Author: Blaž Bratuš, Mechanical Engineer
As is evident from our project portfolio, many of our solutions must ensure reliable operation under harsh conditions and therefore require a robust and durable enclosure capable of protecting the electronic components inside from whichever environmental challenges the device is exposed to.
One of the projects that required this kind of solution was the so-called “Arribada PitStop Turtle Tag”, a tracking system that is used to track and acquire spatial and behavioural data of the endangered sea turtles. Most sea turtle species spend the majority of their time underwater at depths of up to a few hundred meters, so it is crucial for the enclosure to be able to withstand this kind of pressure and remain fully waterproof.
The tracker that we developed features a dismantlable waterproof enclosure. Different designs, materials and sealing methods were proposed and tested to find the optimal solution, which we already described in one of our previous blog posts.
The rubber O-ring string was selected as the most effective sealing method. The sealing of the enclosure was tested and proven multiple times under up to 50 bar of pressure, which is equivalent to the depth of 500 m.
Reliability of the seal joint was influenced by several technical characteristics, such as O-ring material and dimensions, gland dimensions, surface roughness and fastener spacing. When exposed to the higher pressures the deflection in enclosure geometry can cause leakage, which has to be mitigated by ensuring a sufficient level of rigidity. In our case, the APM Hexseal Seelskrews are used to attach the pressure sensor that needs to be placed outside of the enclosure.
The main advantage of using a dismantlable waterproof enclosure is definitely the ability to easily access the electronic components inside for any electronics inspection or replacement, battery replacement etc.
Earlier this year we were approached by the Arribada Initiative to help them develop a similar tracker, but cast in the encapsulation resin to reduce the size of the device.
The approach to cast the electronic components in resin is a bit different than using the enclosure. First, a mould has to be manufactured, which then defines the shape of the final device. For encapsulation of the PitStop trackers, we have used a two-part aluminium mould. The important factors that affect the final device form are manufacturing accuracy and surface finish of the mould, proper assembly and attachment points for the components. Since all the components are cast in the resin, it is still necessary to ensure access to the device electronics for charging, configuration, programming or data transfer for which we’ve used the Mill-Max spring-loaded connectors.
The encapsulation resin offers the same, or better, protection compared to the dismantlable waterproof enclosure. The wide palette of available resins makes it possible to reach a mechanical and sealing fit exactly to the desired application. In our case, we are using the Electrolube polyurethane resin, which has excellent mechanical resistance that is key in this particular application.
The main advantages of using encapsulation resin are smaller dimensions of the device and the lower costs. With the tracker encapsulated in resin, we were able to reduce the size of the tracker for 50%, compared to the tracker with dismantlable enclosure. While cost of manufacturing of a single device might be comparable in the two cases, encapsulation resin technique is much easier to scale up and can be quicker in mid-size series production compared to the dismantlable enclosure.
Based on each specific use-case it is important to thoroughly consider the requirements regarding performance, size, lifetime, environment and cost. At IRNAS we are happy to be able to easily adapt, execute and test both approaches and therefore stay flexible when approaching design challenges that come our way.
About Arribada Initiative
Arribada is breaking down the barriers that inhibit our access to conservation technologies that afford us the ability to do so. They rely on the open approach delivering better, cheaper and more reliable solutions that are ready for the global conservation community to access, so together we can better conserve, monitor and protect our planet.