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Technical Library

General
A Framework for Smart Transducer Interface Systems [conference paper]
Current progress and concepts of the IEEE P1451 Draft Standards for Smart Transducer Interfacing of Sensors and Actuators will be reviewed. Topics include the Network Capable Application Processor Information Model (P1451.1), Smart Transducer Independent Interface (1451.2), Distributed Multidrop Systems (P1451.3), and Mixed-mode Communication Protocols (P1451.4).
Streamlined Test Setup with TEDS Technology [conference paper]
TEDS (Transducer Electronic Data Sheet) Technology packages manufacturer and user-defined information within the traditional analog ICP® transducer. Using the same simple two-wire electrical connection, these smart sensors are now able to identify themselves over a network, allowing completely self-configurable transducer setup. This paper describes how to efficiently use TEDS technology on large multi-channel structural tests, such as modal analysis. An update on the developing smart sensor IEEE P1451.4 standard that describes TEDS is provided. Also, practical equipment additions (from Pocket PCs and PDAs to a 3D sonic coordinate digitizer) are integrated within the system setup solution.
The Fundamentals of Signal Analysis [handbook]
The analysis of electrical signals is a fundamental problem for many engineers and scientists. Even if the immediate problem is not electrical, the basic parameters of interest are often changed into electrical signals by means of transducers. Common transducers include accelerometers and load cells in mechanical work, EEG electrodes and blood pressure probes in biology and medicine, and pH and conductivity probes in chemistry. The rewards for transforming physical parameters to electrical signals are great, as many instruments are available for the analysis of electrical signals in the time, frequency and modal domains. The powerful measurement and analysis capabilities of these instruments can lead to rapid understanding of the system under study.
Time Scale Re-Sampling to Improve Transient Event Averaging [conference paper]
As the drive to make automobiles more noise and vibration free continues, it has become necessary to analyze transient events as well as periodic and random phenomena. Averaging of transient events requires a repeatable event as well as an available trigger event. Knowing the exact event time, the data can be postprocessed by re-sampling the time scale to capture the recorded event at the proper instant in time to allow averaging. Accurately obtaining the event time is difficult given the sampling restrictions of current data acquisition hardware. This paper discusses the ideal hardware needed to perform this type of analysis, and provides analytical examples showing the transient averaging improvements using time scale re-sampling. These improvements are applied to noise source identification of a single transient event using an arrayed microphone technique. With this technique, the averaging is performed using time delays between potential sources and microphones in the array. As a result, the relative time information needed is contained within the measured data and a separate trigger event and event time are not required.
Vibration
Fundamentals of Modal Analysis [handbook]
Modal analysis is defined as the study of the dynamic characteristics of a mechanical structure. This application note emphasizes experimental modal techniques, specifically the method known as frequency response function testing. Other areas are treated in a general sense to introduce their elementary concepts and relationships to one another. Although modal techniques are mathematical in nature, the discussion is inclined toward practical application. Theory is presented as needed to enhance the logical development of ideas. The reader will gain a sound physical understanding of modal analysis and be able to carry out an effective modal survey with confidence. Chapter 1 provides a brief overview of structural dynamics theory. Chapter 2 and 3 which is the bulk of the note, describes the measurement process for acquiring frequency response data. Chapter 4 describes the parameter estimation methods for extracting modal properties. Chapter 5 provides an overview of analytical techniques of structural analysis.
Multi-Tachometer Order Tracking and Operating Shape Extraction [conference paper]
An automobile and a tracked military vehicle were instrumented with multiple tachometers, one for each drive wheel/sprocket and operated with accelerometers mounted at suspension, chassis, and powertrain locations on the vehicles. The TVDFT order tracking method was then used to extract the order tracks from each of the wheels/sprockets and operating shapes estimated based on the order tracks. It is shown that under some conditions a different operating shape is excited by each of the wheels/sprockets simultaneously. This is due to the asymmetries present in the vehicles. The strengths of the TVDFT order tracking method are also shown for this type of analysis which is difficult due to the closeness and crossing of the orders generated by each of the wheels. Benefits of using multiple tachometers and advanced order tracking methods becomes apparent for solving certain types of noise and vibration problems.
The Time Variant Discrete Fourier Transform as an Order Tracking Method [conference paper]
Present order tracking methods for solving noise and vibration problems are reviewed, both FFT and resampling based order tracking methods. The time variant discrete Fourier transform (TVDFT) is developed as an alternative order tracking method. This method contains many advantages which the current order tracking methods do not possess. This method has the advantage of being very computationally efficient as well as the ability to minimize leakage errors. The basic TVDFT method may also be extended to a more complex method through the use of an orthogonality compensation matrix (OCM) which can separate closely spaced orders as well as separate the contributions of crossing orders. The basic TVDFT is a combination of the FFT and the re-sampling based methods. This method can be formulated in several different manners, one of which will give results matching the re-sampling based methods very closely. Both analytical and experimental data are used to establish the behavioral characteristics of this new method.
Shaker/Stinger Effects on Measured Frequency Response Functions [conference paper]
Shaker testing is utilized in the development of many experimental modal tests. The setup of the shaker, stinger and transducers can cause difficulties that are often misunderstood. Many times incorrect measurements are obtained and the test engineer may not realize that the measurements are not appropriate. This paper overviews some of the common problems that are typically encountered. Measurements are made on several structures to better understand some of the common problems observed. These include shaker alignment, stinger arrangement, reciprocity, impedance head difficulties and many other common issues that must be clearly understood in order to make the best possible overall measurements.
Accelerometer Basics
Structure and Function of Accelerometers [article]
Often accelerometers are treated as a "black box" with little regard to the internal structure or function. The wide spread integration of built-in ICP® sensor power into most modern day dynamic data acquisition systems often places two wire, constant current signal conditioning in this "black box" domain as well. As a result, many users have requested more information on the structure and performance of dynamic sensors.
Accelerometer Internal Structure [article]
Last month we discussed the basic function and structure of piezoelectric accelerometers and saw that the output of an ideal performing accelerometer is "straight-line" behavior. This means a flat frequency response in terms of amplitude and phase, as well as amplitude linearity. This month we’ll look at a few of the common designs for a piezoelectric accelerometer’s internal sensing element construction. Both the piezoelectric material (quartz or ceramic) and geometry (Shear, Compression, Inverted Compression or Flexure Beam) are discussed. These designs are applicable whether the accelerometer is ICP® or charge mode operation. More detailed information on the structure of accelerometers can be found on the PCB web site under the technical reference section.
Accelerometer Transduction Types [article]
Accelerometers are transducers that generate an electrical signal output as a result of a mechanical acceleration input to the unit. The most common type of accelerometer operates by the piezoelectric effect. Piezoelectric (PE) accelerometers are generally classified in two groups, low impedance voltage mode (for example, PCB Piezotronics trademarked ICP®) or charge mode. Other types of accelerometer transduction methods include piezoresistive (PR), based upon strain gage technology, and variable capacitive (VC).
