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Post by spinal on Aug 9, 2012 9:16:10 GMT
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Post by tonyb on Aug 10, 2012 8:58:19 GMT
You need to be clear what you are hoping to gain from using TCs over and above alternative methods. I did have a look at this when I originally built my wfo a couple of years ago and decided not to bother as, like you, I found that whilst the TCs were pretty cheap the data logging equipment was expensive ~£400 for the 6 to 9 inputs which I think are necessary to get a good feel of heat and temp. I'm not sure whether the prices have come down at all but I don't think so. Its possible to use a hand held multimeter to measure the voltage and therefore temp but for a domestic situation the hassle and limited benefit doesn't seem worth it to me. Maybe someone will do this type of project on a Raspberry Pi. I'm pretty sure there is a post on here in the last 3/4 months of someone fitting TCs, try a search of the forum.
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Post by spinal on Aug 10, 2012 9:58:42 GMT
Ended up and bought 2x 2m TCs... will probably end up fitting 2 or 3 more... reason is simple... I'm a geek an like little blue leds...  Will be nice to see when the hearth bricks are fully up to temp, down to the insulation. Similarly, it'll be nice to know if the insulation if stopping the heat, etc... M. |
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Post by turkey on Aug 10, 2012 9:58:48 GMT
depending on how geeky you are there is a thermocouple section where we discussed making our own logger based on arduino (i think I would prefer .NET micro), even making it yourself will cost a bit especially for 10 inputs. lukemiller.org/index.php/2010/08/a-thermocouple-datalogger-based-on-the-arduino-platform/seems to be the basis for a decent logger which has 8 inputs. It does not seem cheap but I suspect the costs he has for the thermocouple could be reduced some what. |
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Post by spinal on Aug 10, 2012 11:30:10 GMT
Very interesting... may try, but with Raspberry Pi... looks cheaper than an arduino...
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Post by dougclay on Aug 12, 2012 13:18:40 GMT
I knocked up a 4 way logger/display last month before I went on holiday. It works really well but there's plenty of room for improvement  I used MAX31855 thermocouple chips that I got as free samples and logging to some eeprom chips that I had already. The display is a 2x40 LCD from an old server appliance Backlit and only 5v). I used the Arduino because I had one and the libs are already written for all of the components but as the MAXIm chips use SPI you could use simple Atmega or PIC chip. The raspi has less GPIO pins so the number of individual SPI slaves is limited, so you would have to use a separate controller/multiplexer. I really only pay attention to the TCs in the domw and floor surface, the ones under the floor and under the the under floor insulation are just there to show that the insulation is working and improving with each firing... I started off the other thread as I thought there might be more interest and was even thinking of getting some pcbs printed but I guess it's too geeky for this forum... wrong kind of breadboard and not oven chips ;-) dougclay |
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Post by turkey on Aug 12, 2012 15:19:03 GMT
. I guess it's too geeky for this forum... wrong kind of breadboard and not oven chips ;-) dougclay epic quote. I suspect folks would use a pre made unit but perhaps are not able to do or understand the roll your own project. I think the LCD sounds ace, but an sd card to easily get the data onto a pc would be brilliant. |
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Post by dougclay on Aug 13, 2012 0:35:27 GMT
;-)
I just used what I had available and what I could get for free, but yes an SD card would be nice... I'll also add some proper pcb tc sockets but I haven't found a cheap source for those...
atm, the LCD just shows the current temp from each channel, I'll add some more modes when I have a spare rainy day :-)
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Post by spinal on Aug 13, 2012 8:23:07 GMT
I would definetly be interested in a pcb... but I reckon you could do away with the arduino (it only needs to poll temp after all - not run quake ) and replace it with a single PIC. Just being lazy, and I could google this, but how do you convert the variable voltage from the TCs into a temperature? M. |
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Post by DuncanM on Aug 13, 2012 8:43:13 GMT
I'd have thought there would be quite a high demand if someone is skilled enough with electronics to make a kit that can support x amount of thermocouples at a much lower price than the manufactured kits. If someone were to do it and offer to people on these forums I could see a few people wanting them. I certainly would had I not almost finished my build!
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Post by spinal on Aug 13, 2012 9:37:06 GMT
Had a quick look, the voltages in question are tiny (50uV per degree C) makings a clean power supply quite critical. That said, a simple amplier can be picked up for £5 or so (I'm looking at a MAX31855 on ebay). You'll need say, 8 of these for a 8x board. (£40) Add to that a few resistors (it's a 3.3 volt device, so you'll need to compensate to connect to a 5v PIC); an LCD screen, some board; a nice 9v holder... I reckon they could be done for £50-60 all in (not counting development time and thermocouples.) May be able to make it cheaper by getting them bulk made in China, but usually the MOQ I've seen to get any substantial reductions are about 100 units. I think I'll just get a few TCs, and a few separate £10 controllers on ebay and go that way M |
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Post by tonyb on Aug 13, 2012 17:59:22 GMT
Dougclay, I'm interested in your experiences of actually using the TCs, do you think they are of much practical benefit? How many do you have and where are they positioned? Do you find any particular TC position to be more useful than others? Lots of questions |
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Post by dougclay on Aug 13, 2012 19:00:29 GMT
Hi Tonyb,
I fitted 4 as a retrofit, but I wish I had added more. One in the dome and one just poking out out between the floor bricks. The other 2 were just to test the underfloor insulation really... the sensor below the vermicrete stays fairly constant at 18-25C f, it originally went higher but this has improved after firing. The sensor on top of the vermicrete, under the floor bricks surprised me by how long it takes for the heat to permeate through from the upper surface and how long that heat stays in the brick afterwards.
I will for sure use more TC's next time, just so that I can average out the readings across whole surfaces or areas.
Most practical benefit comes from being able to measure temp once the door goes in for baking... but also when firing up, even though you can tell just by how the fire and smoke behave, it's useful to be able to see at a glance whether the floor is up to temp as well as the dome...
dougclay
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Post by cannyfradock on Aug 13, 2012 19:15:35 GMT
....interesting reading guys. I'm following the thread but I'm guilty of taking more OUT of this thread than I could ever put back in....
...I'm still learning...
Terry
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I used MAX31855 thermocouple chips that I got as free samples and logging to some eeprom chips that I had already. The display is a 2x40 LCD from an old server appliance Backlit and only 5v).
