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Author: Subject: PID cotrolled heating mantle
Hazard to Others

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[*] posted on 19-5-2023 at 12:55
PID cotrolled heating mantle

I have been looking at some of the newer Chinese heating mantles on ebay and some have a PID controller and a temperature probe.

Does anyone have any idea if this type of mantle would regulate temperature with the probe disconnected? Just I expect unlike a hotplate measuring the mantle temperature is probably harder so I am not sure.
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International Hazard

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[*] posted on 19-5-2023 at 23:27

This is probably only glitz. PID are meant to control complex loads such as electrical engines which display significant capacitive/inductive loads. A heating mantle is just a resistor, so it can overshoot somewhat at first (because of thermal inertia), but there’s no need to use anything more complex than a simple duty cycle regulator.

Given that the mantle somehow wraps around the flask, the use of a probe is superfluous. There will be a small thermal gradient from the heating element to the inside of the flask, but it should be offset easily by setting the temperature a few pegs higher. Use a thermometer.
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[*] posted on 20-5-2023 at 00:01

A PID controller is an excellent choice if used to achieve and maintain a particular temperature below b.p.

A constant power dimmer/thyristor/TRIAC phase controller is more suitable for boiling at a constant rate (refluxing or distilling)

Many Pid controllers have a variable to adjust maximum power,
so can be used as a constant power source for heating,
but control would be by accessing and modifying parameters.

CAUTION : Hobby Chemist, not Professional or even Amateur
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[*] posted on 20-5-2023 at 00:34

One of the many reasons I took a working hotplate and hacket it.
Its ugly, but works great. It takes a lot of time to get it perfect
Exact details will vary from model to model
Simply intercept the power going to the heating element and insert a relay.

Heating by controller has a list of pros amd cons.

The biggest con being what happens of your temperature probe falls out, or is no longer submerged in solution. The mantle will kick on full power. Cracking glassware.
Next is the limited functionality of cheap controllers.
You want to be able to easily set your PID parameters.
Calculations are easy, fine tuning a pain in the butt

If their is intrest 8 can dig up my pcb and bom from the unit I built about a 2 years ago.
$150 for the total cost, and a many hours of fine tuning the software.
Wifi, touchscreen, 3 thermocouple inputs, 3 5v 100ma outputs, sdcard and stage programmable

"You can't do that" - challenge accepted
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