Quartz vs Ceramic [article]
Over the years there has been a great deal of discussion over the merits of selecting either quartz or ceramic as the sensing element for a piezoelectric accelerometer. This month we’ll review the benefits of each, along with citing the certain applications where either one or the other excels....pun?
Similarities Between ICP and Charge Mode [article]
Understanding similarities of charge output and ICP® voltage output acceleration measurement systems.
Specification and Behavior of Accelerometers [article]
Ever heard the old saying, "No one believes the results of a theoretical analysis except the analyst. And everyone believes the results of an experiment, except the experimentalist"? In the test and measurement world this applies to the fact that vibration sensors are structures just like cars, computers, satellites and machinery that they are used to test. This means that accelerometers undergo stress and show strain, they move, bend, deflect and often show signs of their real world behavior. Test engineers and technicians need to understand the real world behavior of their measurement equipment to ensure that both valid data and valid results are produced.
Benefits of Understanding ICP Sensor Bias [article]
ICP sensors require a constant current power source providing 2 to 20 mA at 18 to 28V DC. In most applications, 2 to 4 mA current is adequate. In special applications driving long cables (>100ft) at high frequencies (100k Hz), higher current is required to avoid high frequency attenuation. For specifics, please view the driving ICP sensors over long cables reference nomograph.
The Trouble with Signal Cables [article]
The reliability of the measurement system is no better than that of the input cable, whose primary function is to transmit electrical signals from the accelerometers to the data acquisition system.
How Long Should an Accelerometer Cable Last [article]
"How long should a cable last?" This is the question often asked by test engineers making vibration measurements. In the past, we discussed the Trouble with Data Acquisition Cables. Length of life adds a new dimension to the conversation. So... should a cable last 2 minutes, 2 hours, 2 years or longer? The answer: It depends a great deal on proper care when installing the cable and the operating environment. As a test engineer, you may be able to come up with an estimated life expectancy based on your experience with defined measurement parameters, operating environment and installation procedures used in your specific application.
Discharge Time Constant [article]
New users of piezoelectric (PE) type accelerometers are always fascinated with the concept of zero biased response. Maybe it’s the general prevalence of slow speed, static type measurements, or maybe it’s the dominance of "mechanical oriented" people in the vibration test/measurement field, but AC coupled operation is always a question of early intrigue. The discussion of AC coupling, discharge time constants (DTC) and system operation inevitably follows.
ICP Accelerometer Options [article]
Within the world of ICP sensing there are some common options that can be applied to almost any typical accelerometer. Here is a quick review of the most common options. How many of them are you familiar with? This list contains the PCB® model number prefixes and a brief description of the options.
Why Calibrate? [article]
A good friend of mine always says, "Calibration is like getting a teenage boy to brush his teeth... They are always looking in mirrors and may comb their hair a hundred times a day, but never want to take the time in the morning to brush their teeth." From my observations, even in the business of test and measurement, it seems that appearances get all the attention and the sound practices of calibration, verification and maintenance are often an afterthought...
Cable Consideration and Constant Current [technical note]
Operation over long cables may affect frequency response and introduce noise and distortion when an insufficient current is available to drive cable capacitance. Unlike charge output systems, where the system noise is a function of cable length, ICP® sensors provide a high voltage, low impedance output well-suited for driving long cables through harsh environments.
An Introduction to TEDS [article]
Have you ever stared at your accelerometer (with its arcane model number neatly etched), only to wonder about the useful information like: What is the high or low frequency point? What is the exact sensitivity? Or when was this last calibrated? Without reflecting on sanity, you wish, "if only this little guy could talk." Well it turns out that now they can. Sensors with Transducer Electronic Data Sheet (TEDS) capability provide a standardized means for various types of sensors to "tell" the data acquisition system (or test personnel) their specifications on demand. At the International Modal Analysis Conference (IMAC) in Orlando this year, the Modal Shop's Structural Test Product group manager, Mr. Marco Peres, gave a talk about the history and current status of the TEDS in the dynamic sensor industry. While estimates of the number of TEDS accelerometers in service are approaching 200,000 units, there are many test professionals who are still learning.
Decoding the Accelerometer Specification Sheet [presentation]
How to understand an accelerometer specification sheet beyond the sales and marketing jargon.
Accelerometer Calibration Procedure Basics [article]
The beginning of the year is often a time for reorientation and a quick refresher on the basics of any operation. Accelerometer calibration is one such discipline that relies on "the basics" as fundamental to accurate operation and reporting. Small mistakes in these three critical areas can lead to significant errors in the outcomes of the calibration process…
Piezoelectric Transduction Basics [article]
One popular natural transduction phenomenon, which mystified early man, is the piezoelectric effect. Squeezing a crystal such quartz or tourmaline generates an electrical charge. The simple hydraulic analogy illustrated helps explain the piezoelectric effect. A saturated sponge resembles a crystal saturated with electrons. As any material, both are elastic and deflecting either one with a force liberates a quantity which fills a container to some head or potential, representing the applied force.
Accelerometer Technologies and Performance [presentation]
Accelerometer technologies and performance characteristics explained.
Does TEDS Add To My Uncertainty? [article]
A vibration/structural test customer in Italy, brought us this perplexing observation. After entering and writing the sensitivity of a 100 mV/g in to the TEDS (Transducer Electronic Data Sheet) storage memory of his accelerometer, his data acquisition software would then read and display the value as 0.010 V/(m/sec2). Glancing at the single zero to right of the digit one, he became concerned that the TEDS functionality was limiting the "resolution" of the recorded calibration value to within 10%? (=0.001/0.010 Which is the resolution of the display divided by the setting.) To understand the answer to this question….
State of the Union - TEDS [question and answer]
Mr. Marco Peres, STP Product Manager, answers some of the common questions about TEDS, templates and versions, as well as giving a glimpse of where things are headed.
Calibration and Engine Vibration Monitoring [article]
So you think your work environment is tough? You have multiple projects, competing priorities, shifting deadlines and drastically limited resources. Well at least you have a padded chair, nearby coffee and an office/lab. Now imagine the "work environment" of an aircraft engine monitoring accelerometer…the environment can be: hot to 1200 deg F (650 deg C), wet to 100% humidity condensing, violent seeing shocks up to 1000 g and precarious often on cantilevered mounting brackets and snaking in a cable around components and through passages to the signal conditioning and/or engine monitoring unit (EMU). Sounds like an environment worse than the biggest earthquake, the hottest desert and the wettest rainforest…
Characterizing Accelerometer Mounting [article]
We often get asked the question, "How do I mount a triaxial accelerometer to calibrate the (in plane) X and Y axes, when there is only a single Z axis mounting hole?" Clearly the Z axis stud mount poses no problems, but questions follow such as, "Can I adhesively mount it on the cap or case?" or "Why can’t I get my accelerometer to pass in the off axes direction?" Our answer is always the engineering favorite, "Well… it depends." Lets take a look at the problems in a little more detail…
Novel Uses for Accelerometers [article]
I have to admit that one of my geeky, guilty pleasures is screening my daily Google alerts for accelerometer related news and developments. This daily distraction gives me a few minutes of "mind candy." It is really amazing to see just how far the humble accelerometer has come to be used by people, products and processes.
