NTS News Center

Latest News in Testing, Inspection and Certification

NTS News Center - Latest News in Testing, Inspection and Certification

Aerospace Industry Update: AS91XX Series of Standards Transition Deadline Approaching

As I’m sure our Aerospace industry clients are aware the AS91XX:2016 series of standards (AS9100, AS9120 and AS9110) has undergone a major revision with release dates late last year.

The aerospace standard AS9100 was published on 20th September 2016. AS9120 and AS9110 were also published in November 2016.  The aerospace standards have the same transition deadline as the ISO 9001:2015 standard, September 2018. Therefore the AS standards were released approximately eight months after the ISO 9001:2015 standard, the “three year” transition will actually be less than 18 months for aerospace companies.

NTS sister division, NQA is the leading quality management systems registrar to the aerospace industry. If you would like to learn more about the transition and how NQA is helping our aerospace clients through it, click here.

Q & A: Do I need a fixture for vibration testing?

Vibration Testing FixtureQuestion: One of the Qualification test requirements for my product includes vibration testing. Do I need to provide a test fixture in order to perform the vibration test?

Answer: The primary purpose of a vibration test fixture is to adapt the service mount of the unit under test (UUT) to the vibration test equipment (shaker, slip plate, etc) and to transmit the intended vibration to the UUT with as much fidelity as possible.

In order to accomplish these goals, a fixture should include good engineering design, specific materials and precision fabrication. Of course, all of these factors combine to make vibration fixturing both relatively expensive and time consuming to produce. This is undoubtedly why many companies seek to forego the design and build of dedicated fixturing and to seek other means of attaching their test items to the vibration equipment or simply leave it up to the test lab.

When no fixturing is provided, the test facility must find a way to attach the test item to the vibration equipment however they can. This usually means strapping or clamping the articles using eye bolts and nylon straps or threaded rod and clamp bars placed across the test item. As you can imagine, there are compromises inherent in this approach.

First, most test specifications are written with the assumption that the vibration will be input at the service mount of the test article. Strapping or clamping items to the vibration equipment rarely allows for this.

The second challenge is that there is a limit to the force that can be applied to an item by strapping or through clamp bars. Therefore, coupling between the test item and vibration system is usually compromised. This typically results in a frequency selective transmission of the vibration with some frequency bands being under the desired amplitude and other frequencies being over the intended amplitudes. The net result can be an under-test or over-test of the test article.

Finally, control of the input vibration levels can be compromised due to the ambiguity of sensor placement for control and monitor accelerometers. These locations are usually provided as an aspect of good fixture design.

So when vibration testing of your product is required, always weigh the time and expense of fixturing against all of the possible compromises inherent in the undefined approaches of clamping/strapping or “best way” mounting as decided by the test facility.

Vibration Fixture Basics

VibrationBy Randall Cobb, P.E.  Inside Sales Manager, NTS Detroit.

Vibration testing is a necessary part of many programs, and there are a wide variety of vibration types, but the one thing every test has in common is that the energy must be transmitted into the test sample with some kind of fixturing. Fixturing can be as simple as mounting bolts into a flat plate, or it can be an elaborate weldment with responses tuned to match the final assembly. The best fixturing is rigid, lightweight, and simple. The following is a list of general guidelines to aid in choosing the best fixturing for your test sample.

Rigidity: A fixture should be very stiff in order to transmit the vibration without adding extra noise. A flexible fixture can resonate at test frequencies, affecting the amount of energy transmitted to the test sample, and thus test quality. A very flexible fixture may be difficult to control and will require a more powerful vibration system, affecting both quality and price. At 2000 Hz, a 1 g sinusoidal input only requires 0.000005” of shaker displacement. It doesn’t take much fixture bending to affect that!

Weight: A fixture with extra mass will require more force to vibrate at a given amplitude (g-level). Low mass fixtures will allow multiple samples to be tested simultaneously, improving costs per part and test throughput. Fixtures should be low profile and keep the sample as close to the system input as possible. Eliminate unnecessary features, but don’t skimp on material if it will affect stiffness.

