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Old 05-13-2013, 01:10 AM   #1
brant740
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Has anyone attached a ds18b20 directly to the side of a kettle or keggle? I am not talking about using a well or compression fittings or drilling any new holes. I was thinking of using a DS18B20 sensor with thermal grease and a tab of JB waterweld to hold the sensor tight to the kettle. Would the kettle metal temperature be a fair representation of the water temp?

 
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Old 05-13-2013, 03:36 PM   #2
crane
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I don't think this will e a very accurate way to measure temperature, nor would it be a robust solution. I assuming you would solder wire to each leg of the sensor and cover it with heat shrink. The legs on electrical components are not meant to put up with much stress. The weight if the cable would break the legs quicker than you would expect.

Measuring the outside surface of the kettle is not going to be the same as measuring the inside surface. It's going to come down to the equation where the temp difference between inside and outside surfaces are equal to the thermal resistance of the material multiplied by the amount of heat being transferred through the kettle wall. There will always be heat transfer when you have a heated liquid inside the pot therefore there will a delta across the kettle wall. You may be able to compensate for this but you still need to deal with the robustness problem first.

I do like the idea you are presenting but I think to make it work well will require a bit more effort than you describe to make it robust and therefore you may end up with something more involved and complicated than simply drilling a hole for a thermal well.

 
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Old 05-13-2013, 04:04 PM   #3
brant740
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Thank you for the insight. I think I can get around the fragile legs by tacking the head of the sensor, heat shrinked legs and the wire with water weld epoxy. This should immobilize the sensor and transfer stress point to where the wire is attached.

My admittedly noon question is how does a ss well differ from a ss kettle on detecting temps? Should heat transfer be similar?

 
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Old 05-13-2013, 07:14 PM   #4
crane
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The thermal well is submerged with water in all directions except where it contacts the kettle but usually this is far enough away from the sensor that you can consider the thermal well to be completely surrounded by water. Therefore the tip of the well where the sensor is will be very close if not the same temp as the water. Once in equilibrium there will be no thermal transferred through the thermal well or temp sensor, whereas there will always be heat transferred through the kettle wall.

At my last company I worked on a problem where we were trying to roughly measure the temperature of water or steam inside of a pipe by measuring the outside surface of the pipe. We were able to come up with a solution that worked half ass when there was no airflow, but as soon as you added the slightest airflow the delta between inside pipe temps and surface temps changed by a lot. The surface temp of kettle will vary depending on air temperature and wind speed.

 
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Old 05-14-2013, 02:59 PM   #5
Indian_villager
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These are cheap.
http://www.brewershardware.com/Straight-Tubes/

 
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Old 05-14-2013, 07:27 PM   #6
brant740
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That makes sense. I suppose I will have to bite the bullet and go with a well. I do have premade stainless probes, but I wanted to limit the number of holes in my kettle.

 
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Old 05-15-2013, 05:55 AM   #7
helibrewer
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Quote:
Originally Posted by brant740 View Post
That makes sense. I suppose I will have to bite the bullet and go with a well. I do have premade stainless probes, but I wanted to limit the number of holes in my kettle.
I fill my thermowells with mineral oil (cutting board oil) which really improves heat transfer within the well.
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Old 05-15-2013, 01:32 PM   #8
alien
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Stainless is not a terribly good conductor of heat as metals go so where you put the probe matters. Plus you need to insulate. I would recommend a small, flat thermistor which will give you a better contact than a DS18B20.

http://www.rapidonline.com/electroni...mistors-61185/

 
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