Nontraditional Uses of ICP™ 'Power' Sensors [conference paper]
Modern dynamic signal analyzers (DSAs) provide ICP sensor power as the de-facto standard for dynamic sensor signal conditioning. From the humble beginnings of single- and dual-channel analyzers of the late 1960s and early '70s, modern analyzers serving the sound and vibration market have matured into PC based, modular structures typically providing multiples of 4, 8, or 16 channels. The liberal channel counts of these modern analyzers result in available 'space' for a new class of ICP additional sensors such as microphones, strain gages and tachometers...
What's Wrong With My Accelerometer? [article]
A frequently asked question about measurements made with piezoelectric (PE) vibration sensors is related to the measurement parameters. After completing a test and evaluating data, the test engineer observes obvious signs of problems with his data, such as the decay in baseline voltage or drops in the coherence of forced response frequency response function (FRF) measurements. Many things can affect the data from a PE Accelerometer including...
Shock and Vibration Sensor Applications
Modal Array Accelerometers [article]
There are literally thousands of different models of accelerometers available. This is due to each measurement application having slightly different goals and constraints, as well as different weightings as to which sensor specifications can be compromised. There are frequency ranges, amplitude g ranges, resolutions, packaging/connector configurations, weight, environmental considerations, etc… With all the combinations and permutations, how is a user to wade through the volumes of models and feel confident in making a technically and economically sound choice? The short answer is application assistance. Be sure your chosen vendor provides knowledgeable, professional support people who can promptly assist with your phone call, email or request for a visit.
Accelerometer Application Focus on Seismic Sensors [article]
Piezoelectric accelerometers are well suited for seismic vibrations studies. They are completely self contained and self generating from an inertial frame of reference. This eliminates the challenges with relative vibration found in optical/laser methods, as well as dual ended attachment coil based methods, such as LVDTs. The second most common challenge with seismic measurements is the limited excitation levels of seismic events. In terms of acceleration, the g level falls off exponentially for a constant displacement as frequency decreases, thus seismic events typically exhibit small acceleration levels...
Triaxial Accelerometer [article]
By far, the most popular configuration of piezoelectric accelerometers for large/multichannel users is the integral triaxial accelerometer. The implementation of a single 4 pin sensor signal connector allows for a common ground and overall 3 to 1 reduction in cabling. While on the surface, this may seem trivial, consider that many typical users are now in the hundreds of channels for standard vibration tests in the automotive and aerospace industries. This is also relevant to the consumer appliance/durables market space where sound and vibration quality has stepped to the forefront of marketability and customer preferences.
Accelerometers for Flight Test Applications [article]
Of the various testing and evaluation methods, flight test is by far one of the most important in the development, design, and validation of an aircraft. Mathematical models, safety, comfort, and performance targets are verified through specific testing of each aircraft system under real flight operating conditions...
Accelerometer Considerations in ESS, HALT & HASS [article]
Environmental Stress Screening (ESS), Highly Accelerated Life Testing (HALT) and Highly Accelerated Stress Screening (HASS) each involve long duration cycling in terms of vibration, often accompanied by cycled temperatures and/or pressures. These extremes of vibration, temperature and/or pressure, which are physically taxing and are intended to prove, degrade or terminate the functioning of the product or structure under test, can be just as taxing on the monitor accelerometers providing feedback to the vibration controller.
Accelerometer Considerations for Automotive Modal/NVH [article]
Classical and operating modal analyses are important tools for understanding and optimizing dynamic automotive structural behaviors, leading to stronger and safer automobiles; lighter construction yield; improved fuel consumption and performance, ride quality, handling, and NVH. From the measured vibration data and modal analysis, engineers are able to construct dynamic models of vehicles and substructures. The dynamic models predict resonant frequencies, damping values and deflection patterns for each mode of vibration. Frequency ranges of interest may be sub-one hertz to a few hertz in terms of ride handling and from 10 hertz to 500 hertz for full vehicle operating data and body-in-white modal tests.
Introduction to Industrial Accelerometers [article]
The basics of acceleration sensing for the plant floor come from the same measurement/laboratory grade instruments we have been using for years. However, the packaging of industrial accelerometers differs significantly from their laboratory style heritage. At the core of an industrial style accelerometer is still a piezoelectric crystal. Piezoelectric (PE) accelerometers have become the defacto standard for machinery and process vibration for a number of reasons...
Miniature Sensors for Testing Small Structures [article]
Most dynamics people think of structural testing as the system vibration study of large structures like automobiles, aircraft or civil structures. However, the ever increasing push for smaller, lighter, and more powerful in the mobile electronics world (phones, disk drives, subnotebooks, etc) creates a unique set of challenges for structural test engineers. First and foremost is often simply finding space to locate a response accelerometer! This article discusses a number of other specialized measurement considerations for ultra-small or ultra-light test structures…
Vibration Measurement at High Temperatures [article]
"What do I have to do to measure vibration at high temperature?" is a common question for the extreme environments found in the automotive, aerospace and industrial vibration measurement fields. Various sensor considerations come into play including sensing element material, casing/connector construction, signal conditioning and cabling. Since there is no single right answer to this question, as you might imagine, the answer depends on just how high the temperature is…
Industrial Vibration Accelerometer Performance [conference paper]
The implementation of industrial vibration monitoring sensors and associated signal conditioning as an integral part of industrial predictive maintenance programs has proven, for many maintenance and plant engineers, to be an effective strategy for reducing downtime and improving overall machinery health. Vibration monitoring technology is widely used because...
Accelerometers for Health and Usage Monitoring Systems (HUMS) [paper]
Health and Usage Monitoring Systems (HUMS) are gaining wide acceptance as an effective predictive maintenance strategy in helicopters and some fixed wing aircraft. Due to the large number of critical flight safety systems on aircraft, particularly rotating systems on helicopters, vibration monitoring technology is effective in the detection and prevention of catastrophic mechanical failures. HUMS started more than 15 years ago, as a safety system and has evolved into a front-line strategy for reduction of aircraft maintenance costs.
Pressure Sensor Applications
[no articles]
Strain Measurement Applications
'Light Flight' - New Technologies for Dynamic Strain Measurement Sensors [article]
Strain measurements are demanding to new autonomous and intelligent materials affordability. New technologies are under development. This article offers a brief summary of a series of tests that have been carried out at C.I.R.A. laboratories in Italy comparing new fiber optic sensor system using strain gauges (for static) and piezoelectric sensors (for dynamic).
