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Water Resistant

I’m a nerd. I love learning new things and I especially love it when something I’ve learned intersects with my work. As Robert Frost puts it, “my object in living is to unite my avocation with my vocation”.

So, when I got an Apple Watch Series 3 for my birthday, I was puzzled by the fact that it was rated “50m water resistant”, whereas my wife’s Series 1 is rated IP68. What gives? I thought this was the same thing? Or at least very similar.

Many of the instruments we sell at Homershams are rated IP67 or IP68 and only through studying my birthday gift did I get to properly understand what this means.

Ingress Protection (IP) is relatively well known, but there are some subtle details I wasn’t aware of.

The first digit of the IP rating is protection from solid object ingress. 6 is as high as this goes, and it means that the instrument is completely protected from dust ingress.

The second digit is water. The scale goes from nothing to eight.  Various web sites reproduce variations on the chart below. (this one is from consumer.org.nz)
But what is not mentioned, even implicitly, is that there is a line under the 6 rating. One might incorrectly assume that IPx8 is more waterproof than IPx5 and that’s not necessarily true.  There is a progression from 1-6 but then it changes. Numbers 7 & 8 refer ONLY to immersion, and NOT to exposure to sprayed water.
Consume smallerr

There’s a clue in the specifications for the Sony Xperia 1 phone for example

Sony  Annotation 2019-05-22 101507

Sony’s specification tells us that the Xperia 1 can be immersed up to 1-metre for 30 minutes (IPx8) but also that it can withstand jets of water at low pressure (IPx5)

It came to my mind when one of our wonderful Additel 680W gauges came in for service full of water. “It’s IP68”, I thought, “how can this be?”. I know now that because it was subjected to sprayed water (possibly at high pressure) this is why the case seal was breached.

So back to my watch. Where many electronic devices use the IP code above (IEC 60529), wristwatches now use another standard (ISO 2281). In the past, standards were very imprecise or didn’t exist at all. Watches may not use the term “waterproof” at all under the standard; they say “water resistant” and a pressure or depth to which this applies.
ISO watch

You may well be surprised to learn that your watch labelled, “30 water resistant” is only splash and rainproof!

I know engineers tend to be all about the sciences and not the arts, but just in case you’re a kindred spirit, here’s a link to Robert Frosts great poem, "Two Tramps in Mudtime".


By the way, I had to look up the word “avocation”. It means a hobby.
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