Material Selection: Unfortunately, vibration fixtures are not always made of the most inexpensive materials available. Steel and Aluminum have roughly the same strength to weight properties, so it might make sense to pick steel as the less expensive option. However, aluminum has a density much lower than that of steel, and features can be made much larger and stiffer with no weight penalty. This makes it the superior material for high-frequency vibration. 1

For very high-performance fixtures, magnesium will sometimes be used as its performance is even better than aluminum. The tradeoff is difficulty in machining and much higher fixture costs.

Complexity: The best vibration fixtures are simple, with the minimum number of features. Vibration testing is not only stressful to the sample, but also to the fixturing. Extra features and thin sections can add more potential for unwanted resonances, and more components that can fatigue and break. Simple fixtures are usually less costly up front, and cost less over the long run.

It is advisable to use through-bolts for sample mounting instead of tapped holes whenever possible. Threads fatigue after heavy use and a nut and bolt can be cut away and replaced at the test site, but extracting a damaged threaded insert may require a trip to the machinist’s shop. If you must have a tapped hole, use a steel threaded insert (E-Z Lok or Keensert type), rather than a helical insert (Heli-Coil or STI type), and never thread a fastener directly into aluminum!

Other Considerations: Most vibration testing is performed in a single axis, and repeated in each orthogonal axis (X, Y, & Z). Vibration systems can either be vertical or horizontal, and fixtures are often rotated 90° to perform two of the three axes on a horizontal surface. If you only have one vibration system available, it may make sense to design a fixture with mounting holes on more than one surface so it can be rotated for each axis of testing.

Since few test parts are so simple they can mount directly to the shaker, most fixturing is a compromise of the qualities above. Samples may need to be mounted in a specific orientation, or have features that must be supported above the vibration table. Welded fixtures are often necessary since it is not always practical to carve a fixture out of a single block of aluminum. Be sure weld joints are continuous and smooth, with two or even three passes if possible.

Validating a Fixture: When a fixture is used for the first time, it is good practice to perform a resonance scan in order to check for any unwanted responses. This is done by instrumenting the fixture with multiple accelerometers, and sending a low-level random signal that covers the entire frequency range intended for the test. If you imagine a tuning fork that rings at a certain frequency (pitch), and that frequency was in the range of the test, then when the test hits that frequency the fixture will start ringing and add more energy into the sample than it should receive. A resonance scan will identify any problem frequencies, and can be performed with or without the test sample in order to observe any effects.

Repeatability/Liability/Fixture Ownership: The standard offering for many test labs is to build a custom fixture for your program, and they will then maintain responsibility for fixture responses. You are paying for the fixture design and build, as well as a guarantee from the test lab this fixture will perform reliably from one test to the next. The major caveat to this service is that the test lab retains ownership of the fixture, because they cannot be responsible for its use and measurements made at other facilities. If you choose to make your own fixture, be sure to review it with the lab during the design phase in order to confirm it will match the test system.

For more information about vibration testing, visit our webpage. You can also contact the author of this article at our Detroit location: 313.835.0044. For more details including specifications on NTS Detroit vibration testing, see our brochure.

Using Programmable Logic Controllers for Test Automation and Process Control

Programmable Logic Controllers, or PLC’s, are basically a small computer with usable inputs and outputs. A PLC can be used to replace a set of relays, both time delay and regular, using counters and timers with input filtering and control. They typically run on ladder line programming (developed to let engineers and technicians use them without extensive programming knowledge) along with a graphic interface for ease of use.

Salt fog ControlThe real advantage of a PLC is flexibility and reliability. NTS Tempe is able to incorporate all of our customer requirements into one unit via a control point on a laptop and make changes on the fly.

The NTS PLC is composed of an OMRON ZEN microcontroller on an open board with solid state relays and terminal strips. The OMRON PLC has up to 6 transistor outputs good to 32VDC 10A, more than enough to either control things directly or drive an SSR (solid-state relay). It has up to 12 inputs 0-32VDC on the base unit that can be either positive or negative, and doubled with expansion units.

In one scenario, our team needed to control a hydraulic cylinder to preload the test item, start vibration for a set amount of time/number of cycles, then release the preload and repeat a specific number of times. In this instance, the PLC controlled the timing of an analog signal directly to the shaker amplifier and provided step signal attenuation on startup to avoid excessive shocks to the test unit from the shaker. A hydraulic cylinder was driven through an SSR and hydraulic valve.

