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Keysight Technologies
Getting The Calibration You Need
If your organization is like most technology companies, test
equipment is an important part of ensuring the quality and
performance of your end products. One of the fundamental values of
test equipment is the confidence you gain from the measurements--
and pass/fail decisions--they produce.
The source of that confidence is the specified accuracy of each
instrument, and the foundation of that accuracy is calibration.
Ultimately, the bedrock beneath that foundation is the service
provider you select to calibrate your instruments.
Application Note
A Practical Example
The concept of getting the calibration you need has real-world implications.
Recently, one of our customers shared its irst-hand experience with calibration
providers. The company was using a variety of Keysight Technologies, Inc.
equipment to verify speciic parameters and speciications in a range of end
products. At the time, they were relying on a third-party provider that had been
the lowest-cost bidder for calibration services.
As a wave of instrument calibrations came due, the company asked Keysight
to help interpret the trace reports that accompanied each instrument. Working
with the customer's quality team, our specialists helped identify the speciic
parameters that could actually be tested with the standards listed in the trace
report. The result: Several key specs either couldn't be tested or weren't being
tested. Consequently, the customer's technical staff performed additional audits
that revealed more problems.
In the aftermath, the customer switched to Keysight as its calibration provider.
As the original equipment manufacturer, Keysight is able to test more
parameters and more points, and perform adjustments that bring out-of-
alignment instruments back into spec. As a result, the customer is now receiving
calibration services that meet or exceed the level of quality it expects in its test
systems and end products.
A quick look at calibration
Calibration is the process of measuring the actual performance of an
instrument-under-test (IUT) using lab instruments that have significantly better
performance than the IUT. The performance of every lab instrument must
be traceable to International System (SI) units through a national metrology
institute such as NIST, NPL or BIPM.
Calibration involves more steps than you might imagine, and the overall process
is diagrammed in Figure 1. Performance tests compare the instrument's actual
performance to published (i.e., "data sheeted") specifications. In the ideal case,
the service provider will test the performance corresponding to all data-sheeted
specifications, for all installed options, every time. If the instrument passes all
tests, the process is concluded: The instrument is within specification and you
can use it with confidence.
Yes
Calibration starts here Repair starts here
Run performance No Run adjustments No Diagnose and
Pass? Pass?
tests tests order parts
Yes
Done Install new parts
Figure 1. Flow diagram for the calibration process, including repair (if needed).
If the instrument is observed to be out-of-specification, the ideal case is for
the service provider to perform adjustments and then re-test the instrument.
As shown in the diagram, the process either loops back and starts over or, for
an instrument that cannot be adjusted into spec, detours to the "hardware
repair" path. Repair begins with a diagnosis of the problem and the ordering
of necessary parts. Once the repair has been completed, adjustments are
performed and the calibration process loops back to the performance tests.
After the instrument passes all performance tests, it is once again ready to
make accurate measurements. To minimize turnaround time and manage cost,
the service provider should be able to perform adjustments and repairs in-house
(i.e., without sending the instrument to another service provider).
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Selecting a suitable service provider
Ensuring that you get the calibration you need has several important
dimensions. To help you map out your requirements, the rest of this paper
presents an approach that is illustrated in Figure 2. It starts with a three-step
process that will help highlight your most important calibration needs (first three
boxes in Figure 2). Next is a set of short checklists that will help you evaluate
potential service providers and select the one best-equipped to meet your
specific needs (yes/no loop in Figure 2).
No
Does Yes
Step 3: Define Assess service
Step 1: Identify Step 2: Identify vendor
essential records providers vs. your Done
key instruments key specifications meet your
& reports calibration needs needs?
Figure 2. Flow diagram of a process that will help ensure you get the right calibration for your needs.
Identifying needs and deining documentation
The starting point for getting the right calibration is identifying your most
important requirements. This has three steps:
1. Identify your key instruments
2. Identify the key specifications for each of those instruments
3. Define the types of records and reports you need to document the calibration
status of each important instrument and specification
Let's take a closer look at each of these.
Step 1: Identify key instruments
Every piece of test equipment was purchased for a reason: it may have been
an essential feature, capability, measurement, or specification. In most cases,
you can quickly identify the high-impact instruments your organization depends
on. Examples include high-performance RF or microwave instruments such as
signal analyzers, network analyzers, signal generators, sampling or real-time
oscilloscopes, and high-precision digital multimeters.
Step 2: Identify key speciications
Once you've identified the most important instruments it's time to pinpoint
the key specifications each one must meet to help ensure the success of
your enterprise. A good starting point is to compile a list of requirements for
each instrument. Examples include amplitude accuracy or displayed average
noise level in a signal analyzer, dynamic range or dynamic accuracy in a vector
network analyzer, and phase noise or adjacent-channel leakage-power ratio in
a signal generator. Next, identify the associated accuracy levels and tolerances
for each key specification. Whatever level of accuracy you need, and however
tight your tolerances may be, the instruments used for calibration must be even
better.
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Step 3: Deine essential records and reports
A record of the actual work performed is an essential part of the calibration
process--and your needs will depend on the customers you serve, the
regulatory requirements of the countries you (or they) operate in, your in-house
quality measures, internal or external audit requirements, and more. Examples
include calibration certificates, traceability reports and data reports (i.e., actual
measurement data). As an added convenience, all such reports should be
available in electronic and hardcopy forms.
In all cases, you'll want reports that include information about the instruments
used for performance testing and calibration. Being able to review those
instruments and compare their specifications versus your requirements--
accuracy, tolerances, etc.--is essential to retaining confidence in the
measurements you depend on most.
A final note: The content of calibration documentation varies from one service provider to
another: measurement uncertainty, guard-banded acceptance limits, accreditation body
symbol, and so on. Getting a consistent level of detail can help ensure confidence in the
calibration of your instruments.
Measuring service providers against your needs
When assessing potential providers of calibration services, a general framework
for evaluation is a useful complement to your organization-specific roster of
instruments, specifications and reports. The major sections of that framework
might be accreditation, calibration and documentation.
The following tables are example templates for a vendor-evaluation tool, and
each focuses on one of the three sections described above. To facilitate the
evaluation process, each checklist includes a variety of relevant questions--
open-ended, yes/no or numeric--that will help you assess how a service
provider might perform relative to your specific needs.
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Table 1. Evaluation questions focused on accreditation
Accreditation Provider A Provider B Why this is important
What is your scope of accreditation? The scope of accreditation must