The Importance of Thorough Calibration
Two case studies, two different situations,
one conclusion
Introduction
There is considerable debate as to whether the extent and quality
of testing carried out during an instrument calibration makes a difference
to the bottom-line of the company that owns the instrument. It is
quite difficult to find case studies in which it can be conclusively
shown that a less thorough testing routine has a direct impact on
the quality of the products being tested.
The following examples help to illustrate that inadequate testing
during calibration can lead to erroneous decisions in the production
test area. Coincidentally, they both took place in the same week,
in the same Agilent Service Center.
Case Study 1
Company A is the leading manufacturer of electronic countermeasures
equipment and other secure communications products. Their usual
calibration provider is a large, low-cost Third Party Maintainer
(TPM) in the UK.
Suspecting a problem with the marker counter readout accuracy,
they sent their 8594E Portable Spectrum Analyzer to the TPM advising
of their suspicions. The equipment was returned to them having been
"fully" calibrated, with no fault found (the instrument
was reported to be entirely within specification). Still suspecting
the problem they sent it back, and again it was calibrated and reported
to be in-spec.
The Analyzer was then sent to Agilent, with the same fault suspected.
It was put into the Agilent calibration process and the error was
clearly identified. It was corrected with appropriate adjustments
to the log/lin amplifier and returned to the customer within specification.
Obviously the TPM had not tested that part of the instrument --
particularly unsatisfactory considering they were told of a suspected
problem in that area. The customer is now confident that his instrument
is giving trustworthy information... but now has doubts about the
other equipment he has calibrated by the TPM.
Case Study 2
Company B is a global electronics company serving Aerospace,
Defense,
and Information Technology markets worldwide. The company uses a
major (different) TPM for calibration.
They sent a 11683A Power-meter Range Calibrator to the TPM for
routine calibration. The device was found to be outside specification
on two ranges and a "Conditional" calibration certificate
was issued. The customer knew his equipment well and was in total
disbelief that it was out-of-tolerance. He sent it to Agilent for
a second opinion.
It was tested manually while cold and after being warmed-up. On
both occasions the measured values were found to be lie in the middle
of the specification on all ranges. The conclusion is that the TPM
may have been using an intermittent cable or some other poor technique
that produced erroneous test results on some ranges. The customer
has his confidence restored in his Range Calibrator... but not in
his TPM calibration provider.
Conclusions
The two situations were opposite: one instrument was faulty but
reported to be good and the other was good but reported to be faulty.
In both cases the customer could have incurred significant costs
had he not chosen to ask Agilent for a second opinion. Agilent's
high quality, thorough calibration procedures correctly established
the performance characteristics of the equipment and restored confidence
to the customer. Proof beyond doubt that all calibration is not
equal !
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