Hi, A few thoughts on this.
First, I agree with the post that the wire is suspect. Standard telephone wire is not rated for salt water submersion and will probably fail in the time frames you see. They make cables with specific jackets and gel filling that are designed to go in these conditions, and these are usually terminated in dry boxes with the electronics. Since you don't need the dry box, the trick will be how to effectively terminate the cable.
RTV would also not be a first choice, the typical RTVs can produce chemicals that are in themselves corrosive. I would go with a heat conducting epoxy to saturate the area of the sensor and open wiring inside a small piece of pipe or tubing, something like the stainless steel capped tube that they use for thermocouples. I use this epoxy thermal compound in many places where I want a sensor to say put. Then cover the end of that with something that will bond to the cable jacket. An RTV might work here, it depends on the exact cable.
Depending on the failure mode, another way is to deploy multiple sensors and accept and replace failing sensors as they occur. Put a dry box above the water and connect all the sensors to the bus there. The reasons this might not work are the replacement is quite difficult or the failure mode shorts the bus.
jerry On 12/08/2013 12:31 PM, Håkan Elmqvist wrote:
I have for some years monitored sea water temperature with DS1820s and OWFS. I have soldered the sensors to a twisted pair telephone wire and put them into a short piece, ca 50 mm, of 12 mm of copper tubing. The tubes have a 3 mm hole in the middle where I have injected normal RTV one component acetoxy-polymerising silicone. After that I have let the silicone skin to polymerise in air for a couple of days and then put them into the sea. The disadvantage of this seems to be the lifetime of the sensors, which seems to be around a year and a half. Now I have lost my third sensor (I have not done any post mortem) and would like a better method to protect the DS1820. The method must withstand ice.Any tip is appreciated. Håkan
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