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Topic: Interested in meteorite lab project? (Read 3 times) previous topic - next topic

PaulS

The charts on the second link show the current and voltage needed to achieve different amounts of heating/cooling, but they say nothing about how long it takes to achieve that temperature change.

If the rate of change is high, then the possibility of overshoot is great. If the rate of change is low, then that is a lot less likely.

In either case, determining the appropriate on/off times would probably require the use of PID.

Is there any possibility of (at least initially) having a PC near the Arduino, to provide the graphic interface for setting/seeing temperature and cycle iteration and count?

meteoritics

There would be no problem with having a PC on hand during the build/calibrate stage. It would be best if one wasn't needed during subsequent operation.
Came to my mind that in the list of hardware/connections, there will need to be a relay (or equivalent) to switch the polarity of the power to the thermoelectric unit -- to switch it back and forth from heating to cooling. (I'd think that might be separate from the on/off/throttling relay.)  Also, perhaps to set the number of desired cycles in a given run, a simple button could add multiples -- say, 25 per push; in other words, you could select 25, 50, 75, etc. cycles. Obviously, you'd want a display of what you selected.
The Peltier units I've worked with tend to have a low thermal mass, and change temp VERY fast -- getting below freezing on one side and above boiling on the other in a flash. The mass of the item they are attached to (the heat exchanger block housing the sample on one side, and a heat sink on the other) will obviously slow down the temperature change. But overshooting, especially in the heating cycle, is definitely possible.

wildbill

When you're doing this manually, how do you decide when the sample has been through sufficient cycles? Visual inspection? Does it matter if you run extra cycles after it's "done"?

meteoritics

The cycling doesn't need to be precise to the single event. Way too many cycles would degrade the sample (breaking up bits that we don't want broken up); too little means more manual separation left to do (picking things apart under the microscope). Visual inspection would be the determination. Often, we're talking about multiple batches of one sample; in theory, you'd see how many cycles it took to fracture one sample to the desired level, and then just do the others that number of cycles.
That's why I suggested perhaps setting the number of cycles in multiples of one number, like 20 or 25. If 73 did the trick, 80 wouldn't be the end of the world. Certainly wouldn't want to slow the freeze/thaw process by stopping to inspect frequently (we don't even do that when manually cycling).

ajsklar

Hello All,
So please tell us, How did this turn out ??????
Photos ??? Website ???
I am very new to Arduino, So I don't think I can be of much use.
I have been to the Field Museum of Natural History in Chicago
many times years ago when I lived out in the south suburbs ...
If you ever visit Chicago, do spend a day here, well worth it.....

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