View previous topic :: View next topic |
Author |
Message |
Markdem
Joined: 24 Jun 2005 Posts: 206
|
Waterproffing DS18B20 |
Posted: Mon Jan 30, 2006 10:34 pm |
|
|
Hi All, nothing to do with CCS, for once. Is the black plastic on a DS18B20, or any transistor for that matter, waterproof. I am tring to find the temp of water, and thinking about just sealing the wire pins on the sensor, so just half of the black bit is in the water. Do you think it will work?
Thanks, Mark |
|
![](templates/subSilver/images/spacer.gif) |
dyeatman
Joined: 06 Sep 2003 Posts: 1924 Location: Norman, OK
|
|
Posted: Mon Jan 30, 2006 11:46 pm |
|
|
I Googled on waterproof DS1820 and got a lot of stuff.
Basically, no, the sensor is not waterproof. Clear silicone sealant seems to be the waterproofing of choice. |
|
![](templates/subSilver/images/spacer.gif) |
SherpaDoug
Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA
|
|
Posted: Tue Jan 31, 2006 8:20 am |
|
|
Bob Pease of National Semiconductor has recommended removing finger oils and other contaminants from plastic cased chips and transitors by putting them through a houshold dishwasher. I would say the plastic packages are pretty waterproof.
I often use a LM34 analog temperature sensor (TO92 case) in wet environments by soldering it to the end of some shielded twisted pair cable and painting any exposed metal with fingernail polish. Fingernail polish is good stuff. It is available in convient small bottles with a built in brush, comes in a variety of colors, dries fast, is intended to adhere tenatiously to not too clean surfaces, and is easly removed with a benign solvent.
The less thermal insulation you put on the sensor the faster it will react to temperature changes, and the less it will be affected by self-heating error. Self heating is the error in a temperature sensor by the heat it generates by it own operation. _________________ The search for better is endless. Instead simply find very good and get the job done. |
|
![](templates/subSilver/images/spacer.gif) |
Humberto
Joined: 08 Sep 2003 Posts: 1215 Location: Buenos Aires, La Reina del Plata
|
|
Posted: Tue Jan 31, 2006 8:41 am |
|
|
Quote: |
...and painting any exposed metal with fingernail polish. Fingernail polish is good stuff. It is available in convient small bottles with a built in brush, comes in a variety of colors, dries fast, is intended to adhere tenatiously to not too clean surfaces, and is easly removed with a benign solvent.
|
Good point Sherpa.
Just I was wondering the vendors faces while I'm asking for fingernail polish...
Humberto |
|
![](templates/subSilver/images/spacer.gif) |
rnielsen
Joined: 23 Sep 2003 Posts: 852 Location: Utah
|
|
Posted: Tue Jan 31, 2006 9:21 am |
|
|
The black plastic that is used to encapsulate the die is, for the most part, water proof. It _will_ absorb moisture though. I've worked in the semi-conductor industry for quite some time and moisture content of the plastic is a big deal. We have to bake the parts, after encapsulation, to get most of the moisture out and then ship them in a sealed bag with a deseccant to ensure they are dry. Having the part dipped in water, periodically, will not hurt it, though keeping it submerged for long periods might have an adverse affect on it (it can only hold it's breath for so long ).
If you will be submerging parts into water make sure that your wire leads are sealed as well. Silicone is not a good choice as it containes acidic ingredients that could corrode your electrical connections. A good sealant is Loctite's Color Guard. This is the stuff that you can coat tool handles with. It is quite runny, spreads well and dries rather quickly and also remains a little flexible.
Ronald |
|
![](templates/subSilver/images/spacer.gif) |
rwyoung
Joined: 12 Nov 2003 Posts: 563 Location: Lawrence, KS USA
|
|
Posted: Tue Jan 31, 2006 9:53 am |
|
|
rnielsen wrote: | Silicone is not a good choice as it containes acidic ingredients that could corrode your electrical connections. |
Silicone by itself is pretty inert (insert Dow Chemical [spam] implant comment here). It is the curing agents you need to be careful about.
Don't use the clear RTV that has acedic acid (smells like vinegar) as the curing agent. The cheap stuff from the hardware store will definately have acedic acid in it. Check the label.
MG Chemicals and a few others make electrical grade RTV that is non-corrosive. Doesn't seem to dry as hard or have the same "strength" as the clear stuff though. Usually white in color. _________________ Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month! |
|
![](templates/subSilver/images/spacer.gif) |
rnielsen
Joined: 23 Sep 2003 Posts: 852 Location: Utah
|
|
Posted: Tue Jan 31, 2006 12:20 pm |
|
|
Quote: | (insert Dow Chemical [spam] implant comment here) |
Woot! Makes me want to go home and fondle my tubes of caulk.
Actually, I should have said silicone caulking is not a good choice. ![Rolling Eyes](images/smiles/icon_rolleyes.gif) |
|
![](templates/subSilver/images/spacer.gif) |
JBM
Joined: 12 May 2004 Posts: 54 Location: edinburgh, Scotland
|
|
Posted: Tue Jan 31, 2006 4:35 pm |
|
|
As it happens, my company I work for did exactly that - waterproofed DS18B20s.
What we did was to get stainless steel 'caps' made that are about 3cm long (very similar to the metal tip of a digital medical thermometer, only bigger), with an internal diameter jsut big enoug for the TO92 case. Wires were soldered onto the legs of the chip, then heatshrunk. The whole lot whas stuck inside, and then potted with a heat conductive compound.
If you want photos, or deatils of who we got to make up the steel tips, PM me.
-JBM |
|
![](templates/subSilver/images/spacer.gif) |
specialk
Joined: 12 Nov 2005 Posts: 27
|
|
Posted: Tue Jan 31, 2006 10:50 pm |
|
|
JBM wrote: | Wires were soldered onto the legs of the chip, then heatshrunk. | Were they just heatshrunk or did you use adhesive-lined waterproof heatshrink?
-special [k] |
|
![](templates/subSilver/images/spacer.gif) |
JBM
Joined: 12 May 2004 Posts: 54 Location: edinburgh, Scotland
|
|
Posted: Wed Feb 01, 2006 10:03 am |
|
|
We just heat shrunk the legs, then potted the whole lot with the thermal compund inside the steel tips.
-JBM |
|
![](templates/subSilver/images/spacer.gif) |
Markdem
Joined: 24 Jun 2005 Posts: 206
|
|
Posted: Thu Feb 02, 2006 3:48 am |
|
|
Hi All, thank you all very much for the comments. I am not too sure about putting the sensor in a metal casing as i think it may not transfure the heat. I am going to use this in a aquarium, so the heat will not be very high and the resulution i need is very smal, eg i need to know when the water changes by .5 c. I think i will seal half of the sensor with a epoxy resin i have found that is inert and resistant to water, and then apply a thin coat of nail polish (the wife can get that ) to seal the water out.
I will advise how i go..
Thanks, Mark |
|
![](templates/subSilver/images/spacer.gif) |
|