I don't think an aquarium heater will get to 50C. Keep in mind these are
built for keeping tropical fish alive. Most of those wouldn't be too happy
at 50C. For liability reasons I'd expect them to have overtemp cutoff
switches, but I'm only guessing.

Basically, you're looking at a resistive electric heater, whether you use
soldering irons, beverage heaters, waterheater elements, heat lamps, power
resistors, industrial Cal-Rod, or something else, the control options are
basically the same: Relay (solid state or mechanical), Triac (AC), or power
transistors (DC).

Driving any of these from a PIC is reasonably well understood with plenty
of examples.

Keep in mind that with 20+ gallons of water, it's not going to change
temperature very fast. Dependent on insulation, ambient temp and heater
wattage, I doubt the heater would cycle more than every few minutes. So a
slow control algorithm and mechanical relays isn't a bad option.

I don't have all the information about your test, but I'd probably look
into a (small) standard residential hot-water heat circulation pump, build
a heater with a few pipe fittings and a water heater element, and run it
through the tank. If you pumped the same water that's in the tank it would
also provide agitation.

Some water heater elements have a threaded mount, IIRC it matches 1-1/2
inch iron pipe thread... Add a Tee, a nipple longer than the element, and a
couple adaptors and you have a heater.

-Denny


> The oxygenation sensor this is intended to test takes 5-10 minutes to
> settle; we want to test it over 72 hours or so.
>
> Accuracy in temp is unimportant, really, just so long as it doesn't get
TOO
> hot.  All we need is a heater that is capable of heating the aquarium to
> 50C which can be controlled by some programmable means.
>
> Mike H.
>

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