The goal was to preload the unit to a specified amount measured with a load cell. We simply adjusted the pressure with a precision hydraulic regulator to get the required force. The shaker was then started and ramped up to the required levels, measured again with a load cell, held for a set time, then ramped down and stopped. We then depressurized the hydraulic cylinder and unloaded the test unit. After things had settled down, this sequence was repeated a few hundred times keeping a count of actual cycles. Using the PLC made all of this relatively easy.

In another instance a PLC was used to replace the entire control system in a liquid to liquid thermal shock machine. It controlled the movement of test items from hot to cold and back and monitored sensors indicating when test items were all the way into a tank or one of the drip positions ensuring that nothing was get out of sequence.

For ease of setup, external solid state timers set tank hold and drip periods driving the appropriate inputs of the PLC. A Watlow F4 controlled tank temperatures. In event of an error, the PLC would stop the test and initiate removal of a test item from the tank, then hold it in a neutral position.

SaltFog ChamberA final example has the PLC controlling all functions in a large salt fog chamber equipped with sulfur dioxide gas. It monitors salt and fresh water levels and fills the tanks from reservoirs as necessary. It also controls air flow to the salt fog towers ensuring air and SO2 are shut off during the fresh water bubbler fill. The PLC also acts as an interface between the Watlow F4 that controls temperature and SO2 cycles and the rest of the chamber. This allows the low level signal from the F4 to also control the system and shuts off the SO2 flow if the temperature goes out of tolerance, the salt fog chamber experiences an interruption or alarm.

NTS Tempe has seen much success using PLCs instead of conventional relays and timers. We recommend that if you have an older piece of equipment to update or need a custom setup, you consider using a PLC instead of traditional equipment. It gives a degree of flexibility along with control and safety that is sometimes difficult to obtain.

If you have any questions regarding the test cases in this article or would like to know how NTS Tempe engineers can apply their expertise to get your product qualified, please call the lab directly at 480.966.5517 or email our technical specialist Harold.Sibert@nts.com

MS Project: A Simple Way to Streamline the Testing Process

At our Rustburg, VA EMI/EMC testing facility, customers have the opportunity to work closely with our tight-knit team; managers and engineers to technicians and administrative staff. To ensure every program runs smoothly from start to finish we utilize Microsoft Project to build and post schedules, providing customers with a detailed timeline of each testing phase. This is especially helpful for complicated projects requiring full EMI testing with multiple pieces of equipment over a long period of time.

Our technical writer in Rustburg has offered this short guide below to get you started with the basics of MS Project. You may find it useful to manage the pre and post-testing phases of development!


Microsoft Project is a powerful project management tool. It has many advantages over Excel, primarily because it is more dynamic and scheduling changes can be easily made following a change in project timeline.

You can track each task of a project, as well as its duration, hierarchy, and resource requirements. This information can then be viewed in numerous different ways, most commonly in a Gantt chart or Timeline. These easy to view, but still very detailed formats, allow the NTS Rustburg team to effectively communicate and exchange project information within our group and with our customers.

Starting a New Project

  • Open Microsoft Project 2013 program
  • Select Blank Project
  • Go to Project Tab, select Project Information, enter Project Start date

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Entering Tasks

  • Double click on cell under Task Name heading in Gantt chart
  • Enter Task Information into dialogue box
  • Name task, enter duration, select Auto Scheduled for Schedule Mode

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  • Tasks can also be added from Task tab, Insert Task
  • Summary Tasks and Milestone Tasks can also be added from Task tab
  • A Summary Task will include tasks below it in the Gantt chart. Summary tasks will be outdented to the left and displayed in bold. The Duration (and Start and Finish dates) of Summary Task will include all of the tasks included in Summary Task.
  • Milestone Tasks mark an event in a project and have a zero day duration.

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Change Working Time

  • Project tab, Change Working Time
  • Project start day was set to 5/25/2015 which is a holiday.  After entering the holiday in the Change Working Time dialogue box, the project Start Date will automatically change (to next working day 5/26/2015).

