is calibrated yearly at an external calibration lab with the Fluke 2190A temperature meter with the thermocouple indicator calibrator, Y2003.  To check the Fluke 2190A, a solution of distilled water and shaved ice bath is used to achieve 0o Celsius.  For the precision of a Fluke 80TK, this is adequate. In the past, my cal lab has used an Omega TRC III to provide an accurate 0o Celsius bath. At additional cost, the 80TK was sent to a lab using the Fluke/Hart Scientific 5612 with the 1502A and a dry well calibrator or Micro Bath. The + 0.004oC accuracy is overkill for the 80TK, but, it was a good doublecheck of the local lab. 

Conclusion
So, after all this research, the chart in Figure 2 could be generated, showing a link back to NIST for the equipment in the lab.  


Figure 2: The unbroken chains from NIST or physical properties to MSI's working equipment. (Click figure to download larger image as a PDF.)

At the top are the national standards for time and voltage.  Below that are the secondary standards used by the calibration labs. The next level is the transfer standards and finally the workload instruments.  An unbroken chain back to either NIST or intrinsic physical standards has been shown.   How does your lab stack up?

About the Author:
John Ambrose, vice president of applications and system engineering, joined Mixed Signal Integration in August of 1997 as applications and system engineering manager. He is responsible for giving technical assistance to customers using MSI's parts. In addition, he evaluates new design prototypes from a user's perspective. In 2008 he was promoted to vice president of applications and system engineering. 

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