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selection table from 300 019-1-0

How Do I Choose Vibration Tests For My Product?

I… I love the way my product’s made
We all worked hard to get it to this stage
I hear the sound of a customer
Throwing my product halfway down the stairs…
(Chorus)
I’m pickin’ up bad vibrations
The equipment’s got agitations
Baaad baaad baaad bad vibrations ooom bop…
– “Bad Vibrations” by the Beached Boys

It’s a little known fact that Brian Wilson from the Beach boys was an environmental test engineer at Big Corp before pop stardom called him away from his first career.

He quickly realised that the hit parade wasn’t ready for ballads about Bellcore or ditties about humidity and switched to songs about the West Coast, cars and surfing. What could have been eh?

What is true however, is that whatever product it is that we make, at some point we have to release it from our development lab and into the big bad world. This raises the question: how well is it going to survive?

 

Why Perform Vibration Tests Anyway?

As we know, there are known knowns, known unknowns, unknown knowns and unknown unknowns…. y’ know?

 

“But James,” you cry, “surely I could just send my product via DHL / UPS / least favourite courier service (delete as appropriate) and achieve the same effect as testing?!”.

Well that’s very true, but I’m sure it’s going to be quite difficult to calibrate Dave the delivery driver, Vinnie the Van, and Winston the warehouse man for a consistent acceleration profile.

Testing is a simulation of what can happen in the big bad world. Like all simulations, it is a sensible average of many different situations. I’m not sure how these standards were originally derived but I’m sure more thought went into them than just kicking a development sample around the car park.

(If not actual thought, then at least a lot of tea and biscuits at the committee meetings, and that’s good enough for me)

Testing it primarily about mitigating risks, both of known risks and unknown risks. Whilst you might not be able to envisage a situation where your product is subject to a 1g, 30Hz vibration, real life might have other plans.

Primarily we are trying to quantify our knowns and unknowns.

 

Common Questions, Regular Requests

A version of one of these questions crops up every month or so.

 

“I want to do vibration testing, is there a standard that I can use?”

“What level of vibration do I need?”

“Do I need to do a random vibration test or is a swept test OK?”

“How do I simulate something being driven around in the back of a van?”

 

Vibration standards are quite often customer driven with a defined procurement specification. How close those specifications are to real life conditions depends on how much research that organisation has done or if they just pulled the numbers out of a hat. Often there is no way to get at the data or decisions that led to those choices and one must take them at face value.

Sometimes serious research goes into these levels, with car manufacturers employing multichannel data recorders and taking the latest model out for a test drive whilst getting tangled in accelerometer cables (safely I’m sure). This ends up being proprietary data so good luck getting your greasy mitts on it unless you happen to be working for them.

For the rest of us without a big budget how do we even make a start? Just go an buy every single BSI standard on vibration testing? Oh wait, we said without a big budget…

In the absence of any customer specification to work to, a good place to start in determining required levels and profiles is with the ETSI Environmental Engineering series of standards.

 

It’s a Splendid Smorgasbord of Shaky Situations

(or a Buffet of Battering if you will…)

 

The root standard ETSI EN 300 019-1-0 v2.1.2 (most recent at the time of writing)  gives an introduction to the “Environmental conditions and environmental tests for telecommunications equipment”. Since this could easily be used to describe most modern electronic equipment then it is widely applicable.

This incredibly useful series of standards are provided for download free of charge, a much more welcome approach to the usual way that standards are sold at high prices.

Not only that but they don’t just cover vibration. They cover the expected environment in terms of

  • Climatic conditions
    • Temperature and rate of change of temperature
    • Humidity
    • Air pressure
    • Solar and Heat radiation
    • Moving air speed (wind)
    • Weather conditions (driving rain, icing, etc)
  • Biological conditions (mold, rats, animals)
  • Concentrations of chemicals
  • Dust levels
  • Vibration and shock levels
  • Earthquake risks

That’s a pretty comprehensive list! The root standard contains a useful table that enables easy selection of a sub part appropriate for your product.

selection table from 300 019-1-0

Each Class has two standards that relate to it:

  • Part 1 (suffix -1-x) specifies the expected environmental conditions for the situations (storage, transportation, in use) and locations (underground, on a ship, etc)
  • Part 2 (suffix -2-x) specifies the recommended test levels and methods/standards for each class.

