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Old 02-03-2009, 02:10 AM   #1
Jared311
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Default Copper Thermowells

Being an engineer, I love DIY projects. Awhile back I decided that I wanted to take the digital path for temperature monitoring of my HERMS setup. I picked out the Maxim DS1624 IC and designed really tiny pcb's to mount it on with latchable connectors on the back. Sorry, my iPhone couldn't focus very well on it because its quite small.




The next step was figuring out a way to submerge these into hot liquids and still get an accurate temperature. I decided to design copper thermowells that I could screw into my kegs standard 1/2" npt couplings.




Finally in this picture you can see how the small sensor fits inside the cap of the thermowell. I am going to use thermal epoxy to mount the chip into the cap. Then I can place the cap back on the thermowell and seal it up using silicon adhesive. The wires then will run through the pipe to the outside of the keg and some insulation will be placed in the ends to prevent heat loss.





I have also designed a main board with a microprocessor that takes in the digital readings from eight sensors and relays them off to my PC via USB. I have finished writing the necessary code to implement the USB communication on my microprocessor and have tested it successfully. Next, I need to finish coding the serial communication with my sensors and then I can finally see how accurate they are and how quick they respond.

thermos.jpg   thermo-sen.jpg   sen.jpg  
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Old 02-03-2009, 02:51 PM   #2
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I think it should work great. Copper has a high thermal mass which will make it slower to react with all that copper, but like was pointed out in the other thread; we're not monitoring critical temps on the Space Shuttle.

It looks like you might have the room to thread the chip in. Could you solder the last joint and then thread the chip from the open and with the wire leads and epoxy it in place?

Nice work.

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Old 02-03-2009, 04:27 PM   #3
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Nicely done, I like that idea a lot.

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Old 02-03-2009, 08:27 PM   #4
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Quote:
Originally Posted by Derrin View Post
It looks like you might have the room to thread the chip in. Could you solder the last joint and then thread the chip from the open and with the wire leads and epoxy it in place?

Nice work.
What do you mean by thread the chip in?

The main reason I wanted to be able to remove the cap was to be able to replace a sensor. I figured if I used silicon epoxy then I could remove the cap rather easily and just place a new cap on that has a new sensor thermally epoxied to it.
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Old 02-04-2009, 10:28 AM   #5
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Quote:
Originally Posted by Jared311 View Post
What do you mean by thread the chip in?

The main reason I wanted to be able to remove the cap was to be able to replace a sensor. I figured if I used silicon epoxy then I could remove the cap rather easily and just place a new cap on that has a new sensor thermally epoxied to it.
I think he means solder all joints and then push the sensor through the top and epoxy it in. Although you mentioned the possibility of replacing the sensors, so that wouldn't work out real well, although you should be able to unsolder the cap. Might be a bit messy.

Any links on the silicone epoxy you are going to use? Is it food grade?
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Old 02-04-2009, 02:37 PM   #6
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I think he means solder all joints and then push the sensor through the top and epoxy it in. Although you mentioned the possibility of replacing the sensors, so that wouldn't work out real well, although you should be able to unsolder the cap. Might be a bit messy.

Any links on the silicone epoxy you are going to use? Is it food grade?
That's what I meant. Replaceable is good. I was thinking copper is cheap enough now that you could replace the whole thing. Either way I'm sure you'll be succesful.
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Old 02-05-2009, 03:00 AM   #7
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Yeah that's a good point, it would be cheap to replace the copper. Then I would definitely have a water proof seal as well.

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Old 03-08-2009, 12:20 AM   #8
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Any links on the silicone epoxy you are going to use? Is it food grade?
So I originally purchased some 100% Silicone Rubber from a random store to seal the joint on the copper tubing. I have stumbled across several websites that argue silicone rubber is food safe, but I am still worried about using it. Especially because I have no idea what kind of temperature it can hold up to.

Any suggestion on a food/temp safe material I could use to seal the copper joint??? I would prefer not to sweat the joint because I think that would be too hot for the chip and silver epoxy.
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Old 03-08-2009, 01:32 AM   #9
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Here is a link to some food grade epoxy: McMaster-Carr, although it's a bit pricey.

I debated back and forth as well on how to seal the ends of the tube. I finally decided that I was just going to solder the tips. I used a vice to crimp the ends into a point, as much as I could. I then used the dremel to round over the edge and then finally added a bit of solder on the end. The pics below were before I did some finish sanding / filing, but you'll get the idea. I hooked up the compression fitting to the air compressor, and tested it in water at 30psi, with no leaks. That's good enough for me.




I'm going to make the wires just long enough to reach all the way to the end. I'll put a drop of epoxy on top of the chip, and then epoxy the wires on the back end of the compression fitting (outside of the kettle, so food grade won't matter). They won't go anywhere that way. I'm using DS18B20s, so they barely fit inside the 1/4" tubing, so I'm fairly confident I'll get an accurate reading.

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Old 03-08-2009, 03:06 PM   #10
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HomebrewJeff, I have one suggestion then that might help you with your approach. Make sure you pre-coat the sides and leads of the chip with silicone so that you don't accidentally short anything out. I did that last night and it worked like a charm. This will allow you to put a good amount of epoxy on the top of the chip to ensure you get good contact.

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