Thermocouple metering / monitoring and datalogging

[dougclay]

Following a conversation with Turkey, we've both looked into cost-effective (cheap) methods of homemade monitoring and logging temperature readings from Thermocouples.
I thought I might open this up for discussion, especially if there is a forum member with a talent for electronics and perhaps the means to help produce something on a larger, cheaper scale.

I'm just experimenting with a development board and ready made plugin add-on boards to add thermocouple amplifiers, data logging, display unit and possibly some wireless communication. After that who knows, perhaps a robot arm to load logs or stoke the fire ;-) or simply an audible low/hi temp alarm...
While easy to assemble these kind of components and relatively easy to program, they are more expensive than the making something dedicated to the job with individual components.

I'm waiting on some parts atm, but I am looking to use some MAX31855K thermocouple chips controlled by an Arduino dev board, logging to SDcard with a simple digit display.

Anybody else out there with an interest, experience, idea, skill in this subject?

Cheers

dougclay

[turkey]

It seems very intersting and whilst I have no experience with th hobby boards I have followed projects before (hackaday.com is great).

I did see someone sells pre fab boards with Max31855 chips and all the gubbins as the audrio will do 5v and the chip wants 3.3v. He did single to quad boards and also shields. He nolonger sells them as there is apparently a shortage of the MAX chips
no idea how the cost compares to adafruit etc..

further research today pointed to

code.google.com/p/tc4-shield/

who have a 4 thermocouple shield for audrino which might be a cost effective way of getting multiple data channels. I think its mostly for roasting coffee but if it takes K type thermo couples it might well be usable for ovens also.

[dougclay]

I think the shortage was last year, if you are referring to the mcleng site I think you mean. The design with these is fairly simple, so I will give this a go.
I have actually ordered free samples of the Max31855 chip direct from Maxim.

the tc4-shield you link to doesn't seem to directly support any particular thermocouple, looks like it converts the voltage to a digital value after another chip measures ambient temp to compensate cold junction then leaves it for the software to calculate actual temperatures. couldn't find any info on what type of TCs they used with this board but the datasheet for MCP3424 shows an example using k-type so it should be within range.
I haven't looked in detail, but this seems to require windows software to do the data logging, although you could add an SD add-on and write your own code.

[turkey]

Ahh free samples that's the way to go, all my chip exploits have been with such samples

Yes the tc4 I think is a manual approach to thermo couple amplification. I don't think the conversion from analog to digital should be too hard from the bits in comments but you need to know more about the main chip it uses I suppose, or details on how the thermo couples work. It can be connected to audrino and I saw on the roasting forum the initial plan was to have it do sd card logging, so not sure if the main board can be programmed to do such a thing.

If the normal chips are available again then perhaps it's not required, I was just looking for quad shields to reduce space, wiring and make life easier / cheaper.

Starting to wish I had placed some thermo couples speculatively in the oven now :/

[Fat Bob]

I am boggled by your technological prowess - I guess Boy Racer WFO's had to arrive - but I personally wouldn't use any technology the ancients wouldn't use.

Surely the idea is to save money and be retro?

[dougclay]

Jun 7, 2012 22:24:02 GMT Fat Bob said:

I personally wouldn't use any technology the ancients wouldn't use.

I see your point bob, but I find lighting the oven a bugger of a job with a couple of rubbing sticks... ;-)

[Fat Bob]

No - Romans used bow dills. But the hearth fire was always kept alive 24/7 by a virgin. The hearth fire was ceremonially relit evey year with fire from the Temple of the Vestial Virgin.

This probably explains why the hearth fires are no longer kept burning 24/7 as they can no longer find Vestial Virgins.

[bookemdanno]

Lighting the oven by rubbing two vestial virgins together would be much more fun!

[DuncanM]

Picking this thread back up, rather than starting a new one...

Has anyone had any luck with a commercial temperature data logger (I don't have the abilities to build one like dougclay and turkey).

My interest has been sparked by doing a test run of a brisket at the weekend. I started the oven up on Saturday and put a few good size logs in it before going to bed. At midday the next day, with the door being off the temp was at 130C. From this point on I had door off. I have a rough idea what temps were but I'd like something more accurate so that I can be even more prepared for cooking things like brisket.

All times estimating fire went out at midnight.

Elapsed Time from Fire being out | Temp (C)
<door off>
12:00 | 130
<door on>
37:13 | 75
52:51 | 55
63:19 | 50

[DuncanM]

I was thinking either this:
www.digital-meters.com/food-c9/eti-oven-thermometer-810-060-p284 (only goes to 300C) but then again, I'd only put it in the oven when temps had dropped below that anyway. Very cheap given it includes the probe with 1metre wire. That being said it doesn't do data logging, but it could be useful to have an alarm go off when the right temperature was reached.

Or this:
cpc.farnell.com/jsp/displayProduct.jsp?sku=IN05779&CMP=CPC-PLA&gross_price=true&gclid=Cj0KEQjwiJiiBRDh3Z-ctPfS5MgBEiQAAlkbQsipS9-qACAzlaRWFIXYlJMT0hubCG2RkmsqwlBZU0kaAoQY8P8HAQ but then I'd need to also buy a type k thermocouple so it's much more expensive, but would allow for data logging.