Actuator, Shaker and Excitation Basics
Advantages of Multiple-Input Multiple-Output (MIMO) Testing Using Low Level Excitation Systems [Conference Paper]
Modal Testing Excitation Techniques [magazine article]
Effects of Shaker, Stinger and Transducer Mounting on Measured Frequency Response Functions [conference paper]
Practical Considerations in Electrodynamic Vibration Exciter Selection [conference paper]
Shaker testing is commonly used as a method for measuring forced input in experimental modal analysis. The setup of conventional shakers, stingers and transducers is often the source of test difficulties and avoidable measurement errors. This paper reviews the basic design of shakers as beneficial to modal testing, and the common problems associated with setup issues and resulting measurement errors. These include shaker selection, shaker alignment, stinger selection, connections, reciprocity assumptions and other common mishaps and misunderstandings.
Intro To Single Input Modal Testing With Shaker Excitation [video]
The practical aspects of setting up a vibration shaker and stinger combination for use during modal testing are covered in this short video tutorial. A crank shaft serves as the test article in this single input testing application. Frequently asked questions are answered step-by-step during the demonstration.
Tutorial in Modal Shaker Excitation [presentation]
This excellent presentation from the International Modal Analysis Conference was coauthored by our own Marco Peres and presented by our friend and colleague Professor Peter Avitabile of the Structural Dynamics and Acoustic Systems Lab at UMass Lowell. Inside you'll find an overview on some shaker excitation techniques commonly employed in modal testing, a review of deterministic and non-deterministic methods, a presentation of excitation techniques that have been developed from a historical standpoint and last Multi-Input, Multi-Output (MIMO) modal testing information.
Do's and Don'ts of Excitation Techniques [presentation]
In his signature style of application, data and explanation, Pete Avitable presented Do's and Don'ts of Excitation Techniques, illustrating practical knowledge on the excitation topics you need to know. While data acquisition and analysis always seem to get the front seat in training, Pete reminds us that it all starts with excitation and to avoid that testing cliché... "Garbage in - Garbage out."
Calibration
ICP Based Reference Accelerometers
ICP based accelerometers have become widely used in the field of vibration measurement as general purpose sensors. Charge mode accelerometers have historically been used as the reference for back to back comparison calibrations. This paper introduces the concept that the use of properly constructed ICP based accelerometers result in a much simpler, more reliable and easier to use calibration system than charge mode accelerometer based systems. Historical data will be provided which documents the long term stability of selected ICP reference sensors. This paper is relevant to anyone evaluating or assessing both secondary and primary accelerometer calibration system performance.
A New Solution for Shock and Vibration Calibration of Accelerometers [conference paper]
Shock and vibration phenomena are present around us in everything that moves. The accelerometer is a class of instruments commonly used to measure that motion, producing an electrical output signal related to the applied motion. Accurate accelerometer calibration is a way to provide physical meaning to this electrical output and it is a prerequisite for quality motion measurements. Systems and standards on comparison methods for accelerometer calibration are discussed, providing an overview on current technology available for calibrating and testing accelerometer performance characteristics.
Air Bearing Shaker for Precision Calibration of Accelerometers [conference paper]
This paper presents the design, construction, and performance testing of a new air-bearing shaker for precision accelerometer calibration in a production environment. The new shaker incorporates a number of novel features. A graphite air bearing provides high stiffness to lateral loading. A Lorentz force "electrical spring" minimizes the low frequency waveform distortion that is typically associated with non-linear deformation of metal or elastomer flexures. Finally, a beryllium armature provides high stiffness, low mass, and high resonant frequency.
Shock and Vibration Calibration of Accelerometers [conference paper]
Accurate accelerometer calibration is a way to provide physical meaning to the electrical output an accelerometer produces when subjected to vibration and it is a prerequisite for quality measurements. The most common shock technique, a pneumatic shock exciter, can perform calibration and linearity checks up to 10,000 g and is one of the most versatile anvil shock type devices available for shock calibration (in terms of amplitude range, pulse duration, repeatability, and traceability to primary calibration methodologies).
Accelerometer Calibration Q&A [question and answer]
Why calibrate a vibration transducer? What is driving implementation of automated calibration systems today? What does the typical engineer need to know about accelerometer calibration related to the standards? What is meant by calibration "traceability" and why is it important? Walk us through the typical process for calibrating an accelerometer. What are some specific challenges in calibrating accelerometers? How often should a user calibrate? Is there any way I can make a quick accelerometer sensitivity check without doing a complete calibration? Why are more modern calibration systems moving toward air-bearing shakers? What is The Modal Shop's role in the calibration and test services market?
Language of Metrology [presentation]
The Modal Shop has been actively presenting one day seminars on dynamic sensing and calibration around the world. This education on the function and structure of dynamic sensors (PE, VC, PR, etc) and the associated methods and means of calibration is key in keeping pace with global growth in acceleration sensing. Ensuring the users' control and confidence in dynamic analysis serves the measurement and engineering community, in everything from aerospace structures to consumer electronics to plant floor efficiencies. Last month, TMS Engineering Team Leader, Mr. Sang Kim, presented in his homeland of Korea. The following is one of his leadoff presentations used to orient the audience in the framework of metrological terminology. This presentation makes a nice primer, or overview, to share with your new hires and also includes a number of handy links to other useful resources.
New Techniques in Primary Accelerometer Calibration [conference paper]
This paper will discuss a newly developed implementation of ISO 16063 style primary accelerometer calibrations. The goal is a laser primary accelerometer calibration system capable of performing low uncertainty primary accelerometer calibrations while maintaining the throughput and simplicity of a traditional back-to-back calibration system.
Accelerometer Transverse Sensitivity Measurement Using Planar Orbital Motion [conference paper]
An apparatus for the measurement of accelerometer transverse sensitivity is described in which a plate constrained to planar motion by air bearing pads is driven in a circular orbital motion by two orthogonally placed shakers. The paper discusses similar measurements made with a resonant rod, which is shown to suffer rotational accelerations which contribute to errors if the seismic center of sensitivity of the accelerometer is not on the centerline of the rod. The constraint to planar motion is shown to eliminate this source of error. In addition, by gathering measurements in all transverse directions during an orbit, the method has advantages in speed over techniques using one dimensional motion, as described in working drafts of ISO 16063-31 "Methods for the calibration of vibration and shock transducers - Part 31: Testing of transverse vibration sensitivity".
Automated Testing of Accelerometer Transverse Sensitivity [conference paper]
A new system for automated testing of accelerometer transverse sensitivity has been designed and implemented at PCB Piezotronics. This paper describes the transverse test system theory, construction, and operation. Transverse sensitivities obtained from the automated system and sensitivities obtained by the manual method described in ISO 5347-11:1993 were found to agree to within the stated uncertainty of 0.3%.
