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
- 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.
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:
|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)
|ETSI EN 300 019-1-1 V2.1.4 (2003-04)
|ETSI EN 300 019-2-1 V2.3.1 (2017-11)
|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)
|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)
|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’t 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.
Characteristic Severity vs Test Levels
The part 1 standards define the environment in terms of “characteristic severity” (see below, dashed blue) which represents the 99th percentile of that level of vibration occurring in the given environment i.e. vibration expected to exceed these characteristics only 1% of the time.
Testing at this “characteristic severity” would represent an over test of the equipment for the environment. So instead, ETSI specify a “Test specification” column (see below, solid red). This is is ETSI’s interpretation of the severity and duration of the test required to prove the EUT will operate in this environment.
I don’t know how his has been derived from the characteristic severity. If I find out I will update this post.
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.