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Dual sensor for oven temperature control


#1

I am going to upgrade my temperature controlled oven which at present uses the G120 and a 5"LCD to a G400S with 7"LCD and I am considering adding a second thermocouple to the top of the oven. At present I have a sensor located near the bottom and this has been very good for temperature control of the oven and it has proven much better than the old mechanically operated temperature controller.

What I am trying to find is suitable algorithms for working with 2 temperature sensors located top and bottom of the oven. Anyone done this before and could offer any insight on how this is done?


#2

Interested to hear if others have dealt with this. I personally would have thought that since you can’t control independently the A and B temperatures (you don’t have two outputs to control) that you would have to treat them as a “joined” measurement of the actual temperature, so you’d need to use some form of averaging calculation that blended the two temps into one for your control algorithm.


#3

I haven’t built what you have Dave, but I am using the technology - look up fireboard labs, they did a kickstarter a year ago for a 4 probe wifi temp monitor/controller that monitors 4 inputs at once, and also now has outputs for relays etc, which could work for you quite nicely. The thing stopped working for me some months back, took it apart, and low and behold a nice little Intel Edison in there… the chip package had just slipped off the main board so i was up and running in no time. Their temp probes are nice quality, and I can get them to work on my BBQ coffee roaster which goes over 600 degrees F, probes do not fail but stop working above that temp… Nice thing it’s potable, battery operated, and I can mount it on the rotisserie using magnets that monitors the internal temp of the BBQ as well as a separate probe that sits in the coffee beans themselves, all on an iphone, while it’s turning around and around lol… You’d just have to link up the output to the oven control. And don’t forget to have a spare probe for sticking in the meat, so the oven will turn off when the internal temp reaches a set point…


#4

Further to the fireboard thermometer, the output channel (which I am not using, it as a recent additional ‘extra’ to the thing) is a ‘fan control’ for outdoor smokers, and it looks like it’s a 12 volt PID control. Guess they programmed all that into the Edison. Have fun!


#5

Cheers jscmanson for the information. I have already ordered the parts and built the enclosure and LCD etc. I have the old NETMF code base to work on so I would prefer to roll my own. PCB is ordered this week. The thermocouple has been super reliable since I build this about 2+ years ago. I don’t need anything with a battery as the oven is mains powered anyway.

Ii will have Internet capability to my phone as I will have WiFi on the board and it will use MQTT to handle the time left, temperature etc.

Thanks for the heads up on the probe for the meat. I have a spare serial port and I2C so I can add this feature later.


#6

The PID programming sounds interesting, changing the cycle time for the elements depending on how close the oven is to set temp etc…I think regular ovens just cycle on/off over a 25 degree spread, or something like that, where the PID would make it ore accurate I would think… I stuck a PID on my electric smoker and it works really well, the temp never varies by more than 5 degrees or so from the set point… have fun!


#7

haha, another BBQ coffee roaster here ! Can I ask about your probes into the bean mass, how did you do that?

There’s a thread here where I showed off my Gadgeteer time announcer / motor controller, but I never bothered with temperature. On my bigger roaster on the other hand, it’s Gadgeteer pimped and am using Artisan to track everything


#8

The current software holds the temp around ±5 degrees too but I may change the PID for the next version so get this a little better on the overshoot, especially at higher temperatures but otherwise I have had great success with this cheap oven (where the electronics I added cost way more than the oven cost me)


#9

Hi Brett, the coffee roaster is a stainless cylindrical basket that mounts on a BBQ’s standard rotisserie rod (see ebay for the roasting baskets). That’s what makes the Fireboard such a useful tool, it mounts on the end handle of the rotisserie, using a couple of magnets, and the probes are mounted permanently on the rotisserie (you need to be careful bringing in the probe wires through the area where the rod rests on the BBQ, just put a copper slip fitting overtop the wires to protect them). One probe is just stuck into the BBQ cavity outside the basket which reads the BBQ cooking temp, and one is threaded into the basket itself and provides a pretty good temperature of the beans that roll around inside the basket. I do 5lbs of coffee beans in 15 minutes. Sorry Dave for hijacking your thread lol!


#10

I shot a poor quality video of the setup before adding the second probe…


#11

No problem. I am a big coffee lover as it is. Just never got into doing my own roasting as with being in Indonesia I can get really good tasting and ready roasted coffee beans for my machine locally.