This table has quick links to each of the Part 1 and Part 2 standards for the various classes for reference:

Content Part 1 – Environment Definition Part 2 – Test Specification and Methods
Root Standard with background and general definitions ETSI EN 300 019-1-0 V2.1.2 (2003-09) ETSI EN 300 019-2-0 V2.1.2 (2003-09)
Storage ETSI EN 300 019-1-1 V2.1.4 (2003-04) ETSI EN 300 019-2-1 V2.3.1 (2017-11)
Transportation ETSI EN 300 019-1-2 V2.1.7 (2013-12) ETSI EN 300 019-2-2 V2.2.1 (2011-11)
Weather Protected Locations ETSI EN 300 019-1-3 V2.3.2 (2009-11) ETSI EN 300 019-2-3 V2.2.2 (2003-04)
Non Weather Protected Locations ETSI EN 300 019-1-4 V2.2.1 (2014-04) ETSI EN 300 019-2-4 V2.4.1 (2015-12)
Underground Locations ETSI EN 300 019-1-8 V2.1.4 (2003-04) ETSI EN 300 019-2-8 V2.1.8 (2019-12)
Ground Vehicle Installations ETSI EN 300 019-1-5 V2.1.4 (2003-04) ETSI EN 300 019-2-5 V3.0.0 (2002-07)
Ship Environment ETSI EN 300 019-1-6 V2.1.4 (2003-04) ETSI EN 300 019-2-6 V3.0.0 (2002-12)
Portable and Non Stationary Use ETSI EN 300 019-1-7 V2.1.7 (2013-12) ETSI EN 300 019-2-7 V3.0.1 (2003-04)

 

“Terrific Tables Batman!”

“Yes Robin, but how do we apply them to our (bat) product?”

 

Let’s invent an imaginary product.

The Monitor-o-Matic 9000 is a battery powered environmental monitor for indoor and outdoor locations. It gets periodically transported around site in the back of a van (maybe not always in its nice Peli case, naughty naughty)

In this instance we could reasonably apply:

  • Storage – the equipment is often kept in the van when not in use which can get pretty hot and cold. So we’ll apply “Class 1.2 Weather protected, not temperature controlled storage locations”
  • Transportation – with a bumpy van, and the M-o-M 9000 not always stored in its box means we’ll pick the harshest tests of “Class 2.3 Public transportation”
  • Usage – Non-Weather Protected Locations could be characterised as locations “…where transmitted vibrations are experienced from machines or passing vehicles. Higher level shocks may be experienced e.g. from adjacent machines.” We’ll choose “Class 4.1E: Non-weather protected locations – extended”

So lets pull out only the vibration requirements from each of these (bear in mind they also call up temperature, humidity, chemical resistance and other factors)

Unsurprisingly (some might say shockingly), transportation forms the biggest risk of vibration and shock to the product. We’ve now got some test levels to work with.

Note that some of the standards don’s account for the product being dropped from height. The storage standard does have a static load test simulating things being stored on top of the product.

Similarly the transportation test has the same static load requirements but adds free fall, toppling and rolling into the mix.

 

Questions to Ask Yourself

We normally ask ourselves what the expected use conditions are for a product. As with anything like this, we must also ask “what are the foreseeable misuse conditions?“.

 

Confession: I’ve Been Seeing Other Standards

This is just a simple guide to using the ETSI standards to make sensible design decisions in the absence of any other good information. However, many standards codify vibration and shock requirements, making the decisions a little easier.

EN 54 for Fire Alarm components has some quite challenging requirements for alarm components. In one shock test I performed for a customer on a smoke alarm the unit pinged straight off it’s base at the lowest shock level, necessitating some further work on the mounting (it subsequently passed no problems).

Military, Automotive and Aerospace sectors will definitely have their own vibration requirements and will commonly be clearly specified as part of the procurement specification.

 

Anyway, I hope you find this useful. Get in touch if you need some further guidance or need to ask any questions.

Cheers,

James

 

 

 

 

10g 16ms half sine shock test profile

EN 60068-2-27 Shock Testing of Anti-Shock Rubber Mounts

We’ve been vibration and shock testing of some heavy equipment designed for the construction environment. This is one of the toughest environments for product environmental testing. It’s wet, it’s dusty, it gets hot and cold… sometimes all at the same time! Not only that but it’s a very physical environment where rough treatment is the norm.

This customer is well versed in the art of protecting their equipment from such conditions using a robust frame with the key part of the product mounted on beefy rubber shock mounts.

This slow motion footage of captured of the unit undergoing shock testing really shows you just how useful these parts are.

Test was being performed to EN 60068-2-27, 10g shocks with a 16ms half sine profile. There is significant pulse pre- and post-loading as the piezolectronic accelerometer I use has a pretty poor low frequency response and this seems to help.

