PIDed kettle/boiler

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Postby syscrusher » Wed Sep 09, 2009 9:38 am

Talk to me about probe placement.

Worth drilling a hole and using some sort of adapter to allow the prove to be inserted while also keep the hole water tight?

Some sort of swagelock part might suit?

Or just hang the thermocouple over the top?

Wire thermocouple vs sheated?

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Postby Jasonscheltus » Wed Sep 09, 2009 12:53 pm

syscrusher, this is what I am thinking about right now.

Currently my ghetto kettle set up has the ol' thermocouple dangling in the water - slightly rusty metal sheath et al.. But seeing as how I want to apply this to water I might want to drink, I think something more permanent needs to be done.

There are large probe type thermocouples that are designed to sit in liquid - whereas the "exposed wire" thermocouples are really only suited to measuring the temperature of gases, as the h2o degrades (and creates build up on) the sensitive thermocouple metals. A large male threaded probe could be inserted through the side of your plastic kettle, but it is much more difficult with metal boilers.

As far as I have gathered, the best solution for a metal boiler, is to drill a small hole then weld a suitable sized nut to the outside (over the hole) for the thermocouple to be threaded through. This required a MIG or TIG welder, neither of which I have.

Another ghetto solution, would be to run the thermocouple probe (and wire) through a copper pipe down into the boiler water, then sealing it so the probe is the only part exposed, and bending it 90 degrees so the thermocouple probe is horizontal to the elements.

This is as far as I have gotten with probe placement. I have my boiler in the shed, and thermocouples coming from HK. I'll update when they arrive.
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Postby syscrusher » Mon Nov 09, 2009 3:10 pm

Finally got around to doing this. Well I put together all the parts a few weeks ago, but just gave it a housing this weekend.

The PID settings could be better. It heats up fast enough, but it overshoots by about 3-4C on the first heat - it keeps pulsing even after it has passed the set point.

It does settle after a couple of minutes, and remains very stable from there on.


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Postby dsc » Thu Nov 26, 2009 1:22 pm

Hi guys,

for some strange reason I don't get notifications for this topic anymore:|

Anyways I got my Omron today and will try to wire something up in the upcoming days. If it works as I want I will put it in a suitable box and stick with it for now, until I have more space to mount a small boiler and do this properly as it should be. I'm going for a thin unsheated TC type T and the reason is that it's easy to take it out from the kettle when pouring. You can of course buy a Swagelok fitting for a sheathed TC, but the kettle is not really suited for this as you want to move it around, pour from it and so on. If you stick a TC on the kettle permanently it's sort of like having the base with the plug at the end stuck to the kettle for good, simply doesn't make much sense in my opinion.

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