The Effect of High Transverse Inputs on Accelerometer Calibration [conference paper]
ISO 16063 part 21 defines the back-to-back comparison technique for accelerometer calibration. Included in its most recent revision is a recommendation for acceptable limits on shaker transverse motion characteristics. The effect of high transverse inputs can be devastating to accurate accelerometer calibration. This paper discusses the differences between mechanical flexure-based electrodynamic shakers and air bearing shakers and the resulting effects on calibration accuracy and uncertainty.
Primary vs Secondary/Transfer Calibration [article]
The question often asked is, "When (or even why) do I need primary calibration?" Metrologists are also curious to know, "What does it cost?" The short answer to "who needs it?", is that primary calibration (as covered in ISO16063-11) is the standardized means to obtain the absolute minimum in uncertainty. But to fully answer this question, one needs to first consider the reasons for calibration. This month’s discussion answers the question from the angle of uncertainties, costs and throughput rates.
Calibration Traceability [article]
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.
Double vs Single Ended Transfer Standard Reference [article]
Vibration calibration methodologies are defined in various sections of ISO 16063. Within this standard, the measurement of accelerometer frequency response calibration can be performed using either primary or secondary means, as stated by ISO 16063 Part 11 (1999) and Part 21 (2003) respectively. Primary accelerometer calibration utilizes a laser interferometer as reference. Secondary calibration techniques use a transfer standard, typically another accelerometer, to calibrate the accelerometer under test and provide traceability to a primary standard.
Overview on Calibration and Measurement Uncertainty [article]
One of the most commonly debated issues among calibration professionals and often least understood by sensor users is the concept of measurement uncertainties. To the novice user, the manufacturer's stated calibration is simply accepted as gospel. However, a closer inspection of the calibration certificate reveals that the calibration lab is actually providing an INTERVAL, within which the value for the device is "certain" to lie and typically includes a statistical probablility distribution statement. This omnipresent and expected interval is typically expressed in a tolerance term of plus or minus some level of percent... aka uncertainty.
Random vs Systemic Calibration Uncertainties [article]
As we discussed in the previous article, there are two types of calibration uncertainties, random and systemic. Since a calibration lab is responsible for correctly reporting their uncertainty, it is important to understand the differences between these types of contributors and how each can be considered. As a framework to differentiate the two types, consider that uncertainties caused by random contributors lend themselves to be determined by statistical measurement methods whereas, uncertainties that are systemic in nature need to be surveyed versus more accurate methods. As an example, in accelerometer calibration...
More Contributors to Uncertainty [article]
There are many factors contributing to accelerometer calibration uncertainty and last month we scratched the surface by discussing some of the major ones. This month we’ll cover a few more. Consider the equation for accelerometer calibration, Vref/Vsut = Sref/Ssut, which states the ratio of the accelerometer output (both reference and sensor-under-test) voltages must be equal to the ratio of their respective sensitivities. Because of the ratio nature of the voltage measurement, it is easy to see that if an external factor effects the voltage measurement...
Statistical Method for Evaluating Uncertainty [article]
The next chapter of our discussion focuses on the statistical methods of evaluating uncertainty. When uncertainty contributors are evaluated, they can either be based on statistical methods (called a Type A evaluation), or by other means (called a Type B evaluation). In previous articles we have discussed some of the other methods used such as the systemic uncertainty from the reference accelerometer. The goal of this article is to discuss statistical methods in greater detail.
Principles of Dynamic Calibration [article]
This is another section of a classic application note by PCB Piezotronics co-founder, Bob Lally. This concise applicable application note covers the core of sensor calibration. It may have been written in the 70's, but it is still a useful resource for teaching young engineers the basic behaviors of measurement systems.
Relative Motion in Calibration [article]
In the back to back calibration method, the known sensitivity of the reference accelerometer combined with its measured output is used to determine the acceleration level of the shaker. This information combined with the measured output of the Sensor-Under-Test (SUT) is used to determine the SUT sensitivity thus completing the calibration. The obvious, yet sometimes overlooked assumption in this method is that both sensors are subjected to the same acceleration input, bringing up the topic of this month’s column.
Proficiency Testing for Calibration Uncertainties [article]
Throughout the past few months, we’ve discussed various contributors to the overall measurement uncertainty of a calibration system. At the end of the uncertainty analysis, it is desirable to test our conclusions to uncover potential errors or oversights and to also learn where improvements can be made. This brings us to the topic of proficiency testing. (Sometimes this is also called: round-robin testing or inter-laboratory comparison.)
Calibration Exciter Transverse Motion [video]
When considering accelerometer calibration and what effects uncertainty, it is important to analyze the exciter and the transverse sensitivity of accelerometers. The exciter acts as the heart of the calibration system, providing an accurate mechanical motion to the transducer.
Interpreting Calibration Results [article]
As you may remember from your studies (or maybe you read the first newsletter in this series), ideal sensors provide straight line performance. That is to say, they treat amplitudes proportionally (straight line linearity), frequencies of interest the same (flat amplitude frequency response), and do not appreciably delay the signal (flat phase frequency response). Hence, the frequency response output plot from an accelerometer and on a calibration system should be a flat line. In the real world, however, things are not perfect...
The Devil is in Accelerometer Calibration Details [article]
When seeking the best uncertainties and most consistent daily verification and operation of your accelerometer calibration system, it pays to know your sensor details. The key to accelerometer calibration is ensuring that everything starts from a "flat line." This means no relative motion between Reference Accelerometer and Sensor-Under-Test, as well as no local resonances and strain effects from connectors and cables.
New Optical Calibration References: Laser Primary and Encoder Low Frequency [article]
This month we'll take a break from discussing world of calibration standards and interpretation of calibration data. Here's a quick update on the latest developments in accelerometer calibration. Considering that optical techniques are becoming more and more commonplace in the sensing industry, we have observed that they also provide some extraordinary benefits when used as references for accelerometer calibration. The Modal Shop and PCB have developed two new optical methods/systems: one for extending low frequency calibration capability and another for further simplifying and expediting laser primary calibration.
Improved Low Frequency Accelerometer Calibration [article]
Accelerometer users in the structural testing field often ask about how to calibrate a sensor's performance at the low end of the frequency response curve. Since most manufacturers start the standard factory calibration at 10 Hz, there is typically no data delivered with an accelerometer documenting its low frequency performance. To measure this data, a supplemental low frequency calibration must be performed.
Improved Low Frequency Accelerometer Calibration [conference paper]
This paper will discuss a newly developed implementation of low frequency accelerometer calibrations below 10 Hz. The goal is an improved low frequency accelerometer calibration methodology capable of performing superior quality measurements with significantly lower uncertainties while maintaining good throughput and the simplicity of traditional back-to-back calibration techniques. By using an optical encoder as the measurement reference instead of a traditional back-to-back reference accelerometer, limitations due to shaker stroke length are nearly eliminated, with the practical limitation for a quality calibration measurement at ultra low frequency being the resolution of the sensor under test itself.