10g 16ms half sine shock test profile

The use of these anti shock mounts isn’t without issue. In this case, the springiness/stiffness of the anti shock mount combined with the mass of the equipment leads to a resonance at around 25Hz with quite large displacement of the main equipment mass.

The losses in the anti shock mounts causes a damping effect leading to a softer, wider resonance. The equivalent of resistance in an LC resonator causing a reduction in the Q of the circuit.

Compared to a much sharper resonance (caused by a different physical structure) the overall gain is much lower. The tradeoff is selecting a stiffer mount to damp the resonances but at the expense of transmitting more force through to the unit under protection.

25Hz soft resonance vs other sharper resonance

 

 

TWITL – Vibration Testing Automotive ECU

This Week In The Lab: This fuel injector controller has to withstand significant levels of vibration being mounted inside the engine bay of a high performance racing car.

The manufacturer and end user can’t afford a field failure so we are giving it a literal shakedown.

We are also monitoring the live performance during testing of the ECU to check for failure points or changes in the characteristics of the system

Vibration and shock testing applies to a wide range of products e.g.

  • Anything that is mobile or at risk of knocks and shocks in it’s end application
  • Industrial equipment working in a plant room or similar environment
  • Anything with moving parts; how robust is it? Are there unknown resonant modes lurking?

Get in touch to discuss your vibration testing requirements, we’d be happy to help.

 

 

 

Q4/17 Updates – A good variety of work!

It feels like it has been a busy couple of months here at Unit 3 Compliance with a wide variety of projects coming through the door.

Q1/18 is already shaping up to be busy with some really interesting products booked in for pre-compliance testing and some nice meaty problems to get our teeth into. I’m looking forward to sharing some of the insights I gain from this work with you.

Here’s a quick roundup of what’s been happening…

EMC Pre-Compliance

Our key area of expertise and always the cornerstone of what we do here at Unit 3 Compliance is EMC pre-compliance testing. In the chambers recently we’ve had ticket machines, water boilers, development kits, and a light/motion sensor. Some with problems that we quickly fixed and some sailed through first time.

One particularly interesting product was an industrial lighting system that needed radiated RF immunity testing at 20V/m. This test loves to mess with products by turning on or off semiconductors that were quite happy as they were thank you very much. In this case, there was an transistor based current limiting circuit that, thanks to one of the transistors demodulating the RF carrier, decided to shut down key parts of the circuit. Replacing it with a resistor removed the problem allowing the customers development cycle to continue.

Microwave Antenna Pattern Measurement

A customer has been leasing the anechoic chamber to make some antenna pattern measurements on a complex microwave antenna system. By loading up the quiet zone of the chamber with extra microwave absorber we were able to provide a highly anechoic (low reflection) environment all the way up to 18GHz.

As part of this exercise we made some rough background noise measurements from 2GHz up to 18GHz revealing very little. This suggests that when we reassembled the chamber in its new home we didn’t leave any gaps!

Vibration Testing

The vibration shaker and amplifier have been fully commissioned after their move. They’ve been getting a good run in performing a 2g sine sweep test on a large 25kg rack mount power supply.

Jigging equipment onto the vibration table is always a challenge, especially for a large and heavy piece of equipment like this one. I like to use 1″ x 1″ x 1/8″ wall aluminium box section (really stiff and light) along with high tensile M10 threaded bar to clamp an EUT of this size. Smaller EUTs can be easily secured to lighter platforms using hot-melt glue, surprisingly effective!

I always find vibration testing fascinating, especially watching various components come in and out of resonance during a sine sweep test. It’s fun to draw parallels between mechanical and electrical resonance, stiffness, impedance and damping.

In this case we found a large resonance that caused a fracture of the base plate due to excessive motion. We suggested a few approaches to stiffening that area, one of which was implemented and successfully removed the resonance.

One piece of equipment I’m going to be designing soon is an LED strobe lamp that synchronises to the output of the vibration controller so that any flexing in resonant modes can be easily spotted. That will make analysis much easier.

Design Reviews

We’ve carried our several sets of schematic and PCB design reviews, from motion sensors to heater controllers, from pump monitors to semiconductor development kits.

Our approach is not only to look at EMC / system level but also to question and educate designers on alternative circuit choices based on our long experience in electronics design. This is part of the value that we give to our customers.

In each case we’ve addressed the circuit design, considering the EMI phenomena and levels that the ports of the design will be exposed to. This is where understanding the tests themselves is so important otherwise the circuit could be susceptible to problems.

We also look at design partitioning in some detail. This is one of the easiest ways to achieve good system level performance (and not just from an EMC perspective) by segregating the design into digital, analogue, power supply and I/O areas with the aim of keeping noise currents where they should be and away from their potential victims.