Hi folks,

For no other reason than Because-I-want-to I want to measure the pool's temperature along it's depth.

To do this I thought of taking a 1.5m length of conduit, cutting it along it's length and drilling holes 15mm apart.
Into these holes, from the inside of the cut tube, I will put a ds18b20, bend the legs 90 degrees, and solder them onto the next one - in effect, lots of ds18b20 connected together.

What I now have is lots of ds18b20 with their bodies in contact with the water. I was going to backfill the now-open side of the tube with something like potting compound or silicone (won't work I think as it's too viscous and won't flow around / in between the legs). Potting compound seems quite expensive if bought of ebay. Volume I would need is roughly 190cm^3.


Is there something else which can be used and is a) happy to stay submersed b) does not cost a too much c) viscous enough to fill voids between legs of the sensors?


Thanks

 

Silicone bathtub caulk is surprisingly low viscosity. Buy a little tube and test.

Alternatively there is this:



Which is quite good if a little messy to work with. Testing would be in order.

 

Hot glue, Epoxy, Acryl sealing compound..

 

There is something called conformal coating which is used to protect electronics from moisture.

 

being in the UK Lexel costs around$75 to ship here

thanks for the suggestions. I had not thought of hotglue. Checking it seems the melt-point is 80-200C depending on options so if I used a low temp one I should be good. Seems the ds18b20 is good to 260C in in reflow (if I am reading that right.)

Epoxy is another good option - I will look into that.

Thanks again

 

Use Acrylic Casting Resin. It has a syrup-like viscosity and good flow. It’s used to make decorations from embedded objects in a clear epoxy material. Plus, it’s sold in bulk, which you’re going to need.

Something like this.

 

Hot glue, Epoxy, Acryl sealing compound..

NOT HOT GLUE!! It is water resistant short term but it seems to absorb water long term.
And now for a question about those sensor connections: Are you planning one common and then a separate wire from each sensor? Yourdescription was not very clear about that part. And I suggest a plastic tube instead of metal conduit so that you can see what you are doing inside the tube.

 

Thanks. I will look for the acrylic resin option too.
@MisterBill2 -
the ds18 are one-wire and you just connect them in parallel. To get the temps you query by index or address. Ultimately, all I have coming out of my tube is 3 wires. 3.3, gnd and data. I've got a 4 "element" option at the moment which dangles in the pool and works well. For fun, I want more resolution over the depth. 4 was quite interesting in seeing the layers of temperatures.

Sorry - was not clear - pvc conduit. The holes drilled will be through the "low" part of the now-half cut pvc conduit, flush inside the tube and then soldered / filled with resin / other.