A Longer Stroke Precision Calibration Exciter [article]
The game of American football is sometimes called a "game of inches." Just as an inch of extra forward progress can determine the outcome of an individual play, an inch (or centimeter) can also determine the quality of your calibration at low frequency. As a rule of thumb, in the low frequency range there is no substitute for a longer stroke exciter. Consider that "normal" calibrations for a 100 mV/g accelerometer are conducted at a constant 1 g acceleration level. This one g constant acceleration is held fixed to the maximum frequency in the range of calibration.
Calibration and Linearity [article]
Another common question I hear, "Is my accelerometer calibration valid for an acceleration level other than what I calibrated at?" The common reason for the question is that automated accelerometer calibration systems traditionally calibrate the various frequency choices at constant acceleration levels like 1G or 10G, yet users can be using the sensors in ranges of hundreds, thousands or tens of thousands of G’s. The answer for most accelerometers is a definite yes, although it is useful to examine the definition of its full scale range...
Instrumented Impact Hammer Calibration [article]
Instrumented impact hammers are a useful and common tool in the structural dynamics and vibration field trouble shooting fields of technology. The hammers, available in sizes from as small as a 0.10 oz (2.9 gm) pencil up to 12 lb (5.44 kg) sledges, are typically configured for a given test by adding an impact tip of specific hardness (soft to nylon to steel) and occasionally a mass extender to add additional inertia for broadening the impact energy pulse in low frequency situations. Due to the unique nature of impact measurements, it is advised by manufacturers that users should calibrate the hammers in the tip/extender configuration that they will be used. For this reason, it is common to calibrate impact hammers a number of times for different tip/extender combinations.
Calibration Demand of the Aerospace and Defense Market [article]
No where is the price of product or mission failure as high as it is in the aerospace and defense markets. A satellite failure can cost hundreds of millions of dollars, while an aircraft or military failure can cost incalculable value in the loss of lives. In response to this inherent market pressure, an extreme level of confidence is required of the test and data integrity. And, as with all measurement situations, confidence starts with the integrity of the calibration. Clearly confidence is the key. This drives aerospace and defense (A&D) organizations to have heightened and specific needs in terms of accuracy, reliability and reputation in their sensor calibrations. This month we’ll outline some of the details to filling these needs in A&D vibration sensor calibration...
Accelerometer Calibration Tutorial [video]
Embracing the profileration of YouTube and videos on the web, we offer a short video presentation on accelerometer calibration. The video describes the basic operation of our accelerometer calibration system.
Common Options for Accelerometer Calibration Systems [article]
Frequency response function (FRF) and single point reference frequency amplitude sensitivity are the most common forms of accelerometer calibration. However, laboratories are becoming more interested in supplemental test capabilities to ensure both the health and performance of their users' accelerometers. The use of the new generation of robust and precise calibration actuators allows for greater control and shaping of input energy to shock and vibration calibration. The techniques are in use around the world by various sensor companies, as well as the leading aerospace and transportation manufacturers.
Lowering the Barriers of Laser Primary Calibration [article]
While the ever lowering of uncertainty is the quixotic quest of the metrology industry, for certain laboratories the lowest possible uncertainty is a must. Of particular note are National Metrological Laboratories, Primary Standards Laboratories (often serving branches of the Armed Services or National Labs), Accelerometer Manufacturers (there are over 150 now) and Accelerometer Calibration System Manufacturers (where there are still only just a few…). Each of these organizations has a specialized metrology function in providing primary calibrations for accelerometers that will be used in precision accelerometer calibration systems as references or transfer standards as called out in ISO16063-21. In these cases, the best measurement uncertainties are needed because the reference, or transfer standard uncertainty, will be directly adding to the overall measurement uncertainty of the calibration system. This is critical since it is most often the single largest contributor to the system uncertainty.
Can I Supply my Own DVM? [article]
As a purveyor of the broadest range of accelerometer calibration systems, we support customers with everything from simple hand-held 1G exciter check devices, compact all-in-one portable systems, desktop automated accelerometer calibration workstations, to the lowest uncertainty laser based accelerometer primary calibration systems. Routinely, customers on a quest to save a little money ask us if they can supply their own Digital Volt Meter (DVM) as part of the system… and being a customer focused company, we always consider the viability of the request. Like most things in life, the answer often is a conditional MAYBE…
Calibrating the Calibration System [article]
Control, confidence and low uncertainties are the hallmark characteristics of a quality metrology laboratory. The basis for this operation is quality calibration equipment, sensor specific operator knowledge, as well as solid business and calibration processes. One vital key in this type of operation is maintaining proper control and calibration of the calibration system. In general, there are three reference calibration paths a laboratory can choose which provide various tradeoffs in downtime, cost and risk…
Evolution of Calibration Reference Accelerometer [article]
In the early days of vibration measurement and calibration, users were plagued by a calibration conundrum that supposedly identical input to accelerometers placed next to each other (or even on top of each other!) on a controlled shaker gave different responses. What at first glance seemed to be a contradiction, quickly began to show what we clearly know now: dynamics occur in ALL structures of ALL sizes...
Calibration and Resonance Search [question and answer]
I see that the frequency response of the reference standard accelerometer is calibrated up to a 20kHz upper limit frequency. So, how does the resonance search function (up to 50 kHz) for the calibration system "calibrate" the sensitivity at frequencies higher than 20kHz?
ED and Reference Limitations in Low Frequency Calibration [article]
Historically, the limiting factors in low frequency accelerometer calibration were a combination of the limited stroke length of electro-dynamic (ED) shakers providing limited acceleration levels at declining low frequencies, and the limited resolution of the piezoelectric reference accelerometer in the presence of the sensor’s rising electric noise floor. By adopting and applying proven technologies in a novel combination, it is now possible for improved simplicity and reduced measurement uncertainties of dynamic vibration calibration at very low frequencies. The commercially available combination of a high accuracy optical displacement reference and ultra-long stroke (>250 mm stroke) calibration grade linear actuator has created a new standard in ultra-low frequency calibration.
Structural Gravimetric Calibration Technique [conference paper]
Structural dynamics play an important role in today's highly technological world. Engineers typically sense, test, model, and modify vibratory behavior to improve how structures function, feel, look, sound, interact or cope. An integral part of this process involves calibration of test instrumentation. In universal structural testing terminology, calibration is testing the functional transfer behavior, including sensitivity and phase, of sensor structures in controlled transactions and environments. An ideal measurement system...
Calibration Standards
Overview of Quality Systems and Standards [article]
Familiar with standards like ISO17025 and ISO16063-21? Already operating under an ISO9001 Quality management system? The world of standards, controlled processes, documentation and audits can sometimes be daunting... To help demystify this world when it comes to accelerometer calibration, we’ll begin by discussing the relationships between the various parts of each these quality system pieces.
Overview of ISO 17025 Competence of Testing and Calibration Laboratories [article]
This is a common question when it comes to understanding the quality system covering the calibration of sensors, like accelerometers. More and more often customers are requiring dynamic test service providers to be certified to the requirements of ISO/IEC 17025:2005 - the standard which covers the "General requirements for the competence of testing and calibration laboratories."
Overview of ISO 16063 Accelerometer Calibration Standards [article]
Last month we talked about how three major standards apply to the world of dynamic sound and vibration measurement. While most are familiar with the sweeping implications of ISO9000, many users are not aware of the level of detail available in ISO16063 specifically covering accelerometer calibration. This month we’ll cover a basic overview of the framework of ISO16063 governing Methods for the calibration of vibration and shock transducers.
ISO 16063-11 Laser Interferometer Method Overview [article]
Primary accelerometer calibration is at the root of traceability for virtually every accelerometer calibration chain in the world: commercial, government, military, academic or vendor. Acceleration calibration via laser interferometry is a primary method because it is an absolute method comparing the measured vibration from a sensor under test to a constant of nature – the wavelength of laser light.
ISO 16063-21 - Calibration via Reference Standard [article]
This standard describes the most common embodiment of laboratory accelerometer calibration. Utilizing either a back-to-back (piggyback) reference standard or a specially constructed reference standard accelerometer imbedded inside a precision calibration exciter, this method provides the speed and simplicity of direct sensor under test (SUT) mounting and calibration. Modern computer controlled calibration systems can provide calibrations and prints of calibration certificates in just a few minutes.
ISO 16063-22 - Shock Calibration via Reference [article]
Part 22 of the vibration and shock calibration standard covers "Shock calibration by comparison to a reference transducer". Compared to the general accelerometer calibration techniques discussed last month, shock calibration is a specialty method. As such, there are a number of accepted apparatus and methods depending on the desired shock acceleration magnitude and pulse width.
Quality System Audits and Proficiency Test Deficiencies [article]
You do it. I do it. Everyone does it. What is "it"?... we make mistakes. In the technical and business world, quality systems have a regularly administered audit component to provide a means for testing and finding these "opportunities for improvement". The Modal Shop’s calibration product group manager, Mr. Eric Seller, recently attended a regional meeting of NCSLi in Ann Arbor, Michigan. Despite the region’s current economic woes and the plight of the American auto industry, the meeting found an upbeat tone with a full house of around 50 metrology practitioners. Of particular interest and usefulness, Eric brought back an excellent presentation by Mr. Robert Knake of A2LA addressing the "Most Common Deficiencies" found during the ISO17025 assessment audit process. We thank Mr. Knake and the A2LA organization for the approval to reprint his presentation in this newsletter.
Quality System Audits and Equipment Control Deficiencies [article]
As a follow up to last month’s article on Calibration Proficiency Deficiency, this month we continue to examine the most common deficiencies in ISO17025 compliance. Cutting right to the chase, this month’s deficiency is the 2nd most common - Infractions in ISO17025 Section 5.5, Equipment. The nature of calibration requires using the proper equipment with known performance, traceability and reliable operation. While this is clearly core to the accurate operation of calibration, ironically, the compliance violations in this area are very common.
Acoustics
PCB Microphone Handbook [handbook]
Pressure variations, whether in air, water or other mediums, which the human ear can detect, are considered sounds. Acoustics is the science or the study of sound. Sound can be generally pleasing to the ear, as in music, or undesirable, referred to as noise. The typical audible range of a healthy human ear is 20 to 20,000 Hz. A Sound Pressure Level (SPL) beyond the detectable frequencies of the human ear can also be very important to design engineers. Noise, Vibration and Harshness (NVH) is concerned with the study of vibration and audible sounds. Vibrations represent a rapid linear motion of a particle or of an elastic solid about an equilibrium position, or fluctuation of pressure level. Harshness refers to the treatments of transient frequencies or shock. Usually treatments are employed to eliminate noise, but in some cases products are designed to magnify the sound and vibration at particular frequencies. The sound produced or received by a typical object, which may be above and below the frequencies that are detectable by the human ear, or amplitudes concerning its resonant frequencies, are important to designers, in order to characterize the items performance and longevity.
Sound Power Measurements [handbook]
Sound power level measurements are gaining recognition worldwide as a means of characterizing a product's acoustic signature. The usefulness of sound power is well known among noise control experts. Unlike sound pressure measurements, sound power tests are independent of measurement environment, making possible direct noise level comparisons between different products. Given 1/3-octave spectra of sound power, noise control engineers can determine the resulting sound pressure level in an enclosure or space and choose the quantity and type of acoustic treatment required. With many international import regulations requiring conformance to noise power test standards such as ISO 7779, the measurement has become increasingly important. Growing interest in sound power level is not restricted to noise control professionals. Appliance and office equipment manufacturers - and their customers - are paying attention too. For competitive reasons, many companies now specify sound power levels in product documentation. Their assumption is that consumers will select a quieter appliance. A final reason for growing popularity of sound power measurements is the sharp drop in costs associated with making the measurement. Instrumentation is less expensive and new test techniques are eliminating the need for costly anechoic or reverberant chambers.
Acoustic Source Location in Vehicle Cabins and Free-field with Nearfield Acoustical Holography via Acoustic Arrays [conference paper]
The technique of Nearfield Acoustical Holography (NAH) is used to identify sources in enclosed spaces with coupled structural and acoustical modes. Pressure measurements made on planes within an enclosure are expanded and projected onto the vibrating surfaces of interest, and active and reactive intensities are calculated. This procedure is applied to locate a known source of acoustic excitation in the interior of a small sport utility vehicle exhibiting strong modal characteristics. Acoustic modes somewhat obscure the source location in the measured pressure distributions, while the reactive acoustic intensity clearly indicates the location of the vibrational input. The NAH technique is also applied to an idling engine with unknown sources radiating acoustic noise into a free-field. The active intensity on the engine surface is reconstructed and the located sources at particular frequencies correlated with rotating engine components.
Comparison of Nearfield Acoustic Holography and Dual Microphone Intensity Measurements [conference paper]
The measurement accuracy of nearfield acoustic holography (NAH) and dual microphone intensity measurement techniques are examined in terms of source identification capabilities and sound intensity level estimates. Inherent differences in the data acquisition and post processing methodologies are investigated. The techniques are applied according to their individual limitation to best evaluate the test structure. The variance of their respective results and how those results aid in engineering solutions is thoroughly discussed.
Resonant Acoustic Method NDT
NDT-RAM Hardware Tutorials [videos]
The most popular training and troubleshooting topics for NDT-RAM hardware. Each tutorial uses live demonstrations to explain different processes and options available with the NDT-RAM Auto System. Topics Include: Basic Test, Part Orientation, Part Alignment, Part Spacing, Hammer Case Adjustment, Hammer Force Adjustment, Ejector Speed Adjustment, Conveyor Speed, Light Tower
NDT-RAM Software Tutorials [videos]
The most popular training and troubleshooting topics for NDT-RAM software. Each tutorial uses an in-software demonstration to explain different processes and features. Topics Include: User Level Differences, Taking Investigation Data, Coloring the Data Traces, Setting Criteria, Setting Additional Criteria, Exporting Data Into Excel, Screen Controls, Adjusting Data Collection, Peak Marks-Data Traces-Range Lines, Light Tower Automation
Fundamentals of Resonant Acoustic Method NDT [conference paper]
Rapid conversion of machined parts to powdered metal and cast is driving industries, especially automotive. Due to the high expectations of both primary manufacturers and end consumers, defects cannot be tolerated even in million piece quantities. There is, in effect, a growing requirement for zero defect supply chain commitments. To achieve zero defect output, manufacturers are making the commitment to move to online NDT. This type of online inspection requires accuracy, reliability, and high throughput. Resonant Acoustic Method NDT (RAM NDT) provides a proven technique exhibiting these pivotal performance requirements and automates economically. RAM NDT tests, reports and screens for most common part flaws in a manner similar to the way NASA tests flight hardware and automotive manufacturers validate their new car designs. Utilizing structural dynamics and statistical variation, RAM NDT provides mature, laboratory proven technology in a robust, economical, process-friendly manner.
Resonant Inspection Applied to 100% Testing of Nodularity of Cast Ductile Iron [conference paper]
Worldwide emphasis on defect-free manufacturing within the automotive sector has driven manufacturers to seek out cost effective methods of 100% inspection. To achieve zero defect output cost-effectively, manufacturers are making the commitment to move to online, automated nondestructive testing (NDT) methods. This type of online inspection requires accuracy, reliability, and high throughput. The Resonant Acoustic Method of Nondestructive Testing (RAM-NDT) is emerging as a type of resonant inspection that is a very efficient method of structural defect discrimination lending itself well to automated online implementation. This paper presents the fundamental principles of the resonant acoustic method and how it is been applied to testing nodularity in ductile iron brake calipers, rotors and anchors.
Physical Basis of the Resonant Acoustic Method for Flaw Detection
Resonant inspection measures the structural response of a part and evaluates it against the statistical variation from a control set of good parts to screen defects. Its volumetric approach tests the whole part, both for external and internal structural flaws or deviations, providing objective and quantitative results. This structural response is a unique and measurable signature, defined by a component’s mechanical resonances. These resonances are a function of part geometry and material properties and are the basis for Resonant Acoustic Method for Flaw Detection. By measuring the resonances of a part, one determines the structural characteristics of that part in a single test. Typical flaws and defects adversely affecting the structural characteristics for powdered metal as would be introduced in the green state are geometry related and typically a result of handling. This paper introduces the physical basis of the technique.
Total Quality with Rapid Through-put of Powdered Metal and Cast Parts for Whole Part Flaw Detection via Resonant Acoustic Method of Inspection [conference paper]
Rapid conversion of machined parts to powdered metal and cast is driving industries, especially automotive. Due to the high expectations of both primary manufacturers and end consumers, defects cannot be tolerated even in million piece quantities. There is, in effect, a growing requirement for zero defect supply chain commitments. To achieve zero defect output, manufacturers are making the commitment to move to online NDT. This type of online inspection requires accuracy, reliability, and high throughput. Resonant Acoustic Method NDT (RAM NDT) provides a proven technique exhibiting these pivotal performance requirements and automates economically. RAM NDT tests, reports and screens for most common part flaws in a manner similar to the way NASA tests flight hardware and automotive manufacturers validate their new car designs. Utilizing structural dynamics and statistical variation, RAM NDT provides mature, laboratory proven technology in a robust, economical, process-friendly manner.
Effect of Crack Size on Natural Frequency Using Resonant Inspection [conference paper]
Resonant Inspection is commonly used by powdered metal part manufacturers to sort quality components from those with structural defects. One of the more common structural defects found in powdered metal parts are cracks, often produced while in the green state. A controlled experiment was designed to investigate the sensitivity of resonant frequency shifts to crack size. This evaluation was intended to generalize and quantify the effectiveness of resonant inspection by generating a variety of crack sizes within a tightly controlled set of production parts. Although data was acquired to quantify how small of a crack the resonant inspection technique can detect, it is important to recognize that these results cannot be applied across all powdered metal parts due to differences in part geometry, mass and stiffness as well as control of production process variations.
Enhanced Resonant Inspection Using Component Weight Compensation [conference paper]
Resonant Inspection is commonly used for quality assurance testing of powder metal components, providing a volumetric whole body approach that detects both external and internal structural flaws or anomalies. This technique measures the structural response, a unique and repeatable signature dependent upon the component's mechanical resonances. Since these resonances are a function of the material properties, certain process variations such as powder density can contribute to uncertainties in the testing technique. This paper presents the results of an enhanced resonant inspection technique, called Adaptive Resonant Acoustic Method, that allows for adaptive, intelligent data processing providing improved quantitative results.
Resonant Inspection as an Automated NDT Method for Sinter Brazed Powder Metal Components [conference paper]
With continued growth of powder metal components in the vehicle, particularly within the power train, the requirement for defect free manufacturing has driven suppliers to seek out cost effective methods of 100% inspection. To achieve zero defect ("Zero PPM") output cost-effectively, manufacturers are making the commitment to move to online, automated nondestructive testing (NDT) methods. This type of online inspection requires accuracy, reliability, and high throughput. Resonant Inspection is emerging as a very efficient method of structural defect discrimination and lends itself very well to 100% inspection of powder metal components. This paper will present the fundamental principles of the resonant acoustic method (RAM NDT), on a structural basis, followed with RAM NDT applied to a variety of sinter braze integrity inspection applications.
Quality Management
The Mistake of Forced Ranking [article]
There's not a good reason to rank or assess your employees' performance. Like there isn't enough politics in the workplace! Command and control managers love to rank employees; there needs to be forced ranking by assessment of performance to be considered a good manager and have a well-run company.
Give this to the boss... [article]
One thing is for sure. Nothing is getting easier. We have more complex products (tried to fix your own car lately?), more complex services and intricate interactions between people, teams, departments, suppliers and sometimes even related companies! In the end, our customers want to be satisfied...or even happy. With so much of our day focused on introverted (company oriented) processes, measures and problems, we can forget that it's the customer and the voice of the customer that really matters. The quality of product or service matters, as does the expectations we set with our customers, as does the manner/ skill/ disposition/ timeliness with which we deliver it. Read this article if you believe your company should walk the walk, in addition to talking the talk.
Statistical Basis for Engineering Decisions [article]
Come with me, dear reader, on a journey to find out why you should embrace, and not run screaming from, your inner statistical geek. But to get there, we have some interesting terrain to cover starting with the human brain.
Lab Lessons Learned from Student Testing, Series 1 [article]
Here is an application note by Purdue University Professor, Doug Adams, sharing a number of educational experiences his students have learned the hard way. Working on an aircraft fuselage with various test methods, readers can either nod their heads...