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Assigning Task Precedence

  • Many tasks during a project must be completed in a certain order, e.g. testing must be completed prior to writing of test report.
  • In Predecessors column of Gantt chart, assign a row number to any task which must be completed before the next. Because tasks are Auto Scheduled, Start and Finish dates will automatically adjust on Gantt chart. Highlighted cells show ant changes in response to assigning Predecessors. Note: Project can’t link a summary task to one of its subtasks.
  • When the inevitable change to your schedule occurs, Project will automatically adjust the schedule and update the dates of tasks that come following the change, e.g. Technical Writer takes 2 days instead of 1 day to write the report.
  • Once you become comfortable entering tasks, there are many other features of Microsoft Project that can be utilized to create a very detailed and powerful project schedule. You can assign resources to a task, such as a Technician, Engineer, or Technical Writer.

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Changing the View

  • Finally, on the Task tab under Gantt Chart, View can be changed to Resource Usage to see how many hours have been allocated to a specific person

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We hope this brief tutorial might encourage you to explore MS Project for your scheduling process!

Bring Your Computer Back From The Dead

Dead ComputerEver have a computer just totally die on you in the middle of testing? Of course, if you’re testing a new product, it’s not that uncommon to have it crash, and sometimes even corrupt the system. The problem is if you’ve still got data on that computer that you need to get to – or even the debug logs to see what happened before every went to heck. Problem is, what do you use to get into your dead computer?

As long as you can still boot from a CD, you’ve got options. Check out this article from PCWorld: Six Downloadable Boot Discs That Could Save Your PC

And don’t forget to back up your system! Even if you can reproduce the data, you probably don’t want to spend the time (and your boss doesn’t want to spend the money on your salary) to get it back.

Using MSXML in your application? Double-check your installation.

Installing MSXMLJust a quick note, if you’re using MSXML (Microsoft XML Core Services), make sure you test and retest your installation routines. If your customers have upgraded to Microsoft Windows XP Service Pack 3, you may run into issues. As of SP3, Microsoft has placed MSXML under system protection so that applications/installations that try to update/remove MSXML fail. The most common occurrence of this has been with Microsoft SQL Server, and Microsoft has posted a work-around on their website. However, last thing you want to be doing is fielding support calls, emails, and tickets because of this issue. We just caught this testing another company’s product and thought we’d pass it along. Hopefully, Microsoft will help developers in handling this issue.

Virtual Machines – Lots of browsers, lots of operating systems

Virtual MachinesWhen you’re trying to test your website with many different web browsers, you often run into problems. In particular, Windows really isn’t designed to have multiple versions of Microsoft Internet Explorer (MSIE) installed at the same time. You could setup multiple platforms and maybe use a KVM to save space, but most of us don’t have the room for all that equipment just sitting around all the time.

As we mentioned in a previous post, a good solution to the issue is to setup multiple “virtual machines” (VMs) on your computer. Each VM has it’s own operating system and storage so you can install a version of Internet Explorer in each virtual machine. We also have previously discussed how you use VMs to learn how to use Linux and try out the various distributions (distros). Many of the distros already have pre-rolled VMs available (via VMware’s site or various image sites like this one for Virtual Box), but sometimes there’s that one distro you want to try without a VM. What do you do? Easy – roll your own.

Rather than going into the details of setting up your own VM, however, Lifehacker has a great article on how to setup, configure and install operating systems into a virtual machine using Virtual Box. Give it a read – it’s a very well done article!

Carbon Copy Cloner – Ghosting for the Mac

Carbon Copy ClonerIf you’re performing testing on a Mac and looking for a simple application to ghost/image the hard drive, take a look at Carbon Copy Cloner. I know it seems like you should be able to just copy all the files to an external hard drive and just select it from the Startup Disk preference pane, but it doesn’t work in MacOS X. And, if you’re doing a lot of configuration testing, installation/uninstallation, etc., it would be really handy to have an identical copy of the hard drive, right? Carbon Copy Cloner (CCC) to the rescue.

Just install CCC (or SuperDuper!) and you can clone a low-level copy of your internal hard drive to another partition or drive. It’s very handy, and if you really want a good backup, you can have it scheduled to update the cloned image so you’ll always have the latest version of all your hard drive files. When my hard drive suffered an unfortunate failure a few years ago, I had no worries – I had an identical copy of my hard drive all setup which allowed me to recover all my work on another Mac. It’s fast, accurate, and donation-ware so you can try it out before you buy.