Article about casing design considerations for wireless marine monitoring environments.
Developing environmental monitoring systems for the marine environment has additional challenges when compared to designing systems for inland shore side operation.
One reason is the fact that the sea is salty. This means that the casings for the wireless marine monitoring equipment must not only be watertight, but also be made from a material that will not easily corrode, such as marine grade stainless steel, or plastic (a good resource for more information on marine plastics is here
Ingress Protection (IP) Ratings of ‘off the shelf’ casings should be checked and considered before purchasing an pre-made solution. For example an IP54 gives: Limited protection against dust ingress.
(no harmful deposit), and Protected against splash water from any direction.
Therefore IP54 would not be suitable for a device or product that is going to be submerged for periods of time. IP68 which gives: Totally protected against dust ingress, and Protected against long, durable periods of immersion in water.
Choosing to have a custom made casing for your product has a number of advantages:
Firstly, with product branding. Having a custom designed and manufactured casing distinguishes and differentiates your product from the competition, and a well designed casing can give your product competitive advantage.
Secondly, by designing a custom made case you can create a more efficient product.
The reason for this is:
a) Space and weight saving can be achieved by eliminating extra space that is available in a pre-designed casing. This could well have cost savings, due to less materials being used in its manufacture. This is especially true in mass production, due to production economies of scale factors.
b) Greater product usability. The user experience, (or UX experience) is important in all products, but particularly in the marine environment where harsh conditions demand easy handling and operation in challenging conditions. A custom casing can be made easier to hold (for portable equipment), and not drop overboard!
c) Product efficiency. By designing a custom enclosure, it can be made to further protect the electronics within, from dust and moisture.
For example using inspiration from nature, a product casing could incorporate a sloping top (a bit like a pine tree shape, so that water naturally runs down the sides.
This design would have practical advantage over an off the shelf rectangle casing, due to the fact that conventional casings rely on gaskets to seal between the lid and the main casing body. The gaskets can fail due to the harsh environment, and even changes in air pressure, which can create a vacuum or pressure differential between the inside of the case and the outside environment.
Another consideration that needs to be taken into account when developing products for the marine environment is Maintainability.
All electronic parts have what is known as an MTBF, or Mean Time Between Failure. This is a statement by the electronic component, or system manufacturers of how long their product is likely to last. Therefore the product design should take the MTBF into account.
By analysing the MTBF data for all parts of the design, the ‘weak link’ can be identified. This will be the component with the lowest MTBF.
Once the component, or system part with the lowest MTBF has been identified (by using manufacturers data), the criticality of that component should be considered.
For example, if the component part in question failed, what effect would it have on the operation of the whole system?
A failed indicator lamp may not affect the operation of the equipment, however a failed thyristor or Micro-controller board would stop the design from functioning.
There is always a balance to be struck between design reliability and cost.
For example, you could design a kettle to last 100 years without maintenance, but the cost would be to great for most consumers, and it would be a financial failure for the manufacturer.
I would suggest that the first question to ask is, how long is the equipment that is being designed going to be deployed for?
Article to be continued, and expanded in near future (when I have the time :-)
(C) 2016 Craig Miles, All Rights Reserved.
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