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| Very stable temperature control |
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| max_torque:
This sort of thing is really best done open loop tbh. The total heat flux drives the temperature, so just put a known and fixed amount of heat in, and wait for it to stabilise! Do it in a large room, where the thermal mass of the room and air is large, and there is nothing to drive any oscillation... |
| HendriXML:
--- Quote from: max_torque on June 28, 2019, 04:41:31 pm ---This sort of thing is really best done open loop tbh. The total heat flux drives the temperature, so just put a known and fixed amount of heat in, and wait for it to stabilise! Do it in a large room, where the thermal mass of the room and air is large, and there is nothing to drive any oscillation... --- End quote --- I understand your reasoning, but the thermal mass and conductivity of air is extremely low. (That's why we use heatsinks.) |
| joeqsmith:
My room temperature varies way to much to be useful. Simple beach towels over the device is a huge improvement. --- Quote from: HendriXML on June 28, 2019, 04:33:49 pm ---I don't have the MM to do high resolution measurements. But looking how the power fluctuates I think the temperature fluctuates around 0.002 deg. This mainly because of the thermal capacity/heat loss ratio. Water is cheap and does its work well. Much better than alu. The active setup is with a 10 cm foam on top. Not the best, but insulating enough. The most stable setup is the one that doesn't lose any heat and needs almost no heater. --- End quote --- It may be worth investing in a decent used DMM. If you are looking at characteristics of diodes, I would have thought you would have been all set with this. In the case of the meat packing box, I want to be able to run at different temperatures. Using the PC to control and record the data as much as possible just makes things easier. If you like watching paint dry and grass grow, this is about 10 minutes of data collected real time as the box is starting to settle at 23.0C with the stacked Peltiers. https://youtu.be/j9YcKQ-2uU8 |
| HendriXML:
--- Quote from: Damianos on June 28, 2019, 04:40:00 pm ---In the past, I played with a circuit very similar to the one at page 16 here: http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=snoa748&fileType=pdf&keyMatch=AN-460&tisearch=Search-EN-Everything I did also a variation, using a second sensor, to make a differential controller for a setting "above the environment temperature" (for testing heatsinks). Except of the "original" parts (LM35, LM10, LM395), I tried also other types with similar results. Unfortunately I have not access to the lab yet, so I can't give more information. --- End quote --- From what I've understood is that K-type sensors are in fact differential temperature sensors. With a hot and cold junction. It should than be possible to use just a pair of those wires to do differential measurements, by reading only one voltage. This might eliminate some errors. Don't know whether this is used in practice. |
| HendriXML:
--- Quote from: joeqsmith on June 28, 2019, 05:05:45 pm ---My room temperature varies way to much to be useful. Simple beach towels over the device is a huge improvement. --- Quote from: HendriXML on June 28, 2019, 04:33:49 pm ---I don't have the MM to do high resolution measurements. But looking how the power fluctuates I think the temperature fluctuates around 0.002 deg. This mainly because of the thermal capacity/heat loss ratio. Water is cheap and does its work well. Much better than alu. The active setup is with a 10 cm foam on top. Not the best, but insulating enough. The most stable setup is the one that doesn't lose any heat and needs almost no heater. --- End quote --- It may be worth investing in a decent used DMM. If you are looking at characteristics of diodes, I would have thought you would have been all set with this. In the case of the meat packing box, I want to be able to run at different temperatures. Using the PC to control and record the data as much as possible just makes things easier. If you like watching paint dry and grass grow, this is about 10 minutes of data collected real time as the box is starting to settle at 23.0C with the stacked Peltiers. https://youtu.be/j9YcKQ-2uU8 --- End quote --- I've gone to so much effort precise measurements with a scope and awg that I indeed earned my right to buy me a bench MM. I will explain this right in the upcoming years to my spouse. To her all these boxes on the bench are probably all the same and some of them are quite recent. :-+ Until than I've to be creative. It is also very nice to see how others build comparable "contraptions". |
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