Traceability in Accelerometer Calibration

In both life and business we are often looking to sort out our relationships by an estimate of integrity.  We want vendors who price fairly and deliver on their promises… We want friends who are of good character and who will stick by us both in up times and in down times… And we continually assess our view of integrity through our interactions each day.  In the calibration world, integrity hinges on a proven/repeatable process (through following procedures with diligence and documented uncertainty calculations) and by measurement traceability, which is each measurement component's chain or link to a national standard or physical constant. 

In the world of vibration calibration there are some major components of the measurement system that require accurate, annual, traceable calibration.  These include major components like the data acquisition system (either DSA in modern systems or meter based in older systems), the reference and sensor-under-test (SUT) signal conditioning, and the vibration reference transducer itself.  The units are the backbone of the integrity of a vibration calibration system and typically undergo daily system validation with a known vibration sensor in addition to receiving rigorous environmental (both handling and environment) control, as well as annual component recalibration.

When it comes time for the traceable recalibration, there are basically four options for traceable calibration.  First is your in-house metrology department, if capable, though most companies are not set up to calibrate references.  Second is the original equipment manufacturer (OEM) of the reference component (or a competitive manufacturer with suitable capability).  Third is the availability of a regional calibration laboratory service provider in your area; and finally, a recognized national lab such as NIST, PTB, NPL, etc.

Regardless of your choice above, you’ll want assurance of quality in your vendor.  This is accomplished through:

1. Discuss/understand and ask who has audited their quality system / procedures.
2. Ask what the relevant standards are (ISO 17025) and if they are accredited by an independent competent body ( A2LA).  The vendor should understand and be able to describe to you  17025 and 16063-21 in terms that you can understand.
3. Ask what type of equipment they are using.  Older meter based sine methods or Modern FFT/DSA methods?  How is their reference sensor calibrated?  Secondary?  Primary?  This will affect their uncertainties which will be transferred to you and should be evaluated against your particular testing requirements.
4. What is their real business focus?  A shaker company?  A meter company? A sensor and system company?  Are they actively developing or following state-of-the-art in vibration calibration?
5. Do they participate in relevant industry conferences like NSCL, MSC or IMEKO?  Do they participate in a global standards process like TC 108 S3 and are they developing the sections in ISO 16063?
6. What is the reputation of the service provider?  How long have they been around and what customer references can they provide?  Ask the references about the service provider's commitment to integrity and customer service.

Some vendors will also offer calibration/traceability tracking services for periodic recalibration helping to ensure your quality and integrity.

In the end your vendor choice should be based on knowledge and trust.  Research your vendor's integrity to ensure the right start to yours.  Choosing the right calibration partner is vital and should be based on capability, experience, accuracy and service.