Hi all,

Someone has made me some probe sensor PCBs..basically a non contact capacitive strip with a temperature sensor on them.

This is to be pushed into soil to measure moisture and temperature..

The top of the probe is housed in a IP65 adaptable box and contains the battery..wireless module etc

The bottom part (probe) needs to be waterproof coated

Any ideas on what is used to do this in marine applications etc?

Thanks

 

Anything that needs to be removed at a later date, Dielectric grease from any automotive store.
If it is a PC board, then there is a special product called Conformal Coating.
Very hard to remove though if repairs needed.
Also good is Glyptal Enamel, comes in spray or 1/2l cans.
Max.

 

I've seen folks use cheap fiberglass resin as potting compound. It's not great for heat dissipation and has bad thermal expansion properties, but that shouldn't be a problem for your probe. You might be able to put the probe into a test tube used as a mold, pour in the resin, and then break away the mold. Coat the inside of the mold with vaseline to allow for easy release.

 

The Krylon Clear that I use would fail instantly in a marine environment. Don't bother with a cheap, easy, spray paint. It isn't good enough.

 

My preference for potting is FibreGlass Autobody filler (Bondo), it doesn't seem to crack as easily and also is nice to shape afterwards if necessary.
Max.

 

Thanks for your replies......I am in the UK and so far have found the conformal coating

http://www.rapidonline.com/SearchResults.aspx?kw=Conformal+Coating

The trouble is the wear factor i.e the user pushing the probes into the soil, compost etc...

 

I think you're being unrealistic. A stainless steel probe will last a few million strokes into soil. If you want this to last 100 years instead of 50 years, pack a spare set of probes with it.

 

A photo of the probe and the part that needs protection may help?
Max.

 

I think you're being unrealistic. A stainless steel probe will last a few million strokes into soil. If you want this to last 100 years instead of 50 years, pack a spare set of probes with it.

Its a standard pcb...with a point on the end..

 

You want to jam a fiberglass circuit board into dirt and expect it to last? I still think you're being unrealistic.

 

Could the part that senses temp. and moisture be a remote from the PCB at least, but if sensing moisture then I assume you cannot cover it?
Max.

 

Could the part that senses temp. and moisture be a remote from the PCB at least, but if sensing moisture then I assume you cannot cover it?
Max.

Its a capacitive none contact coated sensor...works suprisingly well....

 

I've seen the type of thing OP is describing. Google vegetronix if interested. Coated PCB, shoved in dirt, works. I've used a high grade 2 part potting compound from MG chemicals before to waterproof PCBs. It would probably work for you. I don't have the part number, but it's black 2 part stuff, pretty nasty. But it works very well and is flexible after curing, and penetrates all nooks and crannies. Cures better in the oven at low heat, but make sure to put a drip catcher underneath because it turns from thick tarry goop into runny drippy tarry goop before it cures.

 

I think this is it http://www.mgchemicals.com/products...and-encapsulating-compounds/black-epoxy-832b/

 

Following up. Did you find a suitable coating?

 

No luck so far..im in the UK...most of the ideas are US companies etc...I cant see a spray working...maybe something i can apply via a brush?

 

You must have conformal coating there?
Brush or spray.
3M UK
http://solutions.3m.co.uk/wps/portal/3M/en_GB/NovecSurface/Modifers/ConformalCoating/
Max.

 

You must have conformal coating there?
Brush or spray.
3M UK
http://solutions.3m.co.uk/wps/portal/3M/en_GB/NovecSurface/Modifers/ConformalCoating/
Max.

Hi Max..conformal coating is easy enough to get hold of....

http://www.rapidonline.com/SearchResults.aspx?kw=Conformal+Coating

but i dont think its going to be able to be robust enough for it i.e pcb stabbed in and out of soil..needs to be applied very thick if its going to work....

 

I think you would be surprised at its durability, especially when you try to remove it down the road!.
You can always give it a couple of coats?
Max.