Tustin, Equipment Reliability Institute and Rick
Smith, Wyle Laboratories, Inc.
Selecting a laboratory to perform your
vibration test can be daunting.
consider a hypothetical case where a “newcomer” needs a
vibration test performed. (For
a temperature, altitude or humidity test, his questions would be
somewhat different.) Here, his “To Whom It May Concern”
inquiry to several candidate labs might resemble this:
seeking your advice.
My company makes flight (or shipboard or land vehicle) hardware
that I’ll call “widgets”.
Our Air Force (or Navy or Army) contract states that
widgets will be vibration tested to a standard.
My company doesn’t want to invest capital in nor devote
space to shaker, power amplifier and controls, and doesn‘t
want to pay for operator training.
Rather, my company wants to employ a commercial testing
lab. We have
already taken ordinary business precautions such as checking
with the Better Business Bureau.
Candidate labs are ISO (International Standards
Organization) certified and several
belong to A2LA
(American Association for Laboratory Accreditation).
Several are somewhat active in the IEST
(Institute for Environmental Sciences and Technology).
assigned to evaluate candidate labs for these tests.
What should I look for during a visit to each lab?
What questions should I ask?
for your assistance.
The authors suggest the following
urge Joe to visit each lab to (1) discuss his test, (2) discuss
his questions (and any the lab may suggest), and (3) tour the
each visit, he should get information about each facility and
Does the lab have a website Joe can visit for general
the website will describe the lab’s history and pertinent
Does the candidate lab seem willing and able to help Joe
understand his test requirements?
Many of the
words and phrases in standards (such as PSD in g2/Hz)
confuse readers. Some terms seem open to interpretation.
Is the lab able to communicate directly with Joe’s customer at
Joe’s request? What
if something unforeseen needs to be clarified before the test
Have test personnel documented any formal training in vibration
testing, measurement and analysis?
Have test personnel shown Joe, in their personal (or the
lab’s) library, texts that answer Joe’s many questions?
Joe wants his company library to obtain those texts.
Is the lab able to prepare a Test Plan or a Test Procedure that
Joe and Joe’s customer can review and approve well before the
Does the lab have a sufficient number of shakers that the lab
can match Joe’s probable schedule??
These must be sufficiently large (adequate force,
adequate table area, adequate frequency range) to do Joe’s job.
Joe’s customer may call for widget vibration tests at
temperature extremes. Can the eligible lab combine environments?
Can the potential lab perform other types of environmental
tests, if required?
Can the aspirant lab help Joe organize complex test programs?
Does the hopeful lab have the resources to design,
manufacture and experimentally evaluate before use (against what
standards?) the fixture(s) that attach widgets to the shaker? Or
will an outside service be needed?
Can the possible lab safely machine and weld magnesium (which
has been recommended to Joe) and install threaded inserts to
firmly attach our widgets?
Will the competing lab provide and attach accelerometers and
measurement instrumentation systems, including the display and recording
systems, not only to measure and record vibration input to
Joe’s DUT (device under test) but also DUT vibratory
Does the contesting lab have a significant inventory of
Will the lab assist in selecting accelerometer locations?
Beyond the specified test, Joe’s structural analysts and
design engineers want to correlate and validate their
mathematical widget models, and so may ask for additional
accelerometer channels. Can
the lab accommodate this?
Can the candidate lab provide instrumentation to monitor widgets
Some widgets require special power supplies, at 400 Hz, for
require 28 volts DC. Does
the eligible lab provide various power sources?
Some widgets require hot air or other gas flow.
Others require hydraulic oil, gasoline and/or diesel
fuel. Some require pressurization.
Some require static structural loading.
Which of these can the aspirant lab provide?
In addition to ASCII and EXCEL formats, in what other formats
can the hopeful lab provide data?
If DUT resonances result in test failure, will lab personnel
help Joe (and Joe’s designers)
learn from those failures?
Can the potential lab respond on short notice, in case of sudden
need for testing?
Shortly after Joe’s visit, Joe hopes to receive from several
possible labs several written proposals for the anticipated
vibration testing, with fixture design, manufacture and
evaluation shown separately.
Are Joe’s colleagues, and other witnesses that may be
required, welcome to observe tests?
Joe has learned that there are government agencies established
that require their representatives to witness certain tests. Does
the lab have familiarity and close contact with government
witnessing agencies? Does
the lab have a standard procedure to timely notify the
government witness (to avoid test delay)?
Is the suggested lab authorized to handle sensitive information?
Do lab personnel have government security clearances, and
does the candidate lab have a Facility Security Officer?
Joe will need a report
to show the results of each test. What kinds of reports does the
recommended lab offer?
In addition to digital photographs of each setup, what else does
a typical test report include?
How quickly can Joe get reports (after each test is completed)?
Can the competing lab submit reports electronically, as well as
Can the contesting lab provide preliminary test data for review
as tests progress?
The final report should list all equipment used.
The measurement equipment used must have been calibrated
with records traceable to NIST
(the National Institute
of Standards Technology).
Finally, what is each lab’s hourly rate?
Or have the labs other ways to provide estimates for
their services? To
what services do those rates apply?
For what services will Joe’s firm not be charged?