Waterproffing DS18B20

[Markdem]

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

[dyeatman]

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.

[SherpaDoug]

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.
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[Humberto]

[rnielsen]

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

[rwyoung]

[rnielsen]

[JBM]

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

[specialk]

[JBM]

We just heat shrunk the legs, then potted the whole lot with the thermal compund inside the steel tips.
-JBM